On-Orbit Satellite Servicing Study 

Project Report

National Aeronautics and Space Administration

Goddard Space Flight Center

October 2010
On-Orbit Satellite Servicing Study 

Project Report

National Aeronautics and Space Administration

Goddard Space Flight Center

October 2010
“Energy and persistence conquer all things.”

 Benjamin Franklin
 Contents | i

Contents

Figures and Tables iv

Executive Summary 1

Chapter 1: Introduction 5

Study Mandate 6

What Will This Study Contribute? 7

Study Methodology 8

Assumptions 9

Why Is Satellite Servicing Important? 11

What Has Been Done Before? 14

 The Dawn of Satellite Servicing

 Skylab

 Solar Maximum Mission Repair

 Palapa B2 and Westar 6

 Satellite Servicing Gets Its Challenge

 Hubble Space Telescope

 International Space Station, The “Killer App”

 Technology Demonstrators

 NASDA: Engineering Test Satellite VII

 U.S. Air Force: Experimental Spacecraft System

 Demonstration of Autonomous Rendezvous Technology

 DARPA: Orbital Express

 New International Initiatives

 Historical Activities

 The Evolution of Tools and Techniques

Myths about Servicing 27

 “There Is Nothing To Service”

 “Servicing is Costly”

 “Satellites Cannot Be Serviced Unless They Were Designed To Be Serviced”

What Are Appropriate Human and Robotic Servicing Paradigms? 32

Chapter 2: Satellite Servicing: The Vision 35

Refurbishment/Refueling of Satellites in Near-Earth Environments 36

Construction of Large Structures 37

Orbital Detritus Management 38
ii | On-Orbit Satellite Servicing Study Project Report | October 2010

Chapter 3: Satellite Servicing: The Benefits 40

Commercial Benefits 41

Scientific and Technological Benefits 43

Strategic Benefits 45

Outreach Benefits 46

Chapter 4: Satellite Servicing: The Implementation 48

The Map of Servicing Capabilities 49

The Notional Missions 52

 Notional Mission Characteristics

 Mission Design Methodology and Cost Estimation

 Autonomous Rendezvous and Capture Technology

 Robotic Technology

 Astrodynamics

 The L1 Orbit Trajectory Used for Servicing (LOTUS)

Mission Sequence 64

Technology Gap Assessment 67

 Servicer Spacecraft Bus

 Rendezvous and Berthing/Capture/Docking

 Manipulation

 Refueling

 Autonomy

 Satellite Servicing Integration into Mission Design

ISS Demonstration Activities 72

The Recommended Actions 75

 Optimize Engineering Design and Trade Studies 

 Invest in Key Enabling Technologies

 Assess a Range of Customers for Satellite Servicing

 Create Design Recommendations for Future Spacecraft

 Establish Customer/Provider Working Groups

 Integrate the Satellite Servicing Infrastructure with NASA Program Architectures 

 and Priorities

 Execute the Mission Sequence
Contents | iii

Chapter 5: Satellite Servicing: The Challenges 78

Technological Challenges 79

Economic Challenges 80

Making Future Missions More Serviceable 82

 Getting Close Enough

 Mode of Servicing

 Serviceability

 Design Commonality

Chapter 6: Conclusion 86

References 89

Related Historical Materials 92

Acronyms 93

Appendixes 96

Appendix A – Congressional Legislation and Reports Bearing 97

on Science with the New Space Transportation Architecture

Appendix B – RFI Responses Summary 99

 

Appendix C – International Workshop on On-Orbit Satellite Servicing 104

Appendix D – Functional Decomposition of the Activities Required 119

for Satellite Servicing

Appendix E – Results of the Integrated Design Center (IDC) Instrument 141

Design Laboratory (IDL) Study on Autonomous Rendezvous and

(Berthing, Capture, Docking) Sensor Package, and Robots 1 through 3

Appendix F – Notional Mission Studies 153
iv | On-Orbit Satellite Servicing Study Project Report | October 2010

Figures and Tables

Figures

1.1 The Pillars of On-Orbit Servicing vi

1.2 The Gemini Rendezvous and Docking Experiments 5

1.3 Classes of Satellites for Servicing 12

1.4 The Repaired Skylab 14

1.5 Solar Maximum Mission in the Space Shuttle Bay 15

1.6 Palapa B2 Recovery 16

1.7 HST First Servicing Mission: COSTAR Installation 17

1.8 HST Servicing Sophistication Progression 19

1.9 ISS SSRMS Installing Cupola 20

1.10 ISS Solar Array Repair 21

1.11 Robonaut 2 22

1.12 EVA Power Tool Progression 25

1.13 Unique, Purpose-Built, On-Orbit Repair Tools 26

1.14 Astronaut Training Refines the Tools and Improves On-Orbit 26

Performance of the Human-Machine Interface

1.15 AERCam Sprint 33

1.16 Robotic Assistants 33

2.1 Refueling Depot in Use 35

2.2 Refueling Depot Assembly 37

2.3 Orbital Modification 38

3.1 HST SM4 Release 40

3.2 Refueling an Orbiting Communications Satellite 42

3.3 On-Orbit Assembly 44

3.4 Removal of Undesirable Spacecraft 45

3.5 HubbleSite Visits during HST SM4 47

4.1 The Flight Hardware for the Notional Missions 48
Figures and Tables | v

4.2 Seminal Mission Coverage of the Servicing Study Trade Space 50

4.3 Servicing Study Trade Space Regions Covered by Historical Missions 51

4.4 Notional Mission Suite Coverage of the Servicing Study Trade Space 51

4.5 Front-end Robotics Enabling Near-term Demonstration (FREND) System 57

4.6 Ranger Telerobotic Shuttle Experiment 58

4.7 Safety Ellipse 60

4.8 The LOTUS 61

4.9 The Recommended Mission Sequence 64

4.10 Tools for Closing the Technology Gap 67

4.11 Robotic Refueling Mission (RRM) 72

4.12 Dextre Pointing Package (DPP) 73

4.13 Astronaut in Action 75

5.1 Earthrise from the Moon 78

6.1 Returning from Mars 86

Tables

1.1 Table of Recommended Actions 4

4.1 Notional Mission Summary Table 53

4.2 Servicer Costs for Each Notional Mission 55

4.3 Table of Recommended Actions 76
Executive Summary 

In the past two decades, some of the most extraordinary successes in 

space exploration have emphasized the growing importance of on-orbit 

servicing. As space explorers, our challenges have moved beyond simply 

launching complex spacecraft and systems. We are faced with the need 

to more fully exploit the flight systems already launched, to construct 

large structures in situ to enable new scientific ventures, and to provide 

systems that reliably and cost-effectively support the next steps in space 

exploration. A more refined consciousness of the need to reduce, reuse, 

and recycle here on Earth drives towards a similar awareness of these 

needs beyond our planet. The proliferation of abandoned satellites poses 

known hazards to newer members of the constellation, and may occupy 

unique and economically valuable orbital real estate that could be recycled 

for other uses. With the successful completion of a series of Hubble 

Space Telescope repairs, as well as the assembly of the International 

Space Station, we can look forward with confidence to plan such a future. 

Satellite servicing is a tool—a tool that can serve as the “master enabler” 

to create the architectures needed to conquer the next frontiers in space.

Figure 1.1 – The Pillars of On-Orbit Servicing – This graphic highlights 

the three pillars of satellite servicing to date: the space shuttle (lower 

left), the Hubble Space Telescope (right), and the International Space 

Station (upper left).
 Executive Summary | 1

The NASA On-Orbit Satellite Servicing Study, 

mandated by Congress and supported by the 

NASA Advisory Council (NAC), investigates what 

our future may hold. This document, an internal 

report by the Space Servicing Capabilities Project 

at the NASA Goddard Space Flight Center that 

performed the study, captures the work performed 

under this Congressional mandate. Its conclusion 

is unequivocal. Viable plans can be put into place 

to develop a meaningful on-orbit satellite servicing 

capability, allowing us to achieve our key ambitions in 

space using today’s technology and with current and 

projected launch systems. These plans would advance 

our presence in space by enabling more effective use 

of assets at near-Earth locations and by supporting 

future ventures to more distant destinations. This 

report discusses such an initiative.

This study incorporates the results from the 

following major activities: 1) conduct an industrywide Request For Information (RFI) to notify the 

satellite servicing community of an opportunity for 

discussion, 2) conduct the International Workshop 

on On-Orbit Satellite Servicing in March 2010 to 

engage the community, 3) examine notional missions

to bracket the trades involved for possible servicing 

customers, 4) examine near-term in-space hardware 

demonstrations to provide relevant and immediate 

results, and 5) develop and validate ground simulator 

and test bed capabilities that can be used to verify 

satellite servicing flight hardware and software. From 

these results, we suggest a possible mission sequence

and also identify technology gaps that need to be closed 

for the more ambitious future activities.

The 2009 Congressional mandate for this study 

specifically refers to the Constellation architecture 

that was being implemented at that time. The human 

spaceflight architecture has since evolved into a new 

architecture reflected in the NASA Authorization 

Act of 2010. While this report does not assess using 

the now defunct Constellation architecture, we 

believe that it has met the intent of the Congressional 

direction.

One use of this study will be to inform the 

NASA-wide Human Exploration Framework Team 

(HEFT) that is charged with developing the new 

space exploration plans. The comprehensive HEFT 

study is in keeping with the will of the Congress 

and the Administration as expressed in the recently 

signed multiyear 2010 NASA Authorization Bill. 

It will include a study of the development of an 

in-space servicing capability and identify those areas 

where human participation in servicing is required or 

beneficial.

Our introduction dissects some common myths 

about satellite servicing. The main points fall into 

two general categories: “There is nothing to service” 

and “It is too costly to service.” Superficially, these 

statements appear plausible. However, by studying 

the end-to-end life cycle costs of a wide variety of 

missions, it becomes apparent that these myths are 

incorrect except for limited or unlikely situations.

There are constellations of satellites that would 

benefit from refueling and/or orbit modifications. 

These were not designed to be serviceable, although 

current technology could enable such servicing. 

Moreover, the business cases are sound for those 

applications that have a commercial component, thus 

refuting the statement that servicing is too costly. 

Even for those applications that do not have a 

commercial business case, the systems engineering 

rigor of designing a serviceable system improves the 

robustness of the Integration and Test (I&T) flow 

of a project so that this phase takes less time. Since 

I&T is a very high-cost phase of any program, these 

savings should offset the initial systems design work 

that would permit servicing. This is one potential 

paradigm shift in the development and operations of 

space missions that is enabled by satellite servicing. 

Servicing expands the options for mission design, 

providing a potentially cost-effective path for more 

sophisticated and capable systems.

There is general confusion about servicing with 

astronauts. It is more expensive to human-rate flight 

components, and rightly so. However, with new 

servicing architectures, most of the equipment does 

not need to be transported on human-rated vehicles, 

thus avoiding some of this complexity and cost. We 

also separate the categories of servicing to examine 
2 | On-Orbit Satellite Servicing Study Project Report | October 2010

capabilities that it provides. These benefits increase 

overall mission reliability and, where applicable, 

economic value. For extremely high-value assets 

used for scientific or strategic purposes, a repair 

and refurbishment capability provides an extension 

of functionality and utility without the associated 

costs and risks of a new build and launch. In the 

strategic domain, orbital modification through 

satellite servicing provides powerful capabilities that 

could be central to maintaining our national security. 

Conversely, this technical capability would become a 

threat if implemented by unfriendly entities. Finally, 

previous experience shows that successful servicing 

activities on highly visible satellites can act as a strong 

catalyst for intense public interest. 

The fourth chapter, “Satellite Servicing: The 

Implementation,” discusses more concrete issues. It 

summarizes the technical content of the study and 

charts a technically sound implementation path. We 

first identify and define an appropriate “parameter 

space” for discussing satellite servicing capabilities. A set of “notional missions” then examine the 

commonalities and unique capabilities for representative parameter choices. An important observation is 

that most of the satellite-servicing activities or tasks 

required have already been demonstrated in low Earth 

orbit with humans. The challenges lie in extending 

that capability to robots and more autonomous operations at more distant locations where communication 

latency impedes direct ground control for detailed or 

critical operations. These notional missions provided 

the building blocks that the study team then used to 

construct an executable mission sequence, from which 

technology gaps were identified. 

The final chapter, “Satellite Servicing: The 

Challenges,” focuses on key areas that require 

additional work. Here we argue that the technology is 

ready, and that some of the key issues that remain are 

in other realms such as perceived risks and economic 

motivation. It describes these challenges and provides 

a methodology for addressing them.

During our study, several high-level recurring 

themes emerged.

the roles of human, robotic, and combined servicing 

modes. The most routine servicing activities (e.g., 

refueling, orbit modification, and perhaps simple 

repairs) can be accomplished with robotic servicing 

alone. Astronaut involvement would be reserved for 

those tasks that provide sufficient benefits to justify 

the cost and risk.

Our second chapter, “Satellite Servicing: The 

Vision,” shows how an advanced servicing infrastructure enables the next generation of space architectures. 

This infrastructure provides unique capabilities such 

as the ability to construct extremely large space telescopes. Such telescopes (e.g., the Thirty-Meter Space 

Telescope study[1]) would reach beyond the realms 

explored by the Hubble Space Telescope (HST) and 

the James Webb Space Telescope (JWST) to significantly advance our understanding of the Universe. 

The extremely large apertures involved will require 

shifting to a “born-in-space” architecture, in contrast 

to the current practice of assembly and test on Earth. 

An advanced servicing infrastructure also enables 

longer-range transportation capabilities. It would 

provide fuel depots and other services required by 

missions going to destinations far beyond the Earth. 

Even basic servicing capabilities would provide 

refueling, repair, and refurbishment for operating 

satellites, an important means to extend mission 

life and to improve the cost-benefits ratio. In many 

cases, these operations can even be performed on 

legacy satellites that may not have been designed with 

servicing in mind.

The third chapter, “Satellite Servicing: The 

Benefits,” describes broad categories of benefits 

and how these benefits might be quantified. Those 

applications with commercial potential require 

sound business cases. The business cases have been 

made for satellites that support the infrastructure of 

modern society, and in particular, communication 

services. Those applications that are purely scientific 

or exploratory require a rationale that they enable 

extraordinary advancements that are commensurate 

with the cost. Among the key benefits of satellite 

servicing are the refueling, repair, and refurbishment 
 Executive Summary | 3

are important to provide a cost-effective and 

upgradeable servicing infrastructure. Part of 

the initial technology assessment would be to 

further develop these systems and demonstrate 

their adaptability.

4. Launch mass and orbit modification capacity drive servicing mission design. Here, the 

available launch vehicles could impact the 

architecture and even the feasibility and cost 

effectiveness of satellite servicing. For example, 

for reaching distant destinations, there is a 

trade between heavy-lift rockets with refueling 

depots and multiple small launches with onorbit assembly of small modules. These trades 

could also be affected by advanced propulsion systems. Our technology gap assessment 

identifies other investment goals.

5. Astrodynamics is a major factor in mission 

design, especially when there is human presence.

We paid close attention to this aspect for the 

satellite servicing locations that we considered. 

Interesting results include useful orbits that 

support satellite servicing.

6. Satellite servicing is critical to our national 

interests. As a nation, we need to develop this 

capability in order to maintain our leadership 

in space for scientific, commercial, and strategic reasons. 

We have the technologies today to implement a useful, cost-effective, and exciting program that incorporates satellite servicing into humankind’s portfolio 

of spaceflight capabilities. This implementation needs 

to be a partnership of government agencies, industry, 

and academia, as satellite servicing has implications 

and benefits in economic, legal, and scientific arenas. 

Such a program would take advantage of near-term, 

economically viable commercial applications as a 

stepping-stone to more ambitious activities. Table 

1.1, discussed further in “Satellite Servicing: The 

Implementation,” describes a set of near-term recommended actions and their expected results.

1. In examining the range of tasks required for 

servicing, the tasks themselves (and the hardware 

to support them) do not appear to be the limiting factors. Extremely complex servicing tasks 

have already been successfully performed in 

orbit, including operations on legacy satellite customers as well as repairs on hardware 

not originally intended for on-orbit servicing. 

Advanced robotic analogues of these tasks are 

routinely demonstrated on the ground. The 

advancements needed are mostly in the areas 

of increased autonomy to support such tasks 

farther from Earth and the systems engineering to create sufficiently robust servicing 

architectures. While all the technologies and 

techniques are available, their application in 

a mission require maturation. For this, we 

recommend a robust in-orbit verification 

program using accessible platforms such as the 

International Space Station in combination 

with vetted ground simulators and test beds.

2. Legacy satellites can be successfully serviced.

In fact, much of the servicing performed 

to date has been on legacy hardware never 

intended for on-orbit servicing. The range of 

applicable servicing activities includes repair, 

refurbishment, refueling, and orbit modification. Successful implementation requires 

identifying the correct interfaces, developing the appropriate tools, and executing a 

well-planned mission, all of which have been 

demonstrated. Servicing these legacy satellites provides an immediate customer base 

on which to build a future satellite-servicing 

infrastructure. The business case for commercial satellites is favorable if the capability 

is available and well understood. The first step 

of the proposed mission sequence is to realize 

this capability for satellites in Geostationary 

Earth Orbit (GEO).

3. Modular, reconfigurable robotic architectures that are mobile around large structures 
Table 1.1 – Table of Recommended Actions

Recommended Action Result

Optimize engineering design and trade studies for the 

identified mission sequence.

Refined technical and cost assessments.

Invest in key enabling technologies such as 1) increased 

autonomy for robotic systems, 2) improved systems for 

rendezvous/docking/refueling, 3) advanced tools and 

end-effectors for astronauts and robots, 4) modular, 

self-reconfigurable, and mobile robotic architectures and 

systems that can move around large structures in space, 

and 5) advanced imaging/pose-estimating capabilities.

Proven technologies that will serve as the basic building 

blocks for complex servicing activities to allow future 

missions to focus on mission-specific challenges and 

solutions.

Assess a range of customers for satellite servicing. Defined benefits for a suite of executable missions.

Create design recommendations for future spacecraft. Accepted standards for spacecraft design that improve 

serviceability.

Establish customer/provider working groups. A routine venue for discussion and feedback to 

implement lessons learned and best practices.

Integrate a satellite-servicing infrastructure with NASA 

program architectures and priorities.

The benefits of satellite servicing will be exploited where 

available and appropriate.

Initiate plans for executing the missions described in the 

Mission Sequence section (Chapter 4).

Immediate benefits provided by satellite servicing while 

refining the technologies needed for further advances.

4 | On-Orbit Satellite Servicing Study Project Report | October 2010
Chapter 1

Introduction 

Every new frontier brings new challenges and new rewards. Regardless of 

the ultimate motivation for conquering a new frontier, the process takes on 

a familiar cadence. At first, recognition of the frontier and learning how to 

deal with its environment lead to early exploratory missions that come at 

great cost and often with great sacrifice. Next comes the attempt to reap 

economic or other benefits. Finally, as the new frontier becomes more 

familiar, infrastructure development provides the backbone for a continued 

presence that enables using its unique characteristics and provides a 

springboard to the next frontiers. So it is for space.

Figure 1.2 – The Gemini Rendezvous and Docking Experiments – The 

Gemini program in the mid-1960s had to validate, among other things, 

the rendezvous and docking techniques that would be required for the 

Apollo program. The photograph on the left was taken on the Gemini 76 

mission, where Gemini 6 maneuvered to and kept station within 30 cm 

of its sister ship, Gemini 7. Subsequent Gemini missions successfully 

validated rendezvous and docking with used Agena second stages 

(center and right photographs), which were then used to boost the 

docked spacecraft into higher orbits that broke human altitude records. 

This was the beginning of rendezvous and docking technology on-orbit, 

which is a basic capability required for satellite servicing.
6 | On-Orbit Satellite Servicing Study Project Report | October 2010

On-orbit repair and refurbishment have matured to 

the point where they can be applied to fairly complex 

satellite systems. This is evident in the remarkable 

successes enjoyed by the five servicing missions for the 

Hubble Space Telescope. The tools and methodologies 

developed to enable these successes apply equally well 

to a broad range of customer satellites. On-orbit repair 

and refurbishment directly improves overall mission 

reliability and helps to ensure mission success. These 

benefits will become increasingly important as our 

ambitions in space increase and the cost and feasibility 

of major projects become commensurately more 

challenging.

We now have a long-term human outpost in 

space, the International Space Station, that provides 

an unprecedented platform for developing satellite 

servicing technologies and techniques. It is only the 

beginning of humankind’s infrastructure in space, 

and not surprisingly, it has not yet addressed every 

issue. Significant resources are still expended to simply 

ensure basic needs. Nevertheless, it can serve as a 

significant springboard to more distant destinations 

through enabling essential technology development. 

These potential benefits have not escaped Congress 

and the NASA Advisory Council (NAC). Their desire 

to realize these benefits led to the mandate for this 

study. The results from this study are clear:

1. We have the technologies today to realize a viable 

satellite servicing program. Such a program 

can respond to a wide range of foreseeable 

requirements for routine maintenance, 

refueling, and the assembly of large structures.

2. We can articulate a concrete series of actions to 

execute this program. The program is consistent 

with current NASA plans for human and 

robotic exploration and is sufficiently robust 

that it can evolve with NASA’s plans.

Study Mandate

For the past several years, NASA has received formal 

advice, recommendations, and, more recently, 

appropriated funding to develop concepts for satellite 

servicing and assess their values. In 2007, the NASA 

Advisory Council Astrophysics Subcommittee 

recommended that NASA carry out trade studies on 

“in-space operations (and their) potential for assembly, 

servicing, and deployment.”

A year later in NASA’s FY 2008 Authorization, 

Congress also became interested in the importance of 

spacecraft servicing:

The Administrator shall take all necessary steps 

to ensure that provision is made in the design 

and construction of all future observatory-class 

scientific spacecraft intended to be deployed in 

Earth orbit or at a Lagrangian point in space 

for robotic or human servicing and repair to the 

extent practicable and appropriate.[2]

Congress provided further guidance in NASA’s FY 

2009 and FY 2010 appropriations bills. Specifically, 

it linked the servicing of scientific spacecraft with the 

future human spaceflight architecture, viz.,

Therefore, it will be critical that the Constellation 

program demonstrate unique capabilities to 

maintain synergies between free-flying scientific 

spacecraft and human spaceflight endeavors. 

Accordingly, the bill provides $20,000,000 

for NASA to undertake an assessment of the 

feasibility of using the Constellation architecture 

to service existing and future observatory-class 

scientific spacecraft, fully utilizing the unique, 

core expertise and competencies for in-space 

servicing developed by the Goddard Space Flight 

Center and its private sector partners for the 

Hubble Space Telescope.[3]

This document is the internal Project report for the 

required assessment. More complete references related 

to this mandate are provided in Appendix A.

The 2009 Congressional mandate specifically 

refers to the Constellation architecture that was being 

implemented at that time. The human spaceflight 

architecture has since evolved into a new architecture 

reflected in the NASA Authorization Act of 2010. 

While this report does not assess using the now 

defunct Constellation architecture, we believe that 

the study has met the intent of the Congressional 

direction.
What Will This Study Contribute?

Our study provides a balanced assessment of the state of satellite servicing and 

charts a path toward a future where the benefits of satellite servicing will be realized 

and become routine. The resulting paradigm changes could result in new space 

architectures to enable otherwise impossible applications. By charter, our study 

provides the following results.

1. Data-based assessments on the feasibility and practicality of satellite 

servicing.

2. Definition of common design choices and interfaces that make a satellite 

more serviceable, and a description of the benefits of doing so.

3. Assessment of key technologies that enable satellite servicing using any 

architecture envisioned today, and identifying gaps in what will be needed for 

future servicing.

4. The basis for decisions about ground and flight demonstrations of satellite 

servicing technologies and techniques.

More specifically, our study makes available 

designs and operational scenarios of sufficient fidelity 

to permit on-orbit servicing discussions based on data, 

rather than anecdote and mythology. Similarly, our 

results enable identification of servicing scenarios that 

are more—or less—implausible, unaffordable, or too 

complex to carry out (e.g., require too many elements 

to be launched, require human spaceflight capabilities 

that are not planned). These are investigated in detail, 

along with their technology requirements, in a set of 

notional missions and are summarized under Chapter 

4, “Satellite Servicing: The Implementation.”

Finally, our study identifies precursor and 

demonstration programs that should be carried out 

over the next few years to verify key capabilities in 

advance of more ambitious servicing missions. The 

beginnings of this program are the International 

Space Station-based demonstration experiments being 

developed by NASA’s Goddard Space Flight Center 

(GSFC) Satellite Servicing Capabilities Project. These 

experiments are also discussed further in Chapter 4, 

“Satellite Servicing: The Implementation.”

Our study intends to bring up-to-date the understanding of the potential of satellite servicing and to 

contribute to future design work and investments. 

The past two decades have seen extensive research in 

academia and industry, along with significant demonstrated interest in spacecraft upgrading and servicing. 

There have also been some widely quoted myths about 

the value of this capability. Nevertheless, there has 

been no relevant wide-ranging systematic NASA study 

of this activity since the series of satellite servicing 

workshops that ended in 1989. 

Our study identifies design choices and capabilities that are common among many different servicing 

scenarios. This is intended to guide future mission 

concepts to make them more accessible to potential 

servicing systems. Examples include a high degree of 

modularity, standardized interfaces, common electrical and fueling connectors, common fasteners, 

accessibility of key spacecraft systems, etc. These types 

of design requirements also tend to make spacecraft 

Integration and Test (I&T) substantially less expensive. This is discussed under Chapter 5, “Satellite 

Servicing: The Challenges.”

Chapter 1 | Introduction – What Will This Study Contribute? | 7
8 | On-Orbit Satellite Servicing Study Project Report | October 2010

Study Methodology

This internal project report provides the detailed results of the NASA On-Orbit 

Satellite Servicing Study, which includes five major activities. 

1. Conduct an industry-wide Request for Information (RFI) to notify the satellite 

servicing community of an opportunity for discussion. 

2. Conduct the International Workshop on On-Orbit Satellite Servicing in March 

2010 to engage the community. 

3. Examine notional missions to bracket the trades involved for possible 

servicing customers. 

4. Examine near-term in-space hardware demonstrations to provide relevant 

and immediate results. 

5. Develop and validate ground simulator and test bed capabilities that can be 

used to verify satellite servicing flight hardware and software. 

From these, we develop implementable recommendations for a mission sequence 

and identify gaps in the technology required for more ambitious future elements. A 

core team at NASA’s Goddard Space Flight Center (GSFC) performed the day-today work for the study. 

The industry-wide RFI was intended to gather 

information from the providers and customers of 

servicing-related technologies to supplement the 

knowledge base of our core team. A total of 70 RFI 

responses (plus 22 workshop abstracts) were received 

and are summarized in Appendix B. Of these RFI 

responses, 12 were from academia, 42 from industry, 

14 from government organizations, and 2 from 

foreign organizations.

The workshop gathered together experts in satellite servicing for a three-day event to share information. This event drew over 250 participants (234 in 

person and 20 to 30 through the web) and 58 presentations. Some of these participants were invited 

speakers because of their RFI responses. The workshop 

summary is provided in Appendix C.

The notional mission studies used the Integrated 

Design Center (IDC) at NASA GSFC to investigate 

the major trades for various servicing scenarios. A 

total of six notional mission studies were completed in 

seven weeks of IDC time. The results are discussed in 

Chapter 4, “Satellite Servicing: The Implementation” 

and also presented in detail in Appendix F.

The near-term hardware demonstrations started 

the implementation of some technologies that could 

benefit from demonstrations using the International 

Space Station (ISS). These are also discussed in 

Chapter 4.

The team reviewed past literature while 

conducting this study. These works are listed in the 

References and Related Historical Materials sections.

All of these activities were completed prior to the 

end of FY 2010.
Chapter 1 | Introduction – Assumptions | 9

Assumptions

The intent of the notional missions is to explore 

the most revealing areas of the satellite servicing 

trade space rather than to find specific solutions for 

flight projects. In other words, the notional missions 

enabled the team to identify successful engineering 

solutions that can be treated as “existence proofs” in 

subsequent analyses, rather than to produce optimized 

designs for a real mission. The notional missions were 

each developed in a one-week, intensive, and extremely challenging exercise called a design charrette.

Designing a multi-vehicle servicing mission 

within the normal constraints of a one-week charrette 

is particularly challenging given the many inter-vehicle interfaces. Mechanical interfaces are obvious, but 

every subsystem must be considered and addressed. 

For example, if one is to transfer power from a servicer vehicle to a customer vehicle after the two are 

physically mated, one must first define the duty cycle, 

the average and peak loads, and the durations. These 

are either negotiated between the two vehicles if the 

customer is designed to accommodate servicing, or 

dictated to the servicer by a legacy customer. This is 

but one example of the choreography that must be 

crafted for any servicing mission. Therefore, where 

possible, existing satellites and launch vehicles were 

used in the notional mission study process.

This is an important point, as it would be easy 

to misread the intent behind the choice of customer 

satellites in the notional mission suite. Customer 

satellites were chosen solely to facilitate the design 

charrettes and not to favor one particular mission 

over another. For any servicing configuration, the 

interfaces must be understood. In the absence of 

well-defined customer interfaces, valuable time would 

have to be spent considering details such as solar array 

shadowing, communication system relaying, mass 

properties, etc., and this time would be taken away 

from studying the more generally applicable aspects 

of servicing. For example, the Hubble Space Telescope 

(HST) was the customer satellite in Notional Mission 

3 because it is an existing low Earth orbiting satellite 

that was designed to be serviced. Accordingly, its 

interfaces exist and are well known, which allowed the 

study team to develop well-defined requirements for 

those interfaces on the notional servicer (dimensions, 

power, data, etc.). 

The launch system infrastructure assumptions 

also deserve explicit clarification. The Congressional 

language that enabled this study focused on identifying elements of the Constellation architecture that 

enable satellite servicing, such as an airlock for the 

Orion spacecraft. However, as the study progressed, 

In any study of this scope, interactions with external elements cannot be ignored. 

Specific discussions demand assumptions about the external environment that may 

or may not turn out to be correct. This is especially the case for forward-looking 

studies. In this section, we attempt to highlight some of these basic assumptions in 

five areas so that the results can be interpreted in the appropriate context. 

1. Our selection of potential customers. 

2. The agency-wide paradigms that existed and were changed during the study. 

3. How we evaluated launch vehicle considerations. 

4. The human/robotic servicing paradigm. 

5. Customer satellite cooperation levels. 
10 | On-Orbit Satellite Servicing Study Project Report | October 2010

NASA shifted focus toward the “Flexible Path” and 

the Commercial Orbital Transportation Services 

(COTS) concepts discussed by the White House 

Augustine Committee.[4] Since the notional missions 

were intended to identify commonalities and technologies that enable multiple future architectures, we 

deliberately constructed these notional missions to be 

independent of specific Constellation elements. As a 

result, some of the notional missions involve Constellation elements, some involve COTS, and some 

involve sending humans to ever-greater distances from 

the Earth. The interfaces provided by these elements 

allowed us to proceed with the study, but these interfaces should be viewed as example “boundary conditions.” We expect that a different set of boundary 

conditions (for missions with comparable objectives) 

would lead to largely the same conclusions.

The study team also deliberately chose not to 

perform any launch vehicle trade studies. Often 

during the charrettes we would discover that the 

particular launch vehicle chosen was too limiting in 

launch mass, fairing length, or fairing total volume. 

These design obstacles were not resolved with a launch 

vehicle trade. Instead, a larger fairing, more capable 

vehicle, or multiple launches were assumed so that 

the design of that notional mission’s servicer could 

continue. Therefore, we caution the reader against 

drawing conclusions from our use of any particular 

launch vehicle.

The study team discussed the potential servicing 

customers at length as we developed the notional 

mission suite. Existing satellites were selected to define 

reasonable interfaces for designing the servicer. Given 

the diversity of existing and planned satellites, every 

choice involved considerable discussion. For example, 

some members proposed studying a cryogenic tank 

depot instead of a large-aperture telescope mission. 

Intense discussion followed, centered around what 

servicing elements of a tank farm in LEO were 

unique and therefore deserving of one of the design 

charrettes and what elements were already covered. 

In the end, we concluded that Notional Mission 1 

(orbit modification) and Notional Mission 3 (LEO 

Autonomous Rendezvous and Capture [AR&C], 

communication coverage, and battery cycling) 

explored the general servicing elements well enough 

to eliminate the need for a separate charrette.

The decision to use human-robotic scenarios 

for some missions and not others was dictated by 

the desire to explore the unique areas of the satellite 

servicing trade space. Additionally, the Flexible Path 

concept of sending humans to ever-greater distances 

did influence some of the notional mission choices. If 

humans travel beyond LEO, our studies explain how 

satellite servicing is a meaningful activity that exploits 

the unique capabilities brought by a human presence.

Lastly, we define our convention for classifying 

customer satellites from the perspective of satellite 

servicing cooperation. All spacecraft servicing activities begin with an approach, rendezvous, proximity 

operations, and capture sequence that brings the 

servicer and customer spacecraft together. The servicer 

spacecraft is typically the active vehicle during the 

AR&C sequence and the customer vehicle is generally passive (i.e., not maneuvering to translate towards 

the servicer). Where possible, the servicer vehicle will 

always be designed to take advantage of any cooperative features offered by a customer vehicle. Some 

of our notional mission servicers were designed to 

conduct successful AR&C with partially cooperative 

or even non-cooperative customers when necessary. 

A cooperative rendezvous customer is one 

that offers features that make the AR&C sequence 

easier in various ways that will discussed later. By 

contrast, a non-cooperative vehicle does not offer 

such features and may instead have characteristics 

that are hindrances. For completeness, we define 

an uncooperative vehicle as one that is actively and 

deliberately attempting to foil AR&C in one or 

more ways (e.g., evasive maneuvers). The active and 

deliberate nature of the lack of cooperation here is 

what sets an uncooperative vehicle apart from a noncooperative vehicle. Note that uncooperative vehicles 

are beyond the scope of this study. In the sections that 

follow, most legacy satellites would fall into the noncooperative category. Our goal is to help ensure that 

future satellites are cooperative to the degree practical 

for their mission objectives.
 Chapter 1 | Introduction – Why Is Satellite Servicing Important? | 11

Why Is Satellite Servicing Important?

At the most general level, the answer to this question is simple. In order to push 

the boundaries of our ventures into space, we must advance beyond visiting 

destinations in space with sophisticated systems that allow no room for failure, and 

beyond bringing everything we need with us. Closer to Earth, we must be able to 

“pack out our trash” and extract the most utility from expensive space assets. All of 

these activities require some aspect of what satellite servicing capabilities offer.

There are clearly many applications for satellite servicing, each with its own definition of “importance” 

based on the scientific, economic, strategic, and 

societal benefits it offers. For instance, if the goal is to 

travel to distant destinations, depots are a potential 

enabling infrastructure and satellite servicing capabilities are required to construct and stock such depots.

Another important service that satellite servicing 

can offer is the orbital manipulation of existing 

objects, a capacity that enables the removal of debris 

and the reuse of unique orbital real estate. The debris 

issue is a serious one even today in Low Earth Orbit 

(LEO) and Geostationary Earth Orbit (GEO). In 

February 2009, an Iridium satellite collided with a 

spent Russian military satellite.[5] Today, events where 

two satellites come within several kilometers of each 

other occur numerous times each day. As time 

progresses, these unintended orbital intersections 

could lead to catastrophic debris generation in an 

“ablation cascade” or Kessler Syndrome.[6] In addition 

to the dangers of space collisions, the orbital real estate 

at Geostationary Earth Orbit (GEO) is a limited 

resource that is in high demand for communications 

satellites. Thus, strong business and national security 

cases can be made for clearing failed satellites at GEO 

to reuse their orbital slots.

Repair and refurbishment are the most visible 

successes of satellite servicing because of the 

remarkable missions to service the Hubble Space 

Telescope (HST). The life of valuable assets could 

be extended through maintenance and upgrade, 

but there is a more important related point. As our 

ambitions in space increase, the systems required to 

support these ambitions will become increasingly 

more sophisticated. One could argue that such 

systems would fail if satellite servicing were not an 

integral part of the infrastructure. As an analogy, 

consider operating an automobile in an environment 

where no repair facilities were available. No matter 

how well designed the automobile might be, it 

would eventually fail. Without the infrastructure 

and capabilities of “repair shops,” automobiles and 

satellites are only useful until the first major failure.

To better understand the issues surrounding 

servicing activities with existing customer satellites, 

we can use an intuitive categorization developed by 

Henshaw[7] that clarifies their dynamics. Suppose that 

all satellites are placed into one of these analogous 

categories for cars:

1. Fleet – a workhorse car used in car rental 

fleets. It is sturdy, high utility, and very basic 

in terms of technology. Its main utility is in 

providing the ability to get reliably from one 

place to another. Such a car is probably not 

sufficiently valuable to warrant significant 

repair, and once it reaches a certain mileage or 

age, it is removed from service and replaced 

by a newer model. Its spacecraft counterpart 

would be the commercial satellite fleet 

that provides communications services as 

a commodity. Servicing activities for this 

class of spacecraft would center around basic 

maintenance and refueling. If something 
12 | On-Orbit Satellite Servicing Study Project Report | October 2010

should go wrong, the spacecraft would simply 

and most cost- effectively be replaced.

2. Family – a car that is more likely to be 

privately owned. It provides special features 

to support the daily transportation needs 

of a family. If such a car should break, it 

would make sense for the family to repair 

it until such time that major overhauls are 

required. Its spacecraft counterpart would be 

the government spacecraft constellation that 

provides a variety of communications and 

surveillance services, but only to restricted 

customers. Servicing activities here would 

include basic maintenance and refueling, but 

because these are not commodity satellites, 

some level of repair may also be justified to 

maintain strategic capability or service, or to 

“buy time” to allow new technologies to be 

incorporated into their replacements. 

3. Exotic – a state-of-the-art car that is made 

in limited numbers. It provides special 

capabilities that are unique and deemed 

rewarding to the owner. In the case of such 

a car, even a complete refurbishment may 

be justified when it becomes necessary. For 

space missions, these would be the occasional 

cases like the Hubble Space Telescope, other 

astronomical observatories, or reconnaissance 

Figure 1.3 – Classes of Spacecraft for Servicing – Just as different cars receive different levels of maintenance, different 

spacecraft fall into different categories of servicing needs based upon their application. At the top right is a “fleet” of 

commodity communications spacecraft (based on the Orbcomm satellites). These could be compared to a fleet car for a 

rental company and would receive minimal maintenance during their profit-generating lifetime. The two spacecraft at the 

top left (based on the NASA Tracking and Data Relay Satellites) would be used for a more specific application such as 

surveillance or private communications, and would be maintained more extensively like a family car. The bottom spacecraft 

(based on the ATLAST observatory concept) represents a one-of-a-kind observatory, which would be compared to an exotic 

car and is a potential candidate for extensive servicing.
spacecraft. These spacecraft are sufficiently 

high-value and unique that great effort may 

be justified in repairing and maintaining their 

capabilities. 

This classification is illustrated in Figure 1.3. Our first 

observation is that there are many more “fleet” than 

“exotic” cars. The benefits of servicing will be very 

different for these cases.

The ability to refuel commodity communications 

satellites would likely need to be a commodity itself. 

In general, a refueling spacecraft would need to service 

multiple customers in order to be economically 

viable. Such a spacecraft would give the customer 

satellite extended life, providing a continuing revenue 

stream from an already depreciated satellite. To be 

viable, the cost of refueling must be less than this 

additional profit. If something serious were broken 

on one of these commodity satellites, it is not likely 

that mounting a special campaign to repair it would 

make more economic sense than simply launching a 

replacement.

For the family car, however, the application may 

be sufficiently specific that replacements may not be 

readily available. More extensive repairs may therefore 

be desirable if the satellite’s function is required. An 

example would be strategic communication services 

for NASA or the Department of Defense.

The exotic car clearly serves a specific purpose 

that is hard (if even possible) to replace. In this event, 

extensive repairs may be warranted. The gain in 

these cases is almost certainly realized by extending, 

restoring, or improving function.

Clearly, the definition of “importance” depends 

on the application, and each application will impose 

a set of standards against which to gauge that 

importance. This will be discussed more in Chapter 3, 

“Satellite Servicing: The Benefits.”

 Chapter 1 | Introduction – Why Is Satellite Servicing Important | 13
This section reviews some of the seminal missions that have helped to define 

satellite servicing. This is not intended to be an exhaustive list, and the reader 

is referred to other published works for this information.[8,9,10] Throughout this 

discussion, it becomes apparent that, until recently, satellite servicing has 

developed as specific critical needs arose. That is, a problem would present itself 

and, if the necessary technology existed, the problem would be resolved—and 

usually resolved successfully. This is a technology “pull” situation, or a “necessity 

is the mother of invention” strategy. There is now sufficient experience with 

these sorts of situations, both planned and unplanned, that we understand the 

challenges for a wide range of servicing activities. There are also a wide range of 

technologies waiting to be applied to this problem. Thus, we are now in more of a 

“push” situation. Once we establish the vision of what we need to do, we have a 

clear technology path for realizing that vision. 

Figure 1.4 – The Repaired Skylab – Launched in 1973, Skylab was not only NASA’s first space station, it was also the 

Agency’s first human satellite servicing endeavor. A successfully deployed parasol (seen on the top of the central cylinder of 

the spacecraft, nearer to the viewer) restored an acceptable thermal configuration and saved the mission.

What Has Been Done Before?

The Dawn of Satellite Servicing

Skylab 

In the mid-to-late 1960s, even as the Apollo program 

was in full swing, space visionaries were planning 

the follow-on programs that would eventually lead 

14 | On-Orbit Satellite Servicing Study Project Report | October 2010

to launching Skylab on May 14, 1973 (Figure 1.4). 

At launch, NASA’s first space station had already 

faced a tumultuous history. It then immediately 

developed some serious technical problems. These 

problems resulted in a delay of the second launch 

that would bring up the first Skylab crew. The two 
 Chapter 1 | Introduction – What Has Been Done Before? | 15

of flight data in this learning process.” Finally, 

the Board encouraged the assignment of an 

experienced chief engineer to major projects 

such as the Workshop or Airlock. Freed from 

administrative and managerial duties, he 

would ‘spend most of his time in the subtle 

integration of all elements of the system under 

his purview.”[11,12]

Solar Maximum Mission Repair

As spacecraft technology became more refined, so did 

the architectural designs that enabled more efficient 

mission execution. One such early design was the 

Multimission Modular Spacecraft (MMS). This design 

emphasizes a basic tenet: make the standard spacecraft 

parts modular so that 1) they can be repaired and/or 

replaced in space, and 2) ground integration and test 

costs are reduced. That same modularity that allows 

for on-orbit replacement also enables straightforward 

replacement on the ground. We note, however, that 

designing modular spacecraft remains the exception 

rather than the rule, as modularity in spacecraft 

design remains controversial.

The first spacecraft to make use of this 

architecture was the Solar Maximum Mission (SMM), 

launched in February 1980 to investigate solar 

Figure 1.5 – Solar Maximum Mission in the Space 

Shuttle Bay – The Solar Maximum Mission was one of 

the first orbiting spacecraft to be retrieved, repaired, and 

redeployed using satellite servicing. This photograph from 

1984 shows the spacecraft being repaired by astronauts in 

the payload bay of the space shuttle Challenger.

most pressing problems were the failures of the 

micrometeoroid shield and the solar arrays to deploy 

as planned. Micrometeoroid protection was not the 

main issue with the shield as the risk was small and 

not immediate. However, the shield also served a 

more critical thermal management role. Without it, 

the Skylab overheated and its cold-bias configuration 

could not be maintained, threatening its contents as 

well as human habitability and structural integrity. 

These problems aggravated each other because any 

attitude adjustments to maximize solar array output 

would also increase the solar impingement on the 

Skylab and further warm it up. These problems 

had the potential to threaten mission success and 

consequently NASA’s future in human spaceflight and 

space stations.

On May 25, just 10 days after the initial launch 

of the Skylab, the crew launched with some ingenious 

hardware on board, designed to provide a replacement 

thermal shield. After a series of heroic Extravehicular 

Activities (EVAs), Skylab was restored to acceptable 

performance limits on June 8, moving on to complete 

its amazingly diverse mission as NASA’s first space 

station. Despite the formidable challenges, the 

ingenuity of the Skylab team also led to the first 

successful demonstration of on-orbit repair.

The anomalies resulted in an Investigation Board 

that attempted to determine their causes. Among the 

many technical and managerial conclusions reached 

by the Board, several were to have a lasting impact on 

NASA’s ability to ensure mission success. These words 

are no less relevant today than they were when they 

were written almost four decades ago and should be 

applied when planning a successful servicing mission.

One recommendation called for the 

appointment of a project engineer on 

complex items that involved more than one 

engineering discipline. A second warned 

against undue emphasis on documentation 

and formal details: “Positive steps must always 

be taken to assure that engineers become 

familiar with actual hardware, develop 

an intuitive understanding of computerdeveloped results, and make productive use 
phenomena during an active part of the solar cycle. 

It operated until January 1981 when a failure in the 

attitude control system truncated the mission.

Making full use of the MMS design, NASA 

launched an ambitious recovery mission in April 1984 

that fully restored SMM operation until it reentered 

in December 1989 (Figure 1.5). During this repair 

mission, STS-41C, the space shuttle Challenger 

maneuvered close to the MMS and successfully 

captured it. Astronaut EVAs replaced the failed parts, 

and the SMM was redeployed from the Challenger 

payload bay.

This successful first use of the space shuttle to 

repair a valuable asset set the stage for the more 

ambitious undertakings that would follow.

Palapa B2 and Westar 6

Almost immediately after the SMM success, the 

space shuttle was called upon for yet another on-orbit 

servicing challenge. As reported on August 23, 1984 

in New Scientist :

[13]

America’s space shuttle may make its 

second salvage run into space on 2 

November. Encouraged by the rescue and 

repair of the Solar Maximum Mission 

Satellite by shuttle astronauts on 10 April, 

NASA is planning a similar attempt. 

Figure 1.6 – Palapa B2 Recovery – Palapa B2 being 

manipulated by an astronaut in a free-flying Manned 

Maneuvering Unit. Palapa B2 was returned to Earth for 

refurbishment and eventual reflight. 

This time, astronauts would hook on to 

at least one of the two malfunctioning 

communications satellites now drifting 

uselessly...

 The satellites are Palapa B2, owned 

by the Indonesian government, and 

Westar 6, owned by Western Union. 

Last February, shortly after the two craft 

were released from the cargo bay of the 

shuttle, Challenger, both of their upperstage rockets misfired. Neither satellite has 

functioned since. 

On November 8, 1984, Discovery’s STS-51A 

mission launched and deployed two new satellites as 

planned. Subsequently, it successfully retrieved the 

two errant spacecraft through daring and dramatic 

EVAs that saw the use of the astronauts’ free-flying 

Manned Maneuvering Units (MMUs, see Figure 1.6). 

Discovery then returned these satellites to Earth for 

refurbishment and reflight. This dramatic recovery 

of two satellites that had never been intended for onorbit servicing led to the headline, “Insuror Delighted 

By Space Rescue And Implications,” with the quote, 

“What’s happened here goes beyond any commercial 

results and in our judgment ushers in a new era of 

insurance practice in space programs.”[14]

This is an early example of an on-orbit servicing 

activity resulting in commercial benefit. The insurers 

paid the owners of the satellites a total of $180 

million for the initial loss, and were planning on 

recouping $50 million of those costs after the failed 

satellites were retrieved and resold.[15] This plan 

ultimately returned both spacecraft to space in April 

1990, as Palapa B2P and AsiaSat 1.[16]

This interest from the satellite insurance industry 

continues to be relevant today: “Adam Sturmer, vice 

president at Marsh Space Projects, one of the world’s 

three principal space-insurance brokers, said that 

in the last four years, insurance underwriters have 

paid out some $700 million in claims for satellite 

failures caused by propulsion-leak issues or due to the 

satellites being placed into too-low orbits. In either 

case, on-orbit servicing could have sizable appeal to 

operators or underwriters.”[17]

16 | On-Orbit Satellite Servicing Study Project Report | October 2010
 Chapter 1 | Introduction – What Has Been Done Before? | 17

Satellite Servicing Gets Its Challenge

Hubble Space Telescope

The challenges and successes in the early days of 

satellite servicing would presage the maturation of 

this discipline in the 1990s. This was the start of 

the Hubble Space Telescope (HST) era. HST was 

designed specifically to support on-orbit servicing and 

evolved the entire discipline in major ways (Figure 

1.7). It defined the methodologies of crew training, 

coupled with tool design and procedure, testing, and 

verification, to support complex servicing missions. 

“Test, test, and retest” and “train, train, and retrain” 

became the mantras that led to success. Orbital 

Replacement Unit (ORU) and Orbital Replacement 

Instrument (ORI) design improved as the project 

developed experience through the servicing missions, 

ranging from “simple” box removals and replacements 

in the beginning to very intricate board-level repairs 

at the end. These missions also demonstrated how 

to successfully use nominal mission planning, 

preplanning for contingencies, in situ contingency 

assessment, and detailed simulation tools to help 

ensure success.

Deployed by the space shuttle Discovery on 

April 25, 1990, HST suffered international notoriety 

when initial checkout found an optical flaw (spherical 

aberration) in its primary mirror. The HST also 

experienced thermally induced “jitter” or shaking 

from its solar arrays during orbital sunrise and sunset. 

Both of these anomalies blurred the images from an 

otherwise functional observatory. This was the first 

of NASA’s Great Observatories, and, once again, 

the reputation of the agency was at stake. As HST 

targeted those scientific topics that could tolerate 

the imperfect images, NASA initiated an ambitious 

program to restore the capabilities of the observatory 

Figure 1.7 – HST First Servicing Mission: COSTAR Installation – The first Hubble Space Telescope Servicing Mission 

restored the observatory by replacing the High Speed Photometer instrument with the new COSTAR corrective optics, 

designed to correct Hubble’s faulty vision. Both of these modular, telephone-booth sized instruments were designed to be 

replaced in-orbit.
through astronaut servicing. A servicing mission 

had already been planned to support repair and 

refurbishment, but not to resolve such a major and 

unexpected problem.

A series of corrective optics were designed, 

built, and tested as the centerpiece for this task. The 

Corrective Optics Space Telescope Axial Replacement 

(COSTAR) housed one set of optics in an axial 

instrument enclosure that replaced the High Speed 

Photometer, a relatively underutilized instrument 

in the original complement. This innovative optical 

system deployed by internal mechanisms and 

corrected the telescope beam for the remaining three 

axial instruments. The Wide Field and Planetary 

Camera 2 (WFPC2), which contained a second set of 

corrective optics internal to the instrument, replaced 

the original Wide Field/Planetary Camera. NASA’s 

European partner, the European Space Agency 

(ESA), had provided the original solar arrays. ESA 

successfully rebuilt a set of improved solar arrays 

to minimize the thermal sensitivity. Several other 

spacecraft components were also flown to replace/

augment the original set.

On December 2, 1993, after a rapid-development 

program of only three years, the First Servicing 

Mission (FSM) was ready and launched on the space 

shuttle Endeavour (STS-61). This was one of the most 

complex and challenging human spaceflight missions 

ever attempted. In five consecutive days spanning 35 

hours and 28 minutes of EVA, the crew successfully 

performed all of the planned activities. This “mother 

of all servicing missions” was fully successful, restoring 

the originally planned capabilities and in some 

cases improving beyond them. Once again, satellite 

servicing demonstrated its utility.

During this mission, activities focused on 

replacing Orbital Replacement Instruments (ORIs) 

and Orbital Replacement Units (ORUs). This was 

the design intent for HST as well as the servicing 

infrastructure that was planned to support it. 

In addition to repairing the optics (by installing 

COSTAR and WFPC2) and the solar arrays (by 

replacing the old solar arrays and one set of drive 

electronics), this mission also installed coprocessors 

for the flight computer, restored magnetometer 

function, replaced two Rate Sensor Units (gyroscope 

assemblies) and gyroscope electronic control 

units, and installed the Goddard High-Resolution 

Spectrograph redundancy kit. The replacement of the 

magnetometers was the first HST repair that used an 

interface that was not originally intended for on-orbit 

servicing.

In total, this extraordinary achievement was 

successfully repeated four more times over the next 

16 years. This epic has been told in many forms.[18,19]

Here we focus on the satellite servicing aspects.

In February 1997, Servicing Mission 2 advanced 

the scientific power of HST by installing two “second 

generation” instruments. These were ORUs by nature 

since they were designed to be removed and replaced 

by EVA. The Space Telescope Imaging Spectrograph 

(STIS) advanced spectroscopy and enabled studying 

supermassive black holes at the centers of galaxies. The 

Near Infrared Camera and Multi-Object Spectrometer 

(NICMOS) opened up the near-infrared wavelength 

region on HST and enabled study of the distant 

supernovae that are key to solving the Dark Energy 

problem.

There was work to do on the spacecraft side as 

well. One of the Fine Guidance Sensors (FGS) was 

replaced and an electronics control box was added. 

This was the first FGS to incorporate hardware 

for spherical aberration correction. A solid state 

recorder was installed to improve the reliability of 

the engineering data stream, and a reaction wheel 

assembly was replaced. In addition, a Data Interface 

Unit (DIU) was replaced and the set of Solar Array 

Drive Electronics (SADE) that was not replaced on 

the FSM was replaced with a refurbished version 

of the returned unit from the FSM. Some of the 

unexpected damage to the light shield multi-layer 

insulation was repaired in situ using improvised tools 

and materials on board Discovery.

While the FSM still focused on ORU-level 

activities, three servicing developments are worthy of 

note. The DIU interfaces were very challenging and 

required extensive training and testing. This would 

pave the way for even more ambitious electrical 

18 | On-Orbit Satellite Servicing Study Project Report | October 2010
 Chapter 1 | Introduction – What Has Been Done Before? | 19

connector manipulations in the future. Secondly, 

the theme of returning hardware for refurbishment 

and later reinstallation was starting to emerge with 

the refurbished SADE installation. Finally, the 

contingency light shield repairs heralded an era of 

unplanned repairs of significant complexity.

Servicing Mission 3 (SM3) was split into two 

flights (Servicing Missions 3A and 3B) to respond 

to the schedule pressure from failing gyroscopes. 

Indeed, in December 1999, Discovery visited HST 

on SM3A while Hubble was in safe mode because the 

observatory lacked sufficient functional gyroscopes. 

This mission provided a fresh set of gyroscopes in 

addition to a new advanced computer, another 

refurbished FGS, handrail covers, a new transmitter, 

and another solid state recorder. A partial set of New 

Outer Blanket Layers (NOBLs) was installed to 

help manage temperature, as the original insulation 

had degraded with age. Again, the theme of reusing 

refurbished parts was reinforced with the FGS 

reflight. The installation of the NOBLs was the start 

of on-orbit assembly on HST.

In March 2002, Servicing Mission 3B saw 

Columbia carry the “scientific advancement” portion 

of the SM3 manifest. A new camera, the Advanced 

Camera for Surveys (ACS), took over the main 

imaging function from the aging WFPC2 instrument. 

An experimental NICMOS Cooling System (NCS) 

provided the NICMOS instrument with auxiliary 

cooling to permit operation after its cryogen was 

depleted. In addition, this mission installed rigid 

Solar Arrays that provided more power with less area, 

replaced a Reaction Wheel Assembly, replaced another 

set of gyroscopes, and replaced the Power Control 

Unit (PCU). Of note here is that the NCS was a 

custom-made design to respond to an unforeseen 

situation. Its installation required careful planning for 

both the interior of the HST and its exterior, where 

a large radiator was installed to remove the heat from 

a new mechanical cryocooler. This degree of on-orbit 

assembly is now “routine.” The PCU replacement 

also represented a tour de force in training and 

manipulation of a unit with electrical connectors that 

were never intended to be removed and reconnected 

by EVA.

After SM3B came a long hiatus in HST servicing. 

The Columbia tragedy brought a deep examination 

into the roles of human spaceflight. During this 

time, significant advances were made in planning 

and preparing for robotic servicing of HST. Program 

plans and some hardware development were started 

in anticipation of the Hubble Robotic Servicing and 

Deorbit Mission (HRSDM). In April 2005, NASA 

decided that another space shuttle servicing mission 

would be allowed with some additional safety rigor 

incorporated into the mission training and operations. 

Work stopped on HRSDM to focus on the final 

human visit to HST.

In May 2009, Servicing Mission 4 was launched 

on the space shuttle Atlantis. It brought even more 

Figure 1.8 – HST Servicing Sophistication Progression – Servicing the Hubble Space Telescope demanded more than replacing hardware 

that was designed to be serviced. As unexpected issues arose during the past 20 years of the mission, many tasks required developing 

innovative techniques to solve specific problems. From left to right: First, the repair of the light shield during SM2. Second, the installation of 

the New Outer Blanket Layer during SM3A. Third, the attachment of the NICMOS Cooling System external radiator during SM3B. Last, the 

card removal for the Advanced Camera for Surveys Repair during SM4. Each repair required accessing interfaces that were not designed for 

servicing, and each was fully successful.
humankind’s largest artificial satellite, it orbits the 

Earth with a mass of over 385,000 kg (at assembly 

complete), spans 108.5 m in its longest dimension, 

and has 937 m3

 of pressurized volume. Its solar 

arrays cover an area of 3,567 m2

. Eighty-four kW of 

electrical power are distributed to operate ISS systems 

and experiments. The first module, the Functional 

Cargo Block or Zarya, was launched in 1998. The 

Expedition 1 crew of Bill Shepherd, Yury Gidzenko 

and Sergei Krikalev first occupied ISS on November 

2, 2000. There has been a continuous human presence 

in space ever since. About 200 people representing 

15 countries have been on ISS to date. It serves 

as an orbital human outpost where a wide variety 

of research is conducted and where many of the 

technologies needed for human exploration beyond 

Low Earth Orbit (LEO) are being demonstrated. 

ISS demonstrates the value and utility of onorbit construction. The sheer size of the space 

station precludes ground assembly, test, and launch 

as an entire unit. As a result, standard interfaces 

between elements were well defined to facilitate onorbit connection. Ground testing, including space 

qualification tests in thermal-vacuum chambers, 

was conducted at the module or subsystem level. 

Final integration and checkout of each new element 

occurred on-orbit as they were added. Assembly has 

taken 34 shuttle and 4 Russian (two Proton and two 

Soyuz launch vehicles) flights to date (through STS132 in 2010) to deliver and outfit some 33 major ISS 

on-orbit elements. Construction of the ISS has thus 

far required 143 spacewalks—28 from the shuttle 

and 115 from the U.S. Quest airlock—for a total 

of about 900 hours, in addition to 34 spacewalks 

from the Russian Pirs airlock. The total EVA time 

on ISS is more than an order of magnitude greater 

than the total Apollo EVA time. Astronauts have 

performed a variety of on-orbit maintenance tasks 

including clearing solar array panels snagged during 

deployment, repairing a torn array, lubricating the 

ISS Solar-Array Alpha Rotary Joint, and removing 

and replacing failed components such as a Control 

Moment Gyroscope, as well as installation and 

retrieval of external research payloads. Most recently, 

scientific capabilities to HST through the Cosmic 

Origins Spectrograph and the Wide Field Camera 

3. Astronauts performed the first on-orbit circuit 

board replacements through the STIS and ACS repair 

activities. To leave the observatory in the best state 

possible, HST also received new gyroscopes, another 

new Fine Guidance Sensor, new batteries, and a new 

set of NOBLs. In anticipation of a future deorbiting 

requirement, a Soft Capture Mechanism and Low 

Impact Docking System was installed at the aft end of 

HST to provide a standard interface for autonomous 

rendezvous and capture (AR&C).

Each of the five HST Servicing Missions brought 

its own challenges (see Figure 1.8). They were all 

overcome to achieve 100% mission success over the 

course of a two-decade history—an extraordinary 

demonstration of the benefits and versatility of 

satellite servicing.

International Space Station, The “Killer App”

To date, the International Space Station (ISS) is 

arguably the “killer app” for satellite servicing. As 

Figure 1.9 – ISS SSRMS Installing Cupola – In the grasp of 

the Canadarm2, the Cupola is relocated from the forward 

port to the Earth-facing port of the International Space 

Station’s newly-installed Tranquility node. NASA astronauts 

Terry Virts, STS-130 pilot; and Kathryn Hire, mission 

specialist, moved the Cupola, operating the station’s 

robotic arm from controls inside the Destiny laboratory. 

Also visible are a Soyuz spacecraft, the (space shuttle) 

Remote Manipulator System and portions of space shuttle 

Endeavour. This operation is a dramatic demonstration of 

the results of humans and robots working cooperatively. 

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 Chapter 1 | Introduction – What Has Been Done Before? | 21

finer operations than the space shuttle arm or 

SSRMS. This enables activities such as the removal 

of failed components and installation of spare units. 

Dextre can be attached either to the SSRMS, onto 

the ISS Mobile Base System, or to a number of fixed 

locations around the ISS.

The ISS may be used as a platform for developing 

tools and techniques for human and robotic assembly 

of other large structures in space, such as large 

optical telescopes (see Figure 1.10). A number of 

demonstration concepts have been proposed to take 

advantage of the availability of astronaut spacewalks 

and dexterous robotics such as Dextre, as well as the 

utilities and support structures on the ISS.

Dextre is also a tool to develop new dexterous 

robotic applications. Operating telerobotically 

from the ground, it will be used to demonstrate the 

capability to service and refuel a satellite not originally 

designed to be serviced on orbit. The Robotic 

ISS astronauts successfully repaired a failed cooling 

system in an ambitious application of servicing 

capabilities.

ISS internal and external research facilities 

support a broad array of experiments. Internal 

facilities include human and biological test facilities, 

physical science and materials, combustion, and 

fluid science research equipment racks. A nadirfacing, high-optical-quality window is available 

for performing Earth science observations. Three 

basketball-sized Synchronized Position Hold Engage 

Reorient Experimental Satellites (SPHERES) are also 

now available as an ISS facility. These were originally 

developed by the Defense Advanced Research Projects 

Agency (DARPA) to conduct formation flying and 

constellation experiments in the ISS “shirt sleeves” 

microgravity environment.

There are a number of external research facilities 

on the ISS as well. These include several sites along 

the U.S. Truss where four ExPRESS Logistics Carriers 

(ELCs), two zenith and two nadir facing, will be 

attached. Each ELC has two locations where research 

payloads can be installed and operated. External 

experiments can also be installed and operated on 

the Japanese Kibo External Facility and the European 

Space Agency’s Columbus External Payload Facility. 

Robots have played an important part in ISS 

construction and maintenance (see Figure 1.9). The 

space shuttle robotic arm has removed a number of 

new ISS elements from the shuttle’s payload bay and 

transferred them to the larger Space Station Remote 

Manipulator System (SSRMS) for berthing or preinstallation positioning. The SSRMS also provides 

a platform for spacewalking astronauts conducting 

assembly or maintenance operations. SSRMS is 

used to grasp and berth visiting vehicles such as the 

Japanese H-II Transfer Vehicle (HTV) and the future 

SpaceX Dragon and Orbital Cygnus.

The Canadian Special Purpose Dexterous 

Manipulator (SPDM), or Dextre, provides the 

capability to allow some operations previously 

requiring a spacewalk to now be performed 

robotically. Dextre is 3.5 m tall and has two 

independent robotic arms that can conduct much 

Figure 1.10 – ISS Solar Array Repair – While anchored to 

a foot restraint on the end of the Orbiter Boom Sensor 

System (OBSS), astronaut Scott Parazynski, STS-120 

mission specialist, participates in the mission’s fourth 

session of extravehicular activity (EVA) while space shuttle 

Discovery is docked with the International Space Station. 

During the 7-hour, 19-minute spacewalk on November 

3, 2007, Parazynski cut a snagged wire and installed 

homemade stabilizers designed to strengthen the damaged 

solar array’s structure and stability in the vicinity of the 

damage. Astronaut Doug Wheelock (out of frame), mission 

specialist, assisted from the truss by keeping an eye on the 

distance between Parazynski and the array. Once the repair 

was complete, flight controllers on the ground successfully 

completed the deployment of the array.
Refueling Mission (RRM), discussed in Chapter 4, 

will include a number of task boards and refueling 

ports configured to represent typical legacy spacecraft. 

Special tools will be used by Dextre to remove thermal 

insulation, access test ports, cut safety wires, remove 

tertiary and safety caps, and transfer a fluid with 

properties similar to hydrazine (a typical satellite fuel) 

into a receiving tank.

The Dextre Pointing Package (DPP), also 

discussed in Chapter 4, will use Dextre to 

demonstrate a fine pointing capability for future Earth 

and space instruments. DPP, operating in Dextre’s 

grasp, will also observe visiting vehicles approaching 

ISS to evaluate a number of sensors and to assist in 

the development of algorithms and techniques for 

autonomous rendezvous and capture.

Robonaut 2 (R2) is another robotic enhancement 

to ISS. R2 is a “human-equivalent” robot with fine 

hand and joint control (Figure 1.11). It will initially 

operate in the internal pressurized ISS environment. 

Eventually, a variant of R2 may be used as an 

astronaut aid on the outside of ISS.

Over the course of its assembly and utilization to 

date, ISS has put into practice and perfected the best 

lessons learned thus far in satellite servicing.

Technology Demonstrators

The potential of satellite servicing has not escaped the 

attention of most major organizations associated with 

space research. Here we list a few historical and recent 

examples of technology demonstration activities. The 

intent of these activities is to mature key servicing 

technologies to the point where we can confidently 

assemble the systems we are envisioning today.

NASDA: Engineering Test Satellite VII 

On November 28, 1997, the National Space 

Development Agency of Japan (NASDA) launched 

the Engineering Test Satellite Number 7 (ETSVII). It was the first demonstration of autonomous 

rendezvous and docking involving a “chaser” 

spacecraft and a “target” spacecraft. These parts were 

launched together in the H-II rocket fairing. The 

Chase Vehicle included a 2 m robotic arm used to 

grapple the Target. Relative GPS successfully provided 

navigation information to the Chase Vehicle to control 

the maneuvers. This successful mission demonstrated 

basic technologies of rendezvous and docking, not as a 

complete sequence, but in its component parts. It also 

supported several related experiments on teleoperation 

and latency, ORU exchange and assembly of a space 

structure, and dynamic coordination between the arm 

and the spacecraft.[20] It is remarkable that given the 

success of this mission, it would be another decade 

before the next and more complex demonstrations 

would take place.

U.S. Air Force: Experimental Spacecraft System 

Starting in the late 1990s, the United States Air 

Force Research Laboratory built a series of low-cost 

“microsatellites.” Among them were XSS-10, launched 

in January 2003, and XSS-11, launched in April 

2005, both of which demonstrated key technologies 

for satellite servicing. XSS-10 acquired and tracked its 

own second stage, navigated around this object, and 

performed a series of inspections ranging from 100 m 

to 35 m from the second stage. XSS-11 demonstrated 

autonomous operations and in particular, autonomous 

proximity operations. It navigated to several U.S.-

owned objects in space and moved around these 

objects while taking images.

Figure 1.11 – Robonaut 2 – A “human equivalent” robot, 

Robonaut 2 (R2), handles tools similar to the ones it will 

use after its deployment to the International Space station 

in early 2011. 

22 | On-Orbit Satellite Servicing Study Project Report | October 2010
 Chapter 1 | Introduction – What Has Been Done Before? | 23

autonomous docking with NEXTSat and demonstrated fuel transfer as well as some ORU activities such as 

the insertion of a battery into NEXTSat and changeout of a flight computer on ASTRO. During its 

roughly 4-month mission, Orbital Express provided 

confirmation that key technologies needed for satellite 

servicing are now in place. 

New International Initiatives

Deutsches Zentrum für Luft- und Raumfahrt e.V. 

(DLR), the German Space Agency, announced in 

February 2010 that it had awarded contracts for five 

components of its on-orbit servicing demonstration, 

the German Orbital Servicing Mission. The contracts 

are for overall system management, tracking, and 

rendezvous with the customer satellite, disposal of the 

customer satellite, design of the customer satellite, 

and the design of the servicer’s payload, which 

includes a robotic arm and docking mechanism. 

During the on-orbit demonstration, the servicer and 

customer satellite would be launched together and 

would separate once in orbit, similar to the Orbital 

Express mission. The servicer would rendezvous with 

and capture the customer satellite and then guide the 

system into an Earth reentry. Germany looks at this as 

a way to propel their country to the forefront of this 

technology.[22]

Canada’s MacDonald, Dettwiler and Associates 

Ltd. (MDA) announced in March 2010 that it is 

designing a mission to demonstrate satellite refueling 

as well as moving inoperable satellites into “graveyard” 

orbits. The servicer would dock with the satellite’s 

apogee kick motor, peel away insulation, connect to a 

fuel line, and deliver propellant. MDA is prepared to 

finance part of the mission itself, and it is talking with 

potential customers to establish enough of a demand 

to finance the rest of the mission. The eventual 

business model could have customers paying per 

kilogram of fuel that has been successfully added to 

their satellite; the affordable price per kilogram would 

be determined by the additional revenue generated by 

the operator from the extended operational life of the 

satellite. The mission would have an on-orbit life of 

about 5 years and would carry enough fuel to perform 

10 or 11 refueling or retirement missions.[17]

Demonstration of Autonomous Rendezvous 

Technology

The Demonstration of Autonomous Rendezvous 

Technology (DART) mission was launched on 

April 15, 2005, with the intent of demonstrating a 

suite of on-orbit technologies that would support 

autonomous rendezvous and proximity operations. 

This was again a two-component experiment 

consisting of the DART spacecraft and the previously 

launched (1999) Multiple Paths, Beyond-Line-ofSight Communications (MUBLCOM) satellite.

The launch, early orbit, and rendezvous operations were fully successful. The DART subsequently 

used significantly more fuel than planned during the 

proximity operations phase due to a sensor anomaly 

and a non-optimal software response. This resulted 

in a collision with the MUBLCOM and subsequent 

successful triggering of autonomous retirement operations for the DART spacecraft. The mishap report[21]

identified a likely series of events and root causes 

that led to this anomaly. Among the recommendations in the report was a need for stronger systems 

engineering for such a technically challenging project.

It also highlighted that the goals of this mission are 

central to our future endeavors in space, and that its 

classification and acceptance as a “high risk” mission 

(according to NASA procedures, currently specified as 

NASA Procedural Requirements NPR 8705.4, “Risk 

Classification for NASA Payloads”) caused unintended consequences as the project team dealt with the 

usual cost and schedule challenges.

DARPA: Orbital Express

The Orbital Express mission sponsored by the 

Defense Advanced Research Projects Agency 

(DARPA) provided the first demonstration of successful end-to-end robotic satellite servicing activities. The 

system launched on March 8, 2007, and consisted 

of two spacecraft: the Autonomous Space Transport 

Robotic Operations (ASTRO) vehicle and a prototype modular NEXT-generation serviceable Satellite 

(NEXTSat). NEXTSat was designed with servicing 

in mind, and in particular, for servicing by ASTRO. 

During the mission, ASTRO successfully performed 
interesting background material and existing literature 

for that time on aerospace robotics). In addition to 

making recommendations for priority technology 

investments, an interesting conclusion in this report 

is that commercially available robotics systems at the 

time could often be adapted for space applications. 

This conclusion may have been largely due to the very 

limited investments that NASA had made in robotics 

technologies, a situation that has improved but still 

largely exists today. 

NASA’s servicing strategy at that time went 

on to outline a series of increasingly challenging 

objectives: building upon demonstrations at ISS and 

in Low Earth Orbit (LEO), then moving outward 

to Geostationary Earth Orbit (GEO) and other 

locations as the capabilities improved. Likewise, 

the strategy planned for increasingly capable robot 

systems, supported by agency technology investments. 

Throughout, the NASA strategy emphasized 

developing the “business model” basis for servicing: 

Were there sufficient numbers of candidate satellites 

that could be serviced?

Finally, a key element to the NASA servicing 

strategy was the necessity of establishing common 

standards among satellite designs to facilitate servicing 

and upgrading, including modularity of systems and 

commonality of connectors, ports, and grappling 

fixtures.

Ironically, almost exactly a year after the public 

presentation of NASA’s servicing plan, the OMV 

“space tug” that was central to NASA’s servicing 

strategy was cancelled due to budget pressure. 

NASA completed no comparable, high-level 

planning for servicing after the 1989 workshop was 

published, although “lessons learned” on satellite 

servicing were compiled in 1990 (NASA 408-M&R0302-0009) by the On-Orbit Servicing Steering 

Committee, which apparently only met a limited 

number of times. In the 1980s and 1990s, the NASA 

Telerobotics Program funded projects addressing onorbit assembly and servicing, science payload tending, 

and planetary surface robotics. 

Our study confirms these findings from the past, 

with updates based on the advances and experiences 

In May 2010, MDA announced its plan to 

initiate a major investment in the on-orbit servicing 

business, calling it its most promising new business 

venture.[23] By July 2010, MDA seemed to have 

cleared most of the technical hurdles to achieving 

their goal. However, due to lingering and substantial 

financial and liability-related questions, it also 

appeared that their plans might be at risk.[24]

Historical Activities

More than two decades ago, NASA sponsored a 

multiyear series of studies and workshops on various 

topics in satellite servicing. Although the technology 

and candidate “customer satellites” have changed 

considerably, most notably in the capabilities of 

robot and sensor systems, many of the same issues 

assessed in the late-80s were considered in this study. 

In appreciating that 20-year-old work, it is worth 

remembering that neither the ISS nor HST had been 

launched when most of that material was written 

and recommendations were submitted to NASA 

Headquarters for action.

The breadth of satellite servicing studies were 

presented and discussed in four annual conferences 

on satellite servicing, culminating in June 1989 

with the Satellite Services Workshop IV at NASA’s 

Johnson Space Center (JSC-23655). This conference 

summarized much of the preceding half-decade’s work 

and presented priority recommendations to enable 

future servicing in space. Significantly, the NASA 

Headquarters Office of Space Flight draft strategic 

plan for satellite servicing was presented and discussed 

(see also Levin, G. and Erwin, H. Jr., “An Overview of 

the Office of Space Flight Satellite Servicing Program 

Plan,” Acta Astronautica 8 (1988: 55-61). Specifically, 

the strategic plan highlighted use of the ISS with 

the Orbital Maneuvering Vehicle (OMV) and space 

shuttle to achieve four priority goals: (1) refueling or 

resupply, (2) repairing, (3) retrieving, and (4) system 

upgrade. 

Presentations and discussion at this final 

workshop drew upon the recently released Technology 

Assessment for a Robotic Satellite Servicer System (1988, 

JSC 22970, Volumes III and IV; Volumes I and II are 

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 Chapter 1 | Introduction – What Has Been Done Before? | 25

Later in the space shuttle era, servicing tools 

and techniques evolved to make use of EVA and 

robotic tools developed to support the space shuttle’s 

systems and its mission. The most notable robotic 

tool has been the Remote Manipulator System 

(RMS), first flown aboard the space shuttle Columbia 

during STS-2 in November 1981. A teleoperated 

robotic system, the RMS extended the shuttle’s 

capabilities outside the payload bay through grasping, 

positioning, and control. EVA and robotic tools 

would come together for the first time for servicing 

during the Solar Maximum Mission (SMM) repair. 

A specifically engineered servicing tool, the Trunnion 

Pin Acquisition Device (TPAD), was developed to 

support EVA capture of SMM. The RMS ultimately 

grappled the SMM spacecraft and enabled the EVA 

crew to replace and repair SMM components using 

shuttle EVA tools. The successful SMM recovery 

and repair mission showed that servicing using a 

combination of standardized and specific EVA tools 

is possible, and that space shuttle and EVA crew 

capabilities can be enhanced by using those tools.

The HST Flight Systems and Servicing Project 

incorporated the lessons learned from SMM when 

developing the methodologies for the HST First 

Servicing Mission (FSM). Once again, the RMS 

would grapple the customer spacecraft. More 

significant evolution of servicing tools took place 

in the nature of the EVA tools (see Figure 1.12). 

in the intervening years. The development of the 

satellite servicing discipline has taken a somewhat 

less direct path than predicted by previous studies. 

Nevertheless, it has advanced through a combination 

of need, technological readiness, and perhaps most 

importantly, a growing acceptance of its many 

benefits.

The Evolution of Tools and Techniques

As satellite servicing has evolved, so have the tools and 

techniques used to perform its functions. We have 

come to understand that the tools and techniques are 

a central part of any servicing activity. The “actor” (be 

it an astronaut or a robot) always has constraints on 

how it can perform operations. The specific servicing 

task places requirements that may or may not be 

easily satisfied within those constraints. The tools and 

techniques are how the capabilities of the actor are 

transformed into the actions required for the task. 

This evolution can be seen in a brief review of the 

servicing missions performed to date and the tools 

developed for these missions.

During Skylab 2, the first manned mission to 

that facility, repairs to the observatory’s thermal shield 

and solar arrays were performed using human EVA. 

The tool design followed a utilitarian approach with 

telescoping rods, cable cutters and pry bars. Simple 

but effective, these efforts laid the groundwork for 

future servicing tool development.

Figure 1.12 – EVA Power Tool Progression – Astronaut servicing tools have progressed as the complexity of servicing tasks has increased. 

Shown here is a series of EVA power tools—torque-producing, battery-powered, bolt-turning drivers—developed over the course of the 

space shuttle and ISS Programs. From left to right: the original shuttle Mini Power Tool is a low torque, household screwdriver with limited 

capacity and reliability. The Power Ratchet Tool was developed for the HST Deployment Mission to provide high-torque and long battery 

life, and continued in service for all HST Servicing Missions. The Pistol Grip Tool was developed jointly between the HST and ISS Programs, 

as both were in need of a medium-torque, highly accurate, and self-contained tool for precision and construction tasks. The Mini Power 

Tool was developed for HST Servicing Mission 4 as a high-speed, high-precision, illuminated dexterous screwdriver capable of removing 

hundreds of tiny fasteners.
Servicing tool evolution continues to this day, 

with special concentration given to the development 

of robotic tools for ISS demonstration activities. The 

success of on-orbit servicing continues to be directly 

tied to the heritage development of unique servicing 

tools, highlighting the importance of having the “right 

tool for the job.”

The servicing tasks required improved power tool 

performance in areas such as battery life, torque, and 

reliability that drove the tool development activities. 

Figure 1.12 shows the increasing use and necessity of 

power tools that enabled the vastly increased efficiency 

for the sequence of HST servicing missions.

HST servicing missions also required advancements in servicing tool dexterity and specialization 

as the complexity of EVA operations increased. This 

began with replacements of ORUs that were designed 

for EVA changeout (FSM and SM2) and progressed 

to non-EVA friendly ORU replacement and electronics board level repairs (SM3A/B and SM4). Again, 

servicing tool design evolved to meet the challenge 

(see Figures 1.13 and 1.14). By the end of SM4, 

HST repair astronauts had taken on-orbit servicing 

to a new level by not only proving that it is possible 

to remove and contain hundreds of tiny non-captive 

screws, but also by demonstrating how to go well 

beyond the interchange of Orbital Replacement Units 

to executing circuit board-level repair of embedded 

systems. A milestone achievement for servicing tool 

design, HST servicing missions proved that “brain 

surgery” is possible in space through the successful 

repair of the ACS Charge-Coupled Device detector 

readout electronics.[25]

Figure 1.13 – Unique, Purpose-Built, On-Orbit Repair Tools – By the last HST Servicing Mission, servicing tools had progressed to the 

point where tasks that were complex on Earth were successfully completed on-orbit. During the HST Servicing Mission 4, two scientific 

instruments, the Space Telescope Imaging Spectrograph (STIS) and the Advanced Camera for Surveys (ACS), were both partially 

disassembled and repaired on-orbit by astronauts using purpose-built servicing tools. Neither instrument was designed to be serviced 

on-orbit. The disassembly operations required dozens of tiny screws to be removed and then contained to prevent them from floating into 

sensitive areas. The technology of the Fastener Capture Plate (left) facilitated these operations. Additionally, the instruments contained 

electronics boards that had to be replaced. This operation required ensuring that the astronaut be absolutely protected from dangers such 

as sharp edges, while simultaneously protecting the electronics boards from unintended contact and electrostatic discharge (ESD) damage. 

Unique tools such as the Card Extraction Tool and Wire Cutter Tool (middle and right) were created to accomplish these tasks. Today, both 

observatory instruments are operating again, in part because of the dexterity and efficiency made possible by these tools.

Figure 1.14 – Astronaut Training Refines the Tools 

and Improves On-Orbit Performance of the HumanMachine Interface – Astronauts John Grunsfeld and Mike 

Massimino concentrate on their training with the Fastener 

Capture Plate.

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 Chapter 1 | Introduction – What Has Been Done Before? | 27

“There Is Nothing To Service”

Sullivan[8] studied all Earth-orbiting commercial, 

civilian, scientific, and military spacecraft launched 

from January 1984 to December 2003 and found that 

on-orbit spacecraft failures occur on a regular basis. 

Considering potentially telerobotically serviceable 

failures only, on an average annual basis there are 

about 4.4 component level spacecraft failures, 3.8 

more complex systemic failures, and 0.3 deployment 

anomalies. Beyond component and system failures, 

a number of propulsive or refueling servicing 

opportunities also occur—about 1 spacecraft per year 

requires assistance to correct delivery into the wrong 

orbit (need transfer from launch shortfall to GEO), 

about 20 GEO spacecraft reach the end of useful fuel 

(could be refueled or relocated to disposal orbit), and 

about 13 spacecraft perform relocations in the GEO 

belt, using up station-keeping fuel. 

Other opportunities that carry a less direct economic impact also occur. About 20 new spacecraft are 

deployed in GEO each year. Deployment monitoring 

of these 20 satellites is likely of value to many operators. Also, of the active population of GEO spacecraft 

(~200), an annual inspection for micrometeoroid and 

orbital debris damage along with general spacecraft 

health monitoring might become a paying service as 

well. Removal of non-operational spacecraft (~150 

objects) from the GEO belt would reduce the chance 

of catastrophic collision significantly and benefit all 

GEO operators. Altogether, there is a substantial set 

of annual servicing opportunities: 10 dexterous, 20 

GEO refuel, 14 relocation, and more. The potentially 

serviceable failures alone amounted to roughly $750 

million (in FY 2003 dollars) in insured and uninsured 

losses annually between 1994 and 2003. These same 

failures have caused the industry to take a risk-adverse 

approach and to use redundancy, proven technology, 

From the previous sections, it is clear that the extraordinary potential of satellite 

servicing has motivated a significant effort in both studies and practice throughout 

the world. Flight experience demonstrates that the technologies and tools 

to successfully execute servicing missions are well in hand. In spite of these 

successes, some common misconceptions persist. Such figments need to be 

addressed critically in order to enable advances in our paradigms for space 

exploration. In this section we explore three such myths. 

“There is nothing to service” is not true because strong business cases 

have been made for servicing commodity satellites that provide the 

communications infrastructure for modern life. 

“Servicing is too costly” is generally quoted with respect to the HST 

servicing experience, which is not representative of the majority of potential 

future servicing activities. 

“Satellites cannot be serviced unless they were designed to be serviced” is 

demonstrably false since many HST servicing successes were “impossible” 

tasks performed on hardware that was not designed to be serviced.

Myths About Servicing
and long operational lifetimes to attempt to mitigate 

this risk.

One example of an on-orbit failure is Orion 3, a 

Geostationary Earth Orbit (GEO) communications 

satellite that was launched in May 1999. The satellite 

cost $150 million, the launch cost $80 million, and 

there was a $265 million insurance claim after the 

second stage failed to place the satellite in the proper 

orbit.

This trend continues today. According to a 

vice president at one of the world’s three principal 

insurance brokers,[17] in the last four years insurance 

underwriters have paid out some $700 million in 

claims for satellite failures caused by propulsion 

leak issues or due to the satellites being placed in 

the wrong orbit. With its ability to fix some of these 

problems, on-orbit servicing could have a sizable 

appeal to operators and/or underwriters.

The $400 million U.S. Air Force Defense Support 

Program missile warning satellite DSP-23, provides 

a further example. It is drifting eastward through 

the GEO belt at a rate of about 1 ̊ longitude per 

week.[26] Recently, control of Galaxy 15, a GEO 

communications satellite, was lost after five years 

of successful operations. It has also begun to drift 

away from its orbital slot with its communications 

payload broadcasting uncontrolled at near full power, 

potentially causing disruption to other satellites.

Orbital Satellite Services (OSS) claims[27]

that there will be more than 140 commercial 

communications satellites in the next 10 years that 

will be due for decommissioning that would benefit 

from life extension, or about one per month. This 

life extension could be accomplished either by 

attaching a propulsive servicer satellite to the back 

of the customer satellite, as OSS proposes, or by 

adding fuel to the customer satellite. Unfortunately, 

satellites are operated today as airplanes were before 

aerial refueling—with limited scope and flexibility. 

However, on-orbit refueling does more than extend 

the satellite’s life. Lift capacity of current launch 

vehicles limits the amount of fuel available to a 

satellite on-orbit. This prevents military planners from 

developing operations concepts that would consume 

large amounts of fuel. By refueling these satellites 

on-orbit, the ability to use them tactically would be 

enhanced. As one example, faster orbital position 

changes (which would consume more fuel) would 

significantly reduce the drift time to a new location 

in the GEO belt, reducing the repositioning overhead 

time for valuable assets.

The detailed business cases for these potential 

satellite servicing customers certainly need further 

consideration. Closing the business case depends on 

the details of the business, risk posture, insurance 

availability, and other considerations that are specific 

to a particular customer. However, as a part of this 

study, we have found that the claim “there is nothing 

in space to service” is based on outdated information 

or a set of very arbitrary constraints. This study finds 

that with appropriate planning, current technology 

supports refueling, orbit modification, repair, refurbishment, and other modifications of large classes of 

legacy spacecraft in addition to future spacecraft that 

could be designed with servicing in mind. 

“Servicing Is Costly”

In spite of NASA’s decades of successful satellite 

servicing activities, any discussion about the feasibility 

of satellite servicing eventually engenders the assertion 

that servicing satellites just costs too much. It might 

be, “Designing a satellite specifically to be serviced 

will increase the cost by at least XX%,” or, “Why 

service anything when it’s actually cheaper to build 

and launch a new one?” For current spaceflight 

developers, this myth is a strong barrier to candid 

assessments of options for mitigating risks and 

meeting mission objectives in the most cost-effective 

way. Much work has been done in academia and 

industry to describe the cost-benefit equation for 

servicing, yet this myth persists. It must be examined 

and the false portions put to rest as NASA moves 

forward to define future spaceflight architectures.

Many factors contribute to perceptions about 

the cost of servicing, often springing from erroneous 

generalizations of specific facts. Here we summarize 

three perceptions that contribute to the myth: 1) 

the cost of the current servicing paradigm, 2) the 

existence or viability of other servicing paradigms, and 

3) the cost of designing a satellite to be serviced.

28 | On-Orbit Satellite Servicing Study Project Report | October 2010
Several academic theses identify the cost benefit 

of servicing, viable business cases, and cost break 

points for different models of satellite servicing.[8,31,32]

Whether modeling a servicer with a single customer, a 

servicer that visits multiple customers in nearby orbits 

(e.g., a single inclination in GEO), or a constellation 

of servicers covering a larger orbit regime, a viable 

customer base and approach can be identified within 

the parameters studied. Some of these cases describe 

the exotic-car model of multi-billion-dollar missions, 

but most describe fleet or family car servicing models 

(see Henshaw analogy in Chapter 1, “Introduction—

Why Is Satellite Servicing Important?”).

Erdner presents one example in a study where 

he describes a constellation of 15 identical CubeSat 

satellites deployed just below the geostationary belt to 

inspect every satellite in GEO in less than a year.[33]

The goal is to detect any co-orbiting objects close to 

known assets. His cost model estimates this fleet could 

be built and operated for a year for a total mission 

cost of $18 million (in FY 2000 dollars). While his 

well-documented cost model explicitly excludes many 

elements (e.g., launch), even at ten times that cost, 

this paradigm of a group of small inspection satellites 

is remarkably different from that of the sophisticated 

HST servicing missions and far less costly.

In our notional mission suite (see Appendix 

F), we present a servicer concept to autonomously 

rendezvous, capture and move to a super-synchronous 

disposal orbit multiple non-cooperative customers in 

GEO. Although the mission was not optimized for 

cost, the servicer was estimated to cost $545 million 

and could “super-sync” (place in super-synchronous 

disposal orbit) roughly ten non-cooperative customer 

spacecraft in GEO. Such a servicer would enable 

a customer satellite to remain in position until all 

its maneuvering fuel is expended and still comply 

with orbital debris requirements at end-of-life by 

purchasing a super-sync mission from the servicer. 

The same servicer could also be used to dispose of 

inoperable spacecraft.

The next evolution of the space program could 

incorporate such lower-cost models of satellite 

servicing. Rather than costing more, a new spaceflight 

architecture that incorporates refueling and servicing 

The most pervasive perceptions about the cost of 

the current servicing paradigm stem from the hugely 

successful Hubble Space Telescope (HST) servicing 

missions that are widely reported to have cost between 

$1–2 billion each, and to have used astronauts in 

potentially dangerous extravehicular activities to 

perform intricate tasks to refurbish a multi-billiondollar observatory. Even these high numbers may 

underestimate the true cost of servicing HST since 

they do not include the full lifecycle cost of the space 

shuttle. A straightforward business case for servicing 

HST could be made by comparing the several-billion 

dollar initial cost of the telescope against the $1–2 

billion cost for each servicing mission. If the servicing 

mission leaves HST in a “like-new” configuration and 

with expanded capabilities that are congruent with 

scientific demands, then building and launching a 

replacement would appear more expensive. However, 

any cost expressed in billions is a great deal of money, 

and given the high visibility of HST and its servicing 

missions, this enormous price tag has a profound 

influence on the perceptions and beliefs about the cost 

of satellite servicing.

Even with the reality of billion-dollar HST 

servicing missions, it is not realistic to assume that 

any successful servicing mission must follow the HST 

model and thus cost an appreciable fraction of the 

original investment. The cost and the sophistication of 

the tasks clearly place the HST servicing missions in 

the extreme category of servicing, where the business 

case resides more in the incredibly high scientific 

or strategic benefit than in the straightforward cost 

assessment. That case for HST has been made in 

many different ways.[28,29,30] Periodic refurbishment 

has kept this flagship observatory productive for over 

twenty years. The installation of new instruments 

created a state-of-the-art observatory with each 

servicing mission, a cadence that could never be 

supported by launching new observatories. The 

new instruments will also help ensure that the 

observatory’s last years will be its most scientifically 

productive. However, HST is not the only model for 

servicing. More importantly, it is not the right model 

to use in assessing costs for a purely commercial 

business case for servicing.

 Chapter 1 | Introduction – Myths About Servicing | 29
For this cost discussion we group accommodations for servicing into two general categories: 1) 

adding external hardware elements (e.g., grapple 

fixture, rendezvous targets, handrails, holes, 

or handling points) and 2) designing modular 

subsystems with simplified and standardized interfaces. During a servicing mission, both types of 

accommodations transfer task complexity from the 

servicer to the customer, with concomitant reduction 

in the cost and risk of the servicing mission. However, 

for the moment, we only consider the cost that the 

customer satellite incurs during its design, build, 

integration, test, and launch periods. 

The external hardware elements that accommodate the Autonomous Rendezvous and Capture 

(AR&C) phase and enable crew or robots to move 

around the satellite are quite simple. Few have 

moving parts or electronics. As standardized interfaces, the hardware requires no additional design; the 

project only determines where they will be placed. 

Standards provide guidance regarding placement, but 

servicing systems can tolerate wide deviation from 

the standards. The amount of additional hardware is 

a function of the size of the satellite and the type of 

servicing task. For example, the Orbital Express 

mission used a fully cooperative docking mechanism 

(32 kg) and refueling mechanism (50 kg). 

Combined, these added a little more than 3% to the 

mass of an ordinary GEO communications satellite 

(2,500 kg).[31] Such accommodations greatly simplify 

a servicing mission while minimally increasing the 

concept-to-launch costs of a satellite. However, there 

are circumstances where any additional mass requires 

the compromise of other mission objectives (e.g., less 

propellant can be carried, thus shortening the 

mission duration). 

The second category, designing modular 

subsystems with simplified interfaces, is more 

interesting and challenging because it encompasses 

an array of options with associated costs and savings 

at different mission phases. To assess the costs and 

savings of such design principles, it is important to 

understand how satellites are traditionally built.

To some extent, satellites are already designed 

to be modular with well-defined interfaces, because 

could actually reduce cost at the mission, program, 

and agency levels. A refueling infrastructure (e.g., 

a refueler that visits multiple customers) in GEO 

could reduce cost and reduce risk for new missions 

and extend the life of existing, legacy spacecraft 

simply by separating the launch of the majority of 

the propellant from the launch of the high-value 

satellite. A spaceflight architecture that includes a 

refuelable servicer in GEO would shift the risk of 

mission failure, reduce mission cost, increase mission 

performance and flexibility, and potentially enable 

new missions.[31] 

Such ventures do not exist today due to obstacles 

such as liability issues[24] and myths about customers 

or technology readiness. However, their potential 

profitability is well documented, as described in the 

references above. These new ventures would open the 

possibility of a new paradigm for commercial and 

strategic satellites in a serviceable orbit. In the absence 

of servicing, satellite developers are driven towards 

proven, reliable designs and long operational lives. 

These drivers may unnecessarily stifle innovation and 

increase cost.[31] With satellite servicing, new space 

architecture trades are opened up with potentially 

significant cost-benefit improvement.

The third aspect of the “Servicing Is Costly” 

myth is the belief that designing and building for 

serviceability increases the concept-to-launch cost of 

the customer satellite. In response, we consider what it 

means to design for servicing and then assess the endto-end life cycle costs and potential savings of such 

an approach. This report summarizes the question 

of designing a satellite to be completely cooperative 

to servicing (see Chapter 5, “Satellite Servicing: The 

Challenges,” section “Making Future Missions More 

Serviceable”). However, the successful servicing of 

subsystems on HST that were never designed to be 

serviced proves that on-orbit servicing is feasible 

even with legacy hardware. Designing for servicing 

actually describes a spectrum of accommodation 

options. With each servicing accommodation 

that is incorporated into the design, a satellite 

moves gradually from being a non-cooperative (no 

accommodation) customer to a fully cooperative (all 

possible accommodations) customer. 

30 | On-Orbit Satellite Servicing Study Project Report | October 2010
In finding the right balance between the 

additional requirements for servicing accommodations 

and the cost of those added requirements, project 

managers must recognize the extent to which these 

accommodations reduce the risk and cost of the 

Integration and Test (I&T) flow, and what other 

benefits they might bring. A system designed to 

support the replacement of a hardware element onorbit can support similar task times on the ground. 

A system designed to provide easy access to hardware 

elements on-orbit would also provide easy access 

during ground processing. A sufficiently modular 

system that supports fully testing subsystems prior 

to delivery is likely able to proceed with system-level 

integration even as individual components require 

rework. For scientific missions, such a modular 

system allows the infusion of current state-of-the-art 

capability and technology as close as the year before 

launch, improving the discovery potential of the 

mission even if the satellite is never serviced. 

It is impossible to exactly quantify the costs and 

savings of incorporating additional modularity to 

accommodate servicing in the abstract. Every set 

of mission requirements affects the complexity and 

the cost of any specific servicing accommodation. 

However, assessing the options for meeting mission 

objectives and mitigating risks in the most costeffective way is the primary activity of the early design 

phases of every mission. Currently, designing for 

servicing is rarely even considered, in part because of 

the myth that servicing just costs too much.

As NASA integrates servicing into the next 

architecture, government, academia and industry 

developers will begin to accept that servicing 

is another option in the overarching systems 

engineering approach to meeting their objectives. 

They can then perform a cost-benefit analysis 

tailored to their missions, their requirements, and 

their own business cases.

“Satellites Cannot Be Serviced Unless They 

Were Designed To Be Serviced”

Another common myth in the satellite business is that 

on-orbit satellites cannot be serviced unless they were 

designed and manufactured to support it. The basis 

proven subsystems are often built and delivered 

by different organizations or vendors. Ideally, this 

modular approach enables the smooth integration 

of elements and subsystems delivered by separate 

organizations into a functioning system. Thus, satellite 

developers currently design modular systems and 

simplify interfaces because doing so reduces overall 

mission risk and cost. Methods for implementing 

modularity and simple interfaces for ground 

processing and on-orbit performance have evolved as 

we have continued to build on past successes.

It is worth noting that designing a system that 

meets only the on-orbit mission requirements is 

insufficient. Every satellite system must successfully 

tolerate many different configurations and 

environments as hardware moves from manufacturing 

through launch. Typical development phases include, 

for example, subsystem-level testing, handling in the 

gravitational environment on Earth, and the launch 

environment. Each of these phases and environments 

imposes distinct requirements, and each additional 

requirement comes with costs and benefits that 

project managers must trade. Within this context, it 

is perhaps helpful to view servicing as one more phase 

that imposes requirements to be traded with all other 

mission phases. 

With this perspective, we can speak in broad 

terms about the cost of modularity and simplified 

interfaces. Satellite developers currently build modular 

systems as a cost-effective approach for the conceptto-launch flow. Servicing can be considered another 

phase of mission development with requirements 

that drive further modularity and simpler interfaces. 

Many factors affect the cost of accommodating 

servicing in a specific satellite (e.g., the degree of 

challenge in meeting all other requirements, how 

tightly constrained the mission or subsystem is, the 

maturity of the implementation considered, and the 

sophistication of the servicing tasks anticipated). 

However, if one accepts that designing for servicing 

encompasses a spectrum of options, then project 

managers and systems engineers can tailor the level of 

accommodation and sophistication to the demands of 

the mission. 

 Chapter 1 | Introduction – Myths About Servicing | 31
What Are Appropriate Human and Robotic Servicing Paradigms?

When discussing the roles of humans and robots in any space exploration mission, 

two questions often arise: “When should humans be used and when should 

robots be used?” and, “If robots are used, how autonomous do they need to be?” 

Our conclusion is that robots should be used alone where their capabilities are 

sufficient, to minimize unnecessary risk to humans. Astronauts provide the ultimate 

in autonomy and adaptability to changing circumstances. These are fundamentally 

complementary modes of servicing that will need to be balanced and will likely 

work together to advance the art of satellite servicing. 

32 | On-Orbit Satellite Servicing Study Project Report | October 2010

for this myth stems from the belief that 1) without a 

priori rendezvous targets/aids and docking fixtures, a 

servicing vehicle cannot adequately locate and reliably 

rendezvous and dock with an on-orbit satellite, and 

2) without ground-tested cooperative interfaces, a 

servicing vehicle cannot perform any level of servicing 

on a legacy on-orbit satellite that would be of value. 

Both history and analysis demonstrate that these two 

statements are false.

In 2005 to 2006, the Experimental Spacecraft 

System Number 11 (XSS-11) mission demonstrated 

the capability to autonomously perform safe and 

reliable, fully autonomous rendezvous and proximity 

operations with a derelict or “non-cooperative” space 

object. By the time the mission was completed, 

XSS-11 had completed 50+ successful resident 

space object (RSO) rendezvous maneuvers with 

a Minotaur fourth stage; 300+ successful natural 

motion circumnavigations of a non-cooperative RSO; 

successfully demonstrated an on-orbit checkout of a 

collision avoidance system; performed 15+ successful 

station keeping maneuvers; 1,200+ hours of safe, 

autonomous proximity operations; and captured 

2,000+ witness camera images. The XSS-11 mission 

was extremely successful, achieving all of its goals with 

100% mission success and ultimately proving that the 

technology and systems integration knowledge and 

experience are available today to successfully perform 

intricate rendezvous and proximity operations on 

non-cooperative space vehicles and objects. 

With regards to a capture and docking interface, 

most in-space non-cooperative vehicles share a 

number of similar “features” that can be used as 

docking interfaces. The DARPA Front-end Robotics 

Enabling Near-term Demonstration (FREND) 

project has performed ground demonstrations of 

autonomously grappling two such features with a 

robot arm—a vehicle’s Marman clamp ring and bolt 

holes.[34] Both of these features are used to attach 

the spacecraft to the launch vehicle, so they are 

structurally sound capture points. 

And what about servicing a vehicle that was not 

designed to be serviced? The answer obtained through 

years of experience successfully servicing portions 

of the HST that were not originally designed to be 

serviced is simply stated: “The right tool for the right 

task at the right location.” Engineering evaluation 

of existing interfaces (through hardware engineering 

units, design and manufacturing drawings, and prelaunch photos) enables future teams to develop and 

ground test specialized manipulation tools that are 

capable of performing targeted tasks and potential 

contingency operations on-orbit. Coupled with in situ

evaluations of the hardware to be serviced, these tools 

can provide servicing capabilities that include vehicle 

refueling, vehicle hardware upgrades and repair, and 

cryogenic replenishment.
•	 Robots as supplemental eyes: The robot

provides an auxiliary view. NASA evaluated 

such a system during space shuttle mission 

STS-87 in November of 1997 by flying 

AERCam Sprint (Figure 1.15).

•	 Robots as subordinates: The human is the

“primary” worker and robots carry tools and 

fetch hardware for the astronaut, as well as 

prepare and close out worksites. This saves 

limited EVA time for the more demanding and 

critical tasks that need to be performed by a 

human in a spacesuit.

•	 Robots as sidekicks: The robot works alongside

and interacts with the human (Figure 1.16).

•	 Robots as surrogates: When the worksite is

inaccessible to humans (Geostationary Earth 

Orbit [GEO], planetary precursor mission), 

there is limited or no human involvement.

•	 Robots as specialists: When a system is needed

that exceeds the dexterity, strength, positioning 

accuracy, or speed of a human in a spacesuit. 

This is the role robots play in the construction 

industry and in robot-assisted surgery.

•	 Human-robot symbiosis: Use robot

technology to augment or enhance human 

capabilities by creating exoskeleton-type 

The current preference when planning space missions 

is to use Extravehicular Activity (EVA) when humans 

are present (space shuttle and ISS missions) and 

to use robots when humans are not present (e.g., 

planetary exploration), or when “super-human 

powers” are needed (e.g., grappling the Hubble Space 

Telescope with the space shuttle’s robotic arm or 

moving a 15-ton module around the ISS using its 

robotic arm), or to provide a platform for moving 

humans around. This has been an evolving process 

based on the extensive experience and lessons learned 

from the HST servicing missions as well as the 

assembly and maintenance of the ISS. The military 

often uses the 3 “D”s when talking about the role 

of robots—the robots perform the dumb, dirty, and 

dangerous work. As applied to spaceflight, the role of 

robots can be expanded to include the 6 “S”s, which 

follows the evolution of human-robot interaction 

proposed by Akin:[35]

Figure 1.16 – Robotic Assistants – An astronaut in a 

simulated spacesuit is assisted during notional satellite 

servicing tasks by two robotic manipulators: one helping 

to open/hold the door while the other one stows an old 

battery and grabs a replacement. A free-flying camera 

platform observes the operation and captures this 

photograph.

Figure 1.15 – AERCam Sprint – Autonomous 

Extravehicular Activity Robotic Camera Sprint (AERCam 

Sprint) in the cargo bay of the Earth-orbiting space shuttle 

Columbia during STS-87. The AERCam Sprint is an 

experiment that demonstrates using a free-flying video 

camera for remote inspections. It is a 14-inch diameter, 

35-pound sphere that contains two video cameras, an 

avionics system, and 12 small Nitrogen gas thrusters.

 Chapter 1 | Introduction – What Are Appropriate Human and Robotic Servicing Paradigms? | 33
Their conclusion is that neither will get far beyond 

the solar system without the other. They call for a new 

vision of human and robotic spaceflight that they call 

“transhumanism.” It takes into account current trends 

in robotics, artificial intelligence, genetic engineering, 

and other fields that are rapidly changing the nature 

of both humans and robots. This thought is an 

extrapolation of decades of research and simulations 

by the Space Systems Laboratory at the University 

of Maryland demonstrating that the most capable 

and productive method for space operations is to use 

teams of humans and robots working cooperatively 

at an integrated worksite. This fact was stated in a 

different way by Don McMonagle, a former NASA 

EVA Program Manager, when he summarizes, “In the 

future, EVA and robotics will be synergistic, if not 

synonymous.”

Ultimately, it comes down to the fact that 

humans are explorers: we want to go to new places, 

see new things, and experience new worlds for 

ourselves. A lesson that emerges from our previous 

experience exploring Earth and space is that although 

robots will assist, humans will take the lead in 

exploration. Oceanic and Antarctic exploration 

provide an appropriate parallel to the role of humans 

and robots in the exploration of the solar system. 

The evolution of those exploration programs involves 

a mix of forward-deployed robots and humans, 

surface ships and submersibles, autonomous in situ

sensors and vehicles, and researchers working in their 

laboratories—all linked together by global satellite 

networks. The program has evolved a philosophy of 

using the right tool for the right task in the right location. 

Robot systems are becoming more intelligent and 

more capable all the time, extending our reach into 

places we never before imagined. The key to making 

satellite servicing and space exploration successful 

and safe will be to apply the proper balance of human 

and robotic systems without a bias toward one 

approach over the other, as they are fundamentally 

complementary. Failing to exploit this synergy would 

be to ignore the vast experience we have gained 

expanding our frontiers and gaining knowledge on 

and off this planet.

spacesuits, or a “human-in-a-can” for EVA 

in higher-risk environments such as the Van 

Allen radiation belts. 

The notional missions explored as part of our study as 

well as our mission sequence parallel this progressive 

interaction with a set of missions that include evolving 

human-robot interactions. Other than human-robot 

symbiosis (which is the most interesting, has the 

largest potential benefit, and therefore deserves further 

study), the other five roles for robots interacting with 

humans were all explored.

A few principles can guide decisions about the 

appropriate level of robot autonomy. When long 

one-way communication travel times are imposed, or 

the tasks to be performed by the robot are simple and 

well-defined tasks, autonomy has a clear advantage. 

However, when the planned tasks exceed the existing 

or projected capability of automation, another solution needs to be found. As with the human-robot 

interaction paradigms discussed above, humans can 

be part of the solution. All too often the argument is 

made that robots cannot perform a task because of 

their inability to deal with the unexpected. In such 

cases, a robot can be baselined to perform the tasks 

with the human providing assistance when needed, 

either by remotely reprogramming the robot to deal 

with the unexpected circumstance, by supervising the 

operation, or by remotely commanding the robot to 

perform the task. As we will always need to deal with 

the unexpected, humans will always be involved in 

any meaningful exploration. Due to Moore’s Law,[36]

autonomous systems will become more and more 

capable, so the amount of robot autonomy used will 

shift. This is similar to approaches taken with the Deep 

Space One (DS1) mission and the Mars rovers. DS1 

demonstrated new capabilities in spacecraft autonomy 

and autonomous mission operations, during which 

mission developers checked out and invoked progressively more elements of the Autonomous Optical 

Navigation system until the spacecraft was completely 

under autonomous control.[37]

In their book “Robots in Space,”[38] Lanius and 

McCurdy take an interesting look at the competing 

visions for human versus robotic space exploration. 

34 | On-Orbit Satellite Servicing Study Project Report | October 2010
Chapter 2

Satellite Servicing: The Vision

The vision for satellite servicing is straightforward: to refuel, repair, or upgrade 

satellites after they are launched. Most satellites are expensive pieces of hardware that still have much utility after some critical resource has been expended 

or some critical technology has become obsolete. Sending a servicing craft to 

repair or replace a broken critical component or move the satellite into another 

orbit will derive additional utility from what would have been a loss. These 

capabilities develop into on-orbit assembly of large spacecraft that cannot be 

assembled and tested on Earth. Such spacecraft hold the promise of opening 

up new scientific vistas to reach beyond today’s observatories. They could also 

provide depots for fueling spacecraft to venture to distant destinations. 

These servicing capabilities can also be applied to managing orbital 

debris, an area of growing concern in Low Earth Orbit (LEO) as well as 

Geostationary Earth Orbit (GEO).

Figure 2.1 – Refueling Depot in Use – This conceptual rendering shows 

a refueling servicer (right) mated with its well-shielded fuel depot in 

geostationary Earth orbit (see Notional Mission 2 in Appendix F).
Refurbishment/Refueling of Satellites in Near-Earth Environments

One of the most basic servicing activities is to replenish an expendable resource 

or replace worn-out components. With these capabilities comes the extraordinary 

possibility that space-based assets can become better with time, and are no longer 

limited by the programmatic and technical constraints of their original design.

find a special utility in dropping from GEO to pick 

up satellites stranded in transfer orbits (a surprisingly 

common occurrence) and bringing them to their 

intended GEO altitude. 

Other high-value servicing missions could also be 

conducted in other orbits, but likely on an as-needed 

basis. Satellites requiring long “hang-time” over 

northern latitudes use highly elliptical orbits. Large, 

expensive, astronomical observatories work best in 

the cold environments of deep space, such as at the 

second Sun-Earth Lagrange point (SEL2). Critical 

space weather missions stand watch between the Sun 

and the Earth at the first Lagrange point (SEL1). 

Staging depots for trips to and from the Moon, lunar 

orbit, and deeper space destinations are attractive at 

the semi-stable locations in the Earth-Moon system, 

namely Earth-Moon L1 (EML1). All of these orbits 

interact with the Earth’s gravity and are considered 

near-Earth. The Earth-Moon locations, a few days’ 

travel from Earth, would be easily reached with a 

small, crewed spacecraft as well as robotic servicers. 

The Sun-Earth locations, a few months’ travel from 

Earth, would have long-stay human accommodations 

for a crewed mission. A customer spacecraft could also 

travel from an operational SEL2 location to EML1 

for a servicing episode closer to Earth and then return 

to the operational location. Only a small amount of 

propellant is required to transfer between any two 

Lagrange points, though the flight times can be long.

As with the HST, an upgrade of critical components 

to the latest technology can bring a satellite years of 

additional life at a higher capability level that was 

not possible at the time of the design or launch. 

Adding fuel to a satellite can extend its useful life by 

providing additional station-keeping, maneuvering, or 

deorbit propulsion capability. Every sector of satellite 

utilization—commercial, scientific, and national 

security—could use satellite servicing for increased 

efficiency, bringing the benefits of space operations at 

a lower overall cost.

Servicing satellites in near-Earth environments 

can be accomplished in two modes: pre-positioned 

and as-needed. The nature of orbital dynamics is 

such that it is expensive (from a propellant and time 

point of view) to change inclinations. Therefore, 

pre-positioned servicing assets should be placed in the 

most-used orbits. These include the Geostationary 

Earth Orbit (GEO) belt that surrounds the Earth at 

high altitude and low inclination (generally over the 

equator) and the Low Earth Orbit (LEO, 200-1,000 

km altitude) near-polar inclinations. Pre-positioned 

servicers would move in these two orbital regimes to 

satisfy the requirements of many customers. These 

multi-mission, multi-customer servicing vehicles 

must have sufficient propulsion to move amongst 

nearby orbits and would be serviceable and refuelable 

themselves to maintain the most utility (see Figure 

2.1). Highly maneuverable servicers in GEO would 

36 | On-Orbit Satellite Servicing Study Project Report | October 2010
Construction of Large Structures

Three types of large space structures can be enabled by in-space servicing or 

assembly: observatories, depots, and interplanetary spaceships. All three of these 

are physically large, expensive, and not launched from the surface of the Earth 

in one piece or in their operational configuration. Human and/or robotic servicing 

enables these elements to be assembled and configured for operation, tested, and 

even maintained, upgraded, and supplied over a long service life. 

can fix, upgrade, and test the functions of the depot. 

Concepts proposed for post-ISS long-duration habitation facilities offer opportunities to achieve multiple 

goals for scientific and human spaceflight, including 

assembly and upgrade of complex structures.[39]

Large interplanetary spaceships, both crewed and 

robotic, could be put together, configured, fueled 

and thoroughly tested. These expensive craft would 

be verified in near-Earth space before their outbound 

voyage to Mars or beyond. The servicer capability 

would be of such value in this role that it might be 

brought along for the trip.

With such a servicing infrastructure in place, the 

future could have extremely large space observatories 

probing the scientific frontiers in astronomy (looking up) and enhancing collection for Earth science 

and national security (looking down). Very large 

observatories would be launched in multiple pieces 

and require the capabilities of an in-space servicer to 

assemble them. Expensive observatories would benefit 

from servicing to upgrade instruments to the latest 

technology, supporting dramatically more demanding science at a fraction of the cost of building and 

launching an entirely new observatory. Large observatories would likely be precision structures and lightweight for their size (gossamer 

structures), requiring a lighter, 

more precise touch compared 

to the “brawny” manipulation 

needed for depots and interplanetary spaceships.

Satellite servicing could 

provide the large space depots 

to fuel operational craft in 

Earth and near-Earth orbits as 

well as give planetary missions 

an outbound fill-up. Depots 

could be created with the tanks 

and fuel from multiple launches with small, low-cost rockets 

(see Figure 2.2). Long-lived depots could be used many times 

and would be tended by a colocated or visiting servicer that 

Figure 2.2 – Refueling Depot Assembly – This conceptual rendering shows construction of a 

orbiting fuel depot (see Notional Mission 2 in Appendix F).

 Chapter 2 | Satellite Servicing: The Vision – Construction of Large Structures | 37
Orbital Detritus Management

The problem of orbital debris is growing and will reach a tipping point in the near 

future if there is no mitigation. Studies show that even with no future launches, 

the debris from collisions between objects already in orbit will cascade in the 

crowded orbits.[40] This cascade effect, known as the “Kessler Syndrome,” has been 

understood since the 1970s[6] and is already manifesting itself in low Earth orbits 

through recent collisions and near-misses. Removal of several tons of debris per 

year from this critical orbital regime will bring our planet slowly back from the brink 

of runaway orbital debris that would render useless any Earth orbit below 1,000 km. 

the “business case.” Although every nation and 

corporation using these orbits has a vested interest 

in their continued usefulness, it is no one entity’s 

responsibility. In economics, this is “the tragedy of the 

commons.” Demonstrated national leadership and 

international cooperation will be required to mandate 

a program of debris removal. A market based on 

removed debris tonnage will be established when the 

value of an investment in future access to 

space is realized. Many types of debris in 

the polar Low Earth Orbit (LEO) would 

be removed through these efforts: first, 

large intact pieces such as rocket bodies 

and defunct satellites, and eventually 

smaller pieces, down to the limits of what 

can be detected and tracked.

Current international law presents a 

complication to such activities because it 

stipulates that the owners of a satellite also 

own all the orbiting hardware resulting 

from the launch of the satellite.[41]

According to case studies and as upheld by 

international courts, if a spent stage causes 

damage, the owners (and insurers) of the 

satellite that the spent stage put into orbit 

would be liable. Unless the owners 

authorize removal of the “garbage,” the 

chain of responsibility becomes entangled. 

The same vehicle technologies required for servicing 

could be used for debris removal. These include 

orbital maneuvering, autonomous rendezvous and 

docking, and robotic manipulation. It might even 

be that a general-purpose servicing craft could spend 

much of its time in between servicing customers 

working on debris removal. The challenge of orbital 

debris removal is not in the technology, but in 

Figure 2.3 – Orbital Modification – This conceptual rendering shows 

a servicing spacecraft (left) mated with a customer spacecraft (right) 

to effect orbital modification – changing its orbital parameters to suit 

mission needs (see Notional Mission 1 in Appendix F).

38 | On-Orbit Satellite Servicing Study Project Report | October 2010
Of course, the owners would not voluntarily incur the 

added expense of removal unless it were required.

A separate, but related, problem in orbital debris 

removal exists in the GEO belt. There, satellites near 

the end of life are placed into “graveyard” orbits 

above the critical GEO altitude; this is called “supersyncing” a satellite. Currently there is no practical 

way to gauge remaining propellant in zero-gravity, 

so satellite operators retire the spacecraft based on 

estimates with margins. The ability to fully deplete 

station-keeping propellant and rely on a servicer to 

complete the required super-sync maneuver would 

extend the life of every satellite. Other satellites die 

or become uncontrollable before they are supersynced, so a service that moves these satellites into 

the desired end-of-life orbit is necessary in order to 

keep GEO clear for operational satellites (see Figure 

2.3). Again, progress will require national leadership 

or new international standards that set requirements 

on assured end-of-life disposal. Meeting these 

requirements through the guarantee of an on-call 

super-sync service would allow the satellite to 

operate until its station-keeping fuel or some critical 

subsystem was exhausted or failed. This kind of 

service is well-defined and has economic benefit 

to the owners; if provided, the owners of the assets 

could avoid the legal complications discussed above.

 Chapter 2 | Satellite Servicing: The Vision – Orbital Detritus Management | 39
Chapter 3

Satellite Servicing: The Benefits

Ever since the first artificial satellite was launched, we have faced a consistent and 

familiar set of constraints on mission success. Almost any improvement in mission 

capability involves more mass. Mission capability and robustness are thus limited 

by launch technology. The launch process itself is one of the most risky phases for 

a space mission, potentially affecting hardware integrity and function. Unintended 

mechanical interferences or deployment failures may result. Access is limited or 

impossible after launch, causing even small failures or oversights to lead to serious 

consequences. The space environment is very harsh and often unsupportive of 

equipment reliability. Expendables limit operational life, and their quantities need to 

be carefully managed. These are the unavoidable ramifications and challenges of 

spaceflight. What is not unavoidable are the consequences of these constraints. As 

we venture beyond our immediate environment, we have the tools to create robust 

mission profiles that dramatically improve the chances of mission success. Satellite 

servicing holds the promise of altering current paradigms of satellite construction, 

operation, and maintenance to enable reaching this goal. In particular, it is a tool 

that provides the reliability improvements that will be required to meet the upcoming 

challenges in space exploration. 

Figure 3.1 – HST SM4 Release – The view from inside the space shuttle 

Atlantis as HST was deployed after Servicing Mission 4.
 Chapter 3 | Satellite Servicing: The Benefits – Commercial Benefits | 41

Commercial Benefits 

Commercial space applications pervade many aspects of modern life. We have 

live news coverage from almost every corner of the globe. Television networks also 

distribute entertainment programs internationally and instantaneously. Telephone 

networks connect distant locations, and where there are no networks, one can 

connect “direct to satellite.” We can also include the transforming nature of satellite 

positioning systems and satellite imagery. The impacts of these satellite-enabled 

technologies cannot be overstated and affect our quality of life as well as our 

safety. The cost of these services, however, is based on existing models of satellite 

operation. Satellite servicing offers a mechanism for deriving more utility from 

existing assets, thus strengthening the commercial bottom line. In this arena, the 

applications of satellite servicing would most likely be in the areas of refueling and 

orbital modification.

interference. The International Telecommunication 

Union establishes and maintains these allocations, 

which currently are spaced at roughly 2 ̊ intervals 

around the orbital path (some slots may contain 

multiple satellites controlled by the same operator). 

The GEO orbits are not stable. There are disturbances 

from astronomical sources (e.g., the Moon and solar 

wind), as well as effects from orbital mechanics 

(e.g., Earth oblateness). In general, an uncontrolled 

GEO spacecraft would tend to migrate along the 

GEO orbit until it arrives at one of the two stable 

longitudes (gravity well). These satellites need to carry 

expendables to remain operational, to remain in their 

allocated orbital slot, and to support disposal at endof-life. Proper disposal would position the satellite in 

a “graveyard” orbit at a slightly higher altitude and 

then decommission the satellite.

Of primary benefit to these satellites would 

be refueling (Figure 3.2) or, at a minimum, orbit 

modification (Figure 2.3). Every year, approximately 

20 satellites are retired because their propellants are 

exhausted. The satellite is usually otherwise fully 

functional, so replenishment of the propellant is 

a natural means to extract more economic value 

All of the commercial services cited above rely on 

extensive fleets of satellites, orbiting at specific 

locations around the Earth. They provide a 

commodity—information—either in the form of 

a transponder for information relay, imagery, or 

signals to determine position. These commodities are 

provided, bartered, sold, rented, and replenished. All 

decisions about these satellites are business driven. 

Is it economically viable to operate a satellite? If not, 

throw it away. Do we have enough capacity to support 

projected growth? If not, build another satellite.

Many communications and weather-monitoring 

satellites are in Geostationary Earth Orbits (GEO), 

allowing them to occupy an almost-fixed position 

relative to the surface of the Earth. These orbits are a 

limited resource. Ideally, they are circular, equatorial 

orbits (at roughly 35,786 km altitude) with a period 

exactly equal to the Earth’s sidereal rotation period. 

Both the inclination and altitude of the spacecraft 

may vary depending on the mission requirements and 

spacecraft functionality (within 200 km of the ideal 

altitude and 15 ̊ from the equator). Consequently, the 

positions of these spacecraft are carefully regulated 

in order to avoid physical as well as communication 
42 | On-Orbit Satellite Servicing Study Project Report | October 2010

concern due to interference 

with AMC 11, which relays 

digital programming for cable 

television channels.[44]Working 

cooperatively with Intelsat, the 

owner of AMC 11, Société 

Européenne des Satellites, 

successfully avoided service 

interruption through a series of 

evasive maneuvers and by 

temporarily augmenting the 

AMC 11 slot with another 

spacecraft, SES-1. In such cases, 

the ability to rendezvous with 

the errant spacecraft and effect 

orbit modification to put it into 

a benign location would be of 

significant economic value.

Of course, it is also 

possible to perform repairs 

on these satellites. Within the 

automobile analogy, there are 

times when even fleet cars are economically viable to 

repair. One example is to have a robotic arm assist 

in correcting a failed deployment. There are valid 

economic arguments for on-orbit servicing of these 

satellites with the goal of improving technology or 

increasing reliability without increasing the initial 

cost.[31] Such benefits would require a change in the 

current paradigms of satellite architectures.

Most interestingly, Long [31] points out that 

satellite servicing could offer new pathways to 

reduce life-cycle costs. For instance, to reduce cost, 

satellites could be built with less redundancy or with 

provisioning for a shorter life, with the expectation 

that servicing could be used later. Also, high-value 

components might be separated from low-value 

components like fuel so that more reliable launch 

vehicles (i.e., also more expensive) could be used on 

the former, and cheaper ones for the latter. Servicing 

would combine these parts post-launch. These new 

paradigms for satellite development and operations are 

just beginning to be explored.

from the asset and provides a straightforward model 

for establishing the business case.[31]Even without 

refueling, if independent means were available to 

relocate these satellites at end-of-life, roughly six 

months of additional operational fuel could be 

used for revenue generation.[42]These benefits have 

motivated the investigation into Notional Missions 1 

and 2, discussed in Chapter 4.

Because GEO orbital slots are a limited resource, 

there is also the problem of rogue satellites that have 

experienced some sort of failure that prevents them 

from maintaining their assigned orbits. There are 

currently more than 150 dead satellites and rocket 

stages that will drift for centuries in the GEO belt. In 

2008 and 2009 alone, four GEO satellites were left to 

expire without performing end-of-mission orbitraising maneuvers.[43]Most recently, in April 2010, 

Intelsat lost contact with one of its approximately 50 

GEO satellites, Galaxy 15. This satellite, with 

transmitters fully powered, wandered through 

neighboring slots and almost immediately caused 

Figure 3.2 – Refueling an Orbiting Communications Spacecraft – This conceptual rendering shows 

a refueling servicer (left) capturing and refueling a typical communications satellite (right, see 

Notional Mission 2 in Appendix F).
 Chapter 3 | Satellite Servicing: The Benefits – Commercial Benefits | 43

Scientific and Technological Benefits

Scientific and technology development missions are the most likely missions to 

“push the envelope” for some aspect of mission performance. For these types 

of missions, satellite servicing provides the means to update components to 

take advantage of newly developed capabilities. Compared to the 5- or 10-year 

technology “lag” commonly experienced by major scientific missions, a 2- to 3-year 

lag to launch a new technology could significantly improve the scientific return from 

a mission. This is particularly true for technologies that are rapidly developing, such 

as imaging sensors, especially if the refreshment occurs on a regular basis. This 

ability to refresh technology could also drive a different mission model—phased 

capabilities that are based on previous discoveries or otherwise expand mission 

capability in some new way. We can avoid the “all eggs in one basket” problem 

that accompanies a large mission by flying a series of smaller ones instead. The 

repair, refurbishment, and assembly aspects of satellite servicing would be most 

applicable in this arena.

instrumentation could be designed for 

specialized follow-up observations.

4. Correction of design features with unintended 

consequences in order to improve mission 

robustness. In spite of our best practices, we 

will continue to be challenged as systems 

become more complex. Satellite servicing 

offers a unique capability to improve risk 

posture through post-launch operations.

5. Return and reuse of existing assets. In many 

cases, the original design was adequate and 

reuse is a possible strategy to reduce cost. 

Returning space assets to Earth also allows 

for unique studies on the effects of the space 

environment.

Satellite servicing is the “master enabler” for new 

space architectures. In-space construction (Figure 3.3) 

would allow for very large structures that could not 

otherwise be imagined. The ISS is the first example of 

such a structure. The lessons learned can be applied to 

Repair and refurbishment are the obvious first applications with scientific and technological benefits. A 

clear example is the HST model, which we need not 

overstate here. The main benefits of such a model are:

1. Rapid deployment of new technologies to 

improve mission performance by replacing 

subsystems. These would cover scientific 

performance areas such as sensors or 

instrument design, as well as spacecraft 

components such as transmitters, power 

systems, or computers and avionics.

2. Repair and maintenance to keep a unique 

and valuable asset operational, essentially 

improving it beyond its design lifetime or the 

reliability of its subsystems. This includes the 

replenishment of expendables such as cryogens 

as well as spacecraft components.

3. Phased approach to deploying capabilities, 

allowing modification of goals as scientific 

and technological needs demand. In the case 

of scientific missions, subsequent scientific 
44 | On-Orbit Satellite Servicing Study Project Report | October 2010

NASA is currently planning the Flexible Path 

implementation, which involves some potentially 

complex architectures. As these plans become more 

concrete, the benefits of satellite servicing could 

provide the edge for mission success that enables the 

most challenging visions.

future architectures for large observatories, refueling 

depots, power farms, or other large structures. These 

kinds of benefits and applications motivated the 

mission profile for Notional Mission 6, discussed 

further under Chapter 4.

Figure 3.3 – On-Orbit Assembly – This conceptual rendering shows a human and robotic servicer (left) assembling a large 

space telescope (right) in space (see Notional Mission 6 in Appendix F). 
 Chapter 3 | Satellite Servicing: The Benefits – Strategic Benefits | 45

Strategic Benefits 

While strategic interests have not been the focus of this study, a discussion of using 

satellite servicing capabilities for these applications cannot be avoided. Indeed, 

defense organizations have provided some of the most exciting demonstrations 

of satellite servicing technologies to date (e.g., Orbital Express). There is a large 

defense infrastructure for communication and surveillance that is based on many 

similar spacecraft. An ability to maintain this infrastructure is key to maintaining 

national security. Conversely, the ability of other agents to “maintain” these spacecraft could be deemed a threat (Figure 3.4). Since strategic assets span a wide 

range of complexity, the full spectrum of satellite servicing capabilities (refueling, 

repair, refurbishment, orbit modification, and perhaps assembly) would apply.

As in the commercial arena, refueling and expendables 

replenishment is the first step to improving operations 

for a wide range of strategic satellites. There are many 

similarities, even though the cost structure could be 

somewhat different. Military 

communications satellites 

have very similar constraints 

to their commercial counterparts. However, unlike commercial satellites that typically 

remain in a predefined orbit, 

surveillance satellites are able 

to reposition themselves to 

commanded locations, so they 

require more fuel. The more 

fuel they have available, the 

faster they can respond and the 

longer they can operate.

Some strategic satellites 

may approach or exceed 

the complexity of the most 

sophisticated scientific 

observatories. For example, it 

is publicly discussed that HST 

is likely based on the KH-11 

Figure 3.4 – Removal of Undesirable Spacecraft – This conceptual rendering shows an orbital 

modification servicer (left) approaching a military asset (right) for relocation.

series of surveillance satellites,[45] of which there were 

nine or ten. For satellites of this complexity, repair 

and refurbishment could be appropriate servicing 

activities. 
46 | On-Orbit Satellite Servicing Study Project Report | October 2010

The servicing missions to the Hubble Space Telescope 

(HST) engaged public interest like no other NASA 

mission since Apollo. Combining the real-time drama 

of humans performing challenging tasks in space 

with the world’s most well-recognized and beloved 

space observatory puts humans visibly in the midst 

of great scientific achievements. These missions 

reached a remarkably diverse, even jaded, public by 

touching a broad spectrum of interests. They provided 

the ultimate in “Reality TV” to audiences, with the 

stream of live video from the spacewalks presenting 

an unedited look at the drama, energy, synergy, and 

ingenuity of performing complex tasks in space. The 

servicing missions inspire belief and pride in the 

human “can-do” attitude by setting and successfully 

carrying out lofty goals: travel and work in space, 

complete on-the-spot repairs, create and harness 

ingenious technology, engineer innovative tools and 

procedures, become real heroes, do great science, and 

capture the beauty of the Universe. 

The payoff from the astronauts’ “high-wire” acts 

was almost immediately tangible: spectacular new 

Outreach Benefits 

Human presence, breathtaking images, and groundbreaking science are a powerful 

combination that captures the imagination of the public and gives relevance 

to NASA’s missions. So far, such a mix has only been possible in the context 

of servicing missions. The marriage between human spaceflight and orbital 

maintenance of a major scientific research instrument is a unique highlight in 

NASA’s history. It brings with it a wide range of challenges. The solutions to these 

challenges cross multiple disciplines and connect with an equally diverse range of 

public interest. In the future, we expect that this interest will carry over to robotic 

and human/robotic servicing activities in space.

images from the refurbished HST were released to the 

world within weeks of the mission. These have been 

showcased in over 6,000 Internet articles. Without 

the participation of astronauts in HST’s scientific 

mission, the observatory would likely have remained 

much more abstract to the public. It also may not 

have been so revered as a valuable national asset, 

where the public feels ownership and pride. There 

would still be the steady stream of evocative and 

colorful space pictures, but seeing astronauts perform 

surgery on a bus-sized vehicle communicated a sense 

of scale, technological complexity, tangibility, and a 

connection to humanity.

The hours of footage from the HST servicing 

missions, including cameras on the EVA astronauts’ 

helmets, present a “you-are-there” look at the 

danger and challenge of space exploration. Amid 

melodramatic twists and turns and uncertainties, HST 

and its human attendants persevered. Major media 

channels have produced numerous hour-long science 

documentaries that capture and condense this story. 

The recent Hubble 3D IMAX® film documentary has 

More importantly, the ability to approach and 

affect an orbiting satellite has obvious implications to 

the health and safety of the satellite. It is a technology 

that could affect our national security, and is an area 

of obvious military interest. By developing advanced 

commercial, scientific, and technological applications 

for satellite servicing, we have the means to encourage 

the expanded use of space for peaceful purposes.
 Chapter 3 | Satellite Servicing: The Benefits – Outreach Benefits | 47

successful from an outreach perspective. We 

conjecture that with current and future video 

capabilities, the “you-are-there” look and excitement 

can be conveyed for servicing activities involving 

humans, robots, or any combination of the two. 

Public interest will remain high as long as the 

mission conveys a sense of urgency and importance, 

demonstrates complicated tasks, and provides 

quick feedback on the results of those tasks. These 

intangibles are evident in public forums such as web 

sites and blogs after a successful servicing mission.[46]

opened in theaters around the 

world to record attendance. 

The servicing missions 

provide numerous lessons 

for teachers and students: 

teamwork, problem solving, 

overcoming adversity, and 

a “can-do” attitude. The 

missions portray diverse 

teams of scientists, engineers, 

technicians, and managers 

as role models for students. 

The Space Telescope Science 

Institute’s “Amazing Space” 

web site provided educators 

and students across the 

country with an opportunity 

to participate in Servicing 

Mission 4 as it unfolded in 

real time, with daily updates 

and supporting educational 

activities. Internet traffic to 

HubbleSite.org tripled through 

this period (see Figure 3.5). 

Overall, the engagement 

of the public—fueled by the 

excitement of the servicing 

missions and the scientific 

productivity of HST—has been significantly higher 

and longer sustained than other NASA space science 

missions. Such interest has a lasting effect in its 

ability to enhance Science, Technology, Engineering 

and Mathematics (STEM) educational initiatives. 

This reflects the power of satellite servicing in the 

scientific context and its impact on the public.

In the future, we would expect that large 

classes of human or robotic servicing missions 

could engender similar interest. We already have 

the example of the Mars rovers performing robotic 

exploration. This mission was also extremely 

Figure 3.5 – HubbleSite Visits During HST SM4 – This plot summarizes the level of public interest 

during the Hubble Space Telescope (HST) Servicing Mission 4 (SM4) and also during the Early 

Release Observations (EROs)—the first images released from HST after Servicing Mission 4. The 

plot is for the days of the month in May 2009 for SM4 and September 2009 for the EROs.

• Early Release Observations (Released September 9, 2009)

• Peak visits: > 380,000 (seven times normal daily traffic)

• Visits during the event: 1.1 million (typical of a month’s worth of traffic)

• 40% increase in baseline traffic after event

• HST Servicing Mission 4 (May 11–24, 2009)

• Peak visits: >127,000 (three times normal daily traffic)

• Visits during event: 747,000 (approximately 20 days worth of traffic)

• 20% increase in baseline traffic after event
Chapter 4

Satellite Servicing: The Implementation

The transition from concept to reality is never straightforward, especially 

for complex systems with potentially “game changing” rewards and a nonnegligible cost of development. One result of this study is an executable plan 

that provides satellite servicing capability development in conservative steps. 

This plan is based on a systems engineering analysis of the key challenges for 

satellite servicing missions, a set of notional missions to quantitatively explore 

these challenges, a mission sequence that provides immediate benefits while 

validating the designs, and a technology gap assessment that identifies how 

to develop future capabilities. Using the ISS as a versatile test bed, near-term 

demonstrations are underway for some of these key technologies. 

Figure 4.1 – The Flight Hardware for the Notional Missions – This graphic 

shows the flight hardware studied for the six Notional Missions (NMs) 

described in the text and in Appendix F, grouped by orbital location 

of the potential servicing activity. In the lower left corner is low Earth 

orbit, showing NM3—upgrade in low Earth orbit. In the middle band is 

Geostationary Earth Orbit (GEO), showing NM1—orbit modification in 

GEO (left) and NM2—refueling in GEO (right). The upper band represents 

farther away locations, and shows NM4—assembly at Earth-Moon 

Lagrange point 1 (left), NM5—upgrade in highly elliptical orbit (lower 

right), and NM6—assembly at Sun-Earth Lagrange point 2 (upper right).
 Chapter 4 | Satellite Servicing: The Implementation – The Map of Servicing Capabilities | 49

The Map of Servicing Capabilities 

Satellite servicing is a broad term that was not 

precisely defined at the start of this study. The team 

worked to identify factors that could vary and 

thus become significant factors in mission design. 

After much discussion, research, and thought, 

several categories were identified: Task, Execution, 

Rendezvous and Capture, Location, Latency, 

Customer Design, and Customer Attitude. The figures 

that follow display these characteristics in columns, 

with complexity increasing from bottom to top.

Tasks include broad categories of servicing. From 

most simple to most complex, tasks include simple 

orbit modification (which most satellites accomplish 

on their own, but it could be accomplished using a 

tug), three tasks related to refueling, the replacement 

of hardware elements designed to be replaced on-orbit 

(Orbital Replacement Units or ORUs), assembly of 

large structures designed for on-orbit assembly (e.g., 

the International Space Station [ISS]), and the repair 

or replacement of a hardware element that was not 

designed to accommodate servicing. 

Execution can be accomplished with robots, 

humans, or a combination of both, with increasing 

levels of machine autonomy defined as increasing 

complexity. The “human + robot” element appears at 

the simple end of the list because it is a shuttle-style 

grapple arm. The “robotic autonomous” and “robotic 

teleoperated” elements describe more dexterous 

robotic systems.

Rendezvous and Capture describes how a servicer 

will approach and dock with a customer spacecraft. 

There are a large number of ways to carry out an assessment of satellite servicing. 

To enable discussion of disparate applications, one needs a categorization 

system in which to frame the discussion. This study developed and adopted a 

particular scheme that was used initially to characterize and discuss the topic, and 

subsequently to determine the content of detailed case studies.

The least complex method is with humans in-theloop in situ capturing a customer that is designed to 

be serviced (i.e., cooperative). The most complex 

method is a completely autonomous servicer docking 

with a customer that is not designed to be serviced 

(i.e., non-cooperative). 

Location is simply the orbit at which the servicing 

is performed, and increasing complexity is defined as 

increasing distance from Earth. Latency is the time 

required for communication between the Earth and 

the servicing location. Although latency is obviously 

a function of the location, the issue of latency was 

deemed important enough to warrant its own 

column.

Customer Design defines what on-orbit 

servicing accommodations are designed into the 

customer spacecraft. A fully cooperative customer 

has navigational aids (passive or active), a berthing 

mechanism, grapple points, handling fixtures, 

is fully controlled at capture, and then has an 

operational mode that yields control authority to the 

servicer while they are joined together as a “stack.” 

Increasing complexity in this column is defined as 

fewer accommodations, and at the top is a legacy 

customer—a customer spacecraft that is currently on 

orbit with no intentional servicing accommodations.

Customer Attitude defines whether the customer 

spacecraft is under control and can present a favorable 

surface towards the servicer at the time of capture. 

The most complex is a spacecraft that is not controlled 

at all, cannot be commanded, and the dynamics of 
50 | On-Orbit Satellite Servicing Study Project Report | October 2010

At an early stage of the study, it was interesting 

to discover that all the satellite servicing tasks have 

already been largely sampled in flight. It is a common 

myth that servicing happens rarely because the tasks 

are so complex they require the development of new 

technologies. This populated trade space demonstrates 

that, in fact, tasks of great complexity have already 

been accomplished on-orbit. The unsampled region 

of the trade space is described by increasing distance, 

increasing autonomy, and identifying customers with 

decreasing levels of accommodation.

With this understanding of the unexplored 

region of the satellite servicing trade space, the team 

developed a suite of six notional missions designed to 

sample the unexplored region (see Figure 4.4). 

the orbit leave the customer tumbling (spinning about 

one or more axes).

The first use of the trade space figure was to map 

the regions that have been demonstrated in flight 

either as an experiment or as part of a mission. Figure 

4.2 displays the previously demonstrated elements 

and a seminal mission where the work was performed. 

Note that many options have been completed onorbit multiple times; but unless a mission sampled 

a unique additional area of the trade space, only the 

first occurrence is recorded in the figure.

Having mapped these sampled elements, Figure 

4.3 divides the trade space into two regions: elements 

already completed on-orbit (historical) and elements 

that have not been completed on-orbit (unsampled). 

Figure 4.2 – Seminal Mission Coverage of the Servicing Study Trade Space – This graphic maps several missions for satellite 

servicing onto the servicing mission trade space. The colored lines trace the path of these missions through the trade 

space diagram. The Refueling tasks have been split into those using a static feature in the storage tanks called a Propellant 

Management Device (PMD) or those using a diaphragm for propellant management.
 Chapter 4 | Satellite Servicing: The Implementation – The Map of Servicing Capabilities | 51

Figure 4.4 – Notional Mission Suite Coverage of the Servicing Study Trade Space – The notional missions were designed to 

cover every area of the diagram so that we can sample a range of trade space possibilities. 

Figure 4.3 – Servicing Study Trade Space Regions Covered by Historical Missions – This graphic summarizes the regions of 

the trade space diagram that have been sampled already (historical) or are yet to be sampled (unsampled). 
52 | On-Orbit Satellite Servicing Study Project Report | October 2010

The Notional Missions

This study examined a total of six “notional” missions that are intended to span the 

parameter space for the range of possible servicing activities. They follow the map 

of servicing capabilities discussed previously, and provide the basis for engineering 

analyses and trade studies. Appendix F contains more detailed results for all the 

notional mission studies. We summarize these missions here while underscoring 

a few key findings in the areas of Autonomous Rendezvous and Capture (AR&C) 

and robotic technologies, as well as some of the interesting results discovered in 

astrodynamics. In particular, we present a new orbit design that has some unique 

features for human servicing of missions operating at the Earth-Moon Lagrange 

point 1 (EML1).

chosen solely to facilitate the design charrettes and 

not to favor one particular mission. For example, 

HST was the customer satellite in the third notional 

mission because it is an existing, cooperative (designed 

to be serviced), LEO satellite. Its interfaces exist and 

are well known, which allowed the team to develop 

well-defined requirements for those interfaces on 

the notional servicer (dimensions, power, and data). 

Other mission aspects, such as Commercial Orbital 

Transportation Services (COTS) and crew habitats 

were assumed to exist if the mission needed them, 

and these are also not discussed beyond their basic 

interfaces.

Table 4.1 enumerates the high-level characteristics 

of each of the studied missions. Appendix F provides 

additional information for all the notional missions.

Mission Design Methodology and Cost 

Estimation

Once the notional mission suite was identified, 

each mission was developed into a mission concept 

at NASA’s Goddard Space Flight Center (GSFC) 

Integrated Design Center (IDC). The IDC consists 

of two “labs”: the Instrument Design Lab (IDL) 

where conceptual designs of spaceflight instruments 

are formulated, and the Mission Design Lab (MDL) 

where conceptual designs of spacecraft and other 

Notional Mission Characteristics

The team deliberately chose not to research all the 

aspects of the satellite servicing trade space equally. 

Instead we used the servicing capabilities figure to 

identify six discrete servicing scenarios that would be 

examined in detail in a series of design charrettes. We 

called these servicing scenarios “notional” missions 

because they were deliberately designed to investigate 

the unsampled corners of the satellite servicing trade 

space. This allowed us to identify unique obstacles as 

well as the common elements of seemingly disparate 

missions.

Thus, the notional missions do not describe an 

architecture or a map of recommended missions 

(see the “Mission Sequence” section in this chapter). 

In fact, they were not even driven by identifying 

practical or cost-effective solutions for flight projects. 

The notional missions enabled the team to identify 

successful engineering solutions that could be used as 

data in subsequent analyses, rather than to produce 

optimized designs for a real mission.

Where possible, existing satellites and launch 

vehicles were employed in the design process. It is not 

possible to design a servicer spacecraft and a servicing 

mission in one week while simultaneously designing 

the customer spacecraft. Customer satellites were 
 Chapter 4 | Satellite Servicing: The Implementation – The Notional Missions | 53

mission elements to support the instruments and 

science objectives are conducted. The IDC brought 

the study team together with an independent team 

of experienced discipline engineers in an integrated 

design environment that allowed for concurrent, 

focused, and rapid systems design. Since 1997, 

the IDC has conducted over 500 such studies, 

contributing to many successful GSFC flight 

instruments and missions. 

One major advantage of treating the notional 

missions as repeated design charrettes with a 

consistent staff, assumptions, approach, and costing 

tools, is that the resulting engineering products are 

a consistent body of data from which we can make 

comparisons and draw conclusions. In addition, the 

six notional missions provided the study team an 

opportunity to refine and improve the requirements 

at the start of the run and for the combined study and 

IDC teams to build on the insights from the previous 

runs. So, although an identical process was used for 

each notional mission, the products grew more refined 

with each successive notional mission run. This was 

both beneficial and challenging. It was challenging 

because, in the end, the study team must understand 

the feasibility of servicing as well as the business case 

for servicing based on a set of mission studies with 

disparate and progressive refinement. It was beneficial 

because the final, very complex mission studies were 

of such high caliber, and the study team had learned 

so much from the IDC team that they were well 

prepared—in insight and in design products—to do 

the necessary work.

Both IDC labs were used for this effort, with the 

IDL focusing on rendezvous and docking packages 

and robotics, and the MDL providing servicing 

platform and mission designs. IDC customers come 

with mission requirements and work with the IDC 

engineers to create point design concepts to a level of 

detail sufficient to support a hypothetical proposal. 

The IDC customer determines the objectives of 

the assessments and shapes the “run” to meet their 

requirements through real-time decisions with the 

engineers during the study. In our case, the IDC 

customers were Satellite Servicing Study Team 

members with servicing experience from the HST 

Development Project. The level of these studies 

is such that 1) key aspects of the mission concept 

and architecture are defined, 2) top-level mission 

requirements are assessed (e.g., power, mass, uplink/

downlink, mission specific subsystems, navigation, 

avionics, operations), and 3) rough cost estimates are 

generated.

Cost estimates can be difficult to validate, 

especially for systems that have never before been 

built. However, for the purposes of this study, we 

believe that reliable relative cost estimates can be 

obtained for the notional missions considered. The 

absolute costs were reserved for future study.

This study used a commercially available, 

parametric cost-estimating tool called Parametric 

Review of Information for Costing and EvaluationHardware (PRICE-H). PRICE-H was developed 

by the RCA Company in the 1960s for the U.S. 

Navy, Air Force and NASA, and commercialized 

Table 4.1 – Notional Mission Summary Table

Case Orbit Task/Service Task Execution Customer Design Attitude Latency

NM 1 GEO orbit modification robots legacy spinning short

NM 2 GEO refueling robots legacy 3-axis stabilized short

NM 3 LEO upgrade humans (COTS) + robots designed for upgrade 3-axis stabilized short

NM 4 EML1 assembly robots designed for assembly 3-axis stabilized medium

NM 5 HEO upgrade humans (Orion) + robots designed for upgrade 3-axis stabilized medium

NM 6 SEL2 assembly humans (Orion + habitat) 

+ robots

designed for assembly 3-axis stabilized long
54 | On-Orbit Satellite Servicing Study Project Report | October 2010

by PRICE Systems, LLC. PRICE-H estimates 

cost by parametrically defining the hardware to be 

built (starting from a master equipment list), the 

development and manufacturing environments, the 

operational environment, and the overall schedule. 

GSFC’s IDC has more than ten years of 

experience using the PRICE-H tool to develop costs 

for the mission pre-proposal phase. In addition, 

GSFC has used the PRICE-H tool to support over 

100 spacecraft studies and proposal efforts outside the 

IDC, including the recent Step 2 Mars Atmosphere 

and Volatile EvolutioN (MAVEN) and Gravity and 

Extreme Magnetism Small Explorer Mission (GEMS) 

Concept Study Reports, and prior cost studies for 

Aeronomy of Ice in the Mesosphere (AIM) and 

Time History of Events and Macroscale Interactions 

during Substorms (THEMIS) Confirmation Reviews. 

Full mission life-cycle costs are estimated from the 

PRICE-H data by adding non-hardware elements as 

a percentage of the hardware costs. The accuracy of 

this approach and the percentages used are assessed 

periodically using data from independent costing 

agencies and reported costs for flight missions. For the 

notional missions in this study, costs were confirmed 

in parallel through a grassroots costing exercise. The 

result is a point estimate based on the current best 

estimates of parameter values. The next step in cost 

estimation would be to perform a cost risk analysis to 

generate a probabilistic assessment, but this has not 

yet been completed for the notional mission elements.

We reiterate that costing tools and absolute costs 

were not a focus of this study. Instead, we selected 

a specific method for generating costs (PRICE-H), 

and then used the results as one data element in the 

comparisons and general observations about the 

notional missions. It is also worth noting here again 

that cost was not a constraint during the notional 

mission studies. The notional missions were designed 

to probe what is possible, with a resulting cost 

estimate. 

Table 4.2 reports the current-best-estimate 

cost (with no margin) of the servicer designed for 

each notional mission. The servicer is defined as 

everything that launches with the servicing platform 

that is required to perform on-orbit servicing. It does 

not include the launch vehicle, propellant, or any 

hardware that will be installed in the customer. For 

Notional Missions 3 (NM3) and 5 (NM5), the cost of 

an airlock (with associated consumables) and human 

tools is included because they are baselined to launch 

with the servicer. However, in Notional Mission 6 

(NM6), all human-related elements travel with the 

humans rather than with the servicer, so they are not 

included in the servicer cost. Note that even without 

the cost of the human servicing elements or the 

observatory that will be assembled, NM6 requires the 

most costly servicer due to the complexity and sheer 

size of the mission.

Total mission costs were also modeled and are 

reported in the notional mission appendix (see 

Appendix F); however, the disparate mission concepts 

and varying fidelity of customer information make 

true cost comparisons at the mission-level far more 

complex.

In looking at the relative costs of the servicers, it 

is not surprising to find that the servicers designed for 

missions with more ambitious goals cost more. At the 

most basic level, it is commonly understood that costs 

are driven by the mass of the hardware flown, and 

the more ambitious missions require more hardware. 

However, we also learned of the strong dependence 

of cost on design choices that affect reliability, such 

as using “class S” electronic parts (screened for space 

applications), block-redundant designs (flying two or 

three duplicate avionics boxes), and cross-strapping. 

These servicers were designed to be self-serviced (that 

is, no fleet of servicers was assumed to exist, only the 

one under current study), so some systems required 

the same high reliability and long lifetime that affects 

legacy spacecraft. Thus, recreating these notional 

missions with different assumptions about the human 

flight architecture or the existence of a servicing 

infrastructure would profoundly affect the costs. 

It is also worth noting that cost savings were 

realized on robotic elements by assuming a modular, 

self-reconfigurable robotic architecture. The 
 Chapter 4 | Satellite Servicing: The Implementation – The Notional Missions | 55

architecture was assumed in order to create servicers 

with sufficient flexibility to address the needs of 

multiple missions, and one might conclude that such 

flexibility costs more. However, such development 

moves away from the common paradigm of “one-off” 

builds, where every mission receives a custom system. 

Building multiples of smaller subsystems allows 

even a single mission to take advantage of lower-cost 

production runs for robotic components that can be 

assembled into the desired custom configuration. In 

the broader spaceflight architecture, reconfigurable 

robots allow every robotic mission to benefit from a 

single technology development program and larger 

scale production-run costs. The savings of such an 

approach is apparent even in the conceptual phase 

cost modeling.

Autonomous Rendezvous and Capture 

Technology

One of the technical areas we investigated was the 

technology required for Autonomous Rendezvous 

and Capture (AR&C). This study in the Instrument 

Design Lab (IDL) produced several key findings 

and identified areas for future work. The results are 

provided in Appendix E and summarized here.

The first finding is that a capable AR&C sensor 

package can be assembled using current technology, 

and that this package can support the extreme case 

of capturing an uncontrolled, tumbling customer 

spacecraft (see Notional Mission 1 in Appendix F). 

Furthermore, this AR&C sensor package has modest 

mass, volume, and power requirements.

Another key IDL study finding is that during 

AR&C with a legacy (non-cooperative) customer 

Table 4.2 – Servicer Costs for Each Notional Mission

Notional Mission Spacecraft 

Bus Cost 

(FY10)

AR&C 

Cost 

(FY10)

Robotic Elements Cost 

(FY10)

Human Elements 

Cost (FY10)

Servicer 

Total 

Cost 

(FY10) Num Description

NM1 GEO Supersync $140M $75M $330M 

Centralized 

4 @ 2 m Grapple 

None 

Tools in Robotic 

Elements

$550M

NM2 GEO Refueler + 

Depot

$220M $60M $240M

Centralized 

2 @ 2 m Grapple 

None

Tools in Robotic 

Elements

$520M

NM3 LEO COTS 

Refurbish

$670M $60M $350M 

Distributed 

Human Rated 

2 @ 15 m Grapple

$300M 

Airlock, Tools

$1,380M

NM4 EML1 Robotic 

Assemble

$600M $60M $1,330M 

Reconfigurable 

2 @ 15 m Grapple

2 @ 2 m Dexterous Pairs 

None 

Tools in Robotic 

Elements

$1,990M

NM5 HEO Human 

Refurbish

$760M $60M $1,230M 

Reconfigurable

2 @15 m Grapple 

2 @ 2 m Dexterous Pairs

$300M

Airlock, Tools

$2,350M

NM6 SEL2 Human 

Assemble

$2,100M $60M $1,340M 

Reconfigurable

2 @ 15 m Grapple

2 @ 2 m Dexterous Pairs 

None

 All Human Elements 

Launch with Humans

$3,500M
56 | On-Orbit Satellite Servicing Study Project Report | October 2010

spacecraft, the AR&C sensor package must be 

designed to operate with only bearing-angle 

measurements during the early phases of the process 

(without complementary range measurements). This 

requires that the AR&C package include optical 

sensors capable of acquiring the customer spacecraft 

at long range (several hundred kilometers or more). 

This has significant implications for the rendezvous 

trajectory design in terms of the evolution of the 

relative motion geometry and the timing, direction, 

and magnitude of rendezvous maneuvers. In short, the 

rendezvous sequence should be designed to provide 

adequate knowledge of the relative spacecraft position 

and velocity using only bearing-angle measurements. 

Note that this constraint would be relaxed if the 

operating distance of range sensors, such as laser 

rangefinders, could be extended. Note also that this 

constraint is largely removed during cooperative 

AR&C scenarios in which a Radio Frequency (RF) 

ranging signal can be transmitted between the servicer 

and customer spacecraft (though this was beyond the 

scope of the IDL study).

The IDL study also revealed that the usefulness 

of a pan/tilt unit for the AR&C sensor package 

is unclear, since the study did not have sufficient 

scope to complete the trade. A pan/tilt unit, which 

allows for pointing the sensors independent of the 

spacecraft orientation, may provide more flexibility 

in the servicer spacecraft’s attitude profile while 

maintaining AR&C sensor pointing at the customer, 

but at the cost of tripling the AR&C sensor package’s 

mass, increasing its required power by 50%, and 

complicating the pointing-error budget. However, this 

pan/tilt capability would be required if the various 

servicer spacecraft attitude constraints including, 

but not limited to, Sun tracking for solar power, 

communication antenna pointing, and customer 

spacecraft tracking cannot all be simultaneously 

satisfied.

Mission analysis to support the Mission Design 

Laboratory (MDL) studies of the notional missions 

included the design of relative motion trajectories 

to facilitate AR&C between spacecraft on Lagrange 

point orbits for Notional Missions 5 and 6. While the 

necessary trajectory targeting equations to accomplish 

this between spacecraft in LEO or GEO are well 

known, this not the case for spacecraft on Lagrange 

point orbits. Thus, in order to determine the total ΔV 

required for AR&C on Lagrange point orbits (e.g., a 

Lyapunov orbit about EML1 in Notional Mission 5 

and a halo orbit about SEL2 in Notional Mission 6), 

new algorithms had to be developed for the relative 

motion trajectory targeting.

These new AR&C trajectory algorithms revealed 

unusual characteristics of the natural relative motion 

between spacecraft occupying the same Lagrange 

point orbit. They also indicated that there are 

preferred locations on a Lagrange point orbit for 

performing AR&C due to a strong dependence of the 

total required ΔV on the location along the Lagrange 

point orbit at which AR&C is performed.

Computing the ΔV requirements for AR&C 

between spacecraft on highly elliptical orbits was 

driven by the use of the L1 Orbit Trajectory Used for 

Servicing (LOTUS) in Notional Mission 5. While the 

necessary guidance equations are known, we do not 

currently have practical experience with performing 

AR&C in this type of orbit. Our traditional concepts 

of operations for AR&C will therefore have to be 

expanded to properly account for features of the 

relative motion dynamics between spacecraft on 

elliptical orbits in order to ensure safety during 

AR&C.

From these considerations, the areas for future 

work became apparent. One is the need for highfidelity attitude profile analysis to determine whether 

the degrees of freedom for pointing offered by a pan/

tilt unit are necessary, or at least beneficial to the 

point of making a pan/tilt unit a compelling option. 

Other future work topics include analysis of the 

effective operating range of an infrared camera (which 

would provide bearing-angle measurements during 

adverse lighting conditions); analysis of the minimum 

distance at which pose measurements can be acquired 

(since the customer spacecraft will generally be larger 

than the pose sensor field-of-view at distances of 
 Chapter 4 | Satellite Servicing: The Implementation – The Notional Missions | 57

several meters or less); development of guidance, 

navigation, and control algorithms to support safe 

AR&C between spacecraft on highly elliptical orbits 

or Lagrange point orbits; and development of AR&C 

concepts of operations appropriate for spacecraft on 

elliptical orbits.

Robotic Technology

Robotic technology is a second area that benefitted 

from an initial study in the Instrument Design Lab 

(IDL). These results are presented in Appendix E and 

summarized here.

For the six notional missions (see Appendix 

F), the study team developed two distinct robotic 

architectures springing from the current state 

of the art in robotics. Two robotic systems that 

could accomplish the first two notional missions 

(Geostationary Earth Orbit [GEO] super-sync 

and GEO refuel) exist today. The first is the Frontend Robotics Enabling Near-term Demonstration 

(FREND) system,[34] developed by Alliance 

Spacesystems and the Naval 

Research Laboratory for the 

Defense Advanced Research 

Projects Agency (DARPA), and 

designed for a GEO super-sync 

mission (Figure 4.5). 

The second is the Ranger 

system, developed by the 

Space Systems Laboratory at 

the University of Maryland 

as a Low Earth Orbit (LEO) 

technology demonstration 

mission. The Ranger system 

(Figure 4.6) consists of two 

dexterous arms that are 

positioned at the worksite 

by either a grapple arm or a 

positioning leg. It was designed 

to perform inspection, 

maintenance, refueling, and 

orbit adjustment. The tasks it 

can perform range from simple 

task-board operations to very complex EVA worksite 

setup using hardware that was never intended for 

robotic handling. The program also served as a 

training ground for young engineers in a hands-on 

environment.

For the remaining, more ambitious notional 

missions, a robotic architecture was developed that is 

similar to robotic systems used on the International 

Space Station (ISS)—a big grapple arm coupled with 

a pair of dexterous arms.

This study revealed two technology areas within 

robotic systems where development will enable key 

future capabilities. The first is the development 

of modular, mobile robotic systems that can be 

reconfigured on-orbit to optimize their kinematic 

configuration for the wide variety of tasks needed 

for broad-reaching servicing missions. The second is 

improved camera views at the worksite for situational 

awareness.

The last three notional missions highlighted 

the need for robotic systems that can reconfigure 

Figure 4.5 – Front-end Robotics Enabling Near-term Demonstration (FREND) System – The FREND 

system performs full-scale rendezvous and autonomous robotic grapple testing using the Naval 

Research Laboratory’s Spacecraft Proximity Operations Test Bed.
58 | On-Orbit Satellite Servicing Study Project Report | October 2010

a modular system capable of self-reconfiguration for 

DARPA.[47] The Palo Alto Research Center has also 

done some work.[48] This is an active, but unfunded, 

area of research that will empower robots to perform 

the tasks we envision for satellite servicing.

Another need illustrated during the notional 

missions is a way to get visual feedback to the 

operator for better task and situational awareness. 

The approach taken in the notional missions was to 

use cameras on the end of an arm to provide visual 

feedback to the operator. The view could be provided 

by a camera (or stereo pair) attached at the end of 

a separate robot arm that autonomously follows 

the dexterous arm doing the work. Alternatively, 

individual cameras at the end of the dexterous arm, 

end-effector, or tool that is performing the task 

could be used. One limitation to this approach is 

that sensors on the end of arms require power and 

data lines capable of handling large amounts of 

data. This data rate then drives the downlink data 

rate requirements, and even low-resolution images 

at relatively low frame rates create a challenging 

amount of data for the current flight-to-ground data 

infrastructure. In addition, cameras require lighting. 

For task awareness, where the camera is relatively 

close to the work site, lighting can readily be provided 

with some additional power and mounting space. For 

situational awareness, where the camera may be far 

removed from the task or area of concern, lighting 

presents a greater challenge. Alternative sensors exist 

(e.g., infrared cameras), but they are not yet in wide 

use for space robotics systems. 

The notional missions used an approach similar 

to what was developed for the Hubble Robotic 

Servicing and Deorbit Mission: put cameras 

everywhere, as they are “cheap.” The implementation 

of running power and data to the camera systems 

placed around the servicer and potentially to the 

telescope or structure being built highlighted the 

need for a better solution. Several possible approaches 

have been proposed. Data from various sensors 

(visible and infrared cameras, laser radars, stereo 

vision, proximity sensors, etc.) could be integrated 

themselves to save launch volume and mass. These 

missions involved tasks as varied as grappling supply 

barges, moving astronauts or other robots around, 

replacing failed components, and performing 

unforeseen tasks. They demonstrated that systems 

that can adapt by reconfiguring themselves eliminate 

the need to carry multiple systems with innumerable 

custom tools for every conceived task. Stand-alone 

mobility also simplifies the assembly process for 

extremely large observatory structures. For example, 

the International Space Station (ISS) robotic systems 

move around the station exterior using robot data 

and power accommodation “ports” built into the 

ISS exterior. This solution may not be practical for 

large observatories, as the features may only be used 

during the assembly sequence, and power is not 

routinely required throughout the exterior of an 

observatory. However, a robotic system that can move 

around on its own, carrying its own data and power 

accommodations adds flexibility in achieving mission 

objectives. 

Some work has been done to develop such 

systems for space applications, but more development 

is required to enable the ambitious objectives of the 

notional mission suite. The Space Systems Laboratory 

at the University of Maryland developed a concept for 

Figure 4.6 – Ranger Telerobotic Shuttle Experiment – The 

Ranger dexterous manipulator pair mounted to a head 

that is attached to a positioning leg. This hardware was 

designed to be positioned at a worksite using a grapple 

arm or a positioning leg.
 Chapter 4 | Satellite Servicing: The Implementation – The Notional Missions | 59

safe co-elliptic rendezvous strategy was used for 

rendezvous with customer spacecraft on essentially 

circular orbits in the Low Earth Orbit (LEO) and 

Geostationary Earth Orbit (GEO) regimes. In this 

strategy, the servicer spacecraft is placed onto an 

orbit of the same orientation and shape as that of 

the customer, but with a slightly different altitude. 

The rendezvous sequence generally begins with the 

servicer several tens of kilometers below and several 

hundred kilometers behind the customer spacecraft. 

The servicer will naturally drift towards the customer 

spacecraft parallel to its orbit track, where the drift 

rate is proportional to the difference in altitude 

between the orbits. The servicer will periodically 

perform small maneuvers (e.g., Hohmann transfers) 

to gradually raise its orbital altitude as it approaches 

the customer from behind. Once within several km 

of the customer, the servicer begins the proximity 

operations phase and will generally insert itself into 

a small safety ellipse, up to approximately 100 m in 

diameter, centered on the customer spacecraft.

Safety ellipses are natural periodic relative motion 

trajectories in which the servicer spacecraft will fly 

around the customer spacecraft on an elliptical path 

centered on the customer (see Figure 4.7). The time 

required for the servicer to fly around the customer 

once is equal to the customer’s orbit period. The safety 

ellipse motion can be maintained by the servicer 

with a modest expenditure of orbit maintenance fuel. 

Safety ellipses are so named because they are tilted 

with respect to the plane of the customer’s orbit such 

that the servicer never crosses the customer’s velocity 

direction, making the relative motion passively safe. 

Thus safety ellipses provide an efficient configuration 

from which the servicer spacecraft can repeatedly fly 

around the customer to gather situational awareness 

data: collect range, bearing, and pose measurements, 

and allow the relative navigation filter sufficient time 

to converge.

During the final approach phase in a capture 

scenario, the servicer may have to expend considerable 

fuel if the customer spacecraft is in an uncontrolled 

attitude state with appreciable tumble rates. If the 

and interpreted locally (by processors on-board the 

servicer), and then the resulting model of the worksite 

and the broader situation could be transmitted to 

the ground. Camera platforms that can reposition 

themselves at the worksite, possibly by using freeflying camera platforms, could be developed to 

provide flexibility with far less infrastructure. Other 

sensors (e.g., infrared cameras) could be developed to 

provide feedback to the operator with low- or nolighting requirements. This study did not perform any 

trades on the possible solutions, but this was an area 

identified as a key technology ripe for investment and 

system-level maturation.

Astrodynamics

All servicing mission concepts require that the servicer 

spacecraft (whether robotic or carrying humans) 

rendezvous with the customer spacecraft, perform 

proximity operations with the customer spacecraft, 

and then capture, be berthed to, or dock with the 

customer spacecraft. These activities are part of the 

discipline of astrodynamics, in which spacecraft 

perform an intricate “dance” under the influences of 

gravity and thrusters.

The relative motion dynamics between two 

spacecraft in an Earth-centered orbit are well 

understood, particularly in the case where the 

customer spacecraft is on a circular or nearly circular 

orbit. The orientation of the orbit is not generally 

an important factor for relative spacecraft motion, 

whereas the orbit shape (circular or appreciably 

eccentric) does have a strong effect. The characteristics 

of and techniques for performing relative spacecraft 

motion design with the customer spacecraft on an 

eccentric orbit are understood theoretically, but 

performing rendezvous and proximity operations 

with respect to a spacecraft on an eccentric orbit is 

uncommon in practice.

Rendezvous, proximity operations, and capture, 

berthing, or docking can generally be performed 

for modest ΔV (i.e., expenditure of propellant) by 

utilizing one of a variety of sensible strategies. For the 

notional mission studies presented here, the passively 
60 | On-Orbit Satellite Servicing Study Project Report | October 2010

tumble rates are large enough—generally greater than 

1 ̊/s per axis—the ΔV required for final approach 

can become the largest contributor to overall 

rendezvous ΔV. Otherwise, the ΔV required to match 

the customer’s orbit plane prior to the initiation of 

the co-elliptic rendezvous sequence is generally the 

dominant factor in the total rendezvous ΔV (all else 

being equal).

Moving beyond LEO and GEO, Lagrange 

points (also known as libration points) are the five 

equilibrium points found in any Restricted ThreeBody Problem (RTBP). An object placed precisely at 

one of these points with zero velocity will theoretically 

remain at the point indefinitely. An RTBP is a 

configuration of two celestial bodies referred to as 

the primaries, such as the Earth and the Moon, or 

the Sun and the Earth, and a third small body of 

comparatively negligible mass, such as a spacecraft. 

Lagrange points are only points when viewed in 

a rotating coordinate system whose origin is located 

at the center of mass of the primaries. The motion 

of the smaller primary is often modeled as a circular 

orbit about the larger primary, yielding a Circular 

RTBP (CRTBP). The Earth-Moon and Sun-Earth 

systems are well approximated by the CRTBP for 

preliminary mission design purposes. The rotation 

rate of the coordinate system is defined such that the 

centripetal acceleration balances the gravitational 

acceleration between the primaries, thus causing the 

primaries to remain stationary in the rotating frame. 

Thus, the Lagrange points are paths in space rather 

than points when viewed in an inertial (non-rotating) 

coordinate system.

The Lagrange points are conventionally labeled 

EML1 through EML5, as shown in Figure 4.8. While 

they are all equilibrium points, only the EML4 and 

EML5 points are theoretically stable. The EML1 

through EML3 points are theoretically unstable, but 

all five points are in fact unstable when the gravity 

of other solar system bodies is accounted for. This is 

why the Lagrange points of the Earth-Moon system 

are empty of natural debris such as asteroids. However, the near-equilibrium offered by these points in 

practice means that spacecraft can station-keep with 

relatively little fuel expenditure at or near these points 

for an extended period of time. This, along with the 

geometrical advantages offered by these points for 

communication, the sky coverage access for astronomical observations, and a stable thermal environment 

makes the Lagrange points ideal locations for deploying a variety of spacecraft missions.

Spacecraft can be placed into relatively small, 

slightly irregularly shaped orbits about Lagrange 

points. There are three types of Lagrange point orbits: 

Lyapunov, halo, and Lissajous. Lyapunov orbits and 

halo orbits are both periodic orbits, meaning that 

they are nominally closed, repeating paths. Lissajous 

orbits are quasi-periodic and hence do not form 

closed paths, though they will remain in the vicinity 

of the Lagrange point. Lyapunov orbits lie in the 

XY plane of the rotating coordinate system (e.g., the 

plane containing the Earth and the moon), while 

halo and Lissajous orbits do not have to lie in a 

particular plane.

Lagrange point orbits are readily reached from 

Earth with modest launch energy, insertion ΔV, and 

flight time. Additionally, the rich dynamics of RTBPs 

permit interesting trajectories that travel between 

Lagrange points for very little ΔV, though the flight 

Figure 4.7 – Safety Ellipse – By orbiting with a slightly 

different orbital eccentricity and inclination, the servicer 

spacecraft naturally flies around the customer once per 

orbit without crossing the customer’s velocity direction, 

making the relative motion passively safe.
 Chapter 4 | Satellite Servicing: The Implementation – The Notional Missions | 61

times can be relatively long. 

Specialized orbits, such 

as those described in the 

next section, can also be 

designed to meet missionspecific requirements. The 

relatively large size of halo 

orbits about the Sun-Earth 

Lagrange points, such as 

Sun-Earth L2 (SEL2), 

allow a spacecraft stationed 

on those halo orbits to 

receive continuous sunlight 

and thus avoid eclipses. 

Designing eclipse-free 

orbits about Earth-Moon 

Lagrange points is more 

challenging and has been 

identified as a topic for 

future work. Rendezvous 

and proximity operations 

between spacecraft on 

Lagrange point orbits is an 

area in which we have little 

theoretical development 

and no practical experience, 

though it is a key element 

of all servicing missions 

that will take place in the vicinity of Lagrange points. 

Preliminary studies have shown that the ΔV and flight 

times are reasonable for spacecraft rendezvous and 

proximity operations on Lagrange point orbits, but 

more study is required to develop rigorous theory and 

algorithms for the relative motion trajectory guidance, 

navigation, and control.

The L1 Orbit Trajectory Used for Servicing 

(LOTUS)

Notional Mission 5, which involves human/

robotic servicing of a large telescope in the EarthMoon system, presented unique challenges out of 

which the L1 Orbit Trajectory Used for Servicing 

(LOTUS) was born.

In Notional Mission 5, a large telescope 

stationed at Sun-Earth L2 (SEL2) is to return to the 

Earth-Moon system and rendezvous with a robotic 

servicing vehicle. Afterwards, a crew vehicle carrying 

astronauts will rendezvous with the stacked robotic 

servicer and telescope, and servicing will begin. After 

servicing is completed, the crew vehicle returns to 

Earth, the telescope returns to SEL2, and the robotic 

servicing vehicle continues to station-keep in its 

orbit within the Earth-Moon system for 25 years, 

remaining available for future servicing activities. 

Several competing objectives resulted from this 

concept of operations.

Telescope maneuver magnitudes should be 

minimized so as to conserve telescope propellant 

and avoid large structural loads on the telescope. 

Figure 4.8 – The LOTUS – This figure depicts the LOTUS in the context of the mission sequence 

for Notional Mission 5. The robotic servicing vehicle travels to a Lyapunov orbit about EarthMoon L1 (top center red cylinder), where the large telescope later arrives from Sun-Earth L2 to 

be captured. After the servicer and telescope are joined (lower left yellow/red spacecraft), they 

insert into the LOTUS with a very small ∆V and are later met by the crew vehicle (lower left green

spacecraft).The crew vehicle, robotic servicer, and telescope remain together on the LOTUS 

until servicing of the telescope is complete, at which time the crew vehicle deorbits. The LOTUS 

proceeds to naturally carry the servicer and telescope back to L1, where the servicer will reinsert 

into the Lyapunov orbit for long-term station-keeping. The telescope performs a small maneuver 

to exit the Earth-Moon system and return to its operational orbit about Sun-Earth L2 (right).
62 | On-Orbit Satellite Servicing Study Project Report | October 2010

aspects of the mission. The ensuing analysis uncovered 

a class of orbit that is dynamically connected to the 

EML1 Lyapunov orbit. This new type of orbit was 

named the L1 Orbit Trajectory Used for Servicing 

(LOTUS) since it facilitates servicing missions such 

as the one described here, and also resembles a 

lotus flower when viewed in the canonical rotating 

reference frame of the Earth-Moon system.

The LOTUS is a Highly Elliptical Orbit 

(HEO) with a period of approximately 10 days, an 

eccentricity of 0.54, and a perigee of approximately 

84,000 km (which keeps it well above both GEO and 

the Van Allen radiation belts). A spacecraft can enter 

the LOTUS from the EML1 Lyapunov orbit for a 

ΔV of only 10 cm/s, and after 98 days the LOTUS 

will naturally carry the spacecraft back to the EML1 

Lyapunov orbit, at which time the spacecraft can 

reinsert itself into the Lyapunov orbit for a modest 

ΔV of 45 m/s.

The servicer can therefore inhabit the EML1 

Lyapunov orbit for its long-term station-keeping as 

originally planned, and the telescope can rendezvous 

with the servicer on the Lyapunov orbit. Then the 

servicer/telescope stack can easily enter the LOTUS, 

after which the crew vehicle will rendezvous with the 

stack to perform servicing. After servicing, the crew 

vehicle returns to Earth and the servicer/telescope 

stack will naturally return to EML1 a couple of 

months later. At that time, the telescope can separate 

from the servicer and travel back to SEL2, and the 

servicer can reinsert itself into the EML1 Lyapunov 

orbit for station-keeping.

The advantages of the LOTUS for the crew are as 

follows. First, the flight time for the crew to reach the 

LOTUS varies between 0.6 and 3.4 days, depending 

on whether the crew chooses to insert into the 

LOTUS at perigee or apogee. The launch energy for 

the crew to reach LOTUS perigee is only -8 km2

/s2, 

while the launch energy for the crew to reach LOTUS 

apogee is -3 km2

/s2. For reference, the launch energy 

to travel to the Moon is -2 km2

/s2, so launching to 

the LOTUS always requires less launch energy than 

a typical lunar mission. Additionally, the crew always 

has a free return to Earth available when launching 

Additionally, the orbit occupied by the servicer must 

be easily accessible by both the telescope and the 

crew vehicle, and must be able to be maintained for 

a modicum of fuel since the servicer will be expected 

to station-keep for 25 years (which allows for two 

additional servicing missions with some margin). 

Finally, the crew vehicle must be able to fly trajectories 

to and from the servicer’s orbit that yield adequate 

available time for servicing work while respecting 

the crew vehicle’s fuel budget and the maximum 

preferred crew mission duration of approximately 21 

days. Other constraints on the crew vehicle trajectory 

include minimization of exposure to the Van Allen 

radiation belts, avoidance of the Geostationary Earth 

Orbit (GEO) belt, and the option of a free return 

from launch in the event of a crew vehicle systems 

failure.

The first thought was to place the servicer on the 

same Lyapunov orbit that was utilized for Notional 

Mission 4. The advantages offered by this Lyapunov 

orbit include a modest station-keeping ΔV of 60 

m/s (annual) and easy access for the telescope. (The 

telescope can travel between the Earth-Moon L1 

(EML1) Lyapunov orbit and the SEL2 halo orbit for a 

total ΔV of approximately 45–50 m/s and a one-way 

flight time of 50–130 days, depending on conditions.) 

It also offers a free return for the crew from launch, 

modest launch energy (-2.6 km2

/s2) and insertion/

departure ΔV (600 m/s) requirements for the crew, 

and a very tractable ΔV requirement of approximately 

30 m/s (depending on conditions) for Autonomous 

Rendezvous and Berthing (AR&B) between vehicles 

on the Lyapunov orbit.

We determined that the crew will need to have 

15 days of servicing work time available on orbit, 

but the fastest one-way flight time for the crew to 

go between Earth and the EML1 Lyapunov orbit is 

approximately 4.5 days (it can be as long as 6 days), 

and allocating 1 day for AR&B leaves the crew only 

11 days for servicing activities because of the 21-day 

mission limit.

This prompted the search for a different orbit for 

the servicer that could be reached by the crew vehicle 

more quickly without adversely impacting any other 
LOTUS is fully selectable, since the crew can insert 

at and deorbit from any points on the LOTUS. For 

example, the crew can launch into LOTUS apogee 

with a 3.4 day flight time, spend 1 day performing 

AR&B with the servicer/telescope stack, spend 15 

days servicing, and then have a 1.16 day flight back 

to Earth, for a total mission time of 20.56 days, just 

within the 21-day limit. The launch energy for the 

mission is -3 km2

/s2 and the total crew vehicle ΔV, 

including AR&B, is 2,120 m/s. For comparison, 

typical values for a lunar mission are a launch energy 

of -2 km2

/s2 and a total crew vehicle ΔV capability of 

2,800–3,000 m/s.

into the LOTUS. The ΔV required for the crew to 

insert into the LOTUS after launch is 1,800 m/s if 

inserting at LOTUS perigee and 560 m/s if inserting 

at LOTUS apogee. The ΔV requirements are similar 

for the crew to deorbit from the LOTUS and return 

to Earth, yielding a total post-launch ΔV requirement 

for the crew vehicle between 1,120 and 3,600 m/s. 

These combinations of launch energy and total ΔV 

for the LOTUS are all less than for a lunar mission, 

meaning that any lunar architecture for launch and 

crew vehicles is more than capable of utilizing the 

LOTUS.

The key advantage of the LOTUS for servicing 

is that the amount of time the crew spends on the 

 Chapter 4 | Satellite Servicing: The Implementation – The Notional Missions | 63
Mission Sequence 

Figure 4.9 – The Recommended Mission Sequence – This diagram summarizes our recommended mission sequence. The horizontal axis 

represents chronology and time. The top section shows the missions. The bottom section shows the enabling technologies for those 

missions, separated into three technical categories. The vertical axis for the missions conveys a general sense of increased complexity. 

Note that we recommend three parallel paths for development of satellite servicing: maintenance, refurbishment/upgrade, and multi-launch, 

large-scale assembly. These are shown as bands, along with the representative missions. The GEO Fuel mission has two blue arrows 

indicating how it could evolve into a refurbishment/upgrade capability, and also a government or commercial debris removal capability. 

64 | On-Orbit Satellite Servicing Study Project Report | October 2010

There are a rich variety of meaningful servicing missions that could be undertaken 

within the next five years. There are also a number of more challenging, visionary 

missions that are foreseeable further in the future. What we refer to as the “mission 

sequence” is the choice of stepping-stones to get from one to the other. This 

choice will be driven by fiscal constraints, engineering prudence, and—perhaps 

most importantly—the higher-level goals of the Agency.
Our study has assessed the range of satellite servicing 

capabilities against some reasonable assumptions 

to recommend a logical mission sequence. Figure 

4.9 shows our concept for a three-tier progression 

of missions. They progress from the short-term 

achievable (lower left corner) to the long-term 

ambitious missions (upper right corner).

The first tier of missions falls under the category 

of maintenance. As discussed in previous sections, 

there is a strong case for refueling large classes 

of Geostationary Earth Orbit (GEO) satellites. 

There is also a strong case for performing orbital 

modifications. Such services would be of great 

interest for commercial and military satellites, so 

there would be a diverse customer base. The elements 

needed to provide these services were studied in 

Notional Missions 1 and 2. We conclude that the 

first logical mission in this sequence would be an 

all-robotic servicer to GEO that provides both orbit 

modifications and refueling to customers. 

This servicer would have the ability to 

autonomously rendezvous with and capture an 

existing satellite, modify its orbit, and/or transfer 

additional propellant. In some cases, it may be 

beneficial to remove propellant from a nonoperational satellite to reuse it for other satellites. 

These basic technologies are well-established and 

mature. Some were demonstrated in space in the 

Orbital Express mission, others in laboratory 

programs, and some are the subject of ISS verification 

experiments described in later sections.

We propose that the initial sortie for the servicer, 

known as GEOServ, would be to 1) capture a 

derelict satellite, 2) raise its orbit altitude ~350 km 

to the GEO super-synchronous disposal orbit, and 

3) release. This mission profile has the benefit of 

removing a derelict satellite that is a hazard to others 

in the GEO belt, and would provide a highly visible 

demonstration of satellite servicing utility without the 

risk of damaging an operational satellite.

The second sortie for GEOServ would be to 

grapple a functioning U.S. government satellite and 

robotically transfer propellant to it. There would be 

immediate gains for the customer, and the successful 

application of refueling technologies would lower the 

perceived risk for future commercial customers.

The now fully validated and operational GEOServ 

would then proceed from customer to customer 

performing orbit modifications and/or refueling until 

it had just enough propellant remaining to supersync itself. A burgeoning commercial GEO satellite 

refueling industry would be expected to rapidly 

emerge once GEOServ blazes the path.

The success of GEOServ would naturally 

open the door to two types of follow-on missions: 

relocation/orbit modification and refueling. The 

former would execute debris removal services in a 

targeted area, such as the GEO belt, or polar LEO 

where there are 140 large objects.[49] The latter 

would be optimized for refueling and would begin a 

commercial refueling industry. 

In parallel with the maintenance tier, it is 

recommended that a second, more robotically 

challenging set of missions be undertaken. This tier 

is associated with the refurbishment, upgrade, or 

retrieval of on-orbit satellites. A first mission could be 

a Hubble Space Telescope (HST) servicing or disposal 

mission, since more is known about the interfaces 

on HST than on any other legacy vehicle. The 

refurbishment of HST with additional instruments 

and Orbital Replacement Units (ORUs) would spur 

development of additional robotic technology. More 

autonomy could be employed in the execution of 

the robotic tasks. There are obviously other Low 

Earth Orbit (LEO) vehicles that could use upgrades, 

but these would pose much higher risk for this first 

mission since less is known about their interfaces. The 

successful completion of this mission would provide 

confidence that all-robotic servicing of other legacy 

spacecraft is feasible. Other customers could then be 

refurbished/upgraded, such as an infrared imagery 

spacecraft whose cryogen has been depleted.

Another logical follow-on mission in the 

refurbishment and upgrade tier (for legacy spacecraft) 

is the replacement of 19% efficient double-junction 

solar arrays that have radiation-darkened cover glass 

 Chapter 4 | Satellite Servicing: The Implementation – Mission Sequence | 65
with new 27% triple-junction arrays. This would 

provide beginning-of-life power to a legacy spacecraft. 

For example, between 1987 and 1998 there were 

insurance claims totaling $347 million on GEO 

spacecraft with solar array anomalies.[8]

Eventually, as more refurbishment and upgrade 

missions were undertaken, our technical capabilities 

would advance to support modular assembly of very 

large astronomy missions. Rather than designing 

and flying just 3- or 5-year observatories, longduration observatories could be entertained whose 

instruments and bus components would be modular 

so that robotic changeout is easily accomplished, thus 

supporting extremely long operational lifetimes. This 

brings us to the third and final tier of the mission 

sequence.

The third tier is the assembly of large-scale, multilaunch structures that would accomplish the Agency’s 

long-term goals. One such goal is an Earth-departure 

vehicle that could transport humans to Mars on a 

time scale consistent with the requirement of the human spaceflight program. There are many techniques 

and technologies from the ISS that would lend themselves directly to enabling the on-orbit assembly of a 

multi-launch structure such as a cryo-depot, an Earth 

departure vehicle, a trans-planet habitat complex, 

etc. As the architecture for those missions becomes 

defined, the assembly technologies would be mapped 

so that existing capabilities could be cataloged and 

technology gaps could be identified and targeted for 

development.

This three-tier mission sequence presents a logical 

path forward with the end goal of providing a rich set 

of meaningful capabilities that benefit the commercial 

telecommunications industry, government agencies, 

and the human exploration community. It is the 

result of combining the benefits of satellite servicing 

with the notional mission analyses into an executable 

sequence that brings immediate results while setting 

the path for more ambitious future goals.

66 | On-Orbit Satellite Servicing Study Project Report | October 2010
 Chapter 4 | Satellite Servicing: The Implementation – Technology Gap Assessment | 67

Technology Gap Assessment 

Evaluating the notional missions and subsequently constructing the mission 

sequence also resulted in an assessment of the technologies required to implement 

the missions. While many of these technologies are largely in-hand (see Figure 

4.10), the complex system-level algorithms required for fully autonomous 

operations, or the intricate end-effectors and tools used for legacy satellite repairs, 

for example, would benefit from additional verification. We have begun to achieve 

this goal via ISS demonstrations. Future missions would exploit the results of these 

demonstrations. These future missions would also provide the platforms to verify 

even more complex algorithms required for highly autonomous operations in very 

remote locations that have high Earth communication latencies.

envisioned have a box labeled “invention needed 

here.” Deficiencies in technology readiness exist 

mainly in regard to demonstrating the performance of 

integrated servicing hardware and control systems in a 

space environment. For the more ambitious notional 

missions, considerable work is required to integrate 

All of the technologies required for satellite servicing 

exist at a fairly high level of maturity, with the 

exception of those associated with autonomous 

operations. While there can be a fine line between 

classifying a development need as new technology 

or hard engineering, none of the servicing scenarios 

Figure 4.10 – Tools for Closing the Technology Gap – Both the Space Station Remote Manipulator System, shown in action 

(left), and the Relative Navigation System (right, in the space shuttle bay before launch for the Hubble Space Telescope 

Servicing Mission 4) are tools that will demonstrate Autonomous Rendezvous and Capture capabilities and help close the 

technology gap. 
68 | On-Orbit Satellite Servicing Study Project Report | October 2010

and fully exploit the advantages offered by satellite 

assembly and servicing, but this is an issue of effective 

application of technology, i.e., good engineering and 

rigorous existing systems engineering, rather than 

technology development.

To explore further the adequacy of servicing 

technology, the following discussion decomposes 

a satellite servicing system into the spacecraft bus 

element and four key technology areas for the servicer 

element: rendezvous and docking, manipulation, 

refueling, and autonomy.

Servicer Spacecraft Bus

Other than for human spaceflight, the six notional 

missions studied identified no new technology 

requirements for the servicer spacecraft bus. The 

servicer element imposed requirements on spacecraft 

subsystems such as attitude control, electrical 

power, command and control, data handling, 

communications, propulsion, thermal control, and 

structures and mechanisms that are fully mature and 

well within the current state of the art. Advances in 

lighter-weight or more power-efficient components 

and subsystems would, of course, improve capability 

in a given mission class, but no new technologies are 

required for the spacecraft bus.

Rendezvous and Berthing/Capture/Docking

The current experience base provides mature 

technology for rendezvous and docking with 

cooperative, non-spinning customers via teleoperation 

or semi-autonomous control. Rendezvous and docking 

are separated into three sequential phases. The first is 

rendezvous, wherein the servicer vehicle maneuvers 

from hundreds of kilometers to less than 100 meters 

from the customer. Proximity operations close the 

separation to a few meters along the desired approach 

corridor. Finally, the servicer and customer spacecraft 

are coupled via berthing, capture or docking. In 

docking, the servicer maneuvers until contact is made 

with the customer and mechanical couplings engage, 

as performed in the Gemini and Apollo programs in 

the 1960s and currently done by the space shuttle, 

Soyuz, Progress, and ESA Automated Transfer 

Vehicles (ATV) with the ISS. Berthing involves the 

servicer maneuvering to position the customer within 

range of a manipulator arm which grapples the 

customer. The manipulator can then dock the two 

vehicles if both are so equipped. Berthing was used 

on the Orbital Express mission in addition to direct 

docking. Berthing is also the approach used on the 

ISS with the JAXA HTV (H-II Transfer Vehicle). It 

will be the method used by the SpaceX Dragon and 

OSC Cygnus automated resupply vehicles expected 

to fly within the next couple of years under NASA’s 

Commercial Orbital Transportation Services (COTS) 

and Commercial Resupply Services contracts.

Docking or berthing becomes more complex if 

the customer spacecraft is spinning or tumbling out 

of control. Control algorithms must determine the 

spin rate, spin axis orientation, and any nutation. 

Proximity operations must then be planned and 

executed to maneuver the servicer along the 

customer’s spinning approach axis and match spin 

rates prior to grappling or docking (as depicted so well 

in the film 2001: A Space Odyssey over 40 years ago). 

These operations have been simulated on the ground, 

but not yet attempted in space.

Berthing, capture and docking all require 

knowing the “pose,” a term for the combination of 

position and orientation, of the customer relative to 

the servicer. In autonomous docking or grappling, 

cameras or Light Detection and Ranging (LIDAR) 

vision systems identify and track features on the 

customer to allow for a computational determination 

of the customer’s pose. This task has been solved 

for reference fiducials purposely placed on the 

customer spacecraft. If there are no such fiducials, 

other features must be identified and tracked. One 

method would be to use cameras or a LIDAR to map 

the customer’s surface and then compare that map 

to a model of the customer’s exterior to determine 

its pose. These technologies have been demonstrated 

in laboratories (3D LIDAR tracking) and on the 

Orbital Express mission (2D optical tracking). There 

are multiple U.S.- and Canadian-produced LIDAR 
 Chapter 4 | Satellite Servicing: The Implementation – Technology Gap Assessment | 69

sensors and supporting camera systems that have 

been demonstrated in recent years on NASA and 

Department of Defense (DoD) space missions.

The required spacecraft actuators (thrusters 

and capture arms) are technology that has existed 

since the 1970s. It is the sensors and algorithms 

required for autonomous rendezvous and berthing/

capture/docking that have seen development only 

in the last decade. The state of the art for on-orbit 

demonstrations includes non-spinning/non-tumbling 

customers. The next steps for technology development 

should include a demonstration with spinning and/or 

tumbling customer scenarios.

Manipulation

Manipulators, also known as “robot arms,” endeffectors, and tools are necessary for all physical 

interaction between spacecraft, be it berthing, 

Orbital Replacement Unit (ORU) exchange, fluid 

coupling engagement, access panel removal, or camera 

positioning for inspection.

There are a few paradigms when considering what 

to place on the end of the robot arms. One is to use 

an end-effector that provides basic functions, such as 

a parallel jaw grippers, socket driver, etc. This is the 

type of end-effector used on the ISS SPDM system. 

The end-effector can be used for multiple tasks as long 

as those tasks are compatible with the end-effector’s 

limited functions and standardized electromechanical 

mating interface. ORU replacement, for example, is 

a task that can typically be accomplished with such 

an end-effector. The end-effector could be designed 

such that it could be swapped out with another endeffector at the end of the arm. More specialized tasks, 

such as cutting a safety wire, require the end-effector 

to grasp the appropriate specialized tool. The range 

of possible tool designs and applications is nearly 

limitless, and very specialized devices have been built 

and used. Another paradigm is to develop a more 

dexterous end-effector that incorporates tools as part 

of its design. This end-effector/tool combination can 

be exchanged on the end of the arm to perform a 

specific task. This is the general philosophy behind the 

Ranger and FREND robotic systems. An extreme end 

of this spectrum is to develop an anthropomorphic 

hand that requires an extensive tool set for specific 

tasks like in the Robonaut system. These various 

paradigms were studied in the GSFC design lab and 

the results are summarized in Appendix E.

Some evolutionary advances in manipulation 

that would allow for more efficient operations include 

reduced mass and increased speed of manipulators, 

increased spatial resolution touch sensors (haptics), 

non-contact sensors that can detect the presence of 

nearby objects, narrow wavelength band cameras and 

illumination sources to eliminate sensitivity to solar 

glare and harsh direct solar illumination, and more 

autonomous systems. Fusion of manipulator sensory 

data and virtual environment simulation will provide 

teleoperators with “superhuman” senses.

Space robotic manipulation is in various stages of 

maturity. Basic teleoperation of manipulators is well 

established. However, autonomous control requires 

some validation and demonstration. There has been 

extensive teleoperation experience with large arms 

(15~17 m long) such as the space shuttle Remote 

Manipulator System (RMS) and the Space Station 

Remote Manipulator System (SSRMS). These are 

the equivalent of zero-gravity space cranes, and they 

played pivotal roles in assembling ISS. For finer, more 

precise motions and operation in more constrained 

work zones, smaller manipulators are required. The 

use of smaller manipulators for space servicing is 

less mature, with space experience limited to a few 

experiments in space (ROTEX, ETS-VII, and Orbital 

Express) and a few systems coming online now 

(SPDM/Dextre, JEM-Fine Arm, and Robonaut). The 

Viking 1 and 2, Phoenix, Spirit and Opportunity 

manipulators also add to the experience base, and 

some of the technology has been applied to free-space 

servicing tasks.

On the other hand, ground-based industrial robot 

technology is very mature, with nearly one million 

industrial robots now in use worldwide. However, 

space robotics differs from terrestrial applications 

in the structural characteristics of manipulators 
70 | On-Orbit Satellite Servicing Study Project Report | October 2010

and payloads in zero-gravity. Consequently, control 

algorithms for space manipulators must take into 

account flexible-body dynamics and free-body 

contact dynamics. Real-time closed-loop control and 

disturbance reduction will be demonstrated with the 

Dextre Pointing Package (DPP) experiment on ISS.

Manipulator technology (arms, joints, endeffectors, motors) has existed since the 1970s. 

Improvements are being developed now in the areas of 

more diverse sensors suites and autonomous control. 

The state of the art for on-orbit demonstrations 

includes autonomous and teleoperated tasks. The 

next steps in technology development would include 

a demonstration with an access panel and refueling 

manipulation with multiple end-effectors and/or tools. 

These will be a part of the Robotic Refueling Mission 

demonstration that is planned on the ISS.

Refueling

The Orbital Refueling System (ORS) experiment on 

the Shuttle STS-41G mission in 1984 demonstrated 

the ability to refuel satellites in space. Following an 

Extravehicular Activity (EVA) to attach a flexible 

propellant line to a typical satellite valve in the 

payload hardware, six transfers of hydrazine between 

two diaphragm tanks were successfully conducted. 

Additional zero-gravity fluid transfer experiments 

were successfully conducted on Shuttle STS-57 in 

1993 with the Super Fluid Helium On-Orbit Transfer 

(SHOOT) and Fluid Acquisition and Resupply 

Experiment (FARE) test articles.

The ISS is refueled using automated fluid 

couplings incorporated into the docking mechanisms 

on the Russian service module of ISS. Refueling is 

routinely performed by Russian Progress resupply 

vehicles and was also conducted by the ESA Jules 

Verne Automated Transfer Vehicle (ATV) spacecraft. 

In a similar manner, an automated fluid coupling and 

propellant transfer between two docked spacecraft was 

demonstrated by the Orbital Express program.

When joined spacecraft are not equipped with 

automated fluid coupling mechanisms, a manipulator can be used to interconnect a fluid transfer line 

and actuate valves. This will soon be demonstrated on 

the ISS with the Robotic Refueling Mission (RRM), 

which will perform tasks representative of those 

required to refuel a spacecraft using its legacy—i.e., 

not designed for robotic operation—propellant filland-drain valve. Similar fluid coupling and transfer 

demonstrations are needed for cryogenic systems 

applicable to high-specific-impulse propulsion systems 

and instrument cooling.

In addition to refueling via propellant transfer 

between propellant tanks, there is also the option of 

entire tank replacement using robotic manipulation 

in a manner similar to ORU replacement. Fluid 

line couplings can either be incorporated into the 

tank’s mechanical interface or mated via robotic 

manipulation of flexible propellant lines. At an even 

higher level of integration, an entire propulsion 

module—propellant tanks plus thrusters and 

associated plumbing—can be designed as an ORU. 

The Multimission Modular Spacecraft (MMS) 

spacecraft incorporated a replaceable propulsion 

module. Refueling via whole tank replacement has not 

been demonstrated in space (although it is common 

for backyard barbeque grills).

The required spacecraft refueling technology 

is very similar to on-ground filling for simple fuel 

systems. It is autonomous refueling that has seen 

development in the last decade. The state of the art for 

on-orbit demonstrations includes refueling through 

pre-designed connections for docked spacecraft. 

The next steps in technology development include 

a demonstration of the autonomous refueling of a 

satellite that was not designed for on-orbit refueling.

Autonomy

Robot control sophistication ranges from simple 

and direct master-slave teleoperation, to automatic 

operation, and to increasing levels of autonomy. 

Automatic control methods such as those based 

on state-machine approaches, e.g., Experimental 

Spacecraft System Number 11 (XSS-11), are 

mature technologies from established principles in 

cybernetics. For a structured and pre-planned mission, 
an automatic capability is adequate. Autonomous 

capability is required only when the task is unfamiliar 

or complex, or when communication issues exist. 

The benefits of autonomy include improvements 

in efficiency, robustness, and capability. Efficiency is 

improved by the robot performing more tasks prior 

to pausing to await human operator status assessment and approval to proceed. This becomes more 

important when latency—robot-to-operator communication time—is high or when communication 

time periods are limited. Robustness is improved by 

the robot controller analyzing sensor data and tailoring its actions accordingly. The robot control system 

can rapidly and tirelessly process a variety of sensor 

data and perform complex calculations to recognize 

and adjust to changes in the work environment while 

also constantly performing safety and health checks. 

Robustness is also improved due to faster controller response time due to local autonomous control 

eliminating communication-link latency. This same 

data processing capability and quick response time 

also enable some tasks to be performed faster and 

with greater sensitivity and accuracy than possible via 

teleoperation or Extravehicular Activity (EVA). At 

higher levels of autonomy, artificial-intelligence-like 

algorithms enable the robot to learn as it operates and 

improve task planning for future activities. In the last 

few years, much has been learned through higher-level 

applications of industrial robots about how robots can 

efficiently do their tasks. Similarly, the last few years 

have brought much experience with robots being 

operated by and around humans by the military (e.g., 

drones, building reconnaissance, and bomb disposal). 

The expected level of autonomy demonstrated 

in spacecraft has steadily increased. Note that 

any servicing task could be done with any level 

of autonomy. The state of the art for on-orbit 

demonstrations includes autonomous docking 

and Orbital Replacement Unit (ORU) changeout 

for Orbital Express. The next steps in technology 

development would include evaluating several 

levels of autonomy with any and all future servicing 

demonstrations.

Satellite Servicing Integration into Mission 

Design

None of the technology gaps identified above are 

roadblocks to implementing significant use of satellite 

servicing technologies. Looking at the big picture, 

the key work may lie in determining how best to 

take advantage of in-space assembly and servicing to 

expand mission capability while also reducing mission 

cost and risk. What is the optimum balance between 

designing more capable robots versus designing 

space systems to maximize use of a core set of 

standard servicing capabilities and reduce additional 

costs associated with mission-specific servicing 

requirements? How can servicing be exploited to relax 

reliability and redundancy requirements? How can 

the deployment of large space systems be best staged 

to spread out hardware development and smooth out 

resource requirements? These system-level questions 

are not a technology gap, per se, but the answers will 

help inform the decisions that need to be made to 

determine the nature of these gaps.

 Chapter 4 | Satellite Servicing: The Implementation – Technology Gap Assessment | 71
ISS Demonstration Activities

The International Space Station (ISS) is our long-term human and robotic resource 

in space, making it a natural platform on which to demonstrate human and robotic 

systems that support satellite servicing. Several key technologies identified in our 

gap analysis are planned to be validated on ISS near-term via the Robotic Refueling 

Mission (RRM) and the Dextre Pointing Package (DPP) experiments.

The technology to direct the dexterous movements of 

a robotic system on-orbit has been demonstrated by 

the Special Purpose Dexterous Manipulator (SPDM, 

aka Dextre) on the ISS, and on-orbit robotic servicing 

was adeptly demonstrated on cooperative interfaces by 

the Orbital Express mission conducted by the Defense 

Advanced Research Projects Agency (DARPA). 

However, neither of those systems manipulated legacy 

hardware. They both interfaced with hardware that 

was designed for robotic manipulation. Accordingly, 

a risk reduction approach was undertaken that 

performs on-orbit demonstrations of legacy 

hardware manipulation. NASA is maturing selected 

technologies through feasibility demonstrations of 

servicing capabilities on Earth and on-orbit. 

The near-term goals of the Space Servicing 

Capabilities Project (SSCP) are to expand selected 

servicing tasks and technologies and advance them 

to flight or mission status. These goals will be 

achieved through the development and flight of two 

independent payloads to the ISS.

By taking advantage of the ISS infrastructure 

as a platform to test servicing capabilities, these two 

independent payloads will demonstrate the ability 

of a robot like SPDM to meet the current needs of 

selected U.S. space assets at a cost and schedule much 

less than would be the case if these technologies were 

demonstrated on a stand-alone dedicated satellite 

mission.

There are four major stakeholders who stand to 

benefit by these payload experiments: 

•	 The spacecraft users throughout the U.S.

government, who will be able to have their 

spacecraft serviced on-orbit rather than 

replaced.

•	 The aerospace community, which will benefit

from the advancements in technology research 

and development.

•	 The American taxpayers, who will see a more

cost-effective use of their tax dollars.

•	 Future ISS experimenters. By learning to

effectively use the ISS as a test platform, we 

could make significant progress in paving the 

way for subsequent ISS payloads, especially 

those utilizing the unique capabilities of 

SPDM. 

The ISS payload experiments will increase NASA’s 

technical abilities to use robots in space. The SSCP 

will design the flight hardware and Ground Support 

Equipment (GSE) for these payloads. It will also 

execute a demonstration of robotic refueling of a 

spacecraft, as well as the manipulation of a ground 

avionics test port and non-propellant fluid valves. 

The project will provide all the engineering required 

to accomplish these tasks and will coordinate the 

interfaces and required documentation with NASA’s 

Johnson Space Center and Kennedy Space Center. 

Robotic Refueling Mission (RRM)

In preparation for a potential future refueling of an 

orbiting spacecraft, the RRM (see Figure 4.11) will 

validate the capability by performing all the robotic 

72 | On-Orbit Satellite Servicing Study Project Report | October 2010
mission is designed for an operational life of two years 

and will execute the refueling demonstration and 

general robotic operations over a six-month period 

during the two-year window.

Dextre Pointing Package (DPP) 

In preparation for servicing missions requiring greater 

dexterity and tracking capability, the DPP (see Figure 

4.12) will demonstrate the algorithms and control 

mechanisms to locate and point at a specific location 

on Earth or a celestial object, as well as track and 

perform relative state estimation of vehicles visiting 

the ISS. DPP performs attitude determination using a 

star tracker and an Inertial Measurement Unit (IMU). 

It will receive target parameters via commands from a 

ground terminal and will send rate requests to the ISS 

Robotic Workstation Software (RWS) to achieve the 

desired instrument pointing. This closed-loop control 

of Dextre enables real-time pointing and disturbance 

reduction that are beneficial for future servicing 

architectures. 

Not only can the ISS serve as a robotic test bed, 

it can also be used to evaluate the complementary 

nature of human and robotic servicing. Astronauts are 

available for Extravehicular Activity (EVA) servicing 

tasks required for such a mission. The demonstration 

will use the SPDM robot to locate and access the 

multi-layer insulation covering the fuel valve, cut 

multiple safety wires, remove the tertiary cap, remove 

the safety cap, then connect a nozzle tool that will 

turn the actuation nut and transfer a working fluid 

from one tank to the other, and finally disconnect 

from the tank receiving the fuel. On a separate panel, 

SPDM will remove SubMiniature Version A (SMA) 

termination caps from a ground test port, revealing 

exposed coaxial RF connectors. In a subsequent 

mission, coaxial cables will be flown and mated to the 

connectors. This will demonstrate that the capability 

exists to potentially bypass a failed or outdated 

avionics unit on a free-flying asset. Thirdly, there will 

be a fluid access panel on the demonstration hardware 

that will be accessed by SPDM. Using advanced 

robotic tools, SPDM will manipulate these nonpropellant fluid valves to demonstrate the capability 

to replenish fluids on-orbit. This demonstration 

will also include general robotic operations using a 

“busy board.” These boards provide various spacecraft 

interfaces to verify with machine vision algorithms 

(i.e., partial Marman clamp, mock thruster and 

various types of multi-layer insulation patches). The 

Figure 4.11 – Robotic Refueling Mission (RRM) – This 

rendering shows the RRM hardware on the International 

Space Station. This hardware will demonstrate the 

technologies needed for on-orbit spacecraft refueling.

Figure 4.12 – Dextre Pointing Package (DPP) – This 

rendering shows the DPP hardware being used on the 

International Space Station for Earth observations. This 

hardware will demonstrate fine pointing of the robotic arm 

using algorithms developed to support robotic servicing 

operations.

 Chapter 4 | Satellite Servicing: The Implementation – ISS Demonstration Activities | 73
to astronaut training facilities, the Space Servicing 

Demonstration Facilities at NASA GSFC and the 

WVU-NASA Robotics Center for On-Orbit Servicing 

of Space-Based Assets provide essential tools for 

evaluating, practicing, and demonstrating procedures 

for current and future missions. Using the facilities 

in conjunction with proximity operations, hardwarein-the-loop test beds, and neutral buoyancy facilities 

as part of a larger demonstration, test, and validation 

program, full-scale, flight-accurate simulations can be 

performed that meet the requirements for different 

satellites, regardless of their size or specifications. All 

of these facilities help to achieve the goal of being able 

to rendezvous with and service any satellite, in any 

orbit, at any time.

that may or may not include the use of robotic assets 

for items attached to the exterior of the ISS. Also, the 

crew could be used to perform tasks inside the space 

station to demonstrate and evaluate tasks in a zerogravity environment.

Even for demonstration activities, thorough 

validation and verification are still required. Building 

upon the knowledge gained during preparations for 

the Hubble Robotic Servicing and Deorbit Mission 

(HRSDM), NASA’s Goddard Space Flight Center 

(GSFC) and West Virginia University (WVU) 

have developed two unique facilities that deliver 

tool- and task-level, hardware-in-the-loop, contact 

dynamics simulations of any space robot interacting 

with its environment. Similar in concept and scope 

74 | On-Orbit Satellite Servicing Study Project Report | October 2010
 Chapter 4 | Satellite Servicing: The Implementation – The Recommended Actions | 75

The Recommended Actions 

This study has taken a comprehensive look at the history of satellite servicing, the 

current state of servicing-enabling technology and know-how today, and specific 

servicing missions for reaping significant near-term benefits. In the end, no study 

can achieve benefits without appropriate follow-through action and hardware 

commitment. Here we attempt to identify some specific actions that we believe 

would put us on the path toward realizing the benefits of satellite servicing. They 

represent relatively small investments for maturing a discipline that almost certainly 

will change the paradigm of space exploration in the coming decades. These 

actions are identified in Table 4.3 and subsequently discussed in more detail. 

Figure 4.13 – Astronaut in Action – Astronaut Ron Garan, STS-124 mission specialist, participates in the mission’s third 

scheduled session of Extravehicular Activity (EVA) as construction and maintenance continue on the International Space 

Station (ISS). During the six-hour, 33-minute spacewalk, Garan and astronaut Mike Fossum (out of frame), mission specialist, 

exchanged a depleted Nitrogen Tank Assembly for a new one, removed thermal covers and launch locks from the Kibo 

laboratory, reinstalled a repaired television camera onto the space station’s left P1 truss, and retrieved samples of a dust-like 

substance from the left Solar Alpha Rotary Joint for analysis by experts on the ground. The ability to perform such feats onorbit provides the inspiration for developing the art of satellite servicing.
76 | On-Orbit Satellite Servicing Study Project Report | October 2010

and robots, 4) modular, reconfigurable, and mobile 

robotic architectures and systems, and 5) advanced 

imaging/pose-estimating capabilities. Most of these 

technologies are ready for application. By creating 

and exercising satellite servicing systems based on these 

technologies, they will serve as basic building blocks 

to support complex servicing activities. This should 

allow future missions to concentrate on missionspecific challenges and solutions rather than the basic 

tools.

Assess a Range of Customers for Satellite 

Servicing

In most studies to date, the candidates for satellite 

servicing—observatories and other major scientific 

spacecraft or communications satellites—have been 

treated somewhat as generic customers without a great 

deal of detail. The next step will be to include specific 

designs and operations, and in particular, specific 

customers with identified needs and similarities. 

This will result in a suite of executable missions with 

Optimize Engineering Design and Trade 

Studies 

The work reported here is clearly preliminary and 

primarily serves as “existence proofs” of designs for 

astronaut/robotic servicing systems that could carry 

out basic satellite upgrades and servicing. The obvious 

next activity will be to develop the engineering 

designs further, continuing to bear in mind that 

a major goal of our work has been to identify 

technology capabilities that are common among the 

different servicing concepts. This will result in refined 

technical and cost assessments for the proposed 

mission sequence.

Invest in Key Enabling Technologies

There are a small number of key technologies 

that would benefit from early—and sustained—

investments, even at a modest level. These include 

1) increased autonomy for robotic systems, 2) 

improved systems for rendezvous/docking/refueling, 

3) advanced tools and end-effectors for astronauts 

Table 4.3 – Table of Recommended Actions

Recommended Action Result

Optimize engineering design and trade studies for the 

identified mission sequence.

Refined technical and cost assessments.

Invest in key enabling technologies such as 1) increased 

autonomy for robotic systems, 2) improved systems for 

rendezvous/docking/refueling, 3) advanced tools and 

end-effectors for astronauts and robots, 4) modular, 

self-reconfigurable, and mobile robotic architectures and 

systems that can move around large structures in space, 

and 5) advanced imaging/pose-estimating capabilities.

Proven technologies that will serve as the basic building 

blocks for complex servicing activities to allow future 

missions to focus on mission-specific challenges and 

solutions.

Assess a range of customers for satellite servicing. Defined benefits for a suite of executable missions.

Create design recommendations for future spacecraft. Accepted standards for spacecraft design that improve 

serviceability.

Establish customer/provider working groups. A routine venue for discussion and feedback to 

implement lessons learned and best practices.

Integrate a satellite-servicing infrastructure with NASA 

program architectures and priorities.

The benefits of satellite servicing will be exploited where 

available and appropriate.

Initiate plans for executing the missions described in the 

Mission Sequence section (Chapter 4).

Immediate benefits provided by satellite servicing while 

refining the technologies needed for further advances.
 Chapter 4 | Satellite Servicing: The Implementation – The Recommended Actions | 77

defined benefits. An additional result of such an 

assessment is that specific technology needs will be 

identified, should they exist.

Create Design Recommendations for Future 

Spacecraft

A major challenge to having a more efficient national 

aerospace industry is the lack of widely agreed-upon 

standards for spacecraft design that would permit 

more straightforward on-orbit upgrade, refueling, and 

recovery. We recommend that a joint government/

industry working group be established to develop 

basic design standards for such subsystems that would 

be serviceable, such as fueling ports, connectors, 

power systems (batteries, solar arrays), antennas, and 

instruments whose components are likely to take 

advantage of technological improvements. Such 

voluntary design standards would improve the 

on-orbit serviceability of new spacecraft and could 

potentially improve ground processing efficiency as a 

side benefit.

Establish Customer/Provider Working Groups

Work on designs for satellite servicing, including 

development of precursor and demonstration 

experiments, has often proceeded with relatively 

little coordination from the beginning between 

the provider of a new capability and the customer 

(e.g., the satellite owner). We suggest establishing 

regular working groups (or workshops) made up of 

decision-makers who have the authority to direct 

and provide input to develop new capabilities and 

design new generations of spacecraft. These working 

groups would provide routine venues for discussion 

of requirements and feedback to implement lessons 

learned and best practices.

Integrate the Satellite Servicing Infrastructure 

with NASA Program Architectures and 

Priorities

Until very recently, satellite servicing has proceeded 

as an activity relatively isolated from NASA’s scientific 

and human spaceflight architecture. This isolation has 

led to scientific satellites with little or no capability 

to be upgraded, thus reducing the potential scientific 

return on some very expensive missions. It would be 

advantageous for NASA to have a process for assessing 

on-orbit satellite servicing capabilities for future 

missions in order to exploit the benefits of satellite 

servicing where appropriate.

Execute the Mission Sequence

Our recommended mission sequence provides a 

balance of reaping immediate benefits from satellite 

servicing while refining the technologies required for 

more ambitious ventures. These missions are ready 

for execution now and should be incorporated into 

near-term plans for NASA. We recommend that plans 

begin immediately to develop the robotic front-end 

system to support the servicing capability needs 

identified by this study. A commitment by NASA to 

develop an operational servicer, demonstrate its capability on-orbit, and make it available for use will help 

ensure that the design recommendations mentioned 

above will be incorporated into future spacecraft 

designs and that the outputs of the customer/provider 

working groups will have a positive effect.
Chapter 5

Satellite Servicing: The Challenges

This study has summarized the case for, and charted a path towards, a future 

that provides the benefits of an advanced satellite-servicing infrastructure. 

While there are challenges to face, a key finding of this study is that very 

few of these are technical. We have the technologies in-hand to perform 

very sophisticated tasks on worthwhile satellite servicing missions. Further 

technological development is always desirable, but is not required to take the 

first steps in the plan. The challenges lie in several different realms, but with 

perhaps a common theme: insufficient credibility. Our recommended path 

attempts to further strengthen this credibility through sequential demonstrated 

steps so that the achieved benefits will become more commonly accepted 

(e.g., by satellite builders, insurance companies, fleet operators). Reducing the 

perceived and actual risk will increase demand and help to further validate the 

specific business cases.

Figure 5.1 – Earthrise from the Moon – This photograph of Earth rising above the lunar 

horizon was captured by Apollo 8 on December 24, 1968. Apollo 8 was the first human 

spaceflight mission to leave Earth orbit. It subsequently orbited the Moon and safely 

returned to Earth. Among many firsts for the Apollo program, NASA realized that setting 

and achieving an ambitious goal was key to capturing the hearts and imagination of the 

American people. It is an appropriate reminder that the challenges faced by our predecessors were successfully met with a planned sequence of missions designed to validate their 

technologies while performing meaningful work. This extraordinary image is one result of 

their labors. It has come to represent the beauty and fragility of our celestial home for 

generations past, and likely for generations yet to come. 
 Chapter 5 | Satellite Servicing: The Challenge – Technological Challenges | 79

Technological Challenges 

On-orbit servicing of satellites that are designed to be serviced, as well as those 

not designed to be serviced, requires relatively little new technology development. 

However, it does require a disciplined systems approach in order to use existing 

technologies successfully and effectively.

Helium On-Orbit Transfer (SHOOT) mission on 

STS-57 in June 1993, and this work needs to be 

extended to make such operations routine.

On-orbit assembly, Orbital Replacement Unit 

(ORU) changeout, and component changeout are 

also tasks to consider when servicing. The types of 

tasks required for these activities, such as removing 

and containing fasteners, cutting back thermal 

blankets, opening J-hooks, aligning boxes, etc., are all 

typical robotic manipulation tasks. The technology 

for teleoperating a space manipulator is known, and 

has been demonstrated through the utilization and 

test of the space shuttle Remote Manipulator System 

(RMS), the Rotex arm, and the manipulator on the 

Engineering Test Satellite Number 7 (ETS-VII). The 

key to manipulation is having an appropriate endeffector plus the right tooling to do the job. As robots 

are operated throughout the Earth-Moon system via 

teleoperation from Earth, there are system-level trades 

to be performed to determine the appropriate mix 

of autonomous systems and teleoperation using time 

delay mitigation strategies.

More ambitious programs with autonomous 

operations are a challenge, as defined by the 

technologies identified in the technology gap 

assessment. Autonomous operations would 

enable autonomous rendezvous and capture, the 

autonomous exchange of ORUs, sensors, batteries, 

and instruments. A fully autonomous servicing 

mission requires integration of the autonomy 

technologies of planning, state, and health 

information, and decision making as they are proven.

Since satellite servicing requires few new 

technologies, the key challenge lies in integrating 

The first challenge is to ensure that a servicing vehicle 

can locate and then rendezvous and dock with or 

berth to the customer spacecraft to be serviced. With 

existing technologies, this can be (and has been) 

performed through teleoperation, as long as the 

communication link time delays and latencies are 

manageable. A host of sensor systems and software 

packages presently exist (e.g., laser radar, visual-based 

natural feature recognition systems, and collision 

avoidance algorithms) that enable safe rendezvous 

and docking operations. Once outside the limits 

of teleoperation, autonomous operations must be 

considered. This is no different than how we presently 

safely operate our spacecraft around or on distant 

planets in our solar system. Autonomous docking 

was demonstrated on the Orbital Express program, 

and will be developed further very soon with the 

Orion spacecraft and its Sensor Test for Orion 

Relative-navigation Risk Mitigation (STORRM) 

demonstration. Servicing a spacecraft that was not 

designed to be berthed, captured, or docked with can 

be accomplished with some additional planning and 

specialized tool development

When refueling, the challenge is to mate the 

fluid connectors. In some missions, the fluid coupling 

will mate automatically during the docking process, 

such as with Orbital Express. Otherwise, a robotic 

manipulator can be used to mate the fluid connectors 

as in NASA’s planned Robotic Refueling Mission 

(RRM) flight demonstration on ISS. There are no 

new technological challenges to refueling propellant. 

However, there could be a challenge if cryogenic 

replenishment is desired. Deep cryogenic transfers 

have been demonstrated during the Superfluid 
80 | On-Orbit Satellite Servicing Study Project Report | October 2010

Economic Challenges 

Satellite systems may be the only complex systems without a routine maintenance, 

repair, or upgrade program. Typically, maintenance or upgrade means launching 

a new satellite to replace something that may have a fully functional set of 

subsystems. To recoup this high cost, the design lifetimes of satellites are made 

longer, which drives up their cost. 

cost of a servicer and its refueling capacity, his analysis 

showed that the servicer must refuel three to five 

customer satellites to be cost-effective.

Unfortunately, these simplified analyses do not 

tell the entire story, as they do not take into account 

the intrinsic value of servicing, such as providing 

options that allow the mission to adapt to changing 

requirements. They also overlook the effect that a 

servicing paradigm would have on driving down 

costs by encouraging satellites with shorter lifetimes 

and reduced redundancy, thus making them cheaper 

to build. Reynerson[51] considered some of this by 

looking at the additional value provided to a satellite 

operator by servicing as a function of the benefit that 

a customer satellite delivers to its operator, the risk 

associated with servicing, the operator’s perception 

of those risks, and all costs associated with operating 

and servicing the customer satellite. He realized that 

non-monetary benefits include potential military 

and scientific observations, the discovery efficiency 

provided by servicing something like HST, or the 

increased accuracy of weather prediction by installing 

new detectors or sensors on-orbit.

The real economic challenge lies in determining 

the value of servicing and then finding a business 

case that closes. For the simplest case, the economic 

aspects of on-orbit servicing include comparing the 

cost of a servicing mission to the cost of replacing 

the failed satellite as well as the potential returns 

from the serviced satellite. The returns can be 

revenue, scientific data, or continued and improved 

operations. The simplest case is for commercial 

communications satellites. For example, the 1999 

Orion 3 satellite, which cost $150 million (plus $80 

million for the launch) and was inadvertently placed 

in an incorrect orbit, resulted in a $265 million 

insurance payout. The potential operating revenue 

per year was around $43 million.[8] Because the 

design life of the satellite was 15 years, $645 million 

in potential revenue was lost. 

Hubbard[50] looked at the possibility of extending 

a satellite’s life through the use of on-orbit servicing 

and found that fuel depletion has a significant impact 

on satellite operations in geostationary orbit. By 

using a cost-per-year approach and comparing the 

replacement cost of a satellite and its design life to the 

the technologies that already exist into an end-toend mission. As each demonstration leads into full 

missions, each additional mission adds maturity 

and confidence in the component technologies. The 

recommended approach is to follow our mission 

sequence and insert autonomy technologies as they 

mature. The need for autonomy is to supplement 

the system when problems with the teleoperation 

communication system arise, or when in-space 

operations increase the distance from ground control. 

The ultimate goal is a servicing system that is robust 

and capable. The path to this goal requires a strong 

systems engineering approach to combine the 

available technologies, tools, and procedures necessary 

to successfully create such a system.
 Chapter 5 | Satellite Servicing: The Challenge – Economic Challenges | 81

Lamassoure and Hastings[52] developed a general 

way to estimate the value of servicing to space systems 

that took into account the options that servicing 

provides to the decision makers. Their results showed 

that the traditional approach of modeling servicing 

tended to underestimate the value of servicing and 

showed a cost advantage that was smaller than the 

cost uncertainty. Using Globalstar and Iridium 

as examples, their analyses showed that on-orbit 

servicing has significant value for commercial space 

missions in the flexibility it provides.

Rather than directly finding the cost of servicing 

missions, one can examine the break-even cost 

between a program with servicing as part of the 

regular program and a program without servicing.[32]

Servicing was found to act as insurance against 

uncertainty, which included technology growth 

(future instruments provide enhanced capability), 

component failure (critical components fail over time, 

which is mitigated by introducing redundancy into 

current systems), and changing mission requirements 

(more data in different wavelengths or different types 

of measurements).

As seen from these discussions, assessing the 

economic challenges of satellite servicing is a very 

active field. Nevertheless, the general conclusions are 

that there are large classes of commercial satellites 

that could be economically viable to service. Exactly 

how many—and under what conditions—can 

be debated, and depends on some non-economic 

factors, such as perceived risk and whether or not 

satellite servicing capabilities are exploited as a part 

of the total mission design.
82 | On-Orbit Satellite Servicing Study Project Report | October 2010

Getting Close Enough

The first step in any servicing activity is to get close 

enough to a spacecraft to do some work. Thus, our 

goal is to make all potential customer spacecraft 

serviceable from the perspective of Autonomous 

Rendezvous and Capture (AR&C) by ensuring that 

spacecraft are capable of being cooperative customers 

for rendezvous, proximity operations, and berthing, 

capture, or docking. 

Adding the following features and mechanisms 

to a spacecraft make it a cooperative customer for 

AR&C:

•	 Optical retro-reflectors

•	 Radio Frequency (RF) transponders for

ranging and telemetry exchange

•	 Distinct, visible, possibly reflective, surface

features

•	 Grapple fixtures

•	 Proper Attitude Control System (ACS)

modes in flight software for quiescence when 

required

Optical retro-reflectors allow laser-based relative 

navigation sensors on the servicer spacecraft to 

acquire the customer spacecraft at greater distances 

and also provide better tracking quality for bearingangle sensors. The pattern in which retro-reflectors are 

positioned on the customer can also allow optical or 

laser-based sensors on the servicer to measure relative 

attitude at closer ranges during proximity operations 

and final approach.

Radio Frequency (RF) transponders for ranging 

and telemetry exchange serve two important purposes. 

First, the exchange of a two-way ranging signal 

between the servicer and customer vehicle provides 

the servicer with a very accurate estimate of the range 

between the vehicles and aids in far-field acquisition 

of the customer. Onboard processing of these range 

measurements over time helps the servicer spacecraft’s 

onboard relative navigation filter converge more 

rapidly on an accurate solution for the relative state 

of the customer vehicle. This is crucial for onboard 

AR&C guidance calculations. Moreover, the utility of 

the range measurements is enhanced when combined 

with bearing-angle measurements. Second, the 

exchange of telemetry between the vehicles allows 

them to share state information, which can further 

improve the servicer’s relative navigation solution and 

provide important situational awareness data. For 

instance, a developing and unsafe condition onboard 

Making Future Missions More Serviceable 

When it comes to assessing the on-orbit serviceability of a spacecraft, the 

“servicing mission” can be broken down into the different operational phases of 

the mission. At the highest level, these phases can be split out into the following: 

rendezvous, capture, service, release, and on-orbit verification. A more detailed 

discussion of servicing mission elements can be found in Appendix D. There are 

design philosophies, approaches, and implementations that are critical at each 

phase of the mission in order to ensure success. Some of the implementations of 

the “serviceability features” are quite different based on the different phases being 

assessed, but many of the philosophies are similar. The post-servicing phases 

will not be discussed here, as they are not relevant to the design philosophy for 

servicing.
becoming completely quiescent, ensuring that its 

ACS algorithms and actuators will not be attempting 

to counteract the forces and torques imparted by 

the servicer during capture, berthing, or docking 

operations and subsequent mated operations.

Note that the majority of these additional 

features have relatively little impact on the customer 

spacecraft systems. The mass and volume are quite 

small for retro-reflectors, visible surface features, and 

grapple fixtures, and none of them requires power 

or any other accommodations. Some spacecraft 

systems can accommodate this additional mass with 

less of an impact than others. For communications 

spacecraft, even a few kilograms of hardware added 

to accommodate servicing is a few kilograms less of 

station-keeping propellant, which can be translated 

into a number of days lost on-station and a cash value 

of transponder-day leases not available. In these cases, 

the servicer will have to be able to rendezvous with 

a less servicing-friendly target. The RF ranging and 

telemetry system will require an RF transponder, an 

omni-directional antenna, and appropriate signalprocessing algorithms on both spacecraft. The RF 

equipment, including antennas, will have some 

mass and volume, and the equipment will require 

some power. However, the mass, volume, and power 

requirements are typically modest, particularly in 

comparison to other systems. Note also that the 

data bandwidth required for ranging and telemetry 

exchange is typically quite manageable and minimal 

compared to other RF links. Finally, the additional 

ACS modes for quiescence should be no more 

difficult to program than the other standard modes 

in the spacecraft flight software. In short, the single 

greatest challenge associated with making spacecraft 

more serviceable from an AR&C perspective is for 

spacecraft designers and program managers to make 

the choice to do so.

Mode of Servicing

Regardless of the purpose of servicing, a priori

knowledge of the mode of servicing—astronautbased and/or robot-based—is extremely helpful. 

the customer vehicle might be detected by the servicer 

through analysis of the customer vehicle’s telemetry.

Prominent surface features may help visible 

spectrum camera-based relative navigation sensors 

(e.g., a bearing sensor) acquire the customer at 

greater distances by virtue of reflecting sunlight 

more brightly, thus causing the customer vehicle 

to be more visible against the background. Even if 

not particularly reflective, surface features at known 

locations in the customer spacecraft’s body frame help 

natural feature recognition pose sensor algorithms 

measure the relative position and attitude of the 

customer spacecraft when at closer ranges (i.e., during 

proximity operations and final approach). 

Grapple fixtures offer a safe, robust means for 

the servicer vehicle to attach itself to the customer 

vehicle in a berthing or capture scenario. They are 

relatively small mechanical features with shapes and 

protrusions that are attached to the surface of the 

customer vehicle at points on the spacecraft structure 

that are capable of bearing anticipated loads during 

grapple, subsequent berthing or capture, and mated 

operations. The shape and protrusions of the grapple 

fixtures generally offer purchase to the end-effector 

of a robotic arm with grasping capability. While 

they may be specifically designed to be intrinsically 

compatible with a particular type or model of 

end-effector, they should also be designed and 

documented to be generally useful in any grapple 

scenario.

Finally, the availability of proper ACS modes 

ensures that two important conditions will be met. 

First, the customer vehicle will be in an acceptable 

attitude state throughout the AR&C sequence. This 

is especially important during the final approach 

phase, during which the servicer vehicle must engage 

in forced motion along an approach vector fixed in 

the customer vehicle’s body frame. If the customer 

vehicle has any significant attitude rates during this 

phase, the servicer vehicle will have to consume 

significant amounts of fuel to stay on the rotating 

approach axis and complete the final approach. 

Second, the customer vehicle will be capable of 

 Chapter 5 | Satellite Servicing: The Challenge – Making Future Missions More Serviceable | 83
84 | On-Orbit Satellite Servicing Study Project Report | October 2010

very difficult (because they were never intended 

to be serviced). However, due to a combination of 

technology advancements and a creative enough 

engineering team, all challenges were overcome. The 

lesson learned from those missions was to make as 

many interfaces as possible common, accessible, and 

serviceable.

The expression “design for serviceability” can be 

interpreted in a number of ways. Our interpretation 

is that all of the features most people think of when 

they think about servicing should be incorporated 

into the spacecraft design. The more “serviceability” 

features are incorporated into the design from the 

start and documented, the easier the planning will be 

for servicing and its eventual implementation. 

“Designing for serviceability” includes the 

following: common connectors throughout the 

spacecraft; standardized fasteners; workspaces with 

good access and visibility (including good preflight closeout photos); clear markings and labeling; 

alignment guides and cues; Orbital Replacement Unit 

(ORU) mounting with compliance; photographs of 

all harnessing, multi-layer insulation, lockwire and 

any other hardware that drawings cannot adequately 

represent; ORUs with good preflight metrology; good 

preflight photos of ORUs and interfaces; connectors 

that can be remotely driven and blind-mated; 

standardized module mounting; and motions that are 

all simple, and ideally, linear.

From an overall systems perspective, “design for 

serviceability” means modular design, ideally with 

critical functions split among different connectors and 

potentially among different modules. In such a design, 

single connector anomalies do not affect critical 

functions, but only impact redundant functions. 

The redundancy among modules can accommodate 

module replacement so that no critical functions of 

the spacecraft are lost while replacement is occurring. 

A good example of this is replacement of solar arrays, 

batteries, or spacecraft computers. In many current 

spacecraft designs, replacement of any of these would 

cause significant impact to the vehicle. In addition to 

designing-in modularity and redundancy for critical 

functions, there should be hardline input of external 

If a spacecraft can be designed for a specific type 

of servicing, it can greatly enhance the servicing 

efficiency.

There is overhead involved with each mode of 

servicing: humans require handholds, tether points, 

grasp points, visual markings, and specific tooling to 

interface to the worksite. Robots require their own 

form of these items: grasp points, stabilization aids, 

visual aids, targets, and specific tooling.

This is not to say that a spacecraft that is not 

designed for a specific servicing mode cannot be 

serviced. History has shown that it most certainly 

can. However, it must be understood that there are 

additional inefficiencies involved in such a servicing 

mission. Additional tooling and time may be required, 

and unique, innovative approaches for each task may 

be necessary. There are numerous examples where 

on-orbit repairs to hardware that was not designed 

for servicing have been made: all five HST Servicing 

Missions are excellent examples. On each mission, 

repairs were made to HST hardware that was never 

designed or intended to be serviced.

As already noted, there are unique differences 

between the needs of humans and robots in their 

interfaces on the hardware for on-orbit servicing. The 

NASA-funded Space Applications of Automation, 

Robotics and Machine Intelligence Systems 

(ARAMIS) study [53] in the 1980s found that one way 

to deal with this difference is to design the robot endeffectors and tools to interface with EVA interfaces. 

This is not to say that all robot end-effectors should 

mimic the human hand. As the team discovered in 

the second IDL design run, the robot system should 

be designed to take advantage of the “super human” 

capabilities provided by a robot; not the limitations of 

a human hand in a spacesuit.

Serviceability

One of the clear lessons learned from the multiple 

HST servicing missions is the old expression: “Never 

say never.” The HST was designed with different 

modules having different levels of serviceability, 

some being very straightforward and others being 
 Chapter 5 | Satellite Servicing: The Challenge – Making Future Missions More Serviceable | 85

From this an assessment could be made as to the 

ability to service spacecraft using common servicing 

tools (operational assessment tools, robots, endeffectors, robot tools, EVA tools, etc.). By providing 

common interfaces—not just within the spacecraft, 

but also across families of spacecraft, and then across 

agencies (NASA, NOAA, DoD, etc.), and ultimately 

across the aerospace industry with the goal of 

supporting on-orbit servicing—the serviceability of 

spacecraft would be greatly enhanced, even if some of 

those vehicles are never serviced.

An attempt was made to do something similar 

by the American Institute of Aeronautics and 

Astronautics in the early 1990s. Their Guide for 

On-Orbit Spacecraft Servicing[54] was a starting point 

for designers to use when developing serviceable 

spacecraft. To our knowledge, these guidelines were 

never widely applied.

Consequently, one encounters the issues that 

exist today. With regard to certain interfaces, there are 

limited vendors or design options, but in other areas 

of spacecraft design, there are numerous options that 

make design commonality uncertain and unlikely 

(e.g., the proliferation of connector types and sizes, 

and the options for mechanical layout and assembly).

Understanding that there is resistance in the 

spacecraft manufacturing community to adopt such 

guidelines, as a first step designers can simply select 

spacecraft hardware and use them in such a way 

that makes them more accessible. This should not 

make the spacecraft any heavier or more expensive 

to integrate, but it does increase the likelihood that 

it can be serviced, and makes any potential servicing 

task easier. 

power, data, and commands, so that command and 

telemetry between the two vehicles is not dependent 

upon antenna positioning. This would also provide 

the ability to power the serviced vehicle from the 

servicer in the event that solar arrays were shadowed 

or taken off-line for servicing.

It is important to note that servicing has advanced 

well beyond the simple replacement of intended 

ORUs, and a complete replacement of an ORU is 

not always the best approach. The important criterion 

is having an available, well documented, and well 

understood interface. Examples include fuel fittings, 

cryogenic fittings, power bus connections, and 

computer interfaces/ground test ports. Once these 

existing interfaces are identified, appropriate planning 

and tools can usually enable a successful servicing 

approach. For example, on the first HST servicing 

mission, a 386 coprocessor was installed on the DF224 flight computer to provide greater computing 

capability as well as memory redundancy. An existing 

test connector provided access to the internal data 

bus, which served as the communication path for the 

new hardware.

Design Commonality

To elevate the idea of design commonality, there 

would ideally be a set of standards against which 

spacecraft would be designed and evaluated. This may 

start small, perhaps at the government level, then 

expand to include commercial entities, then continue 

to expand from there (see Table 4.3).

Such a rating would determine a spacecraft’s 

commonality against some ideal standard for 

serviceability, as defined in the established standards. 
Chapter 6

Conclusion

This study has surveyed the international community, studied the literature, 

and examined the historical precedent on the vision, benefits, and challenges 

of on-orbit satellite servicing. During the months in which this work was 

carried out, the most common question—and one repeatedly echoed by the 

Satellite Servicing Workshop participants—has been, “Why are we not already 

doing this?” 

Figure 6.1 – Returning from Mars – This conceptual rendering shows 

an astronaut with a robotic assistant preparing a spacecraft at Mars for 

return to Earth. It represents one of the more important future goals of 

in-space servicing that is beyond the scope of this study.
robust servicing architectures. While all the 

technologies and techniques are available, 

their application in a mission requires 

maturation. For this, we recommend a robust 

on-orbit verification program using accessible 

platforms such as the International Space 

Station in combination with vetted ground 

simulators and test beds.

2. Legacy satellites can be successfully serviced. 

In fact, much of the servicing performed 

to date has been on legacy hardware never 

intended for on-orbit servicing. The range 

of applicable servicing activities includes 

repair, refurbishment, refueling, and orbit 

modification. Successful implementation 

requires identifying the correct interfaces, 

developing the appropriate tools and 

procedures, and training for and executing 

a well-planned mission, all of which have 

been demonstrated. Servicing these legacy 

satellites provides an immediate customer 

base on which to build a future satelliteservicing infrastructure. The business case 

for commercial satellites is favorable if the 

capability is available and well understood. 

The first step of the proposed mission 

sequence is to realize this capability for 

satellites in GEO.

3. Modular, reconfigurable robotic architectures 

that are mobile around large structures are 

important to provide a cost-effective and 

upgradeable servicing infrastructure. A part of 

the initial technology assessment would be to 

further develop these systems and demonstrate 

their adaptability. 

4. Launch mass and orbit modification capacity 

drive servicing mission design. Here, the 

available launch vehicles could impact the 

architecture and even the feasibility and costeffectiveness of satellite servicing. For example, 

for reaching distant destinations, there is a 

trade between heavy-lift rockets with refueling 

depots and multiple small launches with onorbit assembly of small modules. These trades 

could also be affected by advanced propulsion 

As we have emphasized in the body of this report, 

the reasons that a highly capable in-space servicing 

system does not now exist are numerous and extend 

over many years; but none are related to technological 

readiness, or available customers, or a viable business 

case. This is evident from the extraordinary successes 

of the few cases where satellite servicing has been used 

to rescue a high-visibility mission. This On-Orbit 

Satellite Servicing Study was undertaken at the urging 

of the NASA Advisory Committee, the National 

Academy of Sciences, the House Authorization 

Committee, and the FY 2009 and FY 2010 NASA 

Appropriations Bills, and has resulted in an in-depth 

system-level assessment of space servicing.

What is needed now to change the paradigm 

of space operations is to expand the deployment of 

enabling capabilities. We have produced recommended actions and missions as one implementation to 

achieve this goal. They will enable us to more fully use 

the assets we already have in space through refueling, 

repair, and refurbishment to derive more economic 

value through extended use. We would also be able 

to manage our spent assets in space so that they do 

not impinge on the valuable orbital locations that 

are essential to everyday life. In the end, our recommendations would create the systems and new space 

architectures necessary to unlock the greatest secrets 

of the Universe and enable human exploration of new 

and distant frontiers.

During this study, several high-level recurring 

themes emerged.

1. In examining the range of tasks required 

for servicing, the tasks themselves (and the 

hardware to support them) do not appear to 

be the limiting factors. Extremely complex 

servicing tasks have already been successfully 

performed in orbit, including operations on 

legacy satellite customers as well as repairs 

on hardware not originally intended for onorbit servicing. Advanced robotic analogues 

of these tasks are routinely demonstrated on 

the ground. The advancements needed are 

mostly in the areas of increased autonomy to 

support such tasks farther from Earth, and 

the systems engineering to create sufficiently 

 Chapter 6 | Conclusion | 87
these next steps. Some of these technologies are being 

demonstrated in near-term ISS activities. Finally, 

we constructed a mission sequence that advances 

satellite servicing as an integral part of a robust and 

meaningful spaceflight architecture. 

As this study drew to a conclusion, the future 

plans for NASA were becoming better defined, as 

expressed in the 2010 NASA Authorization Bill. 

The NASA-wide Human Exploration Framework 

Team (HEFT) is charged with developing the new 

space exploration plans based on this Congressional 

direction. The comprehensive HEFT study will 

include studying the development of an in-space 

servicing capability and identifying those areas where 

human participation in servicing is required or 

beneficial. We anticipate that the results of this study 

will inform the HEFT deliberations and provide 

the basis for developing a strong in-space servicing 

infrastructure to support these new plans.

Of even greater significance is the larger question 

of whether or not we as a nation are going to play a 

leadership role in satellite servicing. If, as announced, 

other countries develop this capability and we do 

not, the strategic and defense implications would be 

extremely dire.

systems. Our technology gap assessment 

identifies other investment goals.

5. Astrodynamics is a major factor in mission 

design, especially when there is human presence. 

We paid close attention to this aspect for the 

satellite servicing locations that we considered. 

Interesting results include useful orbits that 

support satellite servicing.

6. Satellite servicing is critical to our national 

interests. As a nation, we need to develop this 

capability in order to maintain our leadership 

in space for scientific, commercial, and 

strategic reasons.

We return to the question, “What will this study 

contribute?” We investigated a carefully derived 

set of notional missions that provide a data-driven 

basis for assessing the feasibility and practicality 

of satellite servicing. In so doing, we examined 

key aspects of how common design choices and 

interfaces make a satellite more serviceable and the 

challenges in implementing this commonality. We 

also reviewed the technologies needed to implement 

satellite servicing at greater distances from Earth with 

increasing autonomy, and assessed their readiness for 

We are at a turning point in America’s space program. Our nation can 

continue to claim remarkable achievements in science, engineering, technology, and robotic and human exploration in space. As we deliberate the 

sometimes-conflicting goals to form the vision for the next decades, some 

things are very clear. For any meaningful future endeavor in space, success 

is more assured with architectures that include satellite servicing. For our 

national security, a domestic satellite servicing capability is paramount.

88 | On-Orbit Satellite Servicing Study Project Report | October 2010
 References | 89

References

1 [p. 2] Oegerle, W. R., Purves, L. R., Budinoff, J. G., Moe, R. V., Carnahan, T. M., Evans, D. C., and 

Kim, C. K., “Concept for a large scalable space telescope: in-space assembly,” Society of Photo-Optical 

Instrumentation Engineers (SPIE) Conference Series, Vol. 6265 of Society of Photo-Optical Instrumentation 

Engineers (SPIE) Conference Series, July 2006, DOI:10.1117/12.672244.

2 [p. 6] “Public Law 110-422 NASA Authorization Act of 2008,” October 15th, 2008, 122 STAT. 4779. 

3 [p. 6] “Omnibus Appropriations Act, 2009,” 111th Congress, 2009 - 2010.

4 [p. 10] Human Spaceflight Plans Committee, “Seeking a Human Spaceflight Program Worthy of a Great 

Nation,” October 2009. 

5 [p. 11] Iannotta, B. and Malik, T., “U.S. Satellite Destroyed in Space Collision,” SPACE.com, www.space.

com/news/090211-satellite-collision.html, February 2009, Accessed on September 30th, 2010. 

6 [pp. 11, 38] Kessler, D. J. and Cour-Palais, B. G., “Collision Frequency of Artificial Satellites: The Creation 

of a Debris Belt,”Journal of Geophysical Research, Vol. 83, No. A6, 1978, pp. 2637–2646, DOI:10.1029/

JA083iA06p02637. 

7 [p. 11] Henshaw, G., “Orbital Robotic Servicing,” The International Workshop on On-Orbit Satellite 

Servicing, http://servicingstudy.gsfc.nasa.gov/workshop_1_presentations.htm, March 2010, Accessed on 

September 30th, 2010. 

8 [pp. 14, 28, 66, 80] Sullivan, B., Technical and Economic Feasibility of Telerobotic On-Orbit Satellite Servicing, 

Ph.D. thesis, University of Maryland, 2005. 

9 [p. 14] Tatsch, A., Fitz-Coy, N., and Gladun, S., “On-orbit Servicing: A Brief Survey,” Performance Metrics 

for Intelligent Systems Conference, August 2006, Gaithersburg, MD. 

10 [p. 14] “DOCTOR: Developing On-orbit Servicing Concepts, Technology Options, and Roadmap,” Final 

Report of the International Space University, 2007, Summer Session Program. 

11 [p. 15] Schneider, W. C. and Green, Jr., W. D., “Saving Skylab,” Technology Review, Vol. 76, January 1974, 

pp. 42–53. 

12 [p. 15] Compton, W. D. and Benson, C. D., “Living and working in space: a history of Skylab,” NASA 

Special Publication, Vol. 4208, 1983. 

13 [p. 16] Joyce, C., “Next, a mission to search and recover,” New Scientist, Vol. 1418, August 23rd, 1984, p. 4. 

14 [p. 16] UPI, “Insuror Delighted by Space Rescue and Implications,” New York Times, November 13th, 1984. 

15 [p. 16] Wilford, J. N., “Space Salvage: Lost Satellites are the Prize,” New York Times, November 6th, 1984. 

16 [p. 16] Evans, B., Space Shuttle Challenger: Ten Journeys Into The Unknown, Springer, 2007, pp. 104–110, 

Library of Congress Control Number: 2006935328. 

17 [pp. 16, 23, 28] de Selding, P. B., “MDA Designing In-orbit Servicing Spacecraft,” Space News, http://

www.spacenews.com/satellite_telecom/100303-mda-planning-inorbit-servicing-demo.html, March 2010, 

Accessed on September 30th, 2010. 

18 [p. 18] Weiler, E. J., Hubble: A Journey Through Space And Time, Abrams, NY, 2010. 

19 [p. 18] Zimmerman, R., The Universe in a Mirror: The Saga of the Hubble Space Telescope and the Visionaries 

Who Built It, Princeton University Press, 2008.

20 [p. 22] Yoshida, K., “ETS-VII Flight Experiments For Space Robot Dynamics and Control,” The 

International Journal of Robotics Research, Vol. 22, No. 5, 2003, pp. 321–335. 

21 [p. 23] Anon, “Overview of the DART Mishap Investigation Results (For Public Release),” http://www.nasa.

gov/pdf/148072main_DART_mishap_overview.pdf, Accessed on September 30th, 2010.
90 | On-Orbit Satellite Servicing Study Project Report | October 2010

22 [p. 23] de Selding, P. B., “DLR Takes Step Toward In-orbit Servicing Demonstration,” Space News, http://

www.spacenews.com/civil/022410-dlr-takes-step-toward-in-orbit-servicing-demo.html, February 2010, 

Accessed on September 30th, 2010. 

23 [p. 24] de Selding, P. B., “Canadas MDA Sees Business Case for In-orbit Satellite Servicing,” Space News, 

http://www.spacenews.com/satellite_telecom/100506-mda-in-orbit-servicing.html, May 2010, Accessed on 

September 30th, 2010. 

24 [pp. 24, 30] de Selding, P. B., “MDA May Scrap In-orbit Satellite Servicing Plan,” Space News, http://www.

spacenews. com/satellite_telecom/mda-struggling-find-customer-for-satellite-servicing-business.html, July 

2010, Accessed on September 30th, 2010. 

25 [p. 26] Harwood, W., “Intricate space surgery revives Hubble camera,” CNET News, http://news.cnet.com/

intricate-space-surgery-revives-hubble-camera/, May 2009, Accessed on September 30th, 2010. 

26 [p. 28] Weeden, B., “The Ongoing Saga of DSP Flight 23,” The Space Review, http://www.thespacereview.

com/article/1290/1, January 2009, Accessed on September 30th, 2010. 

27 [p. 28] Kaiser, C., Sjöberg, F., Delcura, J. M., and Eilertsen, B., “SMART-OLEV–An orbital life extension 

vehicle for servicing commercial spacecrafts in GEO,” Acta Astronautica, Vol. 63, No. 1-4, 2008, pp. 

400–410, Touching Humanity - Space for Improving Quality of Life. Selected Proceedings of the 58th

International Astronautical Federation Congress, Hyderabad, India, 24-28 September 2007”, DOI: 

10.1016/j.actaastro.2007.12.053.

28 [p. 29] Madrid, J., Macchetto, F., Leitherer, C., and Meylan, G., “The Development of HST Science 

Metrics,” Organizations and Strategies in Astronomy Volume 6, edited by A. Heck, Vol. 335 of Astrophysics and 

Space Science Library, Springer Netherlands, 2006, pp. 133–143, http://dx.doi.org/10.1007/1-4020-4056-

3_10.

29 [p. 29] Postman, M., “The Science Rationale for Servicing and Considerations for Existing and Future 

Space-based Astronomical Observatories,” The International Workshop on On-Orbit Satellite Servicing, 

http://servicingstudy.gsfc.nasa.gov/ workshop_1_presentations.htm, March 2010, Accessed on September 

30th, 2010.

30 [p. 29] Bailey, Z., “Determining the Value of On-Orbit Telescope Servicing,” The International Workshop 

on On-Orbit Satellite Servicing, http://servicingstudy.gsfc.nasa.gov/workshop_1_presentations.htm, March 

2010, Accessed on September 30th, 2010.

31 [pp. 30, 42] Long, A., Richards, M., and Hastings, D., “On-Orbit Servicing: A New Value Proposition for 

Satellite Design and Operation,” AIAA Journal of Spacecraft and Rockets, Vol. 44, No. 4, 2007, pp. 964–975.

32 [p. 81] Bailey, Z. and Baldesarra, M., “The Economic Value of Space Telescope Servicing,” NRC Position 

Paper, http://www8.nationalacademies.org/astro2010/DetailFileDisplay.aspx?id=429, March 2009, Accessed 

on September 30th, 2010.

33 [p. 29] Erdner, M., Smaller Satellite Operations Near Geostationary Orbit, Master’s thesis, Naval Postgraduate 

School, September 2007, http://edocs.nps.edu/npspubs/scholarly/theses/2007/Sep/07Sep_Erdner.pdf.

34 [pp. 32, 57] Lennon, J. A., Henshaw, C. G., and Purdy, W., “An Architecture for Autonomous Control of 

a Satellite Grappling Mission,” AIAA Guidance, Navigation, and Control Conference and Exhibit, August 

2008, Honolulu, Hawaii.

35 [p. 33] Akin, D. L., “Experimental Investigation of Cooperative Human/Robotic Roles In Extravehicular 

Operations,” 28th International Conference on Environmental Systems, July 1998, SAE 981699, Danvers, 

MA.

36 [p. 34] Moore, G. E., “Cramming More Components onto Integrated Circuits,” Electronics, Vol. 38, No. 8, 

April 1965, pp. 114–117.
 References | 91

37 [p. 34] Bernard, D., Doyle, R., Riedel, E., Rouquette, N., Wyatt, J., Lowry, M., and Nayak, P., “Autonomy 

and software technology on NASA’s Deep Space One,” Intelligent Systems and their Applications, IEEE, Vol. 

14, No. 3, May/June 1999, pp. 10–15.

38 [p. 34] Lanius, R. and McCurdy, H., Robots in Space, The Johns Hopkins University Press, 2008.

39 [p. 37] H. A. Thronson, D. F. L., Moe, R., and Sullivan, G., “Review of US Concepts for Post-ISS Space 

Habitation Facilities and Future Opportunities,” AIAA Space 2010, August 2010, paper 818583, Anaheim, 

CA.

40 [p. 38] “LEGEND - NASA’s Three-Dimensional Orbital Debris Evolutionary Model,” NASA Orbital Debris 

Program Office: Orbital Debris Evolutionary Models, http://orbitaldebris.jsc.nasa.gov/model/evolmodel.

html, Accessed on September 30th, 2010.

41 [p. 38] Taylor, M., Orbital Debris: Technical and Legal Issues and Solutions, Master’s thesis, Institute of Air 

and Space Law, Faculty of Law, McGill University, Montreal, August 2006.

42 [p. 42] Galabova, K. and de Weck, O., “Economic case for the retirement of geosynchronous 

communication satellites via space tugs,” Acta Astronautica, Vol. 58, 2006, pp. 485–498.

43 [p. 42] de Selding, P. B., “NASA May Move Orbital Debris Mitigation Off Back Burner,” Space News, 

http://www.spacenews.com/civil/100723-nasa-orbital-debris-mitigation.html, July 2010, Accessed on 

September 30th, 2010.

44 [p. 42] Weeden, B., “Dealing with Galaxy 15: Zombiesats and on-orbit servicing,” The Space Review, http://

www. thespacereview.com/article/1634/1, May 2010, Accessed on September 30th, 2010.

45 [p. 45] Anon, “KH-11 KENNAN,” Wikipedia, http://en.wikipedia.org/wiki/KH-11_KENNAN, Accessed 

on September 30th, 2010.

46 [p. 47] O’Brien, M., “The Hubble Constant: High Interest,” True/Slant, http://trueslant.com/

milesobrien/2009/05/25/567/, May 2009, Accessed on September 30th, 2010.

47 [p. 58] Akin, D. L., Roberts, B., Roderick, S., Smith, W., and Henriette, J.-M., “MORPHbots: Lightweight 

Modular Self- Reconfigurable Robotics for Space Assembly, Inspection, and Servicing,” AIAA Space 2006, 

September 2006, AIAA-2006-7408, San Jose, CA.

48 [p. 58] Yim, M., Rohfas, K., Duff, D., Zhang, Y., Eldershaw, C., and Homans, S., “Modular Reconfigurable 

Robots in Space Applications,” Autonomous Robots, Vol. 14, No. 2-3, March 2003, pp. 225–237, 

DOI:10.1023/A:1022287820808.

49 [p. 65] Klinkrad, H. and Johnson, N. L., “Sustainable Use of Space Through Orbital Debris Control,” 

Advances in the Astronautical Sciences, Vol. 137, Univelt, Inc., San Diego, CA, 2010, also AAS/AIAA Paper 

AAS 10-017, 33rd Annual AAS Guidance and Control Conference, Breckenridge, CO, Feb 6-10, 2010.

50 [p. 80] Hubbard, R., Satellite On-Orbit Refueling: A Cost Effectiveness Analysis, Master’s thesis, Naval 

Postgraduate School, Monterey, CA, September 1996.

51 [p. 80] Reynerson, C. M., “Spacecraft Modular Architecture Design for On-Orbit Servicing,” AIAA Space 

Technology Conference & Exposition, September 1999, AIAA-99-4473, Albuquerque, NM.

52 [p. 81] Lamassoure, E. and Hastings, D. E., A Framework to Account for Flexibility in Modeling the Value of 

On-Orbit Servicing for Space Systems, Master’s thesis, Massachusetts Institute of Technology, June 2001.

53 [p. 84] Akin, D. L., Minksy, M. L., and Thiel, E. D., “Space Applications of Automation, Robotics and 

Machine Intelligence Systems (ARAMIS) - Phase II,” Vol. 3, NASA Contractor Report 3736, NASA, 

October 1983, For Contract NAS8-34381, p. 3.2.7.

54 [p. 85] Moore, J. S. et al., “Guide to Design for On-Orbit Spacecraft Servicing,” Tech. Rep. AIAA G-042-

1991, American Institute of Aeronautics and Astronautics, 1991.
92 | On-Orbit Satellite Servicing Study Project Report | October 2010

These historical materials are provided for general information. They are placed on the study website 

(http://servicingstudy.gsfc.nasa.gov) for reference, since they can be difficult to locate.

i Satellite Services Workshop, Volumes 1 and 2 Final Report, NASA Lyndon B. Johnson Space Center, 

Houston, Texas, U.S. Department of Commerce National Technical Information Service, June 1982.

ii Satellite Services Workshop II, Volumes 1 and 2, NASA Lyndon B. Johnson Space Center, Houston, Texas, 

U.S. Department of Commerce National Technical Information Service, November 1985.

iii EVA Tools and Equipment Reference Book, NASA Lyndon B. Johnson Space Center, Houston, Texas, U.S. 

Department of Commerce National Technical Information Service, November 1983.

iv Guide to Design for On-Orbit Spacecraft Servicing, American Institute of Aeronautics and Astronautics, 

1991.

v Space Insurance: Experience and Outlook, United States Aviation Underwriters, Inc., March 2002.

vi On-Orbit Servicing Experience – A Compilation of Lessons Learned, NASA On-Orbit Servicing Steering 

Committee, Advanced Program Development Division, June 1990.

vii Examination of Prospects for Satellite Servicing – A Common Government/Industry Strategy for the 

Development of Space, Gary Horhsam, NASA Office of Space Flight Advanced Systems, 2002.

viii Space Station Program Robotic Systems Integration Standards, Volume 1: Robotic Accommodation 

Requirements, International Space Station Program, September 1998.

ix SSSWG Meeting #22, Presentation Materials, Satellite Services System, NASA DOD Industry. 

November 1989.

Related Historical Materials
 Acronyms | 93

Acronyms 

ACS Advanced Camera for Surveys (HST)

 Attitude Control System

AERCam Autonomous Extravehicular Activity Robotic Camera

AIM Aeronomy of Ice in the Mesosphere

AR&B Autonomous Rendezvous and Berthing

AR&C Autonomous Rendezvous and Capture (including Grapple, Berthing, and Docking)

ASTRO Autonomous Space Transport Robotic Operations

ATP Authority To Proceed

ATV Automated Transfer Vehicle

C&DH Command and Data Handling

COSTAR Corrective Optics Space Telescope Axial Replacement (HST)

COTS Commercial Orbital Transportation Services

CRTBP Circular Restricted Three-Body Problem

CW Clohessy-Wiltshire 

DARPA Defense Advanced Research Projects Agency

DART Demonstration of Autonomous Rendezvous Technology

DIU Data Interface Unit (HST)

DLR Deutsches Zentrum für Luft- und Raumfahrt e.V. (German Space Agency)

DoD Department of Defense

DPP Dextre Pointing Package (GSFC)

DS1 Deep Space One 

ELC ExPRESS Logistics Carrier (ISS)

DTO Detailed Test Objective

EML1 Earth-Moon Lagrange point 1 (between the Earth and the Moon)

ESA European Space Agency

ETS-VII Engineering Test Satellite Number 7

EVA Extravehicular Activity (“spacewalk”)

FARE Fluid Acquisition and Resupply Experiment

FGS Fine Guidance Sensor (HST)

FREND Front-end Robotics Enabling Near-term Demonstration (Naval Research 

Laboratory, DARPA)

FSM First Servicing Mission (HST)

FT Functional Test 

FY Fiscal Year

GEMS Gravity and Extreme Magnetism Small Explorer Mission

GEO Geostationary Earth Orbit

GN&C Guidance, Navigation and Control

GPS Global Positioning System

GSE Ground Support Equipment
GSFC NASA’s Goddard Space Flight Center (in Greenbelt, MD)

HEFT Human Exploration Framework Team (NASA) 

HEO Highly Elliptical Orbit

HGA High-Gain Antenna

HRSDM Hubble Robotic Servicing and Deorbit Mission

HST Hubble Space Telescope

I&T Integration and Test 

IDC Integrated Design Center (GSFC)

IDL Instrument Design Laboratory (GSFC)

IMU Inertial Measurement Unit

ISS International Space Station

JAXA Japan Aerospace Exploration Agency

JEM Japanese Experoment Module (ISS)

JWST James Webb Space Telescope

LEO Low Earth Orbit

LIDAR LIght Detection And Ranging

LOTUS L1 Orbit Trajectory Used for Servicing

MAVEN Mars Atmosphere and Volatile EvolutioN

MBS Mobile Base System (on ISS)

MDA MacDonald, Dettwiler and Associates Ltd. (Canada)

MDL Mission Design Laboratory (GSFC)

MMS Multimission Modular Spacecraft

MMU Manned Maneuvering Unit

MSS Mobile Servicing Systems (on ISS)

MUBLCOM MUltiple paths, Beyond-Line-of-sight Communications (satellite)

NAC NASA Advisory Council

NASDA National Space Development Agency of Japan

NCS NICMOS Cooling System (HST)

NEXTSat NEXT-generation serviceable Satellite

NICMOS Near-Infrared Camera and Multi-Object Spectrometer (HST)

NOBL New Outer Blanket Layer (HST)

NPR NASA Procedural Requirement

NSSK North South Station Keeping 

OD Orbit Determination

OMV Orbital Maneuvering Vehicle

ORI Orbital Replacement Instrument

ORS Orbital Refueling System

ORU Orbital Replacement Unit

94 | On-Orbit Satellite Servicing Study Project Report | October 2010
OSS Orbital Satellite Services

PCU Power Control Unit (HST)

PMD Propellant Management Device

PRICE-H Parametric Review of Information for Costing and Evaluation – Hardware

R2 Robonaut 2

RF Radio Frequency

RFI Request For Information

RRM Robotic Refueling Mission 

RMS Remote Manipulator System (on the space shuttle)

ROTEX RObot Technology EXperiment

RSO Resident Space Object

RTBP Restricted Three-Body Problem

RWS Robotic Workstation Software

SA Solar Array

SADE Solar Array Drive Electronics (HST)

SEL1 Sun-Earth Lagrange point 1 (between the Sun and the Earth)

SEL2 Sun-Earth Lagrange point 2 (on Sun-Earth line beyond the Earth)

SHOOT Superfluid Helium On-Orbit Transfer (space shuttle mission)

SM3 Servicing Mission 3 (HST)

SM3A Servicing Mission 3A (HST) 

SM3B Servicing Mission 3B (HST)

SM4 Servicing Mission 4 (HST)

SMEX Small Mission EXplorer

SMM Solar Maximum Mission

SPDM Special Purpose Dexterous Manipulator (on ISS, aka Dextre)

SPHERES Synchronized Position Hold Engage Reorient Experimental Satellites

SSCP Space Servicing Capabilities Project (GSFC)

SSRMS Space Station Remote Manipulator System (on ISS)

STEM Science, Technology, Engineering and Mathematics

STIS Space Telescope Imaging Spectrograph (HST)

STORMM Sensor Test for Orion Relative-navigation Risk Mitigation

STS Space Transportation System (space shuttle)

TDRS Tracking and Data Relay Satellite

THEMIS Time History of Events and Macroscale Interactions during Substorms

TPAD Trunnion Pin Acquisition Device

WFPC2 Wide Field and Planetary Camera 2 (HST)

WVU West Virginia University 

XSS-10/11 Experimental Spacecraft System Numbers 10 and 11

 Acronyms | 95
96 | On-Orbit Satellite Servicing Study Project Report | October 2010

Appendixes

These appendixes provide backup information that supports the 

conclusions in this report. There are descriptions of the Congressional 

language that this report responds to, summaries of the RFI 

responses and the Workshop, a description of the systems 

engineering decomposition of what it means to conduct a servicing 

mission, technical summaries of the supporting technologies from the 

Integrated Design Laboratory exercises, and the notional mission 

summaries. Many of these working documents are sufficiently general 

that we hope they will help guide future ventures in satellite servicing.

Figure A.1 – The Hubble Space Telescope after Servicing Mission 4 – 

This photograph captures the Hubble Space Telescope redeployment 

after all the Servicing Mission 4 activities were completed in May 2009. 

This event marked the completion of an extraordinarily successful series 

of servicing missions to this international icon and is a tribute to the 

dedication and effort of the Hubble Space Telescope Team over the past 

two decades. This project report captures some of the rationale for and 

lessons learned from the satellite servicing aspects of these efforts.
 Appendix A – Congressional Language Providing Mandate | 97

Appendix A – Congressional Legislation and Reports Bearing on 

Science with the New Space Transportation Architecture 

(as of 1/15/10)

Public Law 110–422 October 15, 2008

‘‘National Aeronautics and Space Administration Authorization Act of 2008’’

TITLE IV—EXPLORATION INITIATIVE

SEC. 409. SCIENCE AND EXPLORATION.

It is the sense of Congress that NASA’s scientific and human exploration activities are synergistic; science 

enables exploration and human exploration enables science. The Congress encourages the Administrator 

to coordinate, where practical, NASA’s science and exploration activities with the goal of maximizing the 

success of human exploration initiatives and furthering our understanding of the Universe that we explore.

TITLE V—SPACE SCIENCE

SEC. 502. PROVISION FOR FUTURE SERVICING OF OBSERVATORY CLASS SCIENTIFIC 

SPACECRAFT.

The Administrator shall take all necessary steps to ensure that provision is made in the design and 

construction of all future observatory-class scientific spacecraft intended to be deployed in Earth orbit 

or at a Lagrangian point in space for robotic or human servicing and repair to the extent practicable and 

appropriate.

Public Law 111–8 March 11, 2009

“Omnibus Appropriations Act, 2009” (H.R. 1105)

DIVISION B—COMMERCE, JUSTICE, SCIENCE, AND RELATED AGENCIES 

Conference Report

TITLE III – Science

NASA Science

Servicing Opportunities for Science Missions.—Recognizing the historic successes NASA has achieved 

through the servicing of the Hubble Space Telescope, the National Research Council’s recent report 

Launching Science: Science Opportunities Provided by NASA’s Constellation System recommends 

that ‘‘NASA should study the benefits of designing spacecraft intended to operate around Earth or 

the Moon, or at the libration points for human and robotic servicing.’’ This recommendation parallels 

the guidance provided by section 502 of the NASA Authorization Act of 2008 (P.L. 110–422), which 

recommends that provision be made for servicing of future scientific spacecraft to the extent practicable. 

Therefore, it will be critical that the Constellation program demonstrate unique capabilities to maintain 

synergies between free-flying scientific spacecraft and human spaceflight endeavors. Accordingly, the bill 

provides $20,000,000 for NASA to undertake an assessment of the feasibility of using the Constellation 

architecture to service existing and future observatory-class scientific spacecraft, fully utilizing the unique, 

core expertise and competencies for in-space servicing developed by the Goddard Space Flight Center 

and its private sector partners for the Hubble Space Telescope. NASA shall provide to the House and 

Senate Committees on Appropriations a plan for expenditure of this funding no later than 30 days after 

enactment of this Act.
98 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

House Report 111-149 June 12, 2009

COMMERCE, JUSTICE, SCIENCE, AND RELATED AGENCIES APPROPRIATIONS BILL, 2010

TITLE III—SCIENCE

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

Astrophysics other missions and data analysis - Within the amounts provided, not less than 

$50,000,000 is available to continue efforts in the use of the next generation of human space flight 

architecture to service existing and future observatory-class scientific spacecraft as identified in the 

conference report accompanying division B of Public Law 111-8.

Senate Report 111-34 June 25, 2009

COMMERCE, JUSTICE, SCIENCE, AND RELATED AGENCIES APPROPRIATIONS BILL, 2010

TITLE III—SCIENCE

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

Servicing Opportunities for Science Missions.—The Committee provides $50,000,000 to continue efforts 

to use the next generation of human space flight architecture to service existing and future on-orbit 

observatory-class scientific spacecraft as provided for in the statement of managers accompanying 

division B of Public Law 111–8. The Committee directs that this shall be a joint project of the science and 

exploration mission directorates, with supervision provided by the Associate Administrator and the Chief 

Engineer, and shall include technology demonstrations for both robotic and human servicing capabilities.

Ares V.—The Committee believes that the Ares V cargo launch vehicle will be a critical national asset for 

carrying exploration and scientific payloads beyond low Earth orbit to the Moon and beyond. To facilitate 

the earliest possible start of the development of the Ares V, the Committee recommends a funding level of 

$100,000,000.

December 13, 2009

Conference Report to Accompany H.R. 3288 - Consolidated Appropriations Act, 2010

DIVISION B - COMMERCE, JUSTICE, SCIENCE AND RELATED AGENCIES

Astrophysics, servicing opportunities for science missions.- Funding for this activity has been provided 

within funds appropriated under the heading “Space Operations.”

International Space Station (ISS) operations.- Within the amounts provided for ISS operations, 

$50,000,000 is provided to continue efforts in the use of next generation of human space flight 

architecture to service existing and future observatory-class scientific spacecraft as identified in the 

conference report accompanying division B of Public Law 111-8. The activities to be undertaken shall be 

a joint project of the space operations, science and exploration mission directorates, and shall include 

technology demonstrations for both robotic and human servicing capabilities.
 Appendix B – RFI Responses Summary | 99

Appendix B – RFI Responses Summary 

At the start of this study, NASA issued a Request 

For Information (RFI) to provide the satellite servicing 

community with an opportunity to participate in 

the study process by sharing their perspectives on 

satellite servicing. Subsequently, most speakers for the 

International Workshop on On-Orbit Satellite Servicing 

were selected from these responses. If the author of 

an RFI response presented at the workshop, a detailed 

summary appears in Appendix C. RFI responses that 

could not be accommodated by a presentation at the 

workshop are summarized in this appendix.

Advanced Optical Systems, Inc.

RFI Response Number One

Advanced Optical Systems (AOS) is developing enabling 

technology flexible enough to support Rendezvous, 

Proximity Operations, and Docking (RPOD) operations 

for both cooperative and non-cooperative satellites with 

a single sensor system. AOS’s technology extension to 

the ULTOR Passive Prose and Position Engine family of 

6 Degrees of Freedom (DOF) state estimation algorithms 

is called ULTOR ACT, and combines a 2-D camera 

and 3-D Light Detection and Ranging (LIDAR). ULTOR 

ACT is a classic two-plus-two-equals-eight solution in 

which the application of real-time processing of two 

sensor data streams provides a more robust, accurate 

and precise solution than either sensor provides alone. 

ULTOR ACT technology is estimated at TRL 3, but 

given the maturity of each subsystem, AOS expects it 

can reach TRL 5 by 2011 through hardware-in-the-loop 

testing of prototype systems. 

RFI Response Number Two

AOS developed the ULTOR Passive Pose and Position 

(ULTOR P3E) system to provide real-time 6 DOF 

estimates of objects using 2-D data that is almost 

always present on space vehicles for rendezvous 

missions. An earlier version of the technology flew 

on the Hubble Space Telescope Servicing Mission 4, 

STS-125, and AOS is currently working with NASA/

JSC to demonstrate a more advanced version of the 

P3E sensor processing as a candidate Automated 

Rendezvous and Docking sensor for the ORION crew 

capsule using the centerline docking camera. ULTOR 

P3E is extremely portable and has been ported into 

six different platforms, including two different space 

hardware platforms. ULTOR P3E is currently at NASA 

TRL 8 after the SM4 mission to Hubble, and has been 

demonstrated to TRL 5 for the Orion implementation.

RFI Response Number Three

The current AOS product for Automated Rendezvous 

and Docking (AR&D) based on the Advanced Video 

Guidance Sensor (AVGS) design is called ULTOR 

Active. This system includes state-of-the-art detector 

technology and improvements to the processing 

hardware that allow a much smaller footprint while 

providing an order of magnitude increase in accuracy 

over the previous AVGS design. ULTOR Active is 

designed to provide immunity to extreme lighting 

variations, a potential and significant problem with 

most AR&D sensors. The previous AVGS technology 

is evaluated at TRL 8 based on the Orbital Express 

(OE) and Demonstration of Autonomous Rendezvous 

Technology (DART) missions, and the ULTOR Active is 

at TRL 6. 

ARES Corporation

ARES Corporation attributes much of its vast range of 

experience in the aerospace industry to the previous 

experiences of its personnel. Several employees were 

involved in making the tools, fixtures, and procedures 

used in the capture and return of Palapa B-2 and 

Westar VI spacecraft, which were stranded in useless 

orbits when both spacecraft suffered identical failures 

when the carbon-carbon nozzle on each of the perigee 

kick motors shattered approximately eight seconds into 

the perigee burn. ARES personnel helped in a mission 

to capture and return the two spacecraft for repair and 

relaunch. ARES personnel were also involved in the 

on-orbit repair of the LEASAT F3 in 1985 to bypass a 

flawed electronics unit that prevented the spacecraft 

from turning on. ARES’ experience with on-orbit 

servicing could help with a variety of future servicing 

needs. 

CSA Engineering

Vibration and Jitter Control

Vibration control can be divided into several categories: 

vibration suppression, vibration damping, vibration 

cancellation, and vibration isolation. Vibration control 

can use several different power sources, and can serve 

multiple purposes: failure prevention, performance 

improvement, or testing. CSA has developed 

mechanical vibration dampers that have been used 

on the Hubble Space Telescope’s (HST) solar array 

masts and LDCM, in addition to other vibration control 

systems for a variety of applications. Vibration control 

can help do things like reduce optical jitter, aid in-space 

assembly, and protect delicate components during 

launch. CSA continues to pursue enhancements to their 

systems to achieve greater vibration control and new 

mission applications. 

On-Orbit Assembly

On-orbit assembly enables a new class of ultralarge spacecraft that offer greater opportunity and 

potential benefit for scientific, military, and commercial 
100 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

creating a flight support system used in servicing future 

spacecraft. Honeywell is also the incumbent avionics 

supplier for the existing Shuttle Flight Support System. 

Honeywell’s system engineering credentials and process 

for supplying cost-effective support, experience with 

the existing Flight Support System for the Multi-Mission 

Spacecraft, capability to support integration into the 

existing Orion avionics and Control and Data Handling 

(C&DH) system, and capability in supporting robotic 

assistance for both Orion and other spacecraft makes 

them a cost-effective teammate to support Flight 

Support Equipment Trades. 

ITT Corporation

The Hubble Space Telescope and Solar Max missions 

have shown that human spaceflight is an excellent 

resource that can be used for maintenance or repair. 

These missions demonstrated that human spaceflight 

could extend the life of high value on-orbit systems, 

though they were very expensive. The Special Purpose 

Dexterous Manipulator (SPDM, aka Dextre), which 

was delivered to the ISS in 2005, has the manipulative 

resources for some very complicated assembly and 

repair operations. This type of program could reduce 

the cost of future astrophysics missions by providing a 

more robust maturing Technology Readiness Level and 

by demonstrating technologies that are difficult to show 

on the ground or through analysis. ITT is working on 

developing ideas and technologies for such a program. 

Jefferson Institute

To truly enable the unique core expertise and competencies for in-space servicing (human and robotic) by the 

Goddard Space Flight Center and other NASA centers, 

the research aperture needs to be widened to use all 

national and international assets. The Jefferson Institute 

has had the privilege the last two years to assist NASA’s 

Marshall Space Flight Center (MSFC) in the development 

of the Ares V heavy-lift vehicle as a national asset. The 

Jefferson Institute helped develop several workshops 

that were hosted by Ames Research Center, with the 

goal of having MSFC listen to potential users directly in 

an effort to explore what potential users would like to 

see in a new heavy-lift vehicle. To assist GSFC in transforming space servicing from a single user, the Jefferson 

Institute would use variations of the same approaches to 

kindle national interests. 

John Frassanito & Associates

A near-term, high confidence Heavy-lift Launch Vehicle 

(HLV) could be developed using well understood, 

legacy elements of the Space Shuttle system, which 

offers significant performance, reliability, schedule, 

risk, cost, and work force transition benefits. The HLV 

applications. Many challenges exist, but for certain types 

of missions, space-based assembly can offer a highperformance, efficient solution. Whenever physical size 

matters, on-orbit assembly is beneficial, and assembly 

also opens the door for new spaceflight architectures. 

Due to the inhospitable space environment and lengthy 

amount of time required for assembling a large structure, 

robotics become a necessary part of any mission. When 

considering any on-orbit assembly mission, on-orbit 

structural verification and on-orbit management of 

vibration and other motions become key considerations 

in the planning process. CSA and Moog’s strengths in 

space-rated actuators and electronics and expertise in 

the areas of structural dynamics, experimental modal 

analysis and related instrumentation, control system 

design and control-structure interaction, could be 

leveraged for use in on-orbit assembly missions. 

Emergent Space Technologies

Emergent was founded to provide engineering services 

and technology research and development for the 

autonomous space operations industry. Initial emphasis 

was on formation flying and constellations, but with 

NASA’s Constellation Program coming online in the 

early 2000s, Emergent’s focus shifted to autonomous 

rendezvous, proximity operations, and docking 

(ARPOD). Emergent has several relevant technologies, 

including specialized algorithms for designing efficient 

tours of Near-Earth Asteroids for Discovery-class 

missions, which could also be applied to efficient 

transfers of Project Constellation vehicles, Retro-GEO 

orbits, CubeSats for ARPOD mission support, and 

algorithms for safe proximity operations, rendezvous, 

and capture. Emergent has supported GSFC in its 

satellite servicing studies through its work with an 

Instrument Design Laboratory run and a Mission Design 

Laboratory run, and in the post-analysis of Rendezvous 

Navigation Systems data collected during the STS-125 

mission to the Hubble Space Telescope. Emergent’s 

experience in ARPOD and formation flying, combined 

with its subject matter expertise in orbit determination, 

attitude determination and control, maneuver and 

trajectory design, collision prediction and avoidance, 

orbital debris modeling, and systems automation and 

autonomy makes them a great resource for on-orbit 

servicing missions. 

Honeywell Defense and Space

As the avionics supplier for over half of the shuttle 

avionics, the International Space Station (ISS) avionics, 

and the Orion avionics, Honeywell is well positioned 

to support NASA’s Goddard Space Flight Center in 

a trade study defining the feasibility of using existing 

Constellation assets and other space equipment in 
 Appendix B – RFI Responses Summary | 101

controls, launch vehicle control technologies, propulsion 

systems and components technology, technology for 

vibration control, and technology for tactical missiles 

solutions. Moog has significant experience with 

technologies necessary to support the development 

of on-orbit fluid transfer and servicing missions, and 

proposes the development of an on-orbit autonomous 

cryogenic fuel transfer system. Moog has also produced 

six degrees of freedom systems for space applications. 

Finally, Moog proposed a notional mission for space 

debris cleanup. 

NASA’s Goddard Space Flight Center

Using NASA’s Constellation Architecture to Achieve 

Major Science Goals in Free Space

Future space science missions developed to achieve 

the most ambitious goals are likely to be complex, large, 

publically and professionally very important, and at the 

limit of affordability. Consequently, it may be valuable 

if such missions can be upgraded, repaired, and/or 

deployed in space, either with robots or with astronauts. 

A team at Goddard developed a concept for astronautbased in-space servicing at the Earth-Moon L1 and L2 

locations that may be implemented using elements of 

NASA’s Constellation architecture. This libration point 

jobsite could be of great value for major heliospheric and 

astronomy missions operating at Earth-Sun Lagrange 

points. The team explored five alternative servicing 

options that could be available within about a decade, 

and highlights one that appears to be the least costly. It 

most efficiently uses Constellation hardware that appears 

to be available by the middle of next decade: the Ares 

I crew launch vehicle, Orion crew exploration vehicle, 

Centaur transfer vehicle, and an airlock/servicing node 

developed for lunar surface operations. 

LASOPOST

LASOPOST (LEO-Assembled, SEL2-Operated, Phasing 

Orbit-Serviced Telescopes) is a concept for assembling, 

operating, and servicing a broad range of sizes and types 

of space telescopes. The main objective of LASOPOST 

is to enable maximum science capability while requiring 

minimum development of supporting space infrastructure. In the LASOPOST concept, space telescopes 

would be deployed or assembled in a LEO that either 

matched the International Space Station orbit or was 

easily reachable from the ISS orbit in case of deployment 

or assembly issues. After deployment or assembly, the 

space telescope would be checked out and gradually 

boosted to a Sun-Earth Lagrange point 2 orbit for science operations. Periodically, the space telescope could 

be dropped back into a Lunar Phasing Orbit for servicing 

(supported by a crewed Orion capsule), after which the 

telescope could return to SEL2 Orbit. 

could be ready for first flight as soon as 54 months 

after an Authority to Proceed. This refined HLV could 

be developed for less than $8 billion, and operated at 

costs as low as $450 million per launch, depending 

on mission configurations, flight rates, and operating 

concepts. As an example of the on-orbit servicing 

capabilities enabled by this shuttle-derived HLV, John 

Frassanito and Associates describes a 172 metric ton 

prototype Space Based Solar Power satellite that could 

be delivered to GEO starting as early as 2016. 

MDA

MDA has developed unique, reliable robotic solutions 

for more than 30 years. Such robotic systems can 

and have been used as mission enablers, and in the 

future they can enable even more missions in space 

observatory assembly and servicing, satellite servicing, 

orbiting stations and service depots, and space 

exploration. Servicing has already been shown to reduce 

mission risks and costs while providing life-extension or 

performance enhancement, and robotics have been key 

to both human and robotic servicing solutions. Robotic 

systems and servicing have already been demonstrated 

with Hubble and the ISS, and have enabled great 

scientific returns at relatively low costs. With existing 

state-of-the-art robotics onboard, the ISS is an ideal 

development platform for testing new on-orbit servicing 

capabilities. MDA is prepared to support both NASA and 

the CSA in expanded utilization and experimentation 

with the ISS robotic systems. 

Michigan State University

Recently, researchers at Michigan State have developed 

and experimentally tested a computationally efficient, 

general-purpose vision architecture, suited for general 

image understanding in uncontrolled environments. This 

architecture bridges a wide technology gap between 

concrete image features and abstract task concepts, by 

enabling goal-directed deliberative reasoning with pixels. 

Existing artificial vision systems cannot match the performance of a trained human observer. Existing systems 

that control platform motion, sensor-pointing angle or 

perform foveated sensing are brittle in performance. By 

contrast, biological systems like those being developed 

accomplish these tasks seemingly effortlessly. Moving 

the neural processing taking place in the operator’s brain 

to computer processing on a NASA robot platform will 

reduce both operator workload and bandwidth.

Moog Space and Defense Group

Moog has developed several technologies for use in 

space missions which could be applied to on-orbit 

satellite servicing. They have developed advanced 

technology solutions for precision motion and fluid 
102 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

NASA’s Marshall Space Flight Center

The Advanced Technology Large-Aperture Space 

Telescope (ATLAST) is a mission concept for the next 

flagship UV/optical/Near-IR (UVOIR) space observatory, 

to answer some of the most compelling astronomical 

questions, including “Is there life elsewhere in the 

Galaxy?” Two different observatory architectures 

for ATLAST have been explored in detail, but both 

can tackle the same set of scientific goals. Although 

ATLAST requires some technology development, both 

observatory concepts take full advantage of heritage 

from previous NASA missions, as well as technology 

developments currently underway for missions in 

development. The non-cryogenic nature of ATLAST 

makes the construction and testing of the observatory 

much simpler than for JWST, and a key attribute of 

the design of ATLAST is its ability to be serviced and 

upgraded on orbit. 

Northrop Grumman

NASA’s great observatories—the Hubble Space 

Telescope, Compton Gamma-Ray Observatory, 

Chandra X-Ray Observatory, and Spitzer Space 

Telescope—have clearly demonstrated the need for 

multi-spectral observations to unveil the mysteries of the 

universe. These observatories could be accommodated 

with existing launch vehicles, requiring only their antenna 

booms and solar arrays to be folded up. NASA’s next 

generation of large space observatories—James 

Webb Space Telescope (JWST), Space Interferometry 

Mission (SIM), Constellation-X (Con-X), Terrestrial Planet 

Finder Interferometer, and Single Aperture Far Infrared 

telescope (SAFIR)—will use segmented optics with 

complex deployment schemes and/or multiple launches 

and formation flying to satisfy their requirement for 

apertures much larger than the about 5-meter diameter 

of current launch vehicle fairings. If telescope aperture 

sizes continue to follow historical trends, the space 

observatories launched in the 2030 to 2040 period to 

follow up on discoveries by JWST, SIM, Con-X, and 

SAFIR will be too large to be launched and deployed 

from a single launch vehicle. Thus, NASA’s “Vision 

Missions” such as Stellar Imager, Life Finder, SPECS, 

and Planet Imager will require on-orbit assembly. To 

maximize the scientific return from these facilities, they 

should also be designed for on-orbit servicing and 

instrument replacement. 

Odyssey Space Research

Odyssey Space Research is a company focused on 

commercial and government applications of on-orbit 

GN&C and Rendezvous and Proximity operations. 

In-Space Robotic Integration System (IRIS)

It is impossible to plan a construction of large structures 

in space without developing a versatile, reliable, 

and cost-effective joining technology. Also, human 

experience shows that in-space repairs of existing 

assets will be required in order to support our prolonged 

presence in space. Vacuum brazing is a mature 

process used for new construction and repair in many 

aerospace, aircraft, automotive, nuclear, and medical 

systems. Its potential application in space has been 

demonstrated by Russian cosmonauts, as well as by 

the experiments performed on American and European 

payloads. A team at Goddard proposes to develop 

a reliable, safe and cost-effective joining technology 

based on electron beam vacuum brazing for in-space 

construction and repair. Cost of future endeavors such 

as permanent orbital platforms can be reduced and 

risk can be better mitigated by launching compact, 

collapsible pallets containing stowed modular elements 

(struts) of the future structures and assembling them in 

space.

Applications of DMDs for Astrophysical Research

Digital Micromirror Devices (DMDs), used as optical 

switches, provide a most powerful solution that allows 

for the design of a new generation of instruments with 

unprecedented capabilities. A DMD spectrograph 

can take the next step in addressing the next big 

astronomical questions. Utilizing servicing, a DMD 

spectrograph could be installed on the Hubble 

Space Telescope (HST). Equipped with a DMD multiobject spectrograph, HST would represent an ideal 

complement to the James Webb Space Telescope.

SPectroscopic All-sky Cosmic Explorer (SPACE)

Exploiting the enormous advances in nanotechnology, 

SPACE is a mission capable of producing a threedimensional evolutionary map of the Universe over the 

past 10 billion years. SPACE improves the figure of merit 

for knowledge of dark energy by more than an order 

of magnitude and fully discriminates between theories 

of dark energy and theories of modified gravity. SPACE 

achieves its remarkable sensitivity, sky coverage, and 

sampling frequency by performing multi-slit near-IR 

spectroscopy in outer space, fully exploiting the sky 

background about 500 times lower than from the Earth. 

SPACE, originally conceived as a joint ESA-NASA 

project, has won the ESA selection (medium-class) for 

the Cosmic Vision 2015–2025 planning cycle. SPACE, 

as originally proposed, has by far the most exciting 

capabilities, with a scientific potential so broad and 

compelling that it exceeds even the investigation of dark 

energy. 
 Appendix B – RFI Responses Summary | 103

or grappling to effect capture, approaches which levy 

considerable requirements on knowledge of the target’s 

physical geometry, condition, and motion in addition 

to the requisite capabilities for targeting and grappling. 

Teledyne Brown proposes a solution that utilizes a 

filament mesh to passively encompass and capture 

the target body, rather than capture by grappling or 

otherwise directly contacting the target body. This 

capture system is amenable to any disposal system, 

either for boosting to a higher parking orbit, or reentry 

from low-earth orbit. 

Robust, Adaptive Control of Evolving Systems for 

On-Orbit Robotic Servicing

On-orbit robotic servicing of spacecraft has great 

potential as a safe and cost-effective means for 

maximizing the return on the investment in high-value 

space assets, and as a means to enabling complex 

missions that cannot be accomplished otherwise. To 

enable on-orbit robotic servicing will require advanced 

technology and avionics guicxxdance, navigation, and 

control. In particular, the robust attitude control problem 

for evolving systems is a technical challenge that 

heretofore has not been met in a satisfactory manner. 

Teledyne Brown is researching autonomous control of 

a structure during and after the connection or mating 

of two or more components of its subsystem. The 

autonomous assembly of actively controlled subsystems 

is the central element of Evolving Systems. 

Texas A&M University

Optimal Servicing of Geosynchronous Satellites

To be cost-effective, satellite servicing will require the 

servicing vehicle to service numerous satellites, which 

will require raising and lowering of altitude and plane 

changes. Plane changes require a lot of fuel, so any 

servicing architecture will have to minimize the total 

plane change. Consequently, geosynchronous orbit is 

probably the region in which servicing will be the most 

cost effective, because all the satellites are in almost 

the same plane. Researchers at Texas A&M University 

developed a method for optimally visiting numerous 

satellites in geosynchronous orbit. 

Enabling Propellant/Fluid Transfer in Microgravity

Phase separation is a critical technology for pressuredriven fluid transfer under reduced gravity. Texas A&M 

and Boeing designed a propellant transfer system for 

the International Space Station. 

Odyssey is currently working on five spacecraft that 

perform the rendezvous, proximity operations and 

capture (RPOC) operations critical to any on-orbit 

servicing operation. Odyssey believes that some 

of these spacecraft, or major components of the 

spacecraft, could be re-tasked to support on-orbit 

servicing missions. At the very least, the RPOC 

capabilities can be used in the development of an 

on-orbit servicing system. Odyssey has also studied 

the potential applications and implementations of an 

on-orbit servicing system through its own internal 

research as well as through a Small Business Innovation 

Research (SBIR) entitled “Automated Rendezvous and 

Docking Infrastructure to Support Commercial Space 

Development.” In addition to the spacecraft and mission 

design work that Odyssey supports, Odyssey is working 

on a number of relevant technologies such as new 

guidance, navigation and control algorithms; navigation 

sensor techniques; and a very unique testing capability 

to introduce flash LIDAR sensors into closed loop 

hardware-in-the-loop simulation. 

Physical Sciences, Inc.

Physical Sciences, Inc. (PSI) possesses an enabling 

technology that addresses two principal missions: 

on-orbit assembly of modular space systems too large 

or too fragile to launch, and repair or replacement 

of failed or under-performing components. PSI’s 

technology is called AUTOCONNECT (Auto-Configuring 

Electromechanical Interface), which is an intelligent, 

universal, electromechanical interface for autonomous 

space systems assembly. AUTOCONNECT will enable 

rapid on-orbit assembly of space systems—both 

astronaut-assisted and robotic. AUTOCONNECT was 

developed by PSI under sponsorship of NASA’s Marshall 

Space Flight Center and DARPA under Small Business 

Innovation Research programs.

Teledyne Brown Engineering

A Robust, Orbit Mechanics Enabled, Minimal Cost 

Approach to Orbit Debris Remediation

To meet the increasing threat to the safe access to 

space posed by space debris, methods are being 

sought to reduce the amount of large debris in space 

through active debris removal. Capturing large, 

uncooperative debris in either high-, medium-, or lowearth orbit is arguably the most significant challenge 

to orbit debris remediation. Most, if not all, spacebased approaches require active pointing/targeting 
104 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

Appendix C – International Workshop on On-Orbit Satellite Servicing

Capture (AR&C). Other new technologies that are slated 

for development are: a safety spin decouple, materials 

and structures, environmental studies, formation flying, 

lightweight materials, and power and energy solutions. 

Mr. Radzanowski also mentioned that he is focusing 

on servicing technologies that are “enabling” across 

more than one NASA program (namely, the Exploration, 

Mission, and Technology directorates at NASA). He 

also stressed that the community needs to make the 

business case for servicing by incorporating servicing 

into broad concepts and architectures, instead of “oneoff” events.

Dr. Stephen Huybrechts, Vice President, Applied 

Minds, Inc. “Thoughts on On-Orbit Servicing for the 

National Security Community.”

Dr. Huybrechts relayed his personal opinions from 

a background of national security experience. His 

perspective is that while no Department of Defense 

assets are currently designed for servicing, having 

such services available in-orbit would be useful for 

unexpected events or challenges. Such in-orbit services 

would make most sense in orbits with multiple satellites 

(i.e., GEO). He noted that storable propellant might 

not be the area where he would devote technology 

development money, as electric propulsion systems limit 

the need for refueling, and it may be easier to fly extra 

fuel for end/late mission life operations. Rather, servicing 

is useful to fix flaws, rescue stranded assets, and 

remove acquisition delays; overall, to extend the life of 

legacy systems while their replacements work through 

their own delays. He also stressed that flexibility is a key 

attribute of servicing capability, especially when a team 

does not know the mission in advance. 

Ed Horowitz, Founder and Board Member, U.S. Space 

LLC. “The Role of the Private Sector.” 

U.S. Space LLC is a privately financed company 

that provides rapid satellite communication solutions 

to the U.S. and its allies. Mr. Horowitz has significant 

experience with commercial satellites, including Home 

Box Office (HBO). He noted that in the commercial 

satellite field, one must consider the value (revenue 

stream) of the service provided versus the satellite’s 

cost (hardware/operations), as well as the lost value 

(revenue) of business (communication) interruptions. 

He also explained that the business model for a 

replacement satellite is “just-in-time delivery.” Since a 

satellite does not depreciate until it is launched, an asset 

in production or in storage is “better” for accounting 

purposes. However, refueling (especially after full 

depreciation) appears to be a marginal incremental cost 

when compared to the large revenue stream that would 

be enabled by continued satellite operations. It was 

his opinion that opportunities for satellite servicing are 

March 24-26, 2010 

Hosted by NASA’s Goddard Space Flight Center

Executive Summary

An enthusiastic assembly of more than 250 aerospace 

industry leaders, technology companies, universities, 

NASA officials, and other Federal Government 

representatives joined together to discuss and debate 

the current and future state of satellite servicing. 

There was unanimous consent that the time is right 

for meaningful on-orbit servicing to be executed. 

Technology exists today that can enable both roboticonly and human-robotic cooperative on-orbit servicing. 

Robert Strain, Director, Goddard Space Flight Center. 

Mr. Strain opened the Workshop with welcoming 

remarks.

Ron Ticker, Manager for Space Station Development, 

NASA Headquarters; Chairman of International 

Workshop on On-Orbit Satellite Servicing. 

Mr. Ticker reported on the goals of the Workshop, 

the quantity of the RFI responses, and set the stage for 

the presentations to begin. 

Christopher Scolese, Associate Administrator, NASA 

Headquarters. 

Mr. Scolese described the background, history, and 

importance of Multimission Modular Spacecraft, Solar 

Maximum, and the Hubble Space Telescope (HST) to 

satellite servicing. He then explained the International 

Space Station’s (ISS) assembly and robotic integration, 

and the need for more maintenance to extend its life 

to 2020. He finished with a poignant comment about 

the opportunities lost with past space assets such as 

Skylab, and concluded with what can be done in the 

future.

Dave Radzanowski, Deputy Associate Administrator 

for Program Integration, NASA Headquarters. “NASA 

Perspectives on Developing Spacecraft Servicing 

Capabilities.” 

Mr. Radzanowski began with a status report on 

ISS assembly and the directive that it will serve as a 

technology test bed going forward. ISS operations have 

been extended to 2020, which provides time to have 

technology demonstrations launched and installed. 

In the next two years, $2.5 billion are allotted for ISS 

extension. Current U.S. operations are at 50% utilization, 

and we want to get to 100%. Utilization increase will 

be spread across the servicing study, technology 

demonstrations, and other programs. There are two 

main technology demonstration programs: Flagship 

missions and a technology demonstration flight that 

includes fuel transfer and Advanced Rendezvous and
 Appendix C – Workshop Summary | 105

Dr. Matt Mountain (Director, Space Telescope 

Science Institute) opened the session with a compelling 

discussion of the breadth of the scientific return that 

was made possible by a series of successful servicing 

missions to the Hubble Space Telescope (HST). 

However, these observatory upgrade missions took 

place in LEO with the space shuttle, which will soon no 

longer be available. 

However, the future of servicing of scientific 

satellites lies well beyond LEO. Presentations by Dr. 

Dan Lester (Research Fellow, University of Texas, 

Astronomy Department, “Servicing and Lagrange Point 

Operations for Astronomy”), Dr. William Oegerle

(Director, Astrophysics Science Division, NASA’s 

Goddard Space Flight Center, “Servicing ATLAST!”), 

and Dr. Matthew Greenhouse (Astrophysicist, 

NASA’s Goddard Space Flight Center, “Extra-Zodiacal 

Exploration: An Architecture for Servicing-Sustained 

Cosmic Discovery”) summarized the value both of 

different orbits for astronomical observatories, and 

again, the importance of designing observatories that 

can take advantage of being upgraded on orbit.

It was important for the attendees to recognize 

that “servicing” was a term that included more than 

changeout of instruments on a flagship scientific satellite 

or construction of the ISS. Dr. Charley Noecker (Staff 

Consultant, Ball Aerospace & Technologies Corp., 

“External Occulter Planet Finder Mission at L2—A 

Potential ‘Customer’ for Robotic Servicing”) outlined 

how an occulting system to search for extra-solar 

planets might be enabled by advanced space robotics, 

Tom Kessler (Program Manager, Boeing Advanced 

Systems, “NIMITZ”) described the concept for robotic 

on-orbit space debris removal, and Bruce Campbell

(Manager, Integrated Design Center, NASA’s Goddard 

Space Flight Center, “Solar Sail Assembly/Deployment 

in Earth Orbit: An Enabling Capability for an Enabling 

Capability”) discussed the potential of solar sails to 

achieve multiple goals in free space.

On-orbit refueling and fuel depots have been 

identified for years as a future capability that would 

enable missions that otherwise would be very difficult. 

Dallas Bienhoff (Manager, In-Space & Surface 

Systems, The Boeing Company, “LEO Depot Servicing 

Impact on Space Missions”) discussed recent work to 

develop depot concepts in greater depth.

Lunchtime Presentations

Chair: Benjamin Reed

Advanced Materials and Avionics Manager, Space 

Servicing Capabilities Project, NASA’s Goddard Space 

Flight Center

Steven Johnston, Director of Advanced Space 

Exploration, The Boeing Company. “The Future of 

Commercial Human Space Flight.” 

reaching alignment; however, they are still in a formative 

stage and will ultimately be shaped by insurers, 

satellite companies, and technology developers. The 

strategy should be to align NASA (with its technology 

development) with commercial needs while building 

servicing, or at least refueling, into future satellites. When 

an audience member asked if his company would be 

willing to be the anchor customer for satellite servicing, 

he replied, “Yes.” They have designed refueling into their 

satellites at no design cost. Another audience member 

posed the question, “Nobody wants to pay up front 

for satellite servicing, but they want it in a crisis—how 

can we bridge the gap?” His answer was that there will 

need to be at least 12 in-space assets, from both the 

Department of Defense and the commercial sector (UHF 

system) that are either in crisis or on their last fumes. 

They have not been approached with a solution. If they 

were given one, they would compare the amount of time 

that it would take for a satellite servicer vehicle to launch 

versus the amount of time it would take to replace 

existing assets.

Frank Cepollina, Deputy Associate Director, Space 

Servicing Capabilities Project. “Servicing Study 

Objectives.” 

Mr. Cepollina indicated that he has been trying 

to have servicing capabilities built into satellites for 

decades, but nobody thinks in terms of future (servicing) 

needs. Engineers never predict failures or problems 

because they are generally too optimistic. He asserted 

that the da Vinci robot is capable of impressive 

teleoperation, and since that capability exists on the 

ground, it should also be feasible in space. He observed 

that the aerospace community’s desire to implement 

satellite servicing “is not there yet,” and that it needs to 

be coached and encouraged over the next 12 months. 

To that end, his group at NASA’s Goddard Space 

Flight Center is engaged in fabricating hardware that 

will demonstrate refueling on the International Space 

Station (ISS). The goal of these demonstrations is to 

mitigate risk to real satellites. Their development efforts 

also include ground demonstrations that are six months 

ahead of flight experiments. He adamantly believes that 

the time is right to move ahead on flight servicing. It is 

time to stop talking and start building. The workshop 

attendees responded with a cheer of support.

Missions and Customers of Satellite Servicing

Session Chair: Harley Thronson

Associate Director for Advanced Concepts in 

Astrophysics, NASA’s Goddard Space Flight Center

Although the capabilities exist—or will, in the 

near future—to service complex systems in LEO, the 

“business case” or a positive return on investment has 

yet to be fully established.
106 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

Millenia and is close to delivery. Cygnus just completed 

Critical Design Review (CDR) and Phase 2 of the 

Safety Review Panel. Taurus II is beyond CDR and is in 

production and testing.

Barry Miller, Systems Engineer, Lockheed Martin 

Space Services Company. “On-orbit Satellite Servicing– 

Overview of Lockheed Martin Satellite Servicing 

Capabilities and Products.” 

Over the last two years, Lockheed Martin has 

looked at on-orbit satellite servicing from a robotic and 

autonomous standpoint, with the idea of looking at a 

multi-mission servicing concept that is service-oriented 

based, has a fairly long life, and is capable of doing 

several missions. The basic servicing concept overview 

is that Lockheed Martin can deploy the asset and have 

the GEO-focused asset on numerous orbit applications 

in LEO or geosynchronous orbit. Deploying a near-term 

asset, a highly flexible robotic servicer with a chemical 

based propulsion system, would allow you from a 

technology development standpoint to focus on the 

high-risk items that Frank Cepollina mentioned earlier. 

Once the asset is in position it can do several missions, 

including repositioning active or dead satellites. 

Lockheed Martin has also looked at refueling missions 

that carry on-board refueling propellant. One could 

have either a monoprop or biprop system that allows 

you to service satellites that need fuel; or you could do 

repair operations; or perhaps go in and touch something 

that is in failsafe and move it into an un-fail state. That 

kind of asset can then go on and do several missions. 

Periodically, you could refuel your servicer and upgrade 

your own assets through mission customization.

 Lockheed is trying to map where they can use 

low risk capabilities and technologies and marry them 

with some of the more immature technologies to bring 

them together into a servicing architecture that is both 

reliable and responsive to do multiple missions in a short 

amount of time.

Baard Eilertsen, Senior Vice President, Business 

Development, Swedish Space Corporation. “The Orbital 

Life Extension Vehicle—an AOCS Backpack.”

There were two competing programs for the 

commercial satellite business back in the 1980s. The 

commercial satellites had trouble with their launch 

vehicles, and the Swedes developed a system to service 

them. This system has developed with the following 

attributes: cold gas propulsion for maneuvering, electric 

propulsion (20 weeks to get to GEO), and cameras to 

navigate to customer. The Servicer would park at one 

meter and send a probe into the thrust nozzle of the 

customer for attachment. The Servicer would then stay 

attached and act as the ACS until the customer’s end 

of life (EOL). At EOL, the Servicer would super-sync 

the customer, release, and find a new customer. An 

In commercial programs such as 737 airplane 

program, Boeing assumes all the risk. There are about 

200 customers, and the FAA approves the design 

through a well-established process. In contrast, other 

programs are funded by one customer, such as the 

Navy Poseidon program where the Navy retained 

authority. For a commercial crew vehicle program in 

aerospace, there will be a mix where the commercial 

company and NASA would define the requirements. 

For example, NASA would have authority for human 

rating, while Boeing would fund the design and retain 

the design rights. The challenge is to find a business 

model to balance the risk. For instance, if you lose 

one customer for the 737 program it is not the end 

of the world; however, such a situation would be 

catastrophic for satellite servicing. A strong binding 

contract is therefore needed to get servicing started. 

The overarching design drivers for a crew vehicle are: 1) 

that it be safe and reliable, 2) that it be cost effective to 

operate, and 3) that the risk be burned down.

Boeing needs to share costs and design an 

architecture that is built in a smart, simple way. The 

concept needs to be flexible, to accommodate a crew 

from three to seven people, and be modular, lightweight, 

and compatible with many launch vehicles. In addition, 

a combined design, manufacturing, test and training 

center should be created for efficiency.

Bernard Kutter, Manager, Advanced Programs, 

United Launch Alliance. “United Launch Alliance Launch 

Services.” 

United Launch Alliance (ULA) has an extensive 

launch history and plans to have about one launch per 

month in the near foreseeable future. Mr. Kutter reported 

1,300 successful launches; the program should 

therefore be considered extremely safe. The A402 may 

be able to launch a crew vehicle, and a second rocket 

with this capability is in development. ULA has been 

working on the CRYogenic Orbital TEstbed (CRYOTE) 

for a number of years. The tank would sit in a Payload 

Adapter Fitting (PAF) much like LCROSS did. It would 

also take advantage of the extra gas (N2, O2) from the 

rocket’s upper stage. Present capability allows us to 

carry a 9-ton payload to Lagrangian point 2 (L2); a fuel 

depot in orbit would enable a 20-ton payload to L2.

Bob Richards, Vice President, Human Spaceflight 

Systems. “Orbital’s ISS Resupply Service.”

Mr. Richards reported on Cygnus and the Taurus 

launch complex. Cygnus is a cargo vehicle designed 

to resupply the ISS, but it could morph into satellite 

servicing. Orbital sees itself and Cygnus as a turnkey 

system. The Taurus ll launch site is under construction 

at Wallops Island. For Cygnus, Mission Operations at 

Dulles are tied to Mission Operations at NASA’s Johnson 

Space Center. The pressurized model is being built by 
 Appendix C – Workshop Summary | 107

include remote-sensing operators and satellite brokers. 

Commercial satellite servicing is considered a high 

investment risk. Risks include the return on investment, 

cash flow if paid after servicing, and investor confidence. 

Commercial satellite servicing is an unproven market 

with high entry costs, and not enough customers have 

been identified to make it profitable. The concept of 

servicing commercial satellites and extending satellite life 

threatens the existing business model of building new 

replacement satellites.

Charles Miller, Senior Advisor for Commercial Space, 

Office of the Chief Technologist, NASA Headquarters. 

“Should NASA Foster a Commercial Satellite Servicing 

Industry?” 

NASA Headquarters is providing funding to the 

commercial space industry for future technology 

development and the creation of new market. Satellite 

servicing is a potential new commercial market. It 

was suggested that NASA and other government 

agencies could foster a commercial satellite program. 

The National Advisory Committee for Aeronautics 

(NACA) approach was provided as a proven and 

open innovation model. The NACA approach focused 

on industry, with industry being both partner and 

customer. It developed key partnership with all key 

agencies (United States Air Force, the Department of 

Transportation, and the Department of Commerce). 

The guiding strategy was to develop consensus and 

practical solutions. The strategy also included smaller, 

more numerous, and more frequent projects and 

programs. Miller advocated the NACA approach and 

provided numerous examples of NACA successes. 

He also emphasized that the early NACA successes 

did not require a significant amount of cash. NACA 

focused on building a healthy competitive industry. It 

solved a practical aviation problem with a small amount 

of cash. NACA, whose focus was external customers, 

was a critical driver in American aviation. The NACA-like 

options to foster a commercial satellite servicing industry 

are: 1) purchase commercial satellite, 2) fund COTS 

program, 3) joint-sponsor research, 4) loan guarantees, 

5) partner with DoD and national security team, 6) 

identify and help solve other non-technical items (ITAR), 

and 7) develop new technology.

Baard Eilertsen, Senior Vice President, Business 

Development, Swedish Space Corporation. “Market 

Interest in Fleet Management On Orbit Services—A 

Commercial Approach.” 

The on-orbit services are life extension, relocation, 

rescue and deorbiting. For one scenario, a satellite’s 

life can be extended by 12 years. Based on a market 

research of commercial telecom satellite operators, 

satellite servicing has a market if the cost of servicing 

is 30 to 50% of buying a replacement satellite. So this 

obsolete satellite with one or two months of fuel left on 

board would be ideal for experimentation.

Lt. Col. Fred Kennedy, Space Lead, Space & C4ISR 

Branch, Joint Staff/J-8, Dept of Defense. “Orbital 

Express.”

Orbital Express (OE) was designed to demonstrate 

in-orbit servicing. Astro was the servicer; NextSat, the 

customer, was equipped with retro reflectors. Mission 

Operations were located in Kirkland, Huntington Beach, 

and Houston. The two satellites were launched mated 

together. One of the first tasks was to transfer 15 kg 

of Hydrazine from Astro to NextSat without pumps. 

The pumped transfer came later. NextSat also moved 

propellant to Astro. The mission replaced both batteries 

and computers in orbit. Throughout the mission, 

numerous anomalies occurred and were overcome 

with real-time problem solving by the ground ops 

team and the systems onboard the two satellites. For 

example, the biggest problem with rendezvous was 

not collision avoidance, but finding NextSat. Lt. Col. 

Kennedy suggests incorporating sensors that can view 

in all directions (four pi Steridian), and believes that it is 

possible to attach to common satellite fixtures such as 

Marman rings, bolt holes, etc., in the future.

In summary, the OE mission demonstrated the 

technical feasibility of on-orbit docking and servicing. 

This may allow a reduction of redundancy and testing 

(which are expensive) in future missions. He believes 

in-orbit servicing could extend satellite lifetime and 

maneuverability.

Business and Commercial Case for Satellite 

Servicing

Session Chair: Mansoor Ahmed

Associate Director of Flight Projects for the Astrophysics 

Projects Division, NASA’s Goddard Space Flight Center

Keynote Speaker: Joe Rothenberg, International 

Development and Integration, Swedish Space 

Corporation. “Commercial Satellite Servicing Needs and 

Challenges.” 

Servicing commercial satellites hinges on 

investment returns. In the current environment, it takes 

eight to ten years to get a return on an investment from 

a commercial satellite. The upfront funding acquisition 

takes about three years. It takes another three to five 

years to develop and launch a satellite. So, the return 

on investment will be minimum of eight years after 

the project begins. The types of commercial satellites 

will dictate if servicing is warranted and financially 

profitable. If a satellite is small and non-unique, the 

cost of servicing could be the same as launching a 

new satellite. If a satellite is large and unique, it will 

have higher potential for servicing need and return 

on investment. Potential servicing customers may 
108 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

instrument life. Serviceability costs can be estimated by 

assessing the ease of system serviceability. If the system 

design allows for easy servicing through modularity, 

docking interfaces, etc., the servicing cost can be 

predicted with more certainty. Serviceability is also an 

insurance against future uncertainty. If a telescope can 

be serviced to upgrade its detecting capability, then 

the cost of building and launching a new telescope can 

be deferred. Serviceability’s value can be quantified by 

estimating the break-even cost between a program 

with servicing and a program without servicing. A 

baseline example may be a servicing program where a 

telescope would be replaced after two or more failures. 

A servicing model is created in order to compare 

servicing and replacement. Costs are developed for 

servicing and replacement. The difference in cost 

between replacement and servicing defines the upper 

boundary for what a servicing program should cost. It 

is recommended that mission concept design periods 

include a study of satellite servicing. This approach 

should be applied to all expensive long-life satellites.

Barry Miller, Systems Engineer, Stf, Lockheed Martin, 

“On-Orbit satellite Servicing—Is There a Case?” 

There is a market for satellite rescue. A satellite 

that, due to non-catastrophic launch failure, fails to 

achieve its desired orbit may be inserted into the wrong 

orbit. Such an asset could be saved if a satellite were 

launched to capture and relocate the original satellite to 

a correct orbit. 

While a market survey on servicing capability 

showed very little interest in on-orbit repair, it indicated 

that there is a high level of interest in orbit maintenance 

and launch rescue. However, a successful on-orbit 

demonstration of such a capability is required. The 

historical record indicates that 1 out of 120 satellites 

have been lost. The value of servicing depends on 

whether there would be total or partial loss of the 

satellite, the replacement costs, and what is considered 

market value. As the cost of Department of Defense 

(DoD) satellites is unknown, it would be impossible to 

use this technique to assess the value of even a critical 

DoD mission that received servicing.

The diverse and large on-orbit servicing market is 

difficult to estimate and capture. And if the right value 

proposition is poorly defined, the opportunity for a 

servicing market will be closed. Customer interest highly 

depends on the servicing business model, and this 

model requires that the developer assume risk up front.

Human Servicing

Session Chair: Jim Corbo

Systems Engineering Manager, Space Servicing 

Capabilities Project, NASA’s Goddard Space Flight 

Center

tells us that if the cost of servicing is less than 50% of 

a replacement satellite, the servicing is cost-effective. 

A satellite servicing development program with ESA 

financing and oversight took the ConeXpress-OLEV 

through a full and successful Preliminary Design Review. 

An initiated contract with a launcher, Optus, had to be 

cancelled due to cost increase. A new and more costefficient servicing satellite platform project was initiated. 

Commercial satellite operators do not want to pay for 

new technology; however, they may be willing to try if it 

were offered at a reduced cost and risk. Investors are 

not willing to pay the cost above the nominal price. The 

industrial shareholders cannot finance the development 

costs. Investments, strategic partner and financing 

entities are required. Technical solutions to on-orbit 

servicing are ready, and potential customers have 

been identified. But to date, it has been difficult to find 

investors who are willing to take the risk.

Bretton Alexander, President, Commercial Spaceflight 

Federation. “Commercial Human Spaceflight: Context 

and Capabilities.” 

The Commercial Spaceflight Federation includes 

developers and operators. This activity is funded 100% 

privately and does not involve government funding. 

To date, over $1.5 billion has been invested into the 

commercial spaceflight industry. The Federation has 

executive and associate members, with executive 

members providing orbital and suborbital spacecrafts as 

well as spaceports, and associate members providing 

training services, medical services, and life support 

services. The membership represents 2,600 employees 

in 30 states. NASA’s commercial crew program, robotic 

precursor missions, and technology demonstration 

programs promote commercial space industry. 

Specifically, there is much interest in NASA’s technology 

demonstration program. NASA’s COTS program 

has fueled progress and success in the commercial 

industry, as seen by the Falcon 1 success. Currently, the 

commercial industry capability is limited to Low Earth 

Orbit. Its destination missions are LEO servicing and the 

ISS. The potential customers are the U.S. government, 

industry, research, private individuals, and foreign 

clients. Its capabilities include launch and reentry, inspace assembly and servicing, and satellite rendezvous 

and inspection. The goal is to develop a commercial 

spaceflight entity that does not depend on NASA.

Zach Bailey, Graduate Student, MIT Space Systems 

Laboratory. “Determining the Value of On-Orbit 

Telescope Servicing.”

Space astronomy constantly strives to discover the 

new and unknown, and enhanced detecting capabilities 

are key to achieving this goal. As the Hubble Space 

Telescope successfully demonstrated, on-orbit servicing 

can increase science capability as well as extend 
 Appendix C – Workshop Summary | 109

Science on ISS is a multiphase program. One 

proposal is to attach a .5 m to 1 m telescope to confirm 

ISS as a suitable location for telescope observations, 

attach a similar-sized cryogenic telescope to extend 

to near-infrared wavelengths, and augment spectral 

coverage by adding “clone” telescopes. The goal is 

to scale the telescopes to the largest possible ISS 

aperture, potentially to the HST 2.4 m range.

The ISS program objectives are to show scientific 

and engineering results by 2015, which would result 

in a full-scale “great observatory” in 2016–2020. 

This would provide a thousand-fold improvement in 

discovery efficiency over HST and demonstrate key 

technologies for assembling, verifying, and operating 

facilities from ISS.

The science drivers for these new telescopes 

include the thousand-fold increase in gain over HST’s 

Wide Field Camera 3 with Gpxl Infrared sensors. A 

4-Mpxl Hawaii-2RG, SIDECAR ASIC, and 16-Mpxl 2 

x 2 MOSAIC on the NIRCAM will fly on JWST. These 

developments can lead to a direct path for space 

qualification of the 1-Gpxl detectors. This telescope 

would be an excellent survey telescope for JWST and 8- 

to 30-meter class ground-based telescopes.

Concerns for the ISS-based telescopes include 

vibration isolation, EMI, contamination, and field-of-view 

zone constraints.

The advantages of ISS telescopes include: 1) final 

assembly, alignment, and verification on-orbit in zerogravity, 2) allows launches in robust modules, 3) location 

allows for rapid response for maintenance and repair, 

4) allows for regular opportunities for refurbishment 

and augmentation, and 5) attractive baselines for 

interferometry. The benefits to ISS from these telescopes 

include providing a high-profile science program, 

helping to develop robotic assembly and servicing, and 

providing ISS with excellent educational and public 

outreach opportunities as well as recognition.

Max Vozoff, Director, Civil Business Development, 

SpaceX. “Dragon as an In-Orbit Servicing Platform.” 

SpaceX has offices, manufacturing, and production 

facilities in Hawthorne, CA (near Los Angeles) as well as 

a Propulsion and Structural Test Facility in central Texas. 

SpaceX vehicles include the Falcon 1, Falcon 9, and 

Dragon spacecraft.

Falcon 9’s inaugural flight is currently scheduled 

for April 2010 from Cape Canaveral. Falcon 9 is a 

two-stage Evolved Expendable Launch Vehicle (EELV)-

class vehicle designed to meet NASA man-rated safety 

margins and failure tolerances. The Falcon 9 has a 5.2 

m fairing and is capable of carrying 10,500 kg to LEO. 

Ground tests of the Falcon 9 have been completed all 

the way up to release.

The Dragon spacecraft has 3 main sections: 1) the 

nose cone, which is jettisoned after stage separation, 2) 

Keynote Speaker: Dr. John Grunsfeld, Deputy 

Director, Space Telescope Science Institute. “Hubble 

SM4: Space Servicing in Action.”

Dr. Marc Postman, Astronomer, Space Telescope 

Science Institute. “The Science Rationale for Servicing 

and Considerations for Existing and Future Spacebased Astronomical Observatories.” 

On-orbit servicing provides three key functions 

that directly extend or magnify the scientific impact of 

space observatories: 1) restoration of operation by the 

repair of failed components, 2) extension of lifetime by 

the replacement of expendables or life-limited items, 

and 3) expansion of capability by upgrading to newer 

technology.

The benefits of upgraded instrumentation include 

the ability to undertake investigations that were not 

even conceived of when the observatory was launched. 

For example, the study of environments around other 

planets as was done by STIS but had not yet been 

conceived at the launch of HST. Fifth-generation HST 

science instruments have been conceived that could 

give huge increases in scientific output using gigapixel 

CCDs. In theory, launching a series of telescopes with 

updated instruments would have the same effect; 

however, this does not happen. Astronomy is fortunate 

to have one observatory launched per decade, so 

keeping a flagship observatory operational for 20–25 

years is important.

The benefits of lifetime extension by the 

replacement of expendables could be shown on the 

James Webb Space Telescope (JWST). Since JWST 

requires fuel for station-keeping, having the ability to 

refuel JWST could allow it to operate well beyond its 

nominal 10-year lifetime.

In addition, the benefits of on-orbit repair to restore 

operation could be shown on JWST with a repair of 

micro-meteor damage to the sunshield.

Telescopes this large would likely need to be 

assembled in space and would utilize active optical 

systems of segmented apertures, as well as a modular 

serviceable architecture for replacing expendables. 

Existing human spaceflight infrastructure can be used 

as a test bed to develop and advance the technological 

readiness level of human-guided robotic servicing in 

space, including autonomous rendezvous and capture, 

the installation of new avionics and science instruments, 

and life-extension upgrades. Such a pathfinder could 

employ existing, actuated, ultra-lightweight primary 

mirror technology that could be fabricated four times 

faster than conventional glass mirrors.

Dr. Donald Hall, Astronomer, Institute for Astronomy, 

University of Hawaii. “Hubble Legacy Telescopes for the 

International Space Station.” 
110 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

EVAs would be executed via an ISS or shuttle airlock 

using HST-type EVA tools.

SEL2 HSM manifests require 11–160 ton launch 

capability, depending on the whether a depot is used 

and whether an aerobrake return or direct entry return 

is utilized. Having a LEO propellant depot reduces the 

SEL2 HSM Heavy Launch Vehicle requirement from 

70–160 tons to 25–60 tons.

Mike Gold, Director, D.C. Operations and Business 

Growth, Bigelow Aerospace, ”Expanding the Final 

Frontier: Commercial Missions to the ISS and Beyond.” 

The purpose is to create and deploy expandable 

space habitats that expand after launch to their full 

volume. Bigelow says that the habitats offer better 

protection against micrometeor impact than standard 

aluminum structures.

The expandable space habitat has been validated 

on the Genesis 1 and 2 missions. Genesis 2 launched 

in June 2007 on a Russian nuclear missile. Due to the 

success of the Genesis 1 and 2 demonstration flights, 

subsequent test launches were cancelled.

Bigelow is now ready to launch Sundancer, which 

is their first human-rated habitat. A node bus and/or a 

second Sundancer could also be launched to provide a 

Full Standard Module. Bigelow is considering launching 

on either Atlas V or the SpaceX Dragon.

Additional future missions include concepts for 

launches beyond LEO, including L1, L2, or a Moon base.

Dr. Harley Thronson, Associate Director for Advanced 

Concepts in Astrophysics, NASA’s Goddard Space Flight 

Center. “Human Servicing Operations Beyond LEO: 

‘Gateways’ and Precursor Concepts.” 

Two concepts for human servicing beyond LEO have 

been assessed: 1) using elements of Constellation (or 

equivalent) with the goal of achieving the earliest, leastexpensive human servicing missions beyond LEO, and 2) 

a Gateway human operations facility that would build on 

ISS experience to demonstrate the capabilities for longduration human spaceflight and to manage/assemble/

upgrade major on-orbit facilities.

Proposed capabilities offer opportunities for satellite 

servicing throughout the Earth-Moon system by creating 

a servicing “jobsite” at the Earth-Moon libration points. 

The concept of operation is to use a pair of Ares I/EELV 

vehicles to carry astronauts to Earth-Moon L1/L2 jobsites 

within 10 years. The Orion crew exploration vehicle 

would be launched by Ares 1/EELV to LEO. The servicing 

node, including the airlock, robot arm, and storage, and 

a Centaur Earth-to-L1/2 transfer vehicle would launch on 

a second Ares 1/EELV to rendezvous in LEO with Orion. 

The telescopes would then be serviced at the EarthMoon L1/2 location.

The “Gateway” architecture goals including 

understanding how to live in space long-term, continue 

the capsule, which contains the pressurized cargo, crew 

compartment, hatches, thrusters, propellant, parachutes 

and heat shield, and 3) the trunk, which contains 

unpressurized cargo and small deployable satellites. 

The trunk is jettisoned before reentry. Dragon has a total 

payload capacity of 6,000 kg to LEO with a capsule 

down-mass capability of 2,500 kg.

SpaceX has contracts to supply 12 cargo missions 

to ISS between 2010–2015, with a minimum of 20,000 

kg delivered. SpaceX also has plans for a free-flying 

recoverable platform for microgravity research and 

technology demonstration, which will provide regular, 

frequent, commercial access to space. The first 

DragonLab flight is planned for 2011.

The ISS cargo accommodations support power, 

data, and thermal services inside and outside the 

pressurized section.

Dragon can also be used as a generic spacecraft 

bus with the following features:

- 15 m3

 pressurized volume for crew or 

pressurized cargo

- >2,000 W (>4,000 W peak) power for payloads

- Active thermal control for payloads

- Payload mass capacity up to >6,000 kg at 

200 km, >2,400 kg at 600 km, or >1,000 kg 

at 2,000 km

Dragon performs most functions required as an on-orbit 

robotic servicing platform, including proximity sensing, 

relative & absolute navigation; guidance, navigation and 

control; 2-fault tolerance to catastrophic hazards; free 

drift mode; autonomous & remote control modes; and a 

recoverable capsule that can return instruments or tools 

and servicing hardware as well as crew members.

Dragon can accommodate 5–7 crewmember 

configurations for ISS crew transportation. Three-seat 

configurations with pressure suits and EVA equipment 

can also be accommodated. Dragon has no airlock, so 

EVAs would require consumables to replenish the cabin 

air. Servicing tools and instruments can be housed in the 

trunk, with a limited ability to return old equipment in the 

cabin since the trunk is not recoverable.

Dragon has the ability to interface with the Low 

Impact Docking System (LIDS) interface for an HST 

deorbit or servicing mission, and SpaceX has developed 

a straw-man plan for providing robotic servicing to HST.

Dallas Bienhoff, Manager, In-Space and Surface 

Systems, The Boeing Company. “Human Servicing 

Mission: Sun-Earth L2 Telescope.” 

Boeing is developing a Sun-Earth L2 (SEL2) Human 

Servicing Mission (HSM). The Boeing plan uses a crew 

of six (four EVA, one pilot, and one commander) with a 

mission duration of 42–94 days. The crew would launch 

in either the Boeing Crew Vehicle or the SpaceX Dragon 

and would use a Bigelow Sundancer habitation module. 
 Appendix C – Workshop Summary | 111

Manned and unmanned servicing applications 

include routine maintenance to replenish consumables 

and replace/upgrade components, remote servicing 

for unplanned problems, orbit adjustment, and 

spacecraft reconfiguration. Some tasks are considered 

beyond the capability of existing space manipulators; 

however, SNC’s configurations have been developed to 

specifically address some of the current limitations.

Trajectory planning and control requires inverse 

kinematics to calculate the joint angles and motion to 

create the desired tool state. Typical manipulators are 

characterized by multiple copies of offset joints requiring 

extensive calculations and resulting in multiple answers. 

Multiple offsets make it difficult to vary operations 

quickly to handle contingencies. The SNC manipulator 

minimizes the offsets, resulting in inverse kinematics that 

are simpler with single solutions. 

For general use, a 6 Degrees of Freedom (DOF) 

minimum is required for full tool control, while one or 

more additional DOF improves workspace coverage 

and ease of use. Typical manipulators use a 7th DOF 

to control the shoulder-elbow-wrist plane to help avoid 

collisions. SNC’s manipulator includes an 8th DOF by 

utilizing 4 DOF in the shoulder-to-wrist and 4 DOF in the 

wrist-to-tool. The additional DOF in each group allows 

for robust avoidance of collisions, and it also allows the 

inverse calculations to be separated into two 4th order 

problems that are easier than a single 6th or 7th order 

problem.

SNC’s wrist configuration is characterized by a short 

wrist-to-tool distance for better dynamic response and 

less arm movement to accommodate tool movement. 

The short wrist-to-tool distance, combined with the 

skew Roll-Pitch-Yaw-Roll (sRPYR) configuration, 

improves the angular range over conventional wrists. In 

addition, only one sRPYR singularity is possible, so that 

singularity is easily avoidable due to the redundant wrist 

DOF.

Traditional controls utilize two stick control inputs 

and rate control, which make it difficult to stop at a 

desired location and require speeds that must be 

limited for safety. In this case, motion is generally limited 

to one axis at a time. The SNC control configuration 

has 6 DOF in one hand controller for a more natural 

motion. In this case, one operator can operate two 

arms simultaneously, and speed does not need to be 

artificially limited.

For future capability, SNC is developing the Dream 

Chaser human spacecraft under NASA Commercial 

Crew Development (CCDev) funding. The deployment of 

the SNC dexterous manipulator on Dream Chaser could 

provide a capable commercial servicing capability using 

a highly maneuverable space vehicle, human presence 

for real time operation, and an operational system with 

a rapid response time. In this case, servicing could be 

international cooperation, have human exploration on 

the lunar surface, prepare for long-term human voyages 

beyond the Earth-Moon system, and continue the 

on-orbit upgrade and maintenance of complex science 

facilities. The Gateway design uses an inflatable habitat 

launched by a heavy-lift vehicle to Earth-Moon L1/2.

Sam Scimemi, Deputy, International Space Station, 

NASA Headquarters within the Space Operations 

Mission Directorate. “International Space Station 

Assembly Lessons Learned.” 

ISS assembly has evolved over the years, 

requiring more complex external assembly and orders 

of magnitude more EVAs than originally planned. 

In addition, dependence on a single launch vehicle 

significantly set the program back.

From the top level, if another similar complex 

mission were undertaken, we should limit the number 

of assembly missions to less than 10 and require EVAs 

only when absolutely necessary by using more robotic 

and Intra-Vehicular Activy (IVA) assembly. For ISS, the 

investments in EVA over the years made EVA assembly 

tasks the preferred mode of operation, but the ISS 

required nearly 1,000 EVA hours. While most external 

maintenance tasks were designed to be robotically 

compatible, this has not been utilized. SPDM (aka 

Dextre) has been installed on-orbit for two years but still 

has not been used, although a demonstration is planned 

soon using ground controls.

Lessons learned from ISS assembly include:

- Human operations are very compatible with 

robotic operations, as demonstrated by many 

simultaneous EVA and robotic assembly 

operations.

- Robotic operations can be accomplished 

remotely without on-board crew intervention.

- Systems and component designs should be 

accessible and maintained on-orbit, even for 

systems that “do not require” servicing when 

originally conceived.

- System design should be paralleled by 

maintenance and servicing design activities.

Scott Christiansen, Engineering Director, Sierra 

Nevada Corporation—Space Systems. “SNC Advanced 

Manipulator Technology for Spacecraft Servicing.” 

SNC Space Systems Group is a merge of several 

small spacecraft technology companies, such as 

SpaceDev, Inc. and MicroSat Systems, Inc., which 

design, build and test the structures and systems 

that make things move, including motors, hinges, 

and latches. SNC provided several subsystems and 

design support for critical functions on Orbital Express, 

including the launch adapter fitting and capture system. 

Orbital Express showed successful robotic manipulator 

assisted and unassisted autonomous capture.
112 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

- The initiation of Dextre operations was delayed 

because the hardware was ready to fly before 

the procedures were completed.

Question 6: 

For Donald Hall (Institute for Astronomy, University 

of Hawaii): Can the Zero Signal/Noise detectors be 

ready to fly in 24 months? (Question posed by Frank 

Cepollina.)

- Twenty-four months is too soon for Zero 

S/N flight detectors because they need to 

complete more lab tests first. The lab results are 

continuing to improve.

- Once the detectors are shown to be 

reproducible in the lab, it will be easy to bring 

them up to a TRL 6 and beyond.

Question 7: 

For Mike Gold (Bigelow): How can you connect habitats, 

and what vehicle would you use?

- The habitats could launch on Atlas V or a 

Dragon and would be connected on-orbit.

- The Sundancer could be connected to a 

Node Bus (BA 330) on-orbit, and these two 

components would give a habitable environment 

volume greater than the ISS.

Question 8: 

For Mike Gold (Bigelow): How would Sundancer and the 

Node Bus be grappled and docked on-orbit?

- Sundancer docking has been designed to be 

independent; however, it will be tested on orbit 

and then manned prior to docking a Node Bus 

so that humans will be there to assist in the 

grapple and docking as needed.

- Bigelow does not use the LIDS system because 

it was deemed too heavy and too complicated 

for their system.

Question 9: 

For John Grunsfeld (STScI): What percentage of the 

SM4 hardware installation could have been done solely 

by a robot?

- The SM4 mission was not designed for robotics; 

however, we did show great capability for that 

during the HST Robotic Servicing and Deorbit 

Mission (HRSDM).

- For SM4, WFPC2/WFC3 and COSTAR/COS 

could have been done robotically. The batteries 

would need to be installed externally and the 

gyros would need to be installed on WFC3 for 

robotic installation, as was the plan for HRSDM.

Question 10: 

For John Grunsfeld (STScI): What difference would it 

have made to have two robotic arms instead of one?

accomplished by the crew during an EVA, during a 

robotically assisted EVA, or as a fully robotic task.

Question and Answer Session with all of the 

“Servicing with Humans” Session Speakers:

Question 1: 

For Max Vozoff (SpaceX) and/or Dallas Bienhoff (Boeing): 

Can EVAs be conducted from vehicles by a nonreturnable airlock in the trunk? 

- SpaceX has looked at including an airlock 

or inflatable (for tourism, etc.) on the nose of 

Dragon 

- Boeing says this is a viable option that could be 

used on the Genesis 1 or 2 architecture.

Question 2: 

For John Grunsfeld (STScI): Have detailed analyses 

been conducted on the returned HST Servicing Mission 

4 (SM4) hardware to determine the cause of the 

anomalies; i.e., was micro-welding an issue?

- Yes, all the returned parts have been studied 

carefully, including a study of the micrometeor 

hits on the WFPC2.

- It is believed that no micro-welding occurred 

because our parts are coated with Braycote. 

More likely, the issues were caused by 

installation differences in tools, thermal cycling 

while on orbit, and tolerance buildups.

Question 3: 

For Max Vozoff (SpaceX): What is the capacity of Dragon 

for payload return to Earth?

- Dragon can return approximately 2,500 kg.

Question 4:

For Donald Hall (Institute for Astronomy, University of 

Hawaii): How can stability be obtained for an ISS-based 

telescope?

- Imaging for both visible and IR science can be 

controlled by active wavefront control.

- These active wavefront controls would be used 

on ISS as a test bed platform for future freeflying telescopes.

- Currently have some Japanese science active 

on ISS, so stability is being controlled.

- Bigelow says their science focus in microgravity 

is looking at a soft dock between the crew cabin 

and the cargo so it would be close to a free 

flyer.

Question 5:

For Sam Scimemi (NASA Headquarters): Why was there 

such a long delay between the launch of Dextre and its 

first use? What task will Dextre do?
 Appendix C – Workshop Summary | 113

of time to restart design and production. Launch 

vehicles will likely be available to launch humans 

by mid-decade, however, spacesuits will not be 

available to support EVA activities. 

Robotic Servicing Technology

Session Chair: Jill McGuire

Robotic Technology Manager, Space Servicing 

Capabilities Project, NASA’s Goddard Space Flight 

Center

Keynote Speaker: Dr. Glen Henshaw, Roboticist, 

U.S. Naval Research Laboratory. “Orbital Robotic 

Servicing.”

Dr. Henshaw highlighted the differences in servicing 

needs and priorities among commercial, government, 

and NASA spacecrafts. He noted that the basic 

technologies necessary for servicing already exist, and 

the task remains to develop systems that address viable 

business models. It is also necessary to gain “mind 

share” with decision makers and improve technologies 

in order to strengthen the case for robotic servicing. 

Don McMonagle, Vice President of NASA Programs, 

Raytheon Missile Systems. “Raytheon SARCOS Robotic 

Systems: Technology for Application to Satellite OnOrbit Servicing.”

Robotic dexterity and virtual presence are improving 

through the use of sensors, servos, actuators, 

cameras, and communications. Raytheon has several 

teleoperated robots: Dextrous Arm, GRLA, and TOPS 

(teleoperated hand), all of which utilize the master 

and slave relationship and have 10 to 22 degrees of 

freedom. Artificial intelligence research has produced 

robots capable of balancing, juggling, playing air hockey, 

and walking. In all of Raytheon SARCOS’s robotic 

systems, a few technologies are key: servo valves, 

actuators, control and sensor networks, and MEMS 

sensor networks. Several dextrous hand models have 

been developed, including the UTAH/MIT Dextrous 

Hand (UMDH), which has 16 DOF. SARCOS employs a 

behavior-based design approach that defines desired 

objectives and employs quantitative performance 

criteria. Their control approach uses seven levels of 

control that are subdivided into three categories: variable 

control (command production, variable autonomic), 

intrinsic control (fixed autonomic, servo control, passive 

intrinsic properties), and power systems (actuation 

systems, energy storage systems). Raytheon SARCOS 

has developed force-reflecting teleoperated robots 

capable of performing a myriad of tasks in addition 

to producing humanoid systems with 43 DOF and 

a robotic exoskeleton. McMonagle concluded his 

presentation by saying that robotics technology enables 

operations in environments that are inhospitable to 

- It would be more convenient and efficient to 

have two arms working together, especially to 

have the cooperation of a human and a highprecision robot working together.

Question 11: 

For John Grunsfeld (STScI): What criteria should be 

used to decide between human and robotic servicing?

- Robots should be sent to places that a human 

cannot go, such as Jupiter (due to the radiation 

environment).

- For other places where humans could go, such 

as Saturn’s moons, humans and robots should 

work in concert. He recommends growing 

from HST and undersea experience to build on 

robotic technology.

Question 12: 

For John Grunsfeld (STScI): Should EVAs be minimized?

- He loves “magical” EVA time; however, it is 

very risky and not to be undertaken lightly. To 

that end, critical subsystems needing frequent 

servicing should be designed for access from 

inside the vehicle, so that they do not require 

repeated EVAs.

- EVAs should focus on tasks that cannot be 

done from inside a vehicle, such as exploring 

Mars, or for situations requiring quick “thinking 

on your feet.”

Question 13: 

For Sam Scimemi (NASA Headquarters): Does the ISS 

have any long-term lifetime worries?

- Structural analyses support a lifespan to 2028. 

The ISS was designed to be fully serviceable 

and replaceable—even the Solar Arrays or the 

Control Moment Gyroscopes.

Question 14: 

For Max Vozoff (SpaceX): Can Dragon support a fourperson crew? How many two-person EVAs could be 

accommodated?

- Dragon can support five- and seven-person 

crews, although seven crewmembers make the 

space extremely close and is only intended for 

limited-duration flights to the ISS.

- In addition, since Dragon has no air lock, EVAs 

would require venting the entire capsule and 

would require a way to store EVA suits and 

consumables.

- John Grunsfeld added that spacesuits are not 

currently available for many future EVAs, since 

only 11 suits exist, and most of them are on 

the ISS.

- The development of new spacesuits was 

stopped, and it would take a significant amount 
114 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

primitives. Such operations generally require maintaining 

modest contact forces and torques in some number 

of dimensions while “sliding” in the remaining free 

dimensions until some termination condition is met. 

Wilcox concluded his presentation with several key 

elements of a workable satellite servicing system: the 

ability to associate objects in the worksite with their 

associated computer representation, and verification 

back to the operator that correct identification and 

localization has been achieved; the ability of a human 

operator to indicate key physical elements; the ability 

of a remote-site robot to manage forces and torques 

at a reasonable bandwidth and to execute “slideuntil” commands to change the number of DOF of a 

worksite to accomplish assembly, disassembly, repair, or 

maintenance tasks. All of these abilities assume that the 

time-delay to a human operator is a few seconds.

Dr. Robert Ambrose, Chief, Software, Robotics and 

Simulation Division, NASA Johnson Space Center. 

“Dexterous Robotics and the Robonaut Series.”

Robonaut 1 was developed from 1998 through 

2006. Robonaut 2 has been in development from 2007 

to the present. It was publicly released in February 2010 

and is undergoing various forms of testing.

Daniel Rey, Head, Exploration Systems, Canadian 

Space Agency. “CSA Activities in On-Orbit Robotic 

Servicing.”

CSA has delivered three state-of-the-art robotic 

systems for operational use in LEO: the Shuttle 

Canadarm, the ISS Canadarm 2, and the ISS Dextre. 

The Mobile Servicing System (MSS), completed in 2008, 

now has the following capabilities: assembly, inspection, 

payload handling, capture and berthing, cooperative 

servicing (EVA support), and robotic servicing through 

the changeout of Orbital Replacement Units (ORUs). 

The MSS is also self-serviceable on-orbit, with six 

types of robotically friendly ORUs. The accuracy and 

abilities of CSA’s manipulators continue to improve, 

with Canadarm 2 and Dextre both having a sense of 

touch and being capable of automatic accommodation 

of forces and moments during contact tasks. Dextre 

and MSS are capable of performing several additional 

tasks that were envisioned for them in the 1980s, with 

some other tasks only needing an additional tool to 

complete. CSA has several studies regarding on-orbit 

robotic servicing, and finds that “On-Orbit Robotic 

Servicing is an enabling technology that can benefit 

from further TRL advancements and cost reductions.” 

In the future, TriDAR can be used to guide rendezvous 

and docking operations, which are essential to on-orbit 

servicing missions. Dextre’s operations will advance the 

knowledge of on-orbit robotic servicing, and several 

tools will help increase Dextre’s capabilities. The Next 

Generation Canadarm is in development, and will further 

humans and where the tasks are either unknown or ill 

defined.

John Lymer, Chief Engineer, Robotics, MDA 

Corporation. “Robotic Solutions for On-Orbit Servicing.”

MDA’s previous work with robotics provides a 

foundation for the design and execution of future 

servicing missions. Eighty-six shuttle missions have 

employed robotic operations, and there have been 9 

years of ISS robotic assembly and support operations. 

These operations have provided experience in 

operations planning and workarounds, man and 

machine coordination, robotic control from the ground 

(including signal delay and safety), robotic performance 

in zero-gravity, and supportable on-orbit robotic 

equipment. The capabilities for autonomous servicing 

of prepared clients were demonstrated in 2007 with 

the DARPA Orbital Express mission. MDA is also able 

to service clients designed to non-robotic standards, 

as demonstrated by GSFC and MDA’s dexterous 

robotics work with the HST high-fidelity mockup in 

2004–2005. During this work, tools were developed for 

non-traditional robotic tasks, and supervised autonomy 

accommodated up to 7 seconds of command path 

latency. This showed that robotic servicing can be 

applied to a client that is designed to any standard, 

and therefore planned robotic compatibility can be 

non-invasive to a client. The Dextre robot on the 

ISS would provide a perfect test bed for groundcontrolled, dexterous servicing demonstrations. CSA 

funded development to advance Next Generation 

Missions, which will aid exploration missions beyond 

GEO and help optimize mass, cost, and operations. 

Lymer concluded his presentation by saying, “Robotic 

technologies are sufficiently mature for GEO satellite 

servicing.” A cost-effective servicing mission could 

validate the operating principles and value of a 

serviceable space infrastructure. To that end, MDA is 

designing a servicer that can add 50 years of life to 9 

to 11 existing GEO satellites through the resupply of 

propellants, by towing clients to graveyard orbit, or by 

adjusting orbit.

Brian Wilcox, Principal Investigator, NASA Jet 

Propulsion Laboratory. “Lessons Learned at JPL about 

Servicing.”

The Telerobot Project was initiated and funded 

by Ron Larson, Mel Montemerlo, and Dave Lavery 

of NASA Headquarters from 1984 to 1992. It sought 

to develop and demonstrate needed technology for 

satellite servicing and attempted the integration of 

force-reflecting teleoperation with autonomous robotics, 

shared and traded control, predictive displays, and 

more. Wilcox notes that every task can arguably be 

decomposed into a sequence of operations that 

each reduce the number of DOF by one—mechanical 
 Appendix C – Workshop Summary | 115

than 2 meters with objects tumbling up to 1 deg/sec 

about any axis. Robotic hardware and control algorithms 

were developed to autonomously grapple a variety of 

hard points. A fully autonomous grapple was a program 

requirement in the event that tumbling debris may 

prevent ground communications. Several algorithms 

were developed for autonomous capture, including a 

mission sequencer, grapple feature tracking, a trajectory 

planner, and compliance control. 

Todd Colangelo, East Coast Operations Manager, 

Oceaneering Space Systems. “Oceaneering Robotics: 

Parallels to Satellite Servicing.”

Oceaneering International, Inc. is an industry 

leader in enabling humans to perform work safely 

and effectively in harsh environments ranging 

from the depths of the sea to the outer reaches of 

space. Oceaneering is very experienced in subsea 

teleoperation, as they have 248 Remotely Operated

Vehicles (ROV) in use, with an average of over 5,700 

days of ROV operations every month. Oceaneering 

also has virtual simulation capabilities that they use to 

support training, uncover design issues and risks before 

operation, and overlay the work environment in real time 

to eliminate lag issues. They have also developed and 

flown tools for capturing and servicing satellites, and 

have been developing EVA tools since 1978, delivering 

and providing sustaining engineering for 3,659 EVA 

flight tools since 2005. With Oceaneering’s subsea 

operations, they have developed work packages for 

use with similar tasks or in similar work areas, as well as 

standardized tools and interfaces for robotic servicing. 

Oceaneering’s evolution of subsea robotic servicing was 

driven by cost and safety needs, and they are now able 

to work on a variety of packages and tasks at depths 

of up to 20,000 feet. They have created several work 

packages, which are predefined sets of tools packaged 

together for ease of operation on a set of like tasks. 

Their package tasks include fluid storage and injection; 

assembly; testing; power and communication; tool 

storage; and salvaging. Oceaneering’s subsea robotic 

tasks include inspections; removing and replacing 

electronics; assembling electrical, mechanical and fluid 

connections; valve operations, troubleshooting and 

monitoring; leak detection, sealing and fluid insertion; in 

situ testing and commissioning; jacket removal, jumper/

flow line cuts and installation; decommissioning and 

debris removal; and salvaging. Oceaneering’s subsea 

operations are similar to robotic on-orbit servicing in 

mission scenario planning, simulation software, training 

and human factors, situational awareness, and controls 

with time lag and human factors. With current satellites 

having been built before servicing standardization, a 

humanoid robot is the answer to servicing existing 

satellites now. Satellites on-orbit were originally built by 

humans, and human-like scale and dexterity allows the 

increase the functions of on-orbit robotic servicing. CSA 

sees a future of servicing other scientific satellites, such 

as JWST, SAFIR, MUST, ATLAST, and TPF. Some of 

the same technologies developed for on-orbit robotic 

servicing have been and will continue to be used for onorbit servicing and exploration. 

Dr. Dave Akin, Director, Space Systems Laboratory, 

University of Maryland. “Robotic and EVA/Robotic 

Servicing: Past Experience, Future Promise.”

The Space Systems Lab has a background in 

space robotics that includes structural assembly, 

formation flying, orbital maneuvering vehicle operations, 

walking robots, a crane-type positioning robot, and 

multiple cooperating robots. Current robotics projects 

include Autonomous Deep Submergence Manipulators, 

Free-Flying Inspection and Light Transport Robots, 

Lightweight Modular Self-Reconfiguring Robots, 

advanced dexterous robotics, and complex satellite 

servicing. Human systems projects regarding insuit metabolic workload, the Maryland Advanced 

Research/ Simulation (MARS) Suit MX-2, ballasted 

partial gravity simulation, advanced life support systems, 

biomechanics instrumentation, and advanced spacesuit 

gloves are currently underway. Human/Robot Interaction 

Projects include morphing spacesuit components, EVA/

Robot cooperative space operations, an exoskeleton 

shoulder rehabilitation robot, power-assisted spacesuit 

components, and suit-integrated manipulators. The 

Space Systems Lab is working on several design 

activities, including advanced human/robot systems, 

transportation and landing systems, orbital habitats, 

robotic HST servicing, full-scale mockups for human 

testing, lunar and Mars rovers, and planetary surface 

habitats.

Bill Vincent, Aerospace Engineer, U.S. Naval Research 

Laboratory. “Front-End Robotic Enabling Near-term 

Demonstration (FREND) Technologies and Associated 

Servicing Architecture.” 

FREND stands for Front-end Robotics Enabling 

Near-term Demonstration. The DARPA program helped 

to develop and demonstrate a flight robotic arm with 

associated end-effectors and algorithms that can 

perform autonomous, unaided grappling. FREND 

focuses on “space tow truck” operations at GEO (life 

extension, disposal, slot changes, etc.). Three key 

FREND technologies apply to on-orbit robotic servicing: 

in situ characterization, holding relative pose at close 

range, and autonomous robotic capture. No prior 

knowledge of the customer is required, and no standard 

targets or interfaces are required on the customer. 

Techniques to perform in situ characterization of 

customer satellites are necessary to generate a detailed 

approach and grapple plan. Techniques from FREND 

allow for actively holding a relative pose at ranges of less 
116 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

his presentation by reiterating Honeybee’s development 

of technology and products for advanced robotic and 

spacecraft systems, its long history in on-orbit servicing, 

and its new technologies in development for servicing. 

Doyle Towles, Systems and Advanced Technologies 

Manager, ATK Space Systems. “Improved Robotic 

Enablers for Satellite Servicing.”

Doyle Towles of ATK Space Systems discussed 

the various technologies they are helping to develop to 

enable robotic satellite servicing. He noted that improved 

robotic tools provide the capability to perform unique 

and complex tasks. ATK has experience developing 

tools in conjunction with Goddard for manned missions 

such as the HST servicing missions and ISS crew 

operations. These tools allowed astronauts to perform 

complex tasks not originally designed for servicing. 

They have also worked on several robotic tools for the 

Hubble robotic servicing and deorbit mission and the 

ISS Detailed Text Objective (DTO) for refueling. ATK 

is developing tools for use in future robotic missions, 

including a spacecraft capture and docking mechanism; 

lubrication and harness management; thermal blanket 

repair or replacement; improved electronics box level 

replacement and card changeout; and small or stuck 

fastener removal, retention and replacement. They are 

working on smart end-effectors (designed for vision, 

proximity assessment, and tool interfaces), to more 

efficiently perform capture and servicing activities. Mr. 

Towles noted that autonomous rendezvous and capture 

requires advanced sensors and on-board processing, 

and stated that technologies exist to perform simple, 

non-manipulative servicing missions today. Nearterm developments will facilitate the most challenging 

missions. ATK’s kinematic and dynamic simulations 

provide testing and training capabilities to prepare for 

on-orbit conditions. Their thermal control of robotic 

servicing satellites provides improved environmental 

conditions for robotic systems, while their composite 

material technologies provide lightweight, smart 

structures. Mr. Towles concluded his presentation by 

saying that the foundations exist to develop applicable 

technologies for on-orbit robotic servicing, and previous 

technologies can be leveraged to help accomplish new 

tasks. In the near-term, ATK is working on a DTO for a 

refueling capability demonstration on ISS, and efforts are 

underway to develop specific enhancing technologies.

Professor Louis Whitcomb, Professor, Johns Hopkins 

University, “Enabling Technologies for Remote Robotic 

Manipulation with Time Delay.”

The Laboratory for Computational Sensing and 

Robotics (LCSR) was founded by the School of 

Engineering in 2007 as the center for robotics research 

at the Johns Hopkins University. They use the basic 

principles of engineering science to further their research 

use of heritage EVA tools, which saves tool development 

costs. Oceaneering has several lessons learned from 

past servicing missions in sea and space: design 

tasks for single arm operations, minimize fasteners 

and complexity of mechanism actuations, provide 

clear visual and physical access, minimize motion 

requirements, provide alignment guides and targets, 

provide adequate visual cues, maintain loose tolerances 

between parts, limit or minimize forces required to 

operate mechanisms, provide status indicators for all 

activated functions, provide clear identification of objects 

and directional cues, and provide operational margins 

with redundant capabilities. Mr. Colangelo concluded 

his presentation with the statement that deep-water 

robotic servicing is a mature industry that has evolved 

continuously over the past 30 years, and that robotic 

servicing in space, an industry in the earliest stages, 

would benefit from leveraging the lessons of the deep 

water industry. 

Kiel Davis, Vice President, Engineering, Honeybee 

Robotics Spacecraft Mechanisms Corporation. 

“Honeybee Robotics: An Overview of OOS Capabilities.”

Honeybee Robotics are the developers of 

technology and products for robotic systems with 

sensors, manipulators, end-effectors, and tools, as well 

as spacecraft mechanisms capable of deployment, 

positioning, and attitude control. Both their robotic 

systems and spacecraft mechanisms employ 

automation components like motors, transmissions, 

slip rings, EVA/EVR compatible couplings, connectors, 

and fasteners. Honeybee Robotics is a privately owned 

small business equipped with a clean room, machine 

shop, and test facilities, employing over 30 engineers, 

scientists, and inventors. Honeybee’s on-orbit servicing 

background lies in the robotic assembly of large truss 

structures and in helping with the development of 

the Flight Telerobotic Servicer. With NASA Goddard, 

Honeybee has developed the “Capaciflector” Sensor 

Array, HST Tool Box Gripper, and Conformal Gripper. 

Honeybee has also worked on technologies for the 

Orion Crew Exploration Vehicle, surface systems, and 

robots for in situ resource utilization, fabrication, and 

repair. Their 3-D Mini-LIDAR Vision Sensor allows close 

proximity hi-resolution and fast 3-D mapping. Honeybee 

has also developed robust connection mechanisms 

for electrical and fluid connections. These enable 

spacecraft berthing, docking, mooring, electrical and 

fluid power transfer, ORU transfer, and robotic tool 

quick-change. Honeybee is helping to develop Electron 

Beam Free-Form Fabrication, which can be used for 

in situ fabrication and repair. Mr. Davis also shared 

some additional technologies Honeybee is developing, 

including rapid structural assembly, attitude control and 

positioning mechanisms for small satellites, and a webcapture spacecraft docking system. Mr. Kiel concluded 
 Appendix C – Workshop Summary | 117

with cryogens, is needed to bring risk within acceptable 

levels for a large-scale mission. 

Therese Griebel, Space Flight Systems Manager, 

NASA Glenn Research Center. “Solar Electric Propulsion 

Application for Orbital Servicing.”

Ms. Griebel discussed the benefits of solar electric 

propulsion for applications to NASA and on-orbit 

satellite servicing, and noted that it is a technology 

that could be a quick return and would benefit NASA, 

commercial, and DoD customers. With respect to 

propulsion and power systems, Ms. Griebel stated that 

there are several technologies that are at good TRL 

levels and could be applied to a demonstration that 

would be applicable to multiple mission needs. She 

discussed DARPA’s Fast Access Spacecraft Testbed 

(FAST) and the NASA Evolutionary Xenon Thruster 

(NEXT) programs as examples of a power system and 

a propulsion system that could be used together as an 

electric propulsion stage that would quickly integrate 

emerging technologies into an operational spacecraft. 

Joe Cassady, Director, Business Development—

Emerging Space Systems, Aerojet. “Innovative In-Space 

Propulsion for Spacecraft Servicing.”

Mr. Cassady discussed Aerojet’s work with what 

they refer to as “high-efficiency in-space transportation”: 

using solar electric propulsion on the Flexible Path. He 

adamantly declared that electric propulsion is ready, 

and discussed Aerojet’s use of the technology on a 

large number of spacecraft and missions. He noted that 

such propulsion systems will cut the cost of logistics 

in half, and that the technologies need to do so are 

ready for demonstration. Mr. Cassady also discussed 

several areas that deserve investment to further advance 

innovative in-space propulsion.

Joseph Maly, Associate Principal Engineer, CSA 

Engineering, Inc./Moog. “ESPA as Base Vehicle for 

Servicing Missions.”

Mr. Maly discussed CSA’s EELV Secondary Payload 

Adapter (ESPA) ring and its applications as a structural 

building block for on-orbit servicing missions. ESPA is a 

secondary payload adapter that can facilitate numerous 

mission configurations, and is a natural base vehicle for 

servicing missions. He explained several of ESPA’s past 

and potential applications, and concluded by noting that 

the ESPA is a robust adapter structure with a flightproven heritage. 

Warren Frick, Program Manager, Orbital Science 

Corporation. “Satellite Servicing Using the Cygnus 

Advanced Maneuvering Vehicle.”

Mr. Frick discussed the Cygnus vehicle and how 

it can be used for satellite servicing. Cygnus is Orbital 

Science’s modular vehicle that they are designing to 

in design and control, sensing and interpretation, 

human-machine interaction, robotics in extreme 

environments, robotics in medicine, and bioengineering. 

Professor Whitcomb argues that telesurgery framework, 

such as that used with the da Vinci surgical system, 

could be leveraged for use in robotic servicing. He notes 

that virtual fixtures can be used as force and motion 

constraints, while allowing high-level human decisionmaking and low-level robotic accuracy and precision. He 

suggests creating a relationship between images and a 

3-D model for satellite servicing, surveying a spacecraft 

with a camera and extracting features from the images, 

relating the features to the geometry of the spacecraft 

manually, and finally storing each relationship in a 

database. During actual operations, one would obtain 

an image from the spacecraft, extract features, match 

the features to the database, and use robust regression 

to estimate the pose of the spacecraft.

Physics-based simulations can accurately model 

robot dynamics and interactions with the environment, 

while high-level planning and motion planning can 

compute collision-free and dynamically feasible motions 

that enable the robot to accomplish a high-level task. 

Whitcomb concluded his presentation by using the 

Nereus Underwater Vehicle as an example of successful 

remote teleoperation in extreme environments and by 

summarizing the key enabling technologies discussed in 

the presentation. 

Servicing Technology Session

Session Chair: Tupper Hyde

Associate Chief of the Mission Engineering and Systems 

Analysis Division, NASA’s Goddard Space Flight Center

The Servicing Technology session included 

presentations on various technologies with applications 

in satellite servicing. Innovative propulsion, sensing, 

and autonomous rendezvous and capture systems 

were discussed, and many have already flown or are 

ready to be demonstrated in orbit. Presentations also 

discussed test beds for developing technologies, 

and several companies’ experiences with aspects of 

satellite servicing that can be applied in future servicing 

missions. 

Dr. David Chato, Aerospace Engineer, NASA Glenn 

Research Center. “In-Orbit Fluid Transfer for Satellite 

Servicing.”

Dr. Chato discussed in-orbit propellant transfer as 

“game-changing” technology for satellite servicing. He 

noted that in-orbit transfer of hypergolic propellants 

has been demonstrated and is done routinely, and that 

with appropriate development, the in-orbit transfer of 

cryogenic propellants can be taken to the same level of 

technical maturity. He noted that an integrated largescale prototype demonstration, such as Orbital Express 
118 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

missions included an ISS capability verification flight, a 

robotic servicing demonstration, teleoperated support 

demonstrations, and flight testing with non-cooperative 

targets. 

Tom Gardner, Senior Principal Systems Engineer, 

NASA/Space Applications Group, Raytheon. “GN&C 

and Sensors for Rendezvous and Capture; Missile 

Systems Technology Applied to the On-Orbit Servicing 

Challenge.”

Mr. Gardner described Raytheon’s work with 

Guidance, Navigation and Control (GN&C) and sensors 

for rendezvous and capture, and how such technologies 

developed by a missile company through funding by 

the military and the DoD could be used for satellite 

servicing. Raytheon has developed several technologies 

for use with autonomous rendezvous and destruction 

of missiles, and such technologies could be easily 

adjusted to allow for docking instead. Mr. Gardner 

concluded his presentation by noting that there are a 

lot of technologies, especially in the areas of sensing 

and data fusion, that the DoD has spent a lot of money 

developing, and that many of those technologies are 

available and can be used for other applications. 

Dr. Roger Stettner, President, Advanced Scientific 

Concepts, Inc. “3D Flash LIDAR Cameras for OOS 

Applications.”

Dr. Stettner discussed the work that his company, 

ASC, is doing with 3-D flash LIDAR, and how it can 

be used for servicing. ASC’s DragonEye, which flew 

on STS-127, showed that their systems work for 

rendezvous and docking. 3-D flash LIDAR can also be 

used for navigation, detection, and inspection, as it is 

essentially a 3-dimensional video camera that generates 

precise distances and dimensions. ASC is continuously 

developing more advanced and smaller versions of their 

systems, and can often design systems much more 

cost-effectively and quickly than aerospace companies, 

as they are a small company themselves. ASC has 

several new developments that only need a customer 

and funding to progress.

Stéphane Ruel, Project Manager, Neptec. “TriDAR 

Model Based Tracking Vision System for On-Orbit 

Servicing.”

Mr. Ruel described TriDAR, a model-based tracking 

3-D vision system, and its numerous applications in 

space for determining the position and orientation of an 

object. TriDAR can be used for rendezvous and docking, 

robotic manipulation, navigation, or landing. It is very 

helpful in that it can identify unknown targets based on 

their geometry. TriDAR’s flexibility allows adaptability, 

and can help deal with unexpected situations that might 

arise on a servicing mission. TriDAR was demonstrated 

on STS-128 and met great success. 

service the space station. Cygnus is being built right 

now and has the fault tolerance needed to mate with the 

Space Station and be the reentry vehicle. It has been 

through its Phase II safety board, and while it has not yet 

reached maturity, it will have flight experience in 2011. 

Mr. Frick concluded his presentation by saying that the 

Cygnus is versatile and can utilize technologies such as 

the FREND and Robonaut systems for satellite servicing.

Dr. Javier De Luis, Vice President of R&D, Aurora 

Flight Sciences 

Ms. Swati Mohan, Graduate Research Assistant, 

Massachusetts Institute of Technology. “SPHERES as a 

Servicing Testbed.”

Dr. Javier De Luis and Dr. Swati Mohan discussed 

SPHERES as a science test bed for measuring and controlling physical phenomena whose behavior fundamentally changes when in microgravity. SPHERES creates 

a testing facility that is reconfigurable, risk tolerant, and 

allows the testing of low TRL technologies—in particular, 

guidance, navigation, and control algorithms—under 

microgravity conditions. SPHERES can advance satellite 

servicing technology in two ways: through algorithm 

development and through its expansion port, which 

allows the testing of satellite payloads. SPHERES helps 

test capabilities such as autonomous rendezvous and 

docking with a tumbling target and other technologies 

applicable to satellite servicing, with relatively low cost 

and a fast turnaround time. 

Ian T. Mitchell, Division Staff, Charles Stark Draper 

Laboratory. “Autonomous Rendezvous and Proximity 

Operations.”

Mr. Mitchell described Draper Laboratory’s 

experience with autonomous rendezvous and capture 

operations, stating that many satellite servicing and 

exploration missions rely on autonomous rendezvous 

as a critical capability. Draper Laboratory is building 

on past technologies and making advances in areas 

such as propulsion, advanced sensors, and increased 

on-board automation and auto nomy. Mr. Mitchell noted 

that systems engineering is key in the development of 

such rendezvous and capture systems, and Draper 

Lab’s expertise in that area could be helpful to many 

programs. 

Kevin Miller, Ball Aerospace and Technologies 

Corporation. “Advanced Imaging and Relative 

Navigation Technology for Satellite Servicing.”

Mr. Miller discussed Ball’s work with advanced 

imaging and relative navigation technologies as they 

apply to human and robotic servicing. He asserted that 

the critical technologies for satellite servicing are mature 

at the component level, and suggested that future 

systems in need of technology maturation would be 

well served by several demonstration missions. Such 
The term “on-orbit servicing” invokes a multitude of definitions depending on the customer, the provider and the application. To give structure and definition to what it means to perform on-orbit servicing, this appendix presents a systems-level decomposition of the functions and activities performed 

during satellite servicing operations. The result is a high-level framework of generalized functional 

elements. It provides a common starting point for customers to begin formulating mission-specific 

servicing operations and requirements, and to identify technology development needs.

SERVICING MISSION LIFE CYCLE

A servicing mission operational life cycle is established to identify the activities executed during the 

course of a servicing mission. Figure D.1 outlines the mission-level functions performed in a notional 

servicing mission. The numbers in 

the titles identify the sections in this 

appendix that provide additional 

details.

These mission-level activities are 

broken down into greater detail to 

identify the working elements that are 

required to complete the function. The 

end result is a listing of guidelines, premission considerations, and the basic 

activities that make up the servicing 

mission.

HOW TO USE THIS 

INFORMATION

The decomposition presented here 

provides the starting point for defining 

mission-specific requirements. 

Identifying the elements of a 

servicing mission is intended to lead 

to follow-on studies of enabling 

technology needs and mission-specific 

requirements development. The 

flowchart in Figure D.2 illustrates this 

example.

The activities are systemarchitecture independent to allow 

general use in any customer system. 

Because the definitions are architecture 

independent, the functions described 

do not distinguish between human 

or robotic servicing, as the functions 

Appendix D – Functional Decomposition of the Activities 

Required for Satellite Servicing

 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 119

2.8 DEMATE FROM

CUSTOMER SPACECRAFT

2.9 TRANSFER SERVICER

TO NEXT CUSTOMER

SPACECRAFT

2.10 LOITER IN PARKING

ORBIT

SERVICER 

REMAIN

WITH

CUSTOMER

SPACECRAFT?

SERVICE

ADDITIONAL

SPACECRAFT?

2.11 DISPOSAL

NO

YES CONTINUE MATED

OPERATIONS THROUGH

CUSTOMER SPACECRAFT

USEFUL LIFE

2.7.1 SERVICING – RELOCATION

2.7.2 SERVICING – MECHANICAL ASSIST

2.7.3 SERVICING – REPAIR/UPGRADE

2.7.4 SERVICING – RESOURCE REPLENISHMENT

2.7.5 SERVICING – ON-ORBIT ASSEMBLY

2.1 ACHIEVE CUSTOMER 

SATELLITE ORBIT

2.2 PERFORM SERVICER

ON-ORBIT CHECKOUT

2.3 TRANSFER TO PRERENDEZVOUS ORBIT

2.4 RENDEZVOUS WITH

CUSTOMER SPACECRAFT

2.5 PROXIMITY AND 

APPROACH OPERATIONS

2.6 GRAPPLE WITH

CUSTOMER SPACECRAFT

AND CONTROL STACK

YES

NO

Figure D.1: Mission-level functions for a notional servicing mission
120 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

defined need to be accomplished regardless of the presence of humans in space. Decomposing the 

functional elements of on-orbit servicing in this way provides a suitable means of evaluating possible 

system architectures, including human space flight elements, against the functions those systems will 

need to provide.

Technology assessments are a means of evaluating the functions of satellite servicing and 

determining the readiness level of technology to accomplish those functions. Given the wide range 

of functions defined under satellite servicing, it is expected that the level of technology readiness will 

vary. This functional decomposition provides guidance on where resources should be expended in 

order to perform the more complex functions of satellite servicing. The need for experimentation, 

study and technology development will tie to these assessments and aid the justification and business 

case for making those investments. Alternatively, technology assessments can be used to revise 

servicing requirements for specific missions to match technology readiness.

Requirements definition follows technology assessment and development. Servicing-specific 

performance requirements can be derived from the functional decomposition using the identified 

technologies to perform the servicing operations. The resulting requirements will naturally be 

different for providers of servicing functions and their customers.

Figure D.2: Flowchart of a notional servicing mission development cycle
FUNCTIONAL DECOMPOSITION OF SATELLITE SERVICING OPERATIONS

1. PRE-MISSION CONSIDERATIONS

This section is for generic pre-mission considerations that affect the functions performed during the 

interactions between servicer and customer spacecraft.

1.1 SERVICER SPACECRAFT BUS (Req

All servicing spacecraft will require a vehicle–the bus–to provide a support system to the servicing 

payloads that will be used to perform servicing on the customer spacecraft. The main function of the 

servicer spacecraft vehicle is to provide electrical power, commanding, data downlink, thermal control, 

and structural support for these servicing payloads.

1.1.1 Orbit

On-orbit servicing will be performed in the customer spacecraft orbit and all systems will need to be 

designed to function in this environment. Orbit classifications include:

• Low-Earth Orbit (LEO)

• Highly Elliptical Orbit (HEO)

• Geosynchronous Earth Orbit (GEO)

• Libration Point Orbits (Earth-Moon and Sun-Earth)

1.1.2 Mission ∆V Requirements

The bus propulsion system (type and size) will depend on the specific mission ∆V requirements.

1.1.3 Customer Spacecraft ORU and Replenishables Mass

Depending on the servicing mission, the bus may need to accommodate Orbit Replacement Units or 

replenishables (also known as consumables).

1.2 MISSION OPERATIONS

A mission operations plan is developed based on the servicing functions to be performed and may 

include the following:

• Communications

• Command Plan

• Timeline

• Sun-angle or shadowing constraints due to thermal and/or electrical power limits

• Safeing

• Servicer disposal at End-of-Life

1.3 MAINTAINING CUSTOMER AND SERVICER SPACECRAFT CONSTRAINTS

On-orbit servicing activities will need to take into account the operational constraints of both the 

servicer and customer spacecraft. Impacts and risks to violating the constraints of either spacecraft 

will need to be known prior to performing servicing operations. A preferred way of assessing and 

documenting these impacts and risks is through a mission impact analysis that is approved as part of a 

mission operations plan agreed upon by both the provider and customer of the servicing activity. The 

subsections below are some of the identified impact areas where system constraints shall be observed.

 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 121
122 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

1.3.1 Cause no degradation to both servicer and customer vehicle—e.g., hardware damage to 

solar arrays, radiator panels, other external spacecraft appendages.

1.3.2 Maintain power positive mode—customer vehicle attitude, servicer shadowing, customer 

vehicle op power configuration.

1.3.3 Maintain spacecraft components within operate and/or survival temperature limits—

allowable spacecraft attitudes or maneuver/task duration times defined based on transient 

analyses.

1.3.4 Maintain mechanical integrity of customer vehicle/servicer vehicle interface—limit 

servicer applied forces/torques on the customer vehicle to ensure the integrity of the interface.

1.3.5 Maintain contamination level requirement—define required servicer plume direction to 

maintain the contamination requirements of the customer vehicle.

1.3.6 Provide means to mitigate the effects of voltage differentials between customer vehicle and 

servicer.

1.3.7 Operations performed by the servicing spacecraft shall respect the customer spacecraft 

keep out zones and envelopes (planned and negotiated with customer).

1.4 PLANNING FOR AUTONOMY

Some functions of on-orbit servicing can or will be performed autonomously using systems on board 

the servicer spacecraft. Autonomous operations will require additional planning and resources in 

order to execute servicing activities in a safe, precise, and intended manner. The functions performed 

autonomously will need special verification applied prior to execution, and the verification levels 

may change depending on the hazards presented by the system architecture, the operation, and the 

environment. The subsections below are some of the identified activities and actions that will be 

impacted by performing autonomous operations.

1.4.1 Autonomous operations require a GN&C command interface to autonomy control systems 

in order to provide authority and control over the spacecraft. 

1.4.2 If autonomous operations are to be performed, systems will need to be capable of 

switching between operating modes from ground commands.

1.4.3 Autonomous tasks can be accomplished by ground-provided task lists of appropriate 

commands to the current operating mode. Ground authority-to-proceed (ATP) commanding can 

be built into these lists as checkpoints.

1.4.4 If ground-provided task lists are executed as part of autonomous operations, then systems 

will need the functionality to switch between task lists in order to modify the operational steps 

and/or sequence.
1.4.5 Autonomous operations will require the monitoring of performance and status to detect 

unsafe conditions and initiate pre-defined abort sequences. Some examples of items that would 

be monitored and responded to are: 1) sensor/end-effector health, 2) relative position and 

collision avoidance sensors/systems, 3) activation of spacecraft safe mode triggers, and 4) battery 

depth of discharge.

1.4.6 If autonomous operations are to be performed, systems will need to be capable of 

suspending operations if commanded to by the ground or other external source.

1.4.7 If autonomous operations are to be performed, systems will need to be capable of aborting 

operations if commanded by the ground or other external source, i.e., an override needs to be 

provided.

1.4.8 If autonomous operations are to be performed, the servicer spacecraft systems need to be 

capable of executing GN&C abort sequences based on current spacecraft state in response to 

automated or ground commanded abort commands.

2. PERFORM ON-ORBIT SERVICING

This section identifies the activities that together encompass the execution of an on-orbit servicing 

mission. The activities are described at a system-level and in some cases broken down to additional 

details and options that are encountered when planning for servicing.

2.1 ACHIEVE CUSTOMER SATELLITE ORBIT

The first step a servicing spacecraft must complete is to achieve the necessary orbit plane to position 

itself to interact with the customer spacecraft. The first orbital configuration will need to support 

setup, checkout, and commissioning of the servicing spacecraft before any servicing operations begin.

2.1.1 The initial orbital location of the servicer spacecraft shall be part of a mission-specific plan 

with planned inclination, ascension, eccentricity and semi-major axis.

2.2 PERFORM SERVICER ON-ORBIT CHECKOUT

A pre-determined checkout procedure for all systems involved in the servicing operations shall 

be performed prior to performing rendezvous with the customer spacecraft. Given the criticality 

of operations involved in on-orbit servicing (i.e. close proximity operations, fuel transfer, etc), 

confirmation of the functionality of these systems is required prior to interaction with customer 

spacecraft.

2.2.1 Servicing payloads such as robotic systems that rely on telemetry and control need to be 

verified to have positive telemetry and control using all planned operational interfaces prior to 

commencing servicing operations.

2.2.2 Autonomous rendezvous and capture (AR&C) payloads included on a servicer spacecraft 

should be confirmed operational via checkout with a resident space object (RSO) prior to 

commencing servicing operations.

 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 123
124 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

2.2.3 Payloads included on a servicer spacecraft should be verified to be within calibration prior 

to first operational use during servicing operations.

2.2.4 A servicer spacecraft should be equipped with systems capable of providing a visual 

inspection of the servicer spacecraft payloads associated with on-orbit servicing. This is to verify 

status and condition of the payloads prior to interaction with the customer spacecraft. This 

visual inspection can include robotic systems, autonomous rendezvous and capture sensors, 

telecommunication systems, and power systems. 

2.3 TRANSFER TO PRE-RENDEZVOUS ORBIT WITH FIRST CUSTOMER 

VEHICLE

After checkout, the servicer spacecraft performs orbital transitions to position itself to rendezvous 

with the customer spacecraft. This maneuver is designed to position servicer spacecraft within 

close proximity to customer spacecraft to begin the rendezvous phase. Pre-mission analysis shall be 

performed to confirm the design servicer spacecraft trajectory is free of orbital debris and satellites.

2.4 RENDEZVOUS WITH CUSTOMER SPACECRAFT

Rendezvous is the series of activities that are performed in order to 1) acquire and track (via sensors) 

the customer spacecraft to be serviced, and 2) close the relative distance between the servicer and 

customer spacecraft. Rendezvous occurs at relative positions approximately between 1 km and 300 

km apart. The goal of rendezvous operations is to approach the customer spacecraft as quickly, as 

efficiently, and as safely as possible in order to prepare for proximity operations. The following provide 

additional details on the activities that occur during rendezvous operations.

2.4.1 The customer spacecraft will be located (acquired) via long-range sensors (far-field 

acquisition). This applies to Earth orbiting servicing missions (Libration Point Orbit servicing 

missions are excluded).

2.4.2 Following acquisition, the servicer spacecraft closes its relative position with customer 

spacecraft through a series of orbital translational maneuvers. These maneuvers can be 

performed autonomously provided the autonomous operational constraints are maintained. The 

servicer spacecraft shall maintain sensor pointing at the customer spacecraft to provide current 

knowledge of relative position and closer rates. AR&C payloads should be capable of confirming 

no other resident space objects are in the vicinity of the two spacecraft and that conditions are 

ready for proximity operations.

2.5 PROXIMITY AND APPROACH OPERATIONS

Proximity and Approach Operations are the series of activities that are performed in order to 1) 

perform inspection of customer spacecraft to confirm systems are ready for grappling, and 2) 

transition from coarse to fine relative translational maneuvers up to and including maintaining 

relative position and attitude. Proximity and approach and operations occur at relative positions 

approximately between 1 km and 30 m apart. The goal of proximity and approach operations is to 

close the relative position between the two spacecraft as safely as possible given the increased risk of 
collision while performing final checks to prepare for grappling and mating. The following provide 

additional details on the activities that occur during proximity and approach operations.

2.5.1 A primary function of the proximity and approach operation activity is to inspect the 

customer spacecraft, determine its readiness for servicing, and confirm the servicer spacecraft 

approach is proceeding as planned.

2.5.2 The systems of the servicer spacecraft shall be capable of controlling relative position with 

respect to customer spacecraft. This means controlling relative attitude, position and rates. The 

servicer spacecraft will require fine maneuvering capability to accomplish these functions.

2.5.3 The systems of the servicer spacecraft shall be capable of maintaining communication links 

with all appropriate communication partners including servicer to ground, customer spacecraft 

to ground, and (if commanding of the customer spacecraft is performed by the servicer 

spacecraft) servicer spacecraft to customer spacecraft.

 2.5.4 It is during the proximity and approach operations phase that the servicing 

spacecraft should be configured for servicing. This includes solar array positioning, robotic 

reconfiguration, etc.

2.6 GRAPPLE WITH CUSTOMER SATELLITE AND CONTROL STACK

Grappling and the subsequent activities that are performed while grappled (other than servicing) 

are the key activities performed in this mission phase. The term “grappling” refers to the mating or 

joining of the two spacecraft and can result from using planned or unplanned connection points. A 

passive grapple fixture on a customer spacecraft being grasped by an active grapple mechanism on a 

servicing spacecraft is an example of a planned connection point.

Two spacecraft can be considered grappled when the connection between the two is sufficient to 

meet the requirements of the operations performed while connected. This often means grappling will 

need to be performed in two phases—the first phase, where a non-permanent connection is made to 

stabilize or hold the two spacecraft relative to one another, and a second phase where the connection 

between the two spacecraft is rigidized or otherwise reinforced in order to complete the grappling 

maneuver.

Activities that are performed while the two spacecraft are grappled, other than servicing 

operations, include attitude control, communications relay, and inspection. These functions, 

combined with the servicing functions, are referred to as mated operations.

2.6.1 Before grappling can be attempted, the configuration and interactions of the servicer 

and customer spacecraft must be in known conditions that are favorable for grappling. These 

conditions include the health of both spacecraft, attitude and relative positions, and the 

configuration of mating interfaces. 

2.6.2 The status of the grappling connection should be known during grappling. Mated 

operations including verification of mechanical locks and electrical connections as well as 

interface forces at the connection interfaces. Maintaining an allowable interface force at the 

connection interface below a pre-defined maximum is a servicing mission constraint.

 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 125
126 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

2.6.3 During mated operations while grappled, one spacecraft (typically the servicer spacecraft) 

shall perform attitude determination and control for the combined stacked spacecraft. 

Constraints for each spacecraft and their combined interfaces shall be maintained during mated 

operations.

2.7 PERFORM SERVICING (MATED OPERATIONS)

Servicing Operations are the activities that occur between the grappling/mating operations and the 

eventual separation and/or disposal of the spacecraft. It represents the purpose of the servicing mission 

and is tied to the functional objectives of the mission. These functional objectives are outlined in the 

following sections.

2.7.1 Relocation of Customer Satellite

The function of performing customer satellite relocation involves the spatial repositioning of the 

customer satellite to a predetermined position. Relocation servicing functions include (but are not 

limited to) the following.

• Correcting orbital insertion errors.

• Raising satellite orbit to correct for orbit decay.

• Super-synchronizing spacecraft as to not interfere with other current or future spacecraft on the 

same orbital plane or trajectory.

2.7.2 Mechanical Assist

The function of performing mechanical assistance of a customer satellite involves providing an 

external (to the customer spacecraft) source of supporting or promoting the completion of a 

mechanical reconfiguration of the spacecraft as it was originally designed. Mechanical assist servicing 

functions include (but are not limited to) the following.

• Physical manipulation of jammed spacecraft mechanisms (solar arrays, booms, antennae) such 

that they complete their original deployment.

• Physical manipulation of failed mechanisms such that their original function is achieved. 

Example: opening a aperture door with a failed mechanism.

2.7.3 Repair/Upgrade

The function of performing repair or the upgrade of a customer satellite involves returning original 

systems or components to service that are malfunctioning, as a pre-emptive operation for anticipated 

future malfunctions, or to upgrade systems, instruments, or components to take advantage of new 

technology. Repair/upgrade servicing functions include (but are not limited to) the following.

• Replacement of modular components or systems in order to restore the original functionality of 

or to upgrade the spacecraft.

• Disassembly and reassembly of a spacecraft component or system in order to correct a defect or 

malfunction in the system.

2.7.4 Resource Replenishment

The function of resource replenishment involves returning capacity to or providing capacity to a 

customer spacecraft system. Resource replenishment servicing functions include (but are not limited 

to) the following.
• Refueling the spacecraft propulsion system.

• Augmenting a depleted propulsion system by performing orbital adjustments while mated.

• Returning thermal control systems to original state by cleaning thermal control surfaces, adding 

insulation, or replenishing cryogenic fluids.

• Increasing functionality of current systems through added capacity.

Resource replenishment does not involve returning inoperable original systems or components 

to service (repair), but rather increasing the useful life at the subsystem or system level. Resource 

replenishment does not involve replacement of components or systems.

2.7.5 On-o

The function of on-orbit assembly involves performing construction services to create a new on-orbit 

entity. On-orbit assembly servicing functions include (but are not limited to) the following.

• Construction of an on-orbit telescope, which can vary in complexity from relatively simple 

assembly of a few modules launched in an essentially complete state to complex assembly and 

outfitting of hardware launched at the component and subassembly level. 

• Delivery of components or systems to a on-orbit assembly operation (e.g., ISS construction).

• Adding an instrument to an existing spacecraft.

2.8 DEMATE FROM CUSTOMER SPACECRAFT

The demating function of a servicing mission is essentially the inverse of the grappling function in 

that the connecting interfaces between the servicer and customer spacecraft are terminated. This 

may occur in two phases—the relaxation of the rigidized connection followed by the release of the 

temporary connection. All servicer and customer spacecraft constraints shall be maintained and the 

final state of the customer spacecraft—attitude, rate determination, physical configuration—shall be 

confirmed to be within mission guidelines.

2.9 TRANSFER SERVICER TO NEXT CUSTOMER SPACECRAFT

One possible option following the demating from a customer spacecraft is for the servicer spacecraft 

to make preparations to perform servicing on a second customer spacecraft. This would be common 

for a servicer vehicle performing servicing on a constellation of customer satellites that require the 

same or similar servicing functions. This function results in returning to the starting state of the 

mission sequence with the servicer spacecraft having translated to a pre-rendezvous orbital position for 

the new customer. From there the mission functions are repeated. This cycle can continue for as many 

cycles as the servicer spacecraft is designed to complete.

In addition, this mission function could also include a translational maneuver to a servicing depot 

that would allow for the replenishment of the servicer spacecraft systems or consumables that would 

be used to perform servicing on the next customer spacecraft. For example, a servicer spacecraft could 

visit a refueling depot between servicing customer spacecraft in order to replenish its own propulsion 

system as well as to recharge its refueling system.

2.10 LOITER IN PARKING ORBIT

Another possible option following the demating from a customer spacecraft is for the servicer 

spacecraft to make preparations to loiter in a temporary parking orbit while waiting for additional 

 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 127
128 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

servicing opportunities. This would be common for a servicer vehicle performing servicing on 

multiple customer satellites, but the availability of the subsequent customer spacecraft requires a 

delay. This is similar to the transfer servicer function above, but loitering operations imply additional 

considerations. The servicer spacecraft is stored on-orbit until its next usage, and servicer systems need 

to be designed for this inactivity, the length of which may or may not be known. Loitering may also 

require an increase in the life of the spacecraft systems.

2.11 DISPOSE OF SERVICER AT THE END OF LIFE

At the end of its useful life, the servicer spacecraft will need to be dispositioned in accordance with 

NASA NPR 8715.6. The servicer spacecraft can be said to have completed its usable life if any of the 

following occur.

• Servicing activities/mission is complete.

• Failure of servicer spacecraft system, preventing future servicing activities.

• Failure of customer spacecraft, preventing future servicing activities.

• Failure of mating mechanism to disconnect the servicer and customer spacecraft, resulting in 

non-operational assets.

2.11.1 The servicer spacecraft will need to maintain minimum spacecraft resources in order to 

perform spacecraft end-of-life dispositioning.

2.11.2 The servicer spacecraft will need to be capable of performing spacecraft end-of-life 

dispositioning while mated to the customer spacecraft.

2.11.3 The servicer spacecraft will need to be configured safe for disposal per NASA NPR 

8715.6.

3. PREPARING THE CUSTOMER SPACECRAFT FOR ON-ORBIT SERVICING

This section is for design and configuration considerations that customer spacecraft should consider 

implementing in order to prepare for the activities performed in the servicing mission phases.

3.1 DESIGN CUSTOMER SPACECRAFT TO BE SERVICING FRIENDLY

The sections below outline suggested design elements that customer spacecraft can implement in 

order to facilitate on-orbit servicing.

3.1.1 Provide capture aids.

Capture aids are features that by function or presence assist in the grappling operations. An example 

of a capture aid is a grapple fixture mounted on the customer spacecraft. 

3.1.2 Provide navigation aids.

Navigation aids are features that by function or presence assist in the relative navigation between 

the servicer and customer spacecraft during rendezvous, proximity and approach, and grappling 

operations. An example of a navigation aid is a retroreflector mounted on the customer spacecraft.
3.1.3 Provide inter-vehicle communications for separated ops.

Inter-vehicle communications refers to protocols that can transmit status and commanding 

between the servicer and customer spacecraft for the purpose of assisting servicing operations. For 

transmissions that occur during mission phases other than mated operations, this protocol would 

be wireless communication. An example of this type of communication would be the transmission 

of ranging information from the customer spacecraft to an approaching servicing spacecraft during 

proximity operations.

3.1.4 Provide inter-vehicle communications for mated ops.

Inter-vehicle communications refers to protocols that can transmit status and commanding 

between the servicer and customer spacecraft for the purpose of assisting servicing operations. 

For transmissions that occur during mated operations, this protocol can be hardwired or wireless 

communication. An example of this type of communication would be commanding information that 

passes through an electrical grappling interface from the servicer spacecraft to the customer spacecraft.

3.1.5 Provide inter-vehicle power for mated ops.

Inter-vehicle power refers to the transmission of or receipt of electrical power between the spacecraft 

during mated operations.

3.1.6 Provide servicing-friendly mechanical interfaces.

Servicing friendly mechanical interfaces refers to the mechanical connection points that the servicer 

spacecraft uses to manipulate on the customer spacecraft to assist in servicing operations. This 

includes robot-friendly refueling valves, standard size fasteners, and standardized robotic end-effector 

interfaces.

3.1.7 Provide servicing-friendly spacecraft configuration.

Servicing friendly spacecraft configuration refers to status of the customer spacecraft systems that can 

be reconfigured to assist in servicing operations. This includes deployable systems, attitude control 

system modes, and protective systems. An example of this would be slewing the customer spacecraft 

solar array in an orientation that allows greater access for the servicer spacecraft.

3.1.8 Design customer spacecraft for stacked operations.

Designing a customer spacecraft for stacked operations refers to the design of the spacecraft systems to 

support or accommodate the servicer spacecraft. Such systems include mechanical systems (structural), 

power systems, and thermal control systems.

3.2 CONFIGURE CUSTOMER SPACECRAFT OPERATIONALLY

This section outlines the functions that a customer spacecraft can perform during the mission 

sequence in order to assist in its being serviced.

3.2.1 Maneuver to capture attitude.

The customer spacecraft can work in conjunction with the servicer spacecraft for an efficient 

rendezvous and grapple by maneuvering to a pre-determined attitude.

 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 129
130 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

3.2.2 Configure systems for rendezvous and servicing.

The customer spacecraft can assist with servicing mission operations by configuring its systems to 

accommodate the operation. Suggested systems for configuration to aid in servicing operations 

include:

• Power System 

• Optics and Instruments 

• Propulsion System 

• Guidance Navigation and Control

3.3 MISSION CONSTRAINTS

The following constraints are recommended for the interactions between customer spacecraft and 

servicer spacecraft in order to promote successful servicing operations.

3.3.1 Customer spacecraft functionality should be maintained during rendezvous, proximity and 

approach, and grappling operations.

3.3.2 The customer spacecraft should maintain minimum propulsion for disengagement 

maneuvers to re-attempt grappling.

3.3.3 The servicer spacecraft shall not plume customer vehicle such that its solar cells/power 

system are degraded.

3.3.4 The servicer spacecraft shall maintain customer vehicle thermal control capabilities 

(minimize pluming of mirrors, etc).

3.3.5 Servicing loads imparted to customer spacecraft by the servicer spacecraft during mated 

operations shall not exceed structural limits of either vehicle.

3.3.6 The customer spacecraft should have primary and backup grappling points. 
 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 131

ACTIVITY LIST

This activity list complements foregoing functional decomposition of servicing activities by 

illustrating their hierarchical relationships. The table below is a list of activities created by the study 

team to describe the possible actions that may be performed during the servicing mission functions.

Activity List

1 Pre-Mission Considerations

1.1 Servicer Spacecraft Bus

1.1.1 Orbit

1.1.1.1 Low Earth Orbit

1.1.1.2 Highly Elliptical Orbit

1.1.1.3 Geosynchronous Orbit

1.1.1.4 Libration Point Orbits

1.1.2 Mission ∆V Requirements

 1.1.3 Customer Spacecraft ORU and Replenishables Mass 

1.2 Mission Operations

1.3 Maintaining Customer and Servicer Spacecraft Constraints

 1.3.1 Cause no degradation (e.g., pluming appendages)

 1.3.2 Maintain power-positive mode

 1.3.3 Maintain temperature limits

 1.3.4 Maintain mechanical integrity of interfaces

 1.3.5 Maintain contamination requirements

 1.3.6 Provide means to mitigate customer-servicer voltage differentials

 1.3.7 Conform to customer spacecraft kept-out zones and envelopes

1.4 Planning for Autonomous Activities

 1.4.1 Provide GN&C command interface to autonomy control systems

 1.4.2 Provide capability to switch operating modes via ground commands

 1.4.3 Provide capability for scripted autonomy with ground authority-to-proceed gates

 1.4.4 Provide capability to switch between task lists via ground commands

 1.4.5 Provide capability to autonomously monitor performance and status and respond with 

appropriate, pre-defined abort sequences

 1.4.6 Provide suspend mode capability that responds to external commands and flags

 1.4.7 Provide abort mode capability that responds to external commands and flags

 1.4.8 Provide on-board capability to monitor spacecraft state and respond to unsafe conditions 

with appropriate GN&C abort sequences

2. Perform On-Orbit Servicing

2.1 Achieve Customer Satellite Orbit

2.1.1 Launch and insertion into transfer orbit

2.1.1.1 To mission specific designated inclination

2.1.1.2 To mission specific designated right ascension
132 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

2.1.1.3 To mission specific designated eccentricity

2.1.1.4 To mission specific designated Semi-major axis

2.2 Perform Servicer on-orbit checkout

2.2.1 Checkout the robot(s)

2.2.1.1 Verify telemetry and control

2.2.1.2 Release sensor launch locks and checkout sensors

2.2.1.3 Release manipulator launch locks and exercise all actuators

2.2.2 Checkout AR&C system

2.2.2.1 Calibrate sensors (alignment, dark noise, etc)

2.2.2.2 Checkout system with resident space object (RSO) (i.e. upper stage)

2.2.2.3 Verify telemetry and control

2.2.2.4 Release launch locks and exercise all actuators (pan-tilt, scanning lidar, etc)

2.2.3 Checkout remaining servicer systems

2.2.4 Perform inspection of servicer using cameras on robotic arms

2.3 Transfer to pre-rendezvous orbit with first customer vehicle

2.3.1 Ground performs analysis to design servicer trajectory that is free of debris and satellites

2.3.2 Servicer performs translational maneuvers

2.3.2.1 Ground performs orbit determination for servicer

2.3.2.2 Ground plans maneuver(s) to reach desired orbital state 

2.3.2.2.1 Maneuver design constraints include: power, comm constraints (no 

maneuvers in the blind), operational constraints (vehicle and staffing)

2.3.2.2.2 Within relative navigation phase, additional maneuver constraints 

include: lighting constraints, orbital debris/conjunction avoidance, 

customer vehicle readiness, relative navigation sensor acquisition 

constraints

2.3.2.3 Verify maneuver performance from onboard sensor data and ground based 

tracking

2.4 Rendezvous with customer spacecraft

2.4.1 Find customer (far-field acquisition)

2.4.1.1 Point long-range sensors at customer 

2.4.1.2 Acquire customer 

2.4.1.3 Confirm customer acquisition

2.4.2 Close relative position with customer

2.4.2.1 Perform autonomous tasks

2.4.2.1.1 Store a ground updatable sequence of tasks 

2.4.2.1.2 Autonomously execute a sequence of AR&C tasks

2.4.2.1.3 Exercise context-dependent autonomous abort as needed

2.4.2.1.4 Accept ground authority-to-proceed (ATP) commands

2.4.2.2 Maintain sensor pointing on customer. Assume customer has been acquired, good 

knowledge of relative position and rates.

2.4.2.2.1 Compute line-of-sight vector to customer
 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 133

2.4.2.2.2 Determine servicer inertial attitude

2.4.2.2.3 Compute attitude maneuvers and/or pan-tilt platform orientation to 

keep sensor bore sight aligned within LOS vector

2.4.2.2.3.1 Compute required attitude

2.4.2.2.3.1.1 Error budget (required attitude driven by 

sensor error budget)

2.4.2.2.3.2 Estimate current attitude 

2.4.2.2.3.2.1 Compare to Error budget

2.4.2.2.3.3 Compute required torque

2.4.2.2.3.4 Activate attitude actuators (bus GN&C or pan-tilt 

mechanism) to generate torque

2.4.2.2.3.4.1 Compare to error budget (attitude control 

execution error)

2.4.2.3 Determine relative position and rates to customer

2.4.2.3.1 Take sensor measurements

2.4.2.3.1.1 Initialize/calibrate sensors

2.4.2.3.1.2 Relative range and rate

2.4.2.3.1.3 Relative Bearing and Rate

2.4.2.3.1.4 Acceleration during maneuver

2.4.2.3.1.5 Absolute orbit determination (OD) of servicer

2.4.2.3.2 Process measurements - extended Kalman filter

2.4.2.3.2.1 Maintain accelerometer bias knowledge and other filter 

states and covariance

2.4.2.3.2.2 Initialize filter - customer to ground absolute OD solution

2.4.2.3.2.3 Estimate relative position and covariance

2.4.2.3.2.4 Estimate relative velocity

2.4.2.3.2.5 Estimate absolute position of servicer and customer

2.4.2.3.2.6 Estimate absolute velocity of servicer and customer

2.4.2.3.2.7 Perform FDIR (fault detection, isolation and recovery)

2.4.2.4 Translate servicer while respecting servicer pointing requirements

2.4.2.4.1 Maintain servicer Integrity

2.4.2.4.1.1 Servicer power system

2.4.2.4.1.2 Servicer thermal system

2.4.2.4.1.3 Servicer RF comm system

2.4.2.4.1.4 Servicer C&DH system

2.4.2.4.1.5 Servicer GN&C (momentum management, fuel, etc.)

2.4.2.4.2 Provide force in any direction 

2.4.2.4.2.1 Minimize self contamination

2.4.2.4.2.2 Minimize self impingement

2.4.2.4.2.3 Minimize customer impingement

2.4.2.4.3 Determine desired relative position/velocity
134 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

2.4.2.4.3.1 Verify current relative position and velocity

2.4.2.4.3.2 Perform guidance (customizing) per autonomous task 

sequence

2.4.2.4.4 Compute required control impulse (plan maneuver)

2.4.2.4.5 Determine required attitude for burn

2.4.2.4.5.1 Maintain sensor lock and/or “Turn and Burn”

2.4.2.4.6 Deliver required impulse (execute maneuver)

2.4.2.4.6.1 Monitor fuel

2.4.2.4.6.2 Monitor attitude during burn

2.4.2.4.6.3 Determine which thrusters to fire

2.4.2.4.6.4 Maintain attitude during maneuver

2.4.2.4.6.5 Fire thrusters

2.4.2.4.6.5.1 Thruster direction error

2.4.2.4.6.5.2 Thruster magnitude error

2.4.2.4.6.5.3 Latency between command and thruster 

firing

2.4.2.4.6.5.4 Total force required

2.4.2.4.6.6 Monitor/calibrate measured delivered acceleration/torque

2.4.2.4.6.7 Accommodate thruster failure

2.4.2.4.7 Evaluate maneuver performance as determined by sec. 2.2.2

2.4.2.5 Confirm customer neighborhood is free of other Resident Space Objects (RSOs)

2.4.2.5.1 Configure camera

2.4.2.5.2 Configure lighting

2.4.2.5.3 Optically image customer

2.4.2.5.4 Send image to ground

2.4.2.6 Confirm readiness for proximity operations 

2.4.3 Maintain vehicle momentum

2.4.4 Manage servicer autonomy per section 1.4

2.5 Proximity and Approach Operations

2.5.1 Survey/inspect customer

2.5.1.1 Image the customer 

2.5.1.1.1 Receive info on specific area of the spacecraft

2.5.1.1.2 Configure camera

2.5.1.1.3 Configure lighting - servicer or natural

2.5.1.1.4 Take images

2.5.1.1.5 Process and store images

2.5.1.2 Transfer image to ground

2.5.1.3 Ground process image

2.5.2 Control relative position with respect to customer

2.5.2.1 Maintain sensor pointing on customer

2.5.2.2 Measure relative attitude of customer
 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 135

2.5.2.3 Measure relative attitude rates of customer

2.5.2.4 Measure relative position to customer

2.5.2.5 Measure relative position rates to customer

2.5.2.6 Translate servicer (fine maneuvering) See Section 2.4.2.3

2.5.3 Maintain communications 

2.5.3.1 Servicer to ground 

2.5.3.2 Servicer to customer (if customer has the capability) 

2.5.3.3 Customer to ground (if customer has the capability)

2.5.4 Configure servicer for capture (unstow, re-verify and position arms, etc.)

2.5.5 Maintain customer spacecraft constraints per section 1.3 

2.5.6 Manage servicer autonomy per section 1.4

2.6 Grapple with customer satellite and control stack (both human or/and robot)

2.6.1 Prepare to grapple

2.6.2 Verify States (Health) of customer satellite and servicer

2.6.2.1 Obtain state of customer satellite 

2.6.2.1.1 Evaluate customer for suitability for grapple

2.6.2.1.2 Select appropriate end-effector

2.6.2.2 Obtain state of servicer 

2.6.2.3 Receive ATP to begin grappling process 

2.6.2.4 Image worksite

2.6.2.4.1 Minimum frame rate and resolution

2.6.2.4.2 Maintain downlink of required data about worksite

2.6.2.5 Maintain relative navigation

2.6.2.6 Control relative position and attitude to remain in capture box

2.6.3 Grapple the customer

2.6.3.1 Move arms to ready to capture position

2.6.3.2 Engage soft capture as applicable

2.6.3.3 Engage hard capture

2.6.3.4 Autonomous Compliance Control

2.6.3.5 Move arms to stacked configuration

2.6.3.6 Maximum force and torque applied to customer (sensor to detect excessive 

torque)

2.6.3.7 Rigidize arms in stacked configuration

2.6.3.8 Verify grapple Success

2.6.4 Control stack (servicer vehicle controls attitude of combined servicer and customer)

2.6.4.1 Perform attitude determination and control for stack

2.6.4.1.1 Perform maneuvers to estimate mass properties of combined stack

2.6.4.1.2 Control stack attitude as required for servicing task

2.6.4.2 Maintain imparted loads within specifications 

2.7 Perform servicing (mated operations)
136 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

2.7.1 Relocation of customer satellite 

2.7.1.1 Evaluate customer for serviceability

2.7.1.2 Re-orient (combined) vehicle to firing position, include burn

2.7.1.2.1 Pre-burn check gate

2.7.1.2.2 Verify conditions required for burn (rates, attitude, safeing system, etc)

2.7.1.3 Perform orbital maneuver

2.7.1.4 Verify final orbit

2.7.1.5 Deploy Customer

2.7.1.5.1 ATP, separation/release customer

2.7.1.5.1.1 Verify subsequent separation 

2.7.1.5.2 Perform main separation maneuver 

2.7.1.5.2.1 CCAM (collision contamination avoidance maneuver)

2.7.1.5.3 Set servicer to nominal configuration and mode

2.7.1.5.3.1 Verify servicer status

2.7.1.5.4 Set customer to nominal configuration and mode

2.7.1.5.4.1 Verify customer status

2.7.2 Mechanical Assist (hardware stuck)

2.7.2.1 Verify customer satellite and servicing vehicle is ready/configured for mechanism 

deployment

2.7.2.2 Identify anomalous/stuck mechanism

2.7.2.3 Survey mechanism for anomaly/obstruction

2.7.2.4 Identify and provide corrective action

2.7.2.4.1 Monitor and maintain applied forces/torques and motion kinematics 

within limits

2.7.3 Repair/Upgrade 

2.7.3.1 Verify customer satellite and servicing vehicle is ready/configured for hardware 

replacement

2.7.3.1.1 Identify hardware and Interfaces

2.7.3.1.2 Survey worksite 

2.7.3.2 Perform repair or upgrade 

2.7.3.2.1 Maintain integrity of replacement hardware (thermally etc.)

2.7.3.2.2 Verify tool compatibility with interfaces

2.7.3.2.3 Gain access to hardware

2.7.3.2.4 Perform checkout of new hardware

2.7.4 Resource Replenishment

 2.7.4.1 Receive ATP to deploy servicing arm

 2.7.4.1.1 Begin continuous downlink of arm camera

2 .7.4.1.2 Match resolution and refresh rate to task

 2.7.4.2 Retrieve necessary tool

 2.7.4.3 Move arm into position to evaluate worksite (e.g.- refueling valve)
 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 137

 2.7.4.4 Identify port location

 2.7.4.4.1 Image, ground verification

 2.7.4.5 Remove MLI (tool for removal, secure, contamination control)

 2.7.4.6 Cut safety wire (tool for cutting)

 2.7.4.7 Remove cap

 2.7.4.7.1 Place in the temporary storage

 2.7.4.7.2 Retrieve appropriate tool

 2.7.4.7.3 Turn to release

 2.7.4.8 Connect consumable supply line

 2.7.4.9 Open valves

 2.7.4.10 Monitor pressures/temperature of both tanks

 2.7.4.11 Close valve (reach time or pressure limit)

 2.7.4.12 Disconnect consumable supply line

2.7.5 On-Orbit Assembly

2.7.5.1 Receive ATP to deploy servicing arm

 2.7.5.1.1 Begin continuous downlink of arm camera & sensor data

 2.7.5.1.2 Match data resolution and refresh rate to current task

 2.7.5.2 Prepare worksite

 2.7.5.2.1 Survey worksite

 2.7.5.2.2 Verify tool compatibility

 2.7.5.2.3 Configure interfaces

 2.7.5.2.4 Select or verify tools are ready for use

 2.7.5.2.5 Verify ready to proceed

2.7.5.3 Access Stowage

 2.7.5.3.1 Verify integrity of hardware

 2.7.5.3.2 Install tether or secondary restraint

 2.7.5.3.3 Retrieve hardware for assembly

 2.7.5.3.4 If necessary safe and secure stowage container

 2.7.5.4 Execute assembly function for hardware component

 2.7.5.4.1 Position servicing arm

 2.7.5.4.2 Make hardware connection with interface

 2.7.5.4.3 Verify hardware position and orientation within limits for latching

 2.7.5.4.4 Drive latch mechanism as appropriate or send notification of readiness 

for externally commanded latching of interface

 2.7.5.4.5 Remove tether or secondary restraint after assembly step complete

2.7.5.5 Continue until assembly completed, swapping tools as appropriate

2.7.5.6 Receive ATP to re-stow servicing arm

2.7.5.7 Re-stow servicing arm

2.8 Demate from customer spacecraft

2.8.1 Verify servicer state (rates, position)
138 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

2.8.2 Perform post-servicing inspection or monitoring of customer as required

2.9 Transfer servicer to next customer

2.9.1 Ground performs analysis to design servicer trajectory that is free of debris and satellites

2.9.2 Servicer performs translational maneuvers

2.10 Loiter in parking orbit

2.10.1 Servicer configured for loiter/on-orbit storage

2.10.2 Servicer station-keeping maneuvers

 2.10.2.1 Servicer performs translational maneuvers

2.10.3 Servicer momentum unload maneuvers

2.11 Dispose of servicer at end of life

2.11.1 Transfer to disposal location

 2.11.1.1 Perform plane change

 2.11.1.2 Perform altitude change

2.11.2 Safe servicer for disposal

 2.11.2.1 Safe servicer per NASA NPR 8715.6

2.12 Manage servicer Autonomy

2.12.1 Provide GN&C command interface

 2.12.1.1 Commands originating from AR&C 

 2.12.1.2 Command originating from the ground

2.12.2 Receive ground command to switch between operational mission modes

2.12.3 Execute ground-provided task lists appropriate to current operational mode

 2.12.3.1 Validate uplinked task lists

 2.12.3.2 Provide ATP checkpoints

 2.12.3.3 Sequence commands & monitor grapple arm interface to accomplish tasks

 2.12.3.4 Activate sensor/effector HW to accomplish tasks

 2.12.4 Switch between task lists

 2.12.5 Monitor performance and status to detect unsafe conditions and initiate pre-defined abort 

sequences

 2.12.5.1 Sensor/end-effector health

 2.12.5.2 Relative servicer/customer orientation and location – predict servicer/customer 

collisions

 2.12.5.3 Indication of spacecraft safemode trigger

 2.12.5.4 Vehicle battery life remaining

2.12.6 Receive ground commands to suspend execution of task

2.12.7 Receive ground commands to execute abort

2.12.8 Execute GN&C abort sequences based on knowledge of current state in response to 

automated or ground commanded abort commands

3. Preparing the Customer Spacecraft For On-orbit Servicing 

3.1 Design customer spacecraft to be servicing friendly

3.1.1 Provide capture aids

3.1.1.1 Provide grapple aids
 Appendix D – Functional Decomposition of the Activities Required for Satellite Servicing | 139

 3.1.1.2 Provide docking aids

 3.1.1.3 Allow transmission of forces/torques

3.1.2 Provide navigation aids

3.1.3 Provide inter-vehicle communication subsystem for separated ops

3.1.4 Provide inter-vehicle communication subsystem for mated ops

3.1.5 Provide inter-vehicle power for mated ops

3.1.6 Provide servicing-friendly mechanical interfaces 

 3.1.6.1 Provide compatible consumable ports

 3.1.6.2 Provide handling fixtures 

3.1.7 Provide servicing-friendly vehicle configuration

 3.1.7.1 Configure deployables (stowable)

 3.1.7.2 Provide attitude control system modes

 3.1.7.3 Design load limits to accommodate servicer induced impulses

 3.1.7.3.1 Design load limits to accommodate docking

 3.1.7.3.2 Maneuver

 3.1.7.3.3 Servicing

 3.1.7.4 Provide contamination protection

 3.1.7.5 Provide ground path to servicer vehicle interface to minimize ESD

3.1.8 Design customer spacecraft for stacked operations

 3.1.8.1 Power

 3.1.8.2 Thermal

 3.1.8.3 RF Communication

3.2 Configure customer spacecraft operationally

3.2.1 Maneuver to capture attitude

3.2.2 Configure RF communication subsystem

3.2.2.1 Enable inter-vehicle comm (if available and required)

3.2.2.2 Configure comm deployables (HGA,etc.)

3.2.2.3 Verify all downlink paths enabled (ground, TDRS, other comms)

3.2.3 Configure optics and instruments (if applicable)

3.2.4 Configure for contamination control

3.2.4.1 Shutters, deployable covers

3.2.5 Configure prop system for servicing

3.2.5.1 Bleed-off, inter-tank transfer, ullage dump

3.2.6 Configure for thermal protection

3.2.6.1 Pre-heat considerations, deployable radiators 

 3.2.7 Configure power system

 3.2.7.1 Fully charge battery

 3.2.7.2 Configure SA

 3.2.7.3 Set minimum SOC for batteries and include in docking wave-off criteria

 3.2.8 Minimize ESD; Provide ground path to customer vehicle interface
140 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

 3.2.9 Safe customer vehicle systems

 3.2.9.1 Identify safe mode processes that might counter servicing vehicle operations 

(despin, pointing, etc.)

 3.2.10 Command customer to capture mode

3.3 Mission constraints

 3.3.1 Servicing approach, rendezvous, capture attempts shall maintain customer functionality.

 3.3.2 Maintain minimum prop for customer maneuvers and back-off.

 3.3.3 Do not plume customer such that its solar cells/power system is degraded.

 3.3.4 Maintain customer thermal control capabilities (minimize pluming of mirrors, etc).

 3.3.5 Servicing loads imparted to customer shall not exceed structural limits.

 3.3.6 Identify primary and backup capture points on customer. 
 Appendix E – Integrated Design Laboratory (IDL) Payload Element Study Summary | 141

Autonomous Rendezvous and (Berthing, Capture, Docking) Sensor Package

The Instrument Design Laboratory (IDL)—part of NASA Goddard Space Flight Center’s Integrated Design Center 

(IDC)—was enlisted to design an integrated Autonomous Rendezvous & Capture (AR&C) sensor package. The 

design was largely driven by the requirements imposed by the scenario presented in Notional Mission 1—GEO 

Supersync: capture a non-cooperative (possibly rapidly tumbling customer spacecraft) at GEO altitude; repeat for 

10 non-cooperative customers, each with an 80-hour duration, all within five years.

Note that while the sensor package is referred to as the AR&C sensor package, this nomenclature is due to the 

fact that all of the rendezvous, proximity operations, and final approach sequences for Notional Mission 1 concluded 

with capture rather than berthing or docking, since all of the customer spacecraft were non-cooperative vehicles 

that merely needed to be grasped (captured via robotic arms) so that their orbits could be modified by the servicer. 

However, the “AR&C” sensor package described herein is also perfectly suited to Autonomous Rendezvous & 

Berthing (AR&B) or Autonomous Rendezvous & Docking (AR&D) missions. As noted in the sections describing 

AR&(B,C,D) for each of the notional missions, modifications were made to the overall AR&(B,C,D) sensor suite when 

appropriate. For instance, in cases where cooperative spacecraft customers could be assumed, a Radio Frequency 

(RF) ranging and telemetry transponder were added. However, none of the sensors present in the original “AR&C” 

sensor suite were ever removed. For simplicity and congruency with the IDL design nomenclature, the sensor suite 

is referred to as the AR&C sensor package, suite, or system throughout the remainder of this section.

The AR&C sensor suite was designed to provide bearing, range, and pose measurements of the customer 

spacecraft throughout the AR&C sequence, which nominally begins when the servicer spacecraft is approximately 

200–300 km away from the customer. Furthermore, the AR&C package was designed to meet the measurement 

accuracy requirements given in Figure IDL1-1. When AR&C begins is largely determined by the far-field distance 

at which the bearing sensors can first acquire the customer spacecraft; this was conservatively estimated to be 

200–300 km during the IDL study. However, AR&C sensor technology is rapidly evolving, and it is now believed 

that the maximum bearing sensor acquisition range could be as far away as 1,000 km; during cooperative AR&C 

scenarios the inter-spacecraft RF ranging crosslink will certainly be capable of providing range measurements at 

such distances. Nevertheless, there is no particular disadvantage associated with defining the beginning distance 

for AR&C to be 200–300 km, so that convention is maintained except where noted in the individual notional mission 

descriptions.

The AR&C sequence, shown in Figure IDL1-2, was divided up according to spacecraft distance intervals so as 

to specify which sensors and measurements would be available at various distances to the customer. Four logical 

divisions of spacecraft distance during AR&C were identified:

• Far-Field Rendezvous: 200 km–25 km (more generally, > 25 km)

• Near-Field Rendezvous: 25 km–300 m

• Proximity Operations: 300 m–50 m

• Final Approach: 50 m–1 m

To provide measurements during these distance intervals, the AR&C sensor suite consists of the following 

instruments:

• A Modified Star Tracker Electronics Box and Modified Star Tracker Camera Heads from Micro ASC (plus 

baffles) (4)

• Narrow Field of View (NFOV) Camera (2)

Appendix E – Results of the Integrated Design Center (IDC) Instrument 

Design Laboratory (IDL) Study on Autonomous Rendezvous and 

(Berthing, Capture, Docking) Sensor Package, and Robots 1 through 3

Figure IDL1-1: Required Accuracies for Measurement
142 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

• Bearing angle measurements from 200 km–100 m (possibly > 200 km)

• Images from 100 m–25 m for pose determination

• Wide Field of View (WFOV) Camera (2)

• Bearing angle measurements from 200 km–50 m (possibly > 200 km)

• Images from 50 m–1 m for pose determination

• Pose determination down to a distance of 1 m assumes that the camera can focus adequately at such 

short distances and that recognizable physical features of the customer will be present within the field 

of view, since the customer will generally be larger than the field of view at extremely close distances 

such as 1 m, and may be rotating

• Long Range Laser Rangefinder (1)

• Range measurements from 75 km–50 m

• Infrared Camera (1)

• Bearing measurements from 20 km–TBD

• Minimum distance at which bearing measurements can be acquired is currently unknown

• Intended for use during adverse lighting conditions

• Flash/Ranging LIDAR (1)

• Range measurements from approximately 100 km–1 m

• Pose measurements from 50 m–1 m

• Short Range Laser Rangefinder (1)

• Range measurements from approximately 1 km–1 m

The overall AR&C package includes the sensor suite described above as well as two Main Electronics Boxes (MEB) 

modeled after the SpaceCube 2.0. One MEB is active, while the other is fully redundant. The MEB is responsible 

Figure IDL1-2: Rendezvous Sequence
 Appendix E – Integrated Design Laboratory (IDL) Payload Element Study Summary | 143

for processing images from the visible and infrared cameras, along with measurements from the other sensors. 

Additionally, the MEB provides processing for Guidance, Navigation, and Control (GNC) during the AR&C phase 

of the mission. This includes state estimation/propagation, maneuver calculations for autonomous operations, 

and general autonomy. The GNC processing within the MEB also receives inputs from the standard sensors on 

the servicer spacecraft bus which are not considered to be part of the AR&C sensor suite, including the vehicle’s 

star tracker and coarse sun sensors for inertial attitude determination, the inertial measurement unit for measuring 

accelerations due to thrust, and the GPS used for orbit determination (absolute inertial state estimation). During 

AR&C operations, the spacecraft bus enters a mode which allows the GNC function of the AR&C MEB to command 

the spacecraft’s actuators (which are also considered to be part of the standard spacecraft bus and not part of the 

AR&C system proper), including thrusters, reaction wheels, and momentum wheels. In addition to these critical GNC 

functions, the AR&C MEB also performs housekeeping functions, including video compression and storage, power 

distribution, and thermal control. All of the AR&C components are mounted on a pan/tilt mechanism. The total mass 

of the AR&C package is 141.1 kg, its peak power draw is 128.9 W, and its peak data rate is 996 Mbps without 

compression (786 Mbps with compression). 

Pan/Tilt Mechanism

The first design of the AR&C package included a pan/tilt mechanism upon which all of the AR&C sensors and 

both of the MEB were mounted, as shown in Figure IDL1-3. The pan/tilt mechanism has two degrees of rotational 

freedom, and is capable of rotating +/- 60 deg about each of its two axes (pitch and yaw). The goal was to allow 

the servicer to point its AR&C sensors at the customer vehicle continuously with only minimal attitude maneuvers, 

particularly during the complex translational and attitudinal motion that might be required during proximity operations 

and final approach to capture an arbitrarily tumbling non-cooperative customer spacecraft. However, by the end of 

the study it was not clear that the pan/tilt mechanism offered sufficient advantages to outweigh its disadvantages; 

nor was it clear that additional degrees of freedom afforded by the pan/tilt mechanism could not be achieved via 

attitude maneuvers by the servicer, combined with gimbaled solar arrays, gimbaled communications antennae, 

and strategic distribution of AR&C sensor heads around the servicer’s structure. The perceived advantages and 

disadvantages of the pan/tilt mechanism are as follows:

Pan/Tilt Mechanism Advantages

• Can simplify servicer spacecraft pointing requirements

• May result in reduced propellant consumption and/or momentum storage

• Can increase customer spacecraft visibility to the AR&C sensors by increasing the extent of the overall 

AR&C sensor field of regard and the duration for which the customer is within the field of regard

Figure IDL1-3: AR&C on the Pan/Tilt Mechanism
144 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

• Can provide for biasing of sensor orientation, allowing solar image avoidance

• May enable searching for the customer spacecraft (during far-field, and possibly near-field rendezvous) 

without requiring attitude maneuvers

Pan/Tilt Mechanism Disadvantages

• Additional software is required to control the mechanism

• Mechanism control software reliability is low

• Baseline for stereo ranging is lower (compared to distributing sensors on spacecraft bus)

• Higher cost (distributed additional sensors may cost less than the pan/tilt mechanism)

• The inclusion of the pan/tilt platform complicates the pointing error budget

• Adds a source of pointing error

• The spacecraft bus is capable of sufficient pointing accuracy without the pan/tilt system

• Decreases modularity

• Thermal control is complicated

• Variable thermal loads based on platform position

• Difficult to remove heat across the pan/tilt gimbals

• Massive: with a mass of 99.8 kg, it comprises 70.8% of the AR&C system mass

• The power requirement for the pan/tilt mechanism alone is 40 W (2 motors at 20 W each), which comprises 

1/3 of the 128.9 W of total power consumed by the AR&C system.

The pan/tilt mechanism was incorporated into the servicer spacecraft design for Notional Mission 1 (the study 

which immediately followed the AR&C IDL study described herein), but not long afterward it was decided that the 

disadvantages of the pan/tilt system (particularly its large mass and relatively substantial power draw) were not 

outweighed by the potential advantages it offered. Therefore, beginning with Notional Mission 2, the decision was 

made to eliminate the pan/tilt mechanism from the spacecraft design, a decision which was held throughout the 

remainder of the notional mission suite studies. Figure IDL1-4 shows the AR&C sensor suite without the Pan/Tilt 

Mechanism.

Making Spacecraft Serviceable from the Perspective of AR&(B,C,D)

Making spacecraft serviceable from the perspective of AR&(B,C,D) means ensuring that spacecraft are capable of 

being cooperative customers for rendezvous, proximity operations, and berthing, capture, or docking. All spacecraft 

servicing activities begin with an AR&(B,C,D) sequence that brings the servicer and customer spacecraft together. 

Figure IDL1-4: AR&C Sensor Package—No Pan/Tilt Unit
 Appendix E – Integrated Design Laboratory (IDL) Payload Element Study Summary | 145

The servicer spacecraft is typically the active vehicle during the AR&(B,C,D) sequence and the customer vehicle is 

passive (i.e., not maneuvering to translate towards the servicer). 

Fundamentally, a cooperative rendezvous customer is one which does nothing to hinder the AR&(B,C,D) 

process and offers features that make the AR&(B,C,D) sequence easier. By contrast, a non-cooperative vehicle 

does not offer features that facilitate AR&(B,C,D) and may have characteristics that inadvertently hinder AR&(B,C,D). 

An uncooperative vehicle (vs. a non-cooperative vehicle) is one which actively and deliberately attempts to foil 

AR&(B,C,D). Note that uncooperative vehicles are not considered herein.

Adding the following features and mechanisms to a spacecraft design make it a cooperative customer for 

AR&(B,C,D):

• Optical retro-reflectors

• RF transponders for ranging and telemetry exchange

• Visible, possibly reflective, surface features

• Grapple fixtures

• Proper ACS modes in flight software for quiescence when required

Optical retro-reflectors allow laser-based relative navigation sensors on the servicer spacecraft to acquire the 

customer spacecraft at further distances and also provide better tracking quality for bearing-angle sensors. 

Radio Frequency (RF) transponders for ranging and telemetry exchange serve two important purposes. First, 

the exchange of a two-way ranging signal between the servicer and customer vehicle provides the servicer with a 

very accurate estimate of the range between the vehicles and aids in far-field acquisition of the customer. Second, 

the exchange of telemetry between the vehicles allows them to share state information, which can further improve 

the servicer’s relative navigation solution and provide important situational awareness data. 

Visible, possibly reflective, surface features at known locations in the customer spacecraft’s body frame help 

natural feature recognition pose sensor algorithms measure the relative position and attitude of the customer 

spacecraft when at closer ranges (i.e., during proximity operations and final approach). 

Grapple fixtures offer a safe, robust means for the servicer vehicle to attach itself to the customer vehicle in a 

berthing or capture scenario. 

Finally, the availability of proper ACS modes ensures that two important conditions will be met. First, the 

customer vehicle will be in a friendly attitude state throughout the AR&(B,C,D) sequence; this is especially important 

in the final approach phase during which the servicer vehicle must engage in forced motion along an approach 

vector fixed in the customer vehicle’s body frame. If the customer vehicle has any significant attitude rates during 

this phase, the servicer vehicle will have to consume significant amounts of fuel to stay on the rotating approach axis 

and complete the final approach. Second, the customer vehicle will be capable of becoming completely quiescent, 

ensuring that its ACS algorithms and actuators will not be attempting to counteract the forces and torques imparted 

by the servicer during capture, berthing, or docking operations and subsequent mated operations.

Note that the majority of these additional features have relatively little impact on the customer spacecraft 

systems. 

IDL Robot 1

The robot system developed in the first Instrument Design Laboratory run was a “notional” dexterous robot based 

off of two very similar existing space robot systems—Ranger, developed by the University of Maryland’s Space 

System Laboratory, and FREND, developed by Alliance Spacesystems (since acquired by MacDonald, Dettwiler and 

Associates Ltd. [MDA] of Canada) and the Naval Research Laboratory for the Defense Advanced Research Projects 

Agency. The FREND arm was designed to do a very similar task as proposed in Notional Mission 1 (grapple the 

back end of a satellite), and Ranger was designed to do dexterous tasks very similar to those proposed in the other 

five notional missions (refueling, assembling structures, replacing aging and failed spacecraft components, etc.).

The 7 degree-of-freedom (DOF) notional arm developed during the week-long design run has a 3-DOF 

shoulder, 2-DOF elbow, and a 2-DOF wrist as shown in Figure Robot 1-1. Total arm length is approximately 2 

meters, divided equally between the upper arm and lower arm, and the arm fits within a 0.35 m3

 volume. The total 

weight of the arm and associated electronics is 157 kg (with the electronics weighing 34 kg), requires 380 W during 

operations, and can pass 1 Mbps of data.

Each robot joint contains a DC brushless motor, a transmission, a brake, and encoders. The joints also have 

temperature sensors. The end of the arm has a force-torque sensor.
146 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

The notional end-effector (shown in Figure Robot 

1-2) is a basic gripper that can be used to grapple a 

satellite. Cameras and lights (LED illuminators) on the 

end-effector are used to take images of the satellite, 

which are fed to a processor in the electronics box, 

which performs a pose estimate and autonomously 

commands the arm to complete the grapple. A proximity 

sensor is included to assist the autonomous vision 

algorithm. A force-torque sensor mounted between 

the wrist of the robot and the end-effector is used for 

compliance control algorithms, allowing the arm to 

“gently” grapple the customer satellite.

The control electronics (Figure Robot 1-3) are in 

one centralized location in two boxes—the Arm Control 

Electronics (ACE) and the Data Management Unit (DMU). 

The ACE is used for servo control and includes the servo 

boards, boards for data digitization, input/output boards, and any miscellaneous preprocessing needs. The DMU 

supports the autonomous grapple system, and also supports the arm with control algorithms (compliance control, 

health & status information, end-point trajectory calculations, and potentially 

a sequencer of robot motions including collision avoidance). SpaceCube 2.0 

is baselined as the DMU.

Power distribution for the arm comes from the spacecraft bus at 28 

VDC. The arm will also require ±5 VDC for signal and other miscellaneous 

needs. The wire hardness is routed down the outside of the arm using ribbon 

cables.

The arm design incorporates 200-mils thick aluminum shielding to cover 

sensitive components that effectively reduces radiation to 40 krad. This is one 

advantage of having the control electronics located in a centralized location 

instead of distributed along the arm. It also helps with thermal design.

For robot interface, the shoulder joint is hard-mounted to the 

structure. As a payload, the robot is afixed to the spacecraft interface plate 

(honeycomb aluminum), which in turn is attached to the spacecraft structure 

Figure Robot 1-3: Control Electronics

Figure Robot 1-2: Notional End-Effector

Figure Robot 1-1: Notional Robot Arm with a Grapple End-Effector
 Appendix E – Integrated Design Laboratory (IDL) Payload Element Study Summary | 147

with mechanical fasteners. Power, command, and telemetry is passed between the robot and the spacecraft. Its 

interface is though the 1553 spacecraft bus, Spacewire for instrument data, RS-422 to control the sensors, and a 

PCI interface to the joints and end-effector. The robotics executive software on the DMU interfaces with the Vehicle 

Autonomy Manager software on the spacecraft. When launched, the arm is saddled onto its three launch locks in a 

stowed configuration. The fail safe brakes in each joint are on and provide additional means of rigidity for the arm to 

better withstand launch loads.

IDL Robot 2 (End Effector Study)

The goal of the second IDL robot run was to define the interfaces required between the robot arm and the endeffector as well as an initial set of requirements for an end-effector that could accomplish a variety of servicing tasks.

The initial trade study that was completed looked at the pros and cons of various robot end-effector and 

tooling paradigms. The first was an anthropometric end-effector (such as on Robonaut). While this would be a good 

tool to have in the robotic tool box, it is not the ultimate end-effector design as it has too many drawbacks—no 

redundancy in the many moving parts in the fingers; no easy way to pass power, data, and video across to the tool 

without a hard-to-manage-harness; limited clamping force capability (and therefore would not be able to grab and 

hold on to the back of a satellite). The second was a multipurpose end-effector (similar to a Swiss army knife). This 

was dismissed because of the mass and volume required to carry all the tools at the end of the robot. The third was 

an interchangeable end-effector mechanism that would allow different tools to be swapped on and off the end of the 

robot, and this is the option that was explored.

Time was spent determining the services that needed to be passed across the interface between the robot 

arm and the end-effector or on to the tools. The architecture that resulted was one in which a mission could fly a 

few specialized end-effectors for specialized tasks. An end-effector could grasp tools or be used alone if specific 

features are incorporated into the design. For example, adding specialized jaws to the output of an end-effector 

would allow it to grapple a satellite without the need for a specialized tool). Tools could be used by attaching them 

directly to the end of the arm (referred to as the “stump”) or an end-effector. Making the end-effectors very capable 

reduces the complexity (and cost) of the specialized robot tools that interface with the worksite. This hopefully 

leads to a mass and cost savings, as a few “smart” end-effectors can be flown along with many “dumb” tools. 

This concept also offers the greatest flexibility, an expected lower cost, and is a better option for incorporating 

redundancy.

It was determined that three rotary drives were desirable at the output of the end-effector. This would allow for 

high torque, high speed, and low speed drives, thus reducing the need to add transmissions to the tools. One of 

Figure Robot 2-1: End-Effector Interfaces
148 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

these drives would be on the end of the arm and would be passed through the end-effector. A linear drive (also on 

the end of the robot arm and passed through the end-effector) is also needed to actuate certain features in some 

of the tools or to switch settings in a transmission if one needed to be added to any of the tools. In addition to the 

mechanical tool drives that are needed to actuate the tools, it was determined that up to eight analog pairs would 

be needed for sensors such as a force-torque sensor, cameras and LED illuminators, strain gauges, proximity 

sensors, touch sensors, a leak detector, temperature sensor, and a pressure sensor; four pairs of SpaceWire; and 

four pairs for 10A power. A summary of the interfaces are depicted in Figure Robot 2-1.

The end of the arm incorporates a force-torque, electrical connectors, two cameras with LEDs, and a preload 

drive motor as shown in Figure Robot 2-2. As mentioned earlier, the end of the arm (shown in the right-side of 

Figure Robot 2-2) can interface with the end-effector (shown in the left-side of Figure Robot 2-2) or a tool (if a tool 

has the same “B” interface as the end-effector, it can be mounted directly on the end of the arm). Two camera and 

LED pairs on the end of the arm provide visual data to the autonomous of manual process of mating the arm with 

an end-effector or tool, and the preload drive motor is used to complete the connection. In one version, the endeffector also supports the mounting of cameras, lights, a proximity sensor, and a flash LIDAR as shown in the left 

side of Figure Robot 2-2. 

 Figure Robot 2-2: End-Effector and End of the Arm (Stump)

Figure Robot 2-3: Arm (on right) and the End-Effector (on left) 
 Appendix E – Integrated Design Laboratory (IDL) Payload Element Study Summary | 149

The changeout system is very reliable and robust. It is tolerant to temperature variations, and its motors include 

dual windings for redundancy. The mechanical features on its mating flanges provide coarse alignment for connector 

mating. When the end-effector and arm are combined as a system (shown in Figure Robot 2-3) and used on a fiveyear mission, the system has a predicted reliability of 98.9%.

IDL Robot 3 (Reconfigurable Human-Rated Robot)

While Study 1 focused on a robot manipulator system and Study 2 focused on the end-effector design, Study 3 

focused on some key aspects of the robot design. This study took the manipulator to the next level, making some 

fundamental changes to the control architecture and addressing the notion of modularity. The result is not one 

manipulator, but a family of manipulators with varying characteristics. They can be assembled to make the same 

basic arm structure, but they can also be reconfigured or modified with extra parts, leading to new conceptual 

designs. In addition to the manipulator, this effort investigated the node and other support equipment. 

This study does not go into the depth of the previous studies in terms of a defined mission task, joint 

configuration, actuator details, types of sensors, arm reach, work volume, etc. It utilizes information from the two 

previous studies, such as actuator designs, having a force/torque sensor, including capabilities for swappable 

tools, and having toolbox operations. The key change to computer processing is that it is now distributed (made 

local) and the notion of having two centralized electronic boxes is eliminated. Power for the arm comes from the 

spacecraft bus at either 120 VDC or 28 VDC through the nodes or other connections with the platform. These 

arms will still have an external robot arm harness and shielding to mediate thermal and radiation issues. However, 

cabling, thermal protection, and radiation shielding will be a problem due to reconfigurability, and these needs must 

be addressed. The control system for the arm will incorproate a combination of position, force, and rate control. The 

flight software will run on a real-time operating system such as VxWorks and utilize the SpaceCube 2.0 as the flight 

processor. Power, command, and telemetry are still passed between the robot and the spacecraft through a 1553 

spacecraft bus, Spacewire for instrument data, RS-422 to control the sensors, and a PCI interface to the joints and 

end-effector. The robotics executive software will either interface with the Vehicle Autonomy Manager software on 

the spacecraft or the Vehicle Autonomy Manager will have to be moved onto the robot. 

In this system-level study for the robot, key changes included: 1) implementing distributed control electronics, 

2) designing an arm that is reconfigurable and serviceable, and 3) designing a human-rated arm for human-robot 

missions. 

For each of the arm groupings (shoulder, elbow, and wrist), the associated electronics and computer 

processing units are mounted externally in a housing on the actuator structure. These Local Processing Units (LPUs) 

will control the motors, sensors, cameras, safety functions, switches, thermostats, FPGAs, all servo commanding, 

housekeeping, and some communication functions such as Spacewire. A subset of these electronics will be located 

in link modules to support segments.

All the various modules and spares are reconfigurable. To enable reconfiguration, every piece (joints, segments, 

and nodes) has grasp points, as shown in Figure Robot 3-1. The reconfigurable arm increases the serviceability of 

robots by allowing swapping out of failed segments, provides an economy of scale with common interfaces, and 

Figure Robot 3-1: Robot Node, Segments, Grasp Points
150 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

affords the ability to upgrade the arm as necessary. The arm can be reconfigured to accomplish the tasks of a “big 

hauler” or a “dexterous arm.” The study investigated a crane-like arm (Figure Robot 3-2) with a 30 m reach, able to 

manipulate a 30,000 kg payload.

The dexterous arm is a smaller, 2 m long manipulator. Taking the concept of dexterity to the extreme, the 

study investigated what they named the “Max DOF Work-Bot.” The Work-Bot consists of five arms of equal 

length attached to a node: one arm for grappling, two 

dexterous manipulators, and two arms used for video 

and cameras. This configuration provides a total of 43 

DOFs, requires an average of 852 W for operational 

power, and has a total data transfer rate of 230 Mbps. 

The “Big Hauler” and Max DOF Work-Bot” are shown in 

figure Robot 3-2.

Figure Robot 3-3 shows the Node and its 

components. Nodes are used to connect manipulators 

together in pairs and replace the DMUs from the 

previous studies. The nodes are detachable and will 

house a battery, battery support structure, and node 

electronics. When a node is detached, it will employ 

RF communications with the platform. The node can 

go on a “walkabout” on the target with or without the 

spacecraft, moving arm over arm across the target 

and recharging when attached to the spacecraft. There 

are two types of nodes: “smart” nodes and “dumb” 

nodes. The dumb nodes do not have any processing 

capabilities and serve only as structural supports 

between arm segments and to pass power and data. 

The dumb nodes were not thoroughly investigated in 

this study. Smart nodes act as the brains for larger 

robotic tasks, and have a camera on each face, C-type 

interface parts, and an omni-patch antenna. 

The node electronics include arm control, safety, 

mission sequencing, commanding, housekeeping, 

image processing, power management, the Spacecube 

processor, sensors (switches and thermostats), and 

Figure Robot 3-2: “Big Hauler” Configuration (on left) and Max DOF Work-Bot (on right)

Figure Robot 3-3: Node

Figure Robot 3-4: Robot Modular Segments
 Appendix E – Integrated Design Laboratory (IDL) Payload Element Study Summary | 151

communications (i.e. Spacewire, 1553 bus, and RF to 

talk to the spacecraft).

This modular, multi-segment concept allows for 

greater flexibility in on-orbit configurations and can 

reduce the per-segment launch loads. Figure Robot 3-4 

shows how the modular segments could be connected. 

The configuration takes advantage of the typical grasp 

point and the grasp/override point locations. This study 

also investigated the sequence for an on-board asembly 

of a robot arm with the shoulder, link, elbow, link, and 

wrist assembly sequence by another robot manipulator. 

Additional arm pieces are stored in “quivers” attached to 

the outside of the spacecraft (Figure Robot 3-5). 

Due to the reconfigurable nature of the robot 

segments of this study, developing a cost estimate for 

the robot was difficult. A “Cost-Bot” was designed that 

contains each of the segments that was studied, and 

is used only for costing purposes. The Cost-Bot and a single node would have a combined mass of 549 kg. This 

configuration is shown in Figure Robot 3-6. 

The Cost-Bot manipulator has 7 DOF with a shoulder, elbow, wrist, lower arm segment, and upper arm 

segment. The figure is only notional for costing purposes, because in reality, the distance between the shoulder and 

the elbow, and the distance between the elbow and the wrist will be approximately the same. Another Cost-Bot 

configuration (with 0.75 m links) that was not considered a launch configuration is depicted in Figure 3-6. 

Cost of the Robot Systems

As discussed in Chapter 4, cost estimates can be extremely difficult to validate, especially for systems that have 

never been built. A similar problem exists when comparing modeled costs to those reported for systems that have 

been built, since these comparisons require a detailed understanding of what was included in the reported costs. 

Reported development costs for a robotic system could be offset by many factors, such as 1) a vendor using 

previous design or software development experience, 2) parallel development of robotic systems for two different 

customers so that the non-recurring costs were divided between two customers, 3) a build-to-print duplicate of an 

existing, proven design, 4) any cost-sharing arrangements, 5) including or not including flight spares, system-level 

integration and test, etc. in the modeled costs. However, some useful observations can be made by comparing the 

modeled costs of individual components for the notional missions, with reported costs of similar robotic systems 

proposed and flown in the past.

Consider the case of a complex robotic system with two grapple arms and two dexterous pairs, as was 

modeled for the last two notional missions (NM5 and NM6). Of the $1.2B cost reported earlier for the robotic 

Figure Robot 3-5: Node with Quiver

Figure Robot 3-6: Cost-Bot Configuration
152 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

system, $230M ($ FY 10) was for the development of the first 15 m, human-rated grapple arm and $290M ($ FY 10) 

for the development of the first modular, on-orbit reconfigurable pair of dexterous robot arms. 

The additional costs modeled for the robotic system are as follows:

Flight system (including sub-elements listed below) $ 750M

 Design, systems engineering, management, 

 and mission assurance for complete system

 Hardware and electronics for 

 two human-rated grapple arms and 

 two on-orbit reconfigurable dexterous pairs

Engineering test unit for full flight system $ 250M

Flight software (including sustaining engineering) $ 38M

Miscellaneous $ 190M

 ground support equipment, system-level environmental test,

 flight spares, spacecraft-level integration and test

This compares reasonably well to reported costs for the development of the Space Shuttle’s Remote Manipulator 

System (RMS). The original development cost has been reported as $108M ($ FY 81) ($260M in $ FY 10). Based on 

that experience, Cooper (of the Canadian company MacDonald, Dettwiler and Associates) reported in his testimony 

before Congress that the cost for developing a similar grapple arm robotic system for the Hubble Robotic Servicing 

and Deorbit Mission (which was a non-human-rated system) was only $25M (FY 05; $28M in FY 10). In the same 

testimony, a cost of $129M (FY 05; $144M FY 10) was reported for the development of an exact duplicate of the 

International Space Station’s Special Purpose Dexterous Manipulator. So the total cost of developing the grapple 

arm and dexterous pair robotic system would be estimated as $172M (FY 10). 

Using these reported cost data for RMS and HRSDM to predict the cost of developing the complex robotic 

system required for our Notional Missions yields the following. Developing two human-rated grapple arm robotic 

systems ($260M + $28M) and two on-orbit reconfigurable dexterous pairs (2 x $144M) would be expected to 

be roughly $570M. This compares favorably with the cost model for notional mission 6, which showed a $750M 

development cost for two grapple arms and two dexterous pairs. 

It is worth noting that The Aerospace Corporation also modeled the HRSDM robotic system in 2005, with 

quite different results. They estimated $700M ($ FY 05) for the development of the HRSDM robotic system, more 

than four times the $150M ($ FY 05) estimated by Cooper. As indicated earlier in this section, the wide disparity 

between HRSDM estimates could stem from cost elements that were included in the Aerospace model that were 

not included in Cooper’s estimate, (e.g., flight software development, test units, environmental testing) or from cost 

offsets included in Cooper’s estimate that were not included in the Aerospace model (e.g., spare parts borrowed 

from the shuttle RMS program).

Thus, as with any spaceflight hardware, in assessing or comparing cost estimates for robotic systems it is 

crucial to obtain all possible details about the costing tool used and all inputs and assumptions.
 Appendix F – Notional Mission Studies, Notional Mission 1: GEO Supersync | 153

Appendix F – Notional Mission Studies

Introduction

The Satellite Servicing Study Team developed six Notional Mission design concepts for on-orbit servicing. The suite 

of Notional Missions was designed to probe the corners of the unsampled areas of the Satellite Servicing Trade 

Space (see Chapter 4). The six Notional Missions (NMs) are GEO Supersync (NM1), GEO Refueling (NM2), LEO 

Refurbish (NM3), EML1 Robotic Assembly (NM4), HEO Human/Robotic Refurbish (NM5, and SEL2 Human/Robotic 

Assembly (NM6). 

Each notional mission in this appendix includes a model of total mission costs for the purpose of comparison; 

however, disparate mission concepts and varying fidelity of customer information make true cost comparisons at a 

mission-level far more complex. A comprehensive overview of how these cost estimates were generated is provided 

in Chapter 4, “Mission Design Methodology and Cost Estimation.” As stated, cost estimates can be difficult to 

validate, especially for systems that have never before been built. However, for the purposes of this study, we 

believe that reliable relative cost estimates can be obtained for the notional missions considered. The absolute costs 

are reserved for future study.

It is worth reiterating that costing tools and absolute costs are not a focus of this study. Instead, we selected a 

specific method for generating costs (PRICE-H), and then used the results as one data element in the comparisons 

and general observations about the notional missions. It is also worth noting here again that cost was not a 

constraint during the notional mission studies. The notional missions were designed to probe what is possible, with 

a resulting cost estimate. 

Notional Mission 1: GEO Supersync

Mission Study Objectives

The objective of the Notional Mission 1 (NM1) study is to design a Servicer spacecraft that can sequentially capture 

and control several legacy, non-cooperative satellites in nearly co-planar geosynchronous orbits and relocate them 

to a disposal orbit 350 km above the GEO belt. Potential customer satellites in this orbit include Solar Dynamics 

Observatory (SDO) and Geostationary Operational Environmental Satellite (GOES). The Customer satellites are 

assumed to be tumbling at a modest rate of 0.25 degrees per second per axis. The mission design includes an 

estimate of the number of times that the Servicer can rendezvous with, capture, and boost a Customer satellite 

during a series of sorties while remaining within the fuel budget. 

Mission Overview

The Servicer spacecraft launches into geosynchronous orbit and then executes sorties to roughly 10 Customer 

satellites, assuming approximately one degree of orbit plane change between Customers. Orbital dynamics dictates 

that greater plane changes between Customers increases fuel consumption and yields a mission with fewer 

Customers serviced, all else being equal. At the start of the mission, the Customer satellites (at the end of their 

mission life) are on-orbit waiting for a boost to a disposal orbit. The Servicer satellite is equipped with all hardware, 

algorithms, and fuel necessary for supervised autonomous rendezvous and capture (AR&C) and supersync of the 

Customers. The NM1 concept of operations is illustrated in Figure NM1-1.

This study estimated the number of sorties possible based on some simplifying assumptions about the 

distribution of Customer satellite orbits and attitude states. During the second notional mission study, an algorithm 

was formulated to furnish near-optimal solutions to the “traveling salesman” optimization problem for orbit 

rendezvous. This algorithm was utilized with actual orbital data for representative GEO satellites to maximize the 

number of sorties achieved during Notional Mission 2.

The Servicer satellite is launched and inserted directly into GEO in the plane of the first Customer satellite. 

The AR&C sequence begins with the Servicer spacecraft in its delivery orbit 300 km behind and 30 km below the 

Customer spacecraft, as shown in Figure NM1-2. The Servicer uses a combination of co-elliptic drifts and Hohmann 

transfers to gradually close distance with the Customer spacecraft over the course of approximately 4.5 days, at 

which point the Servicer inserts itself onto a safety ellipse about the Customer spacecraft. The Servicer remains on 

the safety ellipse for at least one period of the Customer’s orbit (~24 hours). During this time the Servicer collects 

situational awareness data, confirms the status of the Customer, and performs pose estimation to accurately 

determine its position and attitude relative to the Customer. Once the ground deems the situation safe and the 

relative navigation solutions have converged, the Servicer spacecraft executes a series of maneuvers to acquire 

and translate down a capture axis that constitutes a straight-line approach in the Customer’s body-fixed frame. 

The Servicer maneuvers the robotic arms to within approximately 1 meter of the Customer (placing the arms in a 
154 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

Figure NM1-2: AR&C Sequence

Figure NM1-1: Geosynchronous Supersync Concept of Operations
 Appendix F – Notional Mission Studies, Notional Mission 1: GEO Supersync | 155

predefined capture box). The robotic arms then autonomously grasp the Customer at predefined grapple points and 

complete the capture. 

At this point, the Customer satellite goes into free drift and the Servicer controls the stacked spacecraft. It is 

assumed that non-functional spacecraft will already be in free drift by definition, and furthermore, that functional 

spacecraft can be commanded to go into free drift. The Servicer boosts the stack into a super-synchronous 

disposal orbit (GEO + 350 km) as per NASA-STD-8719.14 (Process for Limiting Orbital Debris). The Servicer 

releases the Customer satellite and then lowers itself to a parking orbit approximately 300 km above GEO. The 

Servicer stays in this parking orbit until the next Customer is ready for removal. Figure NM1-3 illustrates the orbital 

maneuvers performed during Customer capture and boost. After the last Customer is supersynched, the servicer 

and the Customer both remain in the super-synchronous disposal orbit. The NM1 mission life is 5 years, during 

which 10 Customer satellites will be serviced. 

Servicing mission operations are conducted from the NASA’s Goddard Space Flight Center’s (GSFC) Servicing 

Mission Operations Center (SMOC). The AR&C phase is supervised from the ground and includes scheduled hold 

points, during which the ground team assesses the situation and provides permission for the Servicer to proceed 

autonomously between hold points. After the AR&C phase, the robotic activities will be teleoperated from the 

ground. 

System Description

The Servicer spacecraft design includes sensors, algorithms and four robot arms for autonomous capture of noncooperative Customer satellites in geosynchronous orbit and subsequent boost to disposal orbit. This mission 

uses an AR&C package (sensors and avionics) with a pan/tilt unit designed during the associated IDL study (see 

Appendix E). The total AR&C package mass is 141.1 kg; the peak power draw is 128.9 W; the peak data rate is 

996 Mbps (786 Mbps with compression), and the enveloping dimensions of the AR&C sensor and avionics package 

on the pan/tilt unit are 1400 × 750 × 723 mm.

The Servicer has four identical 2 m robot arms affixed to the sides at the front corners. The arms autonomously 

grasp the customer spacecraft and hold it as the Servicer boosts the stack. As a result, the arms are an integral 

component of the Servicer’s AR&C capability. The robot arms are designed to be robust enough to withstand the 

loads generated while de-spinning a Customer. Each arm is attached to the Servicer via a mounting surface that 

houses the arm on the external surface and its centralized control avionics on the internal surface. The mounting 

pallet is then hard mounted to the spacecraft structure, which allows the arms to be fully verified at the assembly 

level prior to integration with the spacecraft.

Figure NM1-3: Orbital Maneuvers Performed during Customer Capture and Boost
156 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

A gripper is envisioned to attach to the grapple points and is equipped with a LIDAR to sense the Customer. 

Except during the AR&C phase, the arms are teleoperated from the ground. The total signal latency from ground 

command to robot motion, including all security measures, is predicted to be less than 3 seconds; the requirement is 

that the latency be less than 7 seconds during a sortie.

The Servicer is a 3-axis stabilized, sun-pointing, fully redundant bus system. The AR&C avionics handle collision 

avoidance while approaching the customer satellite. The two deployable, gimbaled solar arrays are mounted 180 

degrees apart. The power system provides approximately 1,500 W of total average power and has two 100 Ahr 

Li-Ion batteries. The data rate is 10 Mbps, and the system has 250 Gbits of data storage capability. The data 

communication protocols are CCSDS, S-band for housekeeping and X-band for operations. Figure NM1-4 shows 

the Servicer configuration during three phases: launch, deployed and stacked (holding the Customer). 

The baseline Servicer spacecraft design utilizes chemical propulsion. The Servicer dry mass (including 30% 

contingency) is 2,352 kg, with a wet mass of 3,694 kg. This notional Servicer could be launched to GEO on an Atlas 

V with only 7% margin, or on a Delta IV Heavy with 70% margin.

I&T and Schedule

The Servicer mission integration and test (I&T) is executed at the NASA Goddard Space Flight Center. The AR&C 

sensor/avionics package and robot systems are delivered to GSFC ready for integration and test with the Servicer 

vehicle. Both are fully qualified prior to delivery for Servicer I&T. The development schedule is shown in Figure NM1-5.

The Servicer test and verification includes alignment and calibration of bus sensors (e.g., star trackers). 

Deployables (solar array, high gain antenna booms) undergo integrated functional verification at the bus level.

Figure NM1-4: Servicer in Launch, Deployed and Docked Configuration 

Figure NM1-5: NM1 Mission Schedule
 Appendix F – Notional Mission Studies, Notional Mission 1: GEO Supersync | 157

Enabling Technologies

No specific technology needs have been identified for this mission. However, a less massive spacecraft bus would 

decrease launch mass and allow the Servicer to carry more fuel, which would increase the number of Customer 

spacecraft that could be serviced. Additionally, a detailed analysis of the use of solar electric propulsion for this 

mission should be performed. While using solar electric propulsion for the orbit plane change maneuvers between 

Customers would increase the mission duration, it could also allow a significantly larger number of Customer 

satellites to be boosted to super-synchronous disposal orbit by virtue of propellant mass savings. 

Key Assumptions

The ability of the Servicer to capture and “supersync” (place in a super-synchronous disposal orbit) multiple 

Customers depends strongly on the actual masses and attitude rates of the Customers. The masses of Customer 

satellites may vary, though our team made the simplifying assumption that all of the Customer satellites will have 

similar mass properties to the first. Also, the ΔV required for capture depends on the Customers having attitude 

rates of, at most, 0.25 degree per second per axis. However, if some Customers have higher attitude rates, this can 

drive up the ΔV required for capture significantly. For example, if a Customer has an attitude rate of 1 degree per 

second per axis, the capture ΔV is approximately 20 m/s, compared to 2 m/s for the 0.25 degree per second per 

axis case. Generally, all else being equal, the required ΔV for capture increases in proportion to the square of the 

Customer’s attitude rate. Thus, as Customer attitude rate increases, it can begin to compete with the plane change 

ΔV between Customers, and even surpass it to become the main driver of total mission ΔV.

NM1 GEO Supersync Mission

Current Best 

Estimate Phase A-F 

($M, FY 10)

Robot (4 dexterous arms) $330 

AR&C (w/PTU) $75 

Bus $140 

Launch Vehicle $190 

Operations $14 

Everything Else $160 

Total Servicing Cost $910 

Notional Mission 2: GEO Refueling

Mission Study Objectives

The objective of this study is to develop a mission concept, Refueler spacecraft design, and on-orbit fuel depot 

design to facilitate the refueling of multiple Customer spacecraft at GEO. This mission design is intended to address 

the in-orbit refueling portion of the on-orbit servicing trade space.

Mission Overview

Notional Mission 2 (NM2) is designed to refuel satellites in the GEO belt. The NM2 is composed of two satellites: 

the Refueler and the Fuel Depot. The Refueler spacecraft is small and agile, and is designed to carry enough fuel 

to refuel five Customer satellites during a sortie. In between sorties the Refueler spacecraft will rendezvous with 

the Fuel Depot to take on more fuel. The fuel Depot carries sufficient fuel to allow the Servicer to refuel up to 25 

Customer satellites, based on some key simplifying assumptions regarding the distribution of Customer satellite 

orbits. A minimalist approach was taken for the design of the Fuel Depot itself, and consequently, it is only equipped 

with adequate subsystems to exist passively at GEO. Figure NM2-1 presents the on-orbit refueling concept of 

operations.

The Refueler and Depot are launched together on a Delta IV Heavy to 100 km above GEO, where the Depot 

remains. The Refueler nominally delivers fuel to five Customer satellites before returning to the Depot to refuel 

itself. While attached to the Depot during its own refueling, the Refueler executes maneuvers to maintain the Depot 
158 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

Figure NM2-2: Nominal Refueling Mission Scenario

orbit plane (which drifts under the influence of natural perturbations). Figure NM2-2 is the nominal scenario for the 

refueling mission.

The NM2 study assumes mission launch in 2015 and mission life of 10 years. The Figure NM2-3 depicts the 

refueling operations concept, including autonomous rendezvous and capture (AR&C) with the Depot. During each 

AR&C phase, the Refueler AR&C system (sensors and avionics) commands the bus GN&C system. The Customer 

satellites are assumed not to be in uncontrolled attitude states (3-axis stabilized) and are able to enter free drift 

prior to capture. It is further assumed that the Customer satellites each need to receive only 20 kg of Hydrazine per 

refueling.

During nominal operations, the Customer satellite 

is commanded by its ground controllers to enter 

free drift towards the end of the AR&C sequence. 

However, this presumes that the Customer satellite still 

has adequate remaining propellant to be controlling 

its attitude prior to AR&C. If the Customer satellite is 

completely out of fuel before receiving the refueling 

service, then an assumption made in NM1 is applied, 

which is that the maximum uncontrolled Customer 

attitude rates are no more than 0.25 degrees per 

second per axis. However, in contrast to NM1, the 

NM2 study assumes that none of the Customer 

satellites are non-functional. Thus, it is assumed that 

even if the Customer satellite is completely out of fuel 

and not controlling its attitude, the Customer ground 

controllers can still command the Customer satellite’s 

control system to become completely quiescent. This 

will prevent the Customer spacecraft’s control system 

from inadvertently attempting to counteract the forces 

and torques imparted by the Refueler spacecraft during 

mated operations (after refueling and prior to release). 

Figure NM2-1: On-Orbit Geosynchronous Refueling Concept of Operations
 Appendix F – Notional Mission Studies, Notional Mission 2: GEO Refueling | 159

Figure NM2-3: Refueling Concept of Operations and AR&C with Depot

Furthermore, provisions are included in the design of all AR&C sequences in the notional mission suite studies such 

that the Refueler spacecraft can gracefully retreat along the approach axis in response to any anomalies that may 

occur during the final approach phase of the AR&C sequence, and then re-approach when anomalies are resolved. 

This allows multiple capture attempts to be made if necessary, while ensuring the safety of both the Refueler and 

Customer spacecraft.

Refueling mission operations are conducted from the NASA Goddard Space Flight Center Refueling Mission 

Operations Center (MOC). AR&C sequences between the Refueler and the Customer satellites are autonomous 

but supervised by the ground, with scheduled hold points during which the mission operations team assesses 

the situation and provides permission for the Refueler to proceed autonomously between hold points. After the 

AR&C phase, refueling activities will be teleoperated from the ground. To accommodate teleoperation from ground, 

communications will be continuous, thus providing constant telemetry and commanding during refueling. One 

contact per day with the Refuler is planned for monitoring between Customer satellite refuelings. 

Refueler and Depot System Description

The Refueler spacecraft carries the modified AR&C system (without a pan/tilt unit but with four extra cameras), two 

robot arms, two toolboxes, and the refueling system/package. The dry mass for the Refueler spacecraft, including 

payload elements, is 1,894 kg (includes 30% contingency).

After initial separation from the Depot post-launch, the Refueler raises its orbit from GEO + 100 km to GEO + 

127 km in order to drift between the Customer spacecraft below at GEO. As shown in Figure NM2-2, this study 

makes the simplifying assumption that all of the Customer spacecraft are evenly spaced around the GEO belt. A 

further assumption is that Customer spacecraft orbit planes are within ±1° of the equatorial plane. Once the Refueler 

is within 300 km of a Customer, the Refueler will lower its orbit to GEO – 30 km in order to begin the same AR&C 

sequence described in NM1. Accordingly, 20 m/s of ΔV on the part of the Refueler is budgeted for each of these 

AR&C sequences. After capture and refueling, the Refueler releases the Customer and then transfers back to a 

GEO + 127 km orbit to drift to the next Customer. This cycle repeats until six Customers have each had 20 kg of 

propellant delivered to them, at which time the Refueler raises its orbit to GEO + 70 km, drifts to within 300 km of 

the Depot, and executes the standard AR&C sequence with the Depot. After attaching to the Depot and taking on 

propellant, the Refueler performs a maneuver to correct the Depot’s orbit plane (which has drifted by approximately 

1° under the influence of natural perturbations while the Refueler was performing sorties). The Refueler then tops 
160 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

off its fuel tanks and proceeds to conduct further sorties. Once the Refueler and Depot only have enough fuel 

remaining for their disposal, the Refueler will perform AR&C with the Depot once more and then boost the Refueler/

Depot stack to GEO + 300 km for proper disposal.

A parallel study was completed shortly after the MDL study which utilized a special algorithm to perform nearoptimal ordering of the Customer spacecraft, drawing upon a database of orbital elements for actual operational 

U.S. GEO satellites that use Hydrazine propellant. The results of this parallel study demonstrated that—with nearoptimal ordering and proper selection of the first Customer satellite in the sequence—the Refueler design is indeed 

capable of visiting and refueling up to 26 customer satellites. Thus, the Refueler will perform a total of five sorties. 

Four sorties consist of six satellites each, and the fifth sortie consists of two customer satellites.

The Refueler has two 2-m long robots affixed to the front/top of the bus structure on a mounting surface. This 

mounting surface houses the arm on one side with its electronics (DMU & ACE) mounted on its back (or internal) 

surface. The mounting pallet is hard mounted side by side to the Refueler spacecraft structure. The arms perform 

an autonomous capture and will be teleoperated for the refueling tasks. There are two toolboxes on the Refueler. 

These toolboxes can and will be exchanged with toolboxes in the Depot for servicing different Customer satellites. 

Power comes from the bus through the Power System Electronics (PSE) in the Refueler spacecraft. Command and 

control of the robot arm (or signals for data, control, monitoring, and timing) is through the CSI hard lines to the 

avionics/C&DH subsystem on the Refueler bus. 

The Refueler bus structure is of composite truss design with composite/aluminum honeycomb decks. The 

thermal system includes Multilayer Insulation (MLI), heaters, thermistors, thermostats, variable conductance heat 

pipes, and radiators sized for potential full sun load. The RF communication system includes S-band Omni, and 

X-band HGA, capable of 10 Mbps downlink. The solar array has a total area of 7.2 m2 and uses Tj GaAS cells 

with dual-axis SA drives. There are two 100 Ah Li-Ion JSB batteries. The power system is sized for two 72-minute 

maximum eclipse seasons twice per year. The baseline power system electronics system consists of a heritage 28 

VDC battery-dominated bus. The ACS is thruster-based and its components include star trackers, IRU, CSS, and 

GPS. Figure NM2-4 presents the Refueler, robot arms, and bus components. 

The Depot is designed to be a passive spacecraft that can exist passively at GEO with minimal support. The 

dry mass for the Depot is 1,326 kg (includes 30% contingency). Its mechanical structure is of a composite truss 

design with composite/aluminum honeycomb decks. The thermal system includes MLI, heaters, thermistors and 

thermostats. The Depot has no RF communication system and no avionics. It has ~1m2

 of solar array but it has 

Figure NM2-4: Refueler Spacecraft Components and Robot Arms
 Appendix F – Notional Mission Studies, Notional Mission 2: GEO Refueling | 161

no battery. The ACS system passively maintains the Depot in a sun-pointing attitude through use of a deployable 

solar sail and a libration damper. The Depot itself does not have thrusters, but carries both Hz propellant and N2

pressurant. Depot telemetry is read by the Refueler when it is attached to the Depot. The Depot is designed to 

be a passive and cooperative rendezvous customer for the Refueler and therefore has retroflectors mounted on 

its surface. It also contains six toolboxes that can be used by the Refueler to service different Customer satellites. 

Figure NM2-5 shows the Depot and the Refueler together, while Figure NM2-6 shows the Refueler with a Customer 

satellite during refueling.

I&T and Schedule

Figure NM2-7 shows development schedules for the Refueler and Depot. They are scheduled to begin at 

approximately at the same time so that they would complete their individual environmental test programs in time for 

“stack” integration and test and launch no earlier than Fall of 2015.

Enabling Technologies

Enabling technologies for this mission are TRL 6 and above. 

Key Assumptions

Two key assumptions are that the Customer satellites will have rates less than 0.25 deg/sec/axis and that the 

Refueler solar array will have no less than 30% illumination. It is also assumed that two toolboxes on the Refueler will 

be adequate to refuel five Customer satellites at a time, and the additional six toolboxes on the Depot are sufficient 

to refuel the follow-on Customer satellites.

Figure NM2-5: Depot with Refueler Attached Figure NM2-6: Customer Satellite with Refueler Spacecraft Attached

Figure NM2-7: Refueler ahd Depot Schedules
162 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

Notional Mission 3: Robotic and Human Servicing of Satellite in LEO

Mission Study Objectives

The Notional Mission 3 (NM3) study objective is to develop a Servicer spacecraft design to support a non-shuttlebased human/robotic mission to refurbish a cooperative customer satellite in LEO that was designed to be 

serviced. The Servicer carries and accommodates all the robotic elements and tools, the airlock and all associated 

consumables, and all the replacement/upgrade hardware that is to be installed in the customer satellite. The 

Servicer is also equipped with all the necessary sensors and algorithms to perform AR&C with the cooperative 

customer satellite, and to support subsequent cooperative rendezvous and berthing of a Commercial Orbital 

Transportation Services (COTS) crew vehicle with the Servicer and Customer in their mated configuration. The 

Hubble Space Telescope (HST) serves as the cooperative customer satellite in LEO, and the SpaceX Dragon serves 

as the crew vehicle. 

Mission Overview

The NM3 flight segments include the Servicer spacecraft, known as the Dexterous Service Module (DSM), HST, and 

Dragon. The DSM is the only vehicle to be designed during the NM3 study; the HST and Dragon are assumed to 

exist and be ready for use. 

At the start of the month-long servicing mission (see Figure NM3-1), the HST is operating in LEO with a known 

set of required hardware refurbishment/replacement tasks. The DSM launches equipped with two robotic arms, the 

airlock and consumables for five cycles of EVA repress and depress, two active LIDS, tools, and new HST hardware 

to be installed during the mission. After launch and separation, DSM completes orbit insertion into a circular LEO at 

537.5 km and performs systems checkout. Prior to crew launch, DSM completes in-orbit checkout (IOC), performs 

AR&C with HST, and performs predefined robotic get-ahead tasks in a manner that satisfies “operationally safe to 

release” criteria established for previous STS servicing missions. 

Following successful AR&C and servicing get-aheads of HST, the stacked DSM/HST participates in a AR&C 

sequence with Dragon. Following the current plan for International Space Station (ISS) procedures, Dragon 

maneuvers into a defined capture box near the DSM/HST stack, after which the robotic arm on DSM autonomously 

grapples Dragon. A scripted berthing procedure is then executed to mate Dragon to the DSM airlock. A wireless 

communication system allows the Dragon crew to perform the grapple and berth procedures manually if necessary. 

Figure NM3-2 presents the concept of operations.

The four-person crew performs two days of Extravehicular Activity (EVA) during which two EVA crew members 

are assisted by the DSM robotic systems that are operated by the Intra-vehicular (IV) crew. During sleep periods 

between the EVA days, the ground team teleoperates the DSM robots, completing clean-up or get-ahead tasks in 

preparation for the next day’s work. This synergistic combination of dexterous robotic work and human EVA enables 

the servicing mission to accomplish significantly more work during the month-long mission than a human crew 

could during the two planned EVA days.

NM2 GEO Refueling Mission (Servicer + Depot)

Current Best 

Estimate Phase A-F 

($M, FY 10)

AR&C $60 

Robot (2 dexterous arms) $240 

Payload $80 

Bus (Servicer & Depot) $220 

Launch Vehicle $300 

Operations $80 

Everything Else $200 

Total Servicing Cost $1,180 
 Appendix F – Notional Mission Studies, Notional Mission 3: Robotic and Human Servicing of Satellite in LEO | 163

Figure NM3-1: Mission Timeline

Figure NM3-2: Robotic and Human Servicing of Satellite in LEO Concept of Operations
164 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

After completion of the EVA tasks, Dragon is deployed by DSM and the crew proceeds to return to Earth. 

The ground team then teleoperates the DSM robotic arms to complete closeout and HST hardware safing tasks, 

returning HST to nominal operation. The DSM then boosts HST’s orbit by as much as 60 km and deploys HST. 

Finally, DSM performs a deorbit maneuver and reenters the atmosphere. Figure NM3-2 shows the mission timeline, 

and Figure NM3-3 shows the DSM orbital maneuvers during rendezvous with and capture of HST. 

Dexterous Servicer Module (DSM) Description

The DSM consists of a spacecraft bus, robots, tools (in toolboxes), HST hardware, and the necessary sensors and 

algorithms for AR&C with HST and AR&C with Dragon. The AR&C hardware includes the standard sensor package 

without the pan/tilt unit and retroreflectors. The DSM bus contains an active LIDS to which HST is berthed, and 

a CBM/LIDS to which Dragon is berthed. The bus also contains 12 Multi-Function Ports (MFP), which provide 

structural/power/data interfaces to robot arms and other payloads such as the sunshield. Figure NM3-4 shows the 

DSM components. 

Two robots are affixed to the front side of the DSM, with a robot arm on either side of the LIDS mechanism. 

Both arms are human-rated, two-fault tolerant systems with manual override options for critical operations and 

capabilities. A 14 m, two-link robot arm is used to berth and deploy Dragon and to position an astronaut at the 

various worksites during EVAs. The second 7 m robot arm can also position an astronaut, but it is designed to use 

a specialized end-effector to perform more dexterous manipulation. Both arms are hard-mounted to the servicer 

structure, and the arm electronics for each arm are identical, centralized avionics. The arms are teleoperated from 

the ground except while the crew members are conducting an EVA, in which case the arms are operated by an IVA 

crew member in Dragon. Power and data for the robot arm are passed through Robot Mounting Points (RMPs) to 

the DSM bus systems. 

The DSM bus structure is comprised of composite/aluminum honeycomb panel construction with deployable 

payload bay doors. The thermal system includes a 15.5 m2

 radiator with embedded heat pipes, loop heat pipes for 

payload and bus components, thermostatically controlled heaters, multi-layer insulation (MLI), and coatings. The RF 

communication system consists of Ka band High Gain Antennas (HGA) to TDRS, S-band omnidirectional antenna 

to ground, UHF to the Dragon (for video), S-band to the HST, and GPS for orbit determination. The bus contains 

eight 100 Ahr Li-Ion batteries and a 110 m2

 Tj GaAs solar array. The power system buses are block redundant, and 

Figure NM3-3: DSM Orbital Maneuvers to Rendezvous with and Capture HST
 Appendix F – Notional Mission Studies, Notional Mission 3: Robotic and Human Servicing of Satellite in LEO | 165

Figure NM3-4: Dexterous Servicer Module (DSM) Components

Figure NM3-5: DSM/HST Stack

the attitude control system (ACS) is thruster-based with 6-DOF control. Large engines are used for orbit maneuvers, 

while the small engines are for proximity operations and attitude control. During stacked operations, solar-inertial 

attitude supports solar array pointing and worksite shading. The ACS components also include star trackers, 

IMUs, and CSS. The propulsion system has two modes with regulated pressure, allowing either bipropellant or 

monopropellant operation. The total propellant mass is 

4,350 kg. Thrusters are canted 60o from sensitive areas 

to minimize plume-induced structural loads, heating and 

contamination. There are three main flight computers 

with auto FDIR and voting. Figure NM3-5 shows DSM 

and HST mated together. Figure NM3-6 depicts the 

COTS/DSM/HST Stack.

I&T and Schedule

For the purpose of mission study planning, phase A is 

12 months in duration and phase B starts in July 2011. 

The DSM launch date is March 2017, and 39 months 

are allowed for DSM fabrication and integration of bus 

and payloads. The schedule allows staggered payload 

deliveries; the airlock is delivered first during DSM 

fabrication, and EVA tools are delivered last at NASA’s 

Kennedy Space Center (KSC) during prelaunch. The 

conceptual mission schedule is presented in Figure 

NM3-7. 
166 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

Enabling Technologies

No new technology development needs have been 

identified for this mission. 

Key Assumptions

The Hubble Space Telescope (HST) is used as the 

Customer for this run because it is an excellent historical 

source of defined interfaces that drove Servicer 

requirements during actual previous missions. As a 

notional Customer, HST provides known tool, crew, 

and vehicle interfaces, keep-out and “no-touch/nodamage” zones, and limits on plume impingement and 

hardware temperatures. Having set standards for tool 

development over five servicing missions, it is a proven 

test bed for LEO on-orbit repair and refurbishment. 

These well-understood interfaces allowed the study 

team to focus on developing the Servicer.

Figure NM3-6: COTS/DSM/HST Stack

Figure NM3-7: Mission Schedule

NM3 LEO Refurb COTS Mission

Current Best 

Estimate Phase A-F 

($M, FY 10)

AR&C $60 

Robot (2 human rated GAs) $350 

Payload $460 

Servicer Bus $670 

Airlock $200 

Operations $30 

Launch Vehicle $300 

Everything Else $500 

Total Servicing Cost $2,570 
Notional Mission 4: Assembly of the Thirty-Meter Space Telescope (TMST) at EML1

Mission Study Objectives

The Notional Mission 4 (NM4) study objective is to develop a Servicer design concept that provides a platform for 

robots to assemble a Thirty-Meter Space Telescope (TMST) at EML1. The Servicer carries the robotic elements and 

mounting points for the observatory and is also designed to be a passive, cooperative customer vehicle for AR&C 

with the Construction Barges that will be sent to it prior to TMST construction. Additionally, the Servicer will possess 

the sensors and algorithms required to perform AR&C with the TMST for periodic post-construction servicing. All 

subsystems are serviceable and are sized to accommodate the TMST requirements during the two-year assembly 

process. Following the deployment of the assembled TMST, the Servicer remains at EML1 for 20 years and serves 

as a platform for robotic servicing of the TMST or other customers. 

Mission Overview

The NM4 flight segments include the Robotic Telescope Construction Servicer (RTCS) and eleven Barges carrying 

the parts that will be assembled to create the TMST, additional tools, and robot modules. Three of the eleven 

Barges carry hardware needed for the periodic servicing of the TMST. All flight segments are launched on a Delta 

IV Heavy launch vehicle, which limits the mass that can be carried up with the RTCS and dictates the number of 

launches required to complete the entire mission. Thus, at launch, the RTCS consists of a spacecraft bus with 

all the accommodations necessary to complete the assembly mission and AR&C mission phases with a single, 

operational robot arm. The first Barge carries all remaining robotic hardware (in a Quiver) and tools (in a Toolbox), a 

deployable solar array to augment the power system, and the first pieces of the observatory.

The RTCS is launched directly into a high-energy Earth departure trajectory towards the EML1 Lyapunov orbit 

insertion point. The launch energy (C3) is approximately -2.4 km2/s2, meaning that the launch vehicle (and its upper 

stage) has to impart slightly less energy to the RTCS than it would for a lunar mission. The flight time required for the 

RTCS to arrive at the Lyapunov insertion point is approximately 6 days. Upon arrival at the insertion point, the RTCS 

performs a ΔV of approximately 600 m/s to insert itself into the EML1 Lyapunov orbit. This trajectory sequence is 

depicted in Figure NM4-1. The RTCS will station-keep on this orbit while awaiting the arrival of the Construction 

Barges. The characteristics of the EML1 Lyapunov orbit are also shown in Figure NM4-1. The Lyapunov orbit has a 

period of approximately 12.135 days, is approximately 60,000 km in size along its longest axis, and is approximately 

16,850 km wide along its shortest axis. One of the key advantages of this orbit is that the RTCS need only execute 

at most 60 m/s of ΔV annually to maintain the Lyapunov orbit.

 Appendix F – Notional Mission Studies, Notional Mission 4: Assembly of the Thirty-Meter Space Telescope (TMST) at EML1 | 167

Figure NM4-1: Trajectory from Earth to EML1 Lyapunov Orbit
168 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

The Construction Barges launch after the RTCS is on-station in the EML1 Lyapunov orbit. The trajectories they 

fly from Earth are nearly identical to the RTCS trajectory, with one exception. The Barges insert into the Lyapunov 

orbit approximately 1,000 km behind the RTCS, at a time when the RTCS is located at its original insertion point. 

This allows the Barges to exploit features of the natural relative spacecraft dynamics on Lyapunov orbits to help 

them gradually close distance for AR&C with the RTCS over the course of approximately 1 week. Under these 

conditions, the AR&C sequence between a Barge and the RTCS requires only 12 m/s of ΔV from the Barge. 

The Barges are not addressed in this study except to the extent that interfaces drive the RTCS and mission 

design. For example, the AR&C sequences between each Barge and the RTCS drive the specification of hardware 

and algorithms to create a completely cooperative rendezvous system. Similarly, the lengthy operation of two mated 

spacecraft requires an autonomy manager to determine the proper course of action for the stack, should any flight 

element request safing. A workable interface was defined to allow the RTCS design to move forward in cases that 

would otherwise have required detailed Barge design, and it is assumed that the Barge elements can accommodate 

those interfaces.

The NM4 launch date is not before the middle of the 2020s, and the TMST construction period is two years. 

Upon completion, the TMST is deployed to SEL2 for science investigation, and the RTCS remains at EML1 for 

future on-orbit servicing. The RTCS station-keeps on the EML1 Lyapunov orbit for 20 years, available to service the 

TMST or another spacecraft every five years. The RTCS is refurbished to upgrade or repair aging hardware prior to 

each Customer servicing, as well as to receive replacement hardware for the Customer and refuel. After a total of 22 

years on-orbit, the RTCS departs EML1 on a disposal trajectory. 

Figure NM4-2 shows the NM4 concept of operations. The figure illustrates mission sequences from launch to 

RTCS disposal. 

RTCS System Description

The RTCS system includes the spacecraft bus, sensors and algorithms to support the AR&C phases, robots, 

and mounting points for telescope and robots. The AR&C sensor package includes retro-reflectors and RF 

Figure NM4-2: Concept of Operations
transponders for two-way ranging with the Barges 

and the observatory. The robot system consists of two 

6 m arms, a 20 m arm, a robot “quiver,” and robot 

toolboxes. 

The RTCS will be launched in two segments 

(RTCS-I and Construction Barge) and will be assembled 

at EML1 in a final configuration. The two-launch option 

was selected due to launch volume limitations of 

the Delta IV super-heavy launch vehicle. The RTCS-I 

includes all of the spacecraft subsystems except 

deployable solar array with PSE, AR&C package and 

one 6 m robot arm. The Construction Barge will contain 

a deployable solar array with the associated PSE and 

the rest of the robot arms, the Quiver and Toolboxes. 

The completed RTCS dry mass is 6,592 kg (with 30% 

contingency).

The NM4 robot system consists of two dexterous 

6 m arms, a 20 m arm, a robot “quiver”, and robot 

toolboxes. The 20 m grapple arm is used to move 

the dexterous pair to various worksites. The two 6 

m dexterous robot arms are mounted as pairs on 

either side of a box, called a node, and are used for 

dexterous work including assembling and disassembling 

other robots. The barge contains Robot Mounting 

Points (RMP) to which robots can interface and allows 

the 20 m arm to move end-over-end from RMP to 

RMP. There is a robot “motel” which provides safe 

haven for 6 m robot arms, and provides a means for 

electrical recharging and data transfer. The arms will 

be teleoperated from the ground. The 6 m dexterous 

arms use an end-effector to interface with various 

tools needed to accomplish the tasks. There will be 

toolbox(es) located on the servicer for additional tools.

The RTCS bus is made of honeycomb panel 

construction and provides interfaces to the telescope, 

barges, and robot nodes. It is designed for the on-orbit 

assembly and servicing of subsystems and payload 

components. The thermal system is both passive and 

active: it includes heat pipes from component plates to 

radiators, MLI blankets on components, and survival 

heaters for components. The RF communication system 

includes four Ka band 1 m HGAs, two S-band omni antennas, and six Ka band omni antennas. Two HGAs are 

located on the telescope to facilitate a space-to-ground communication link. The Electrical Power System (EPS) is 

designed to accommodate solar electric propulsion. It includes both body-mounted and deployable solar arrays, 

along with twenty-six 100 Ah Li-Ion batteries. The ACS includes two star trackers and two gyros, and the propulsion 

system includes two large and eight small bipropellant Hz/NTO thrusters. The propulsion system also includes four 

gimbaled solar-electric Xenon thrusters. The RTCS contains six flight computers and two solid state recorders. The 

solid state recorders offer a 4 Tb user capability. 

The RTCS bus is designed to be serviceable. The mechanical components in bays are mounted to thermal 

conductive plates to allow serviceable access. The RF communication system has A-side and B-side boxes for Ka 

to/from ground. The solar array has extra interface ports so that additional solar array sections may be added during 

servicing. There are three PSE boxes and thirteen battery boxes. The ACS and propulsion system have A-side 

and B-side serviceable components. The Avionics system has A-side and B-side boxes for active support during 

servicing after a single fault. Figure NM4-3 shows the RTCS with the robotic arms and solar arrays deployed. Figure 

NM4-4 shows the RTCS (robot arms stowed) attached to the observatory during the final stage of construction.

 Appendix F – Notional Mission Studies, Notional Mission 4: Assembly of the Thirty-Meter Space Telescope (TMST) at EML1 | 169

Figure NM4-3: RTCS with Robot Arms and Solar Array Deployed

Figure NM4-4: RTCS with TMST
170 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

I&T and Schedule

The conceptual mission schedule is shown in Figure NM4-5. The notional project start date is July 2018, allowing 

12 months for Phase A and 14 months each for Phases B and C. A total of 36 months are allocated for spacecraft 

fabrication and integration and test for the bus and payloads. This conceptual schedule allows for technology 

development activities and will be support launch in the middle of the next decade.

Enabling Technologies

Xenon refueling components, Ka band omni antennas, and transponders are currently TRL 5. These will need to be 

brought up to TRL 6 before launch. Robot system power loads and radiator sizing may have been too conservative, 

and should be revisited in the future. The telescope assembly sequence should be reevaluated to make the 

assembly more efficient and to off-load requirements onto the RTCS.

Key Assumptions

The RTCS is in two pre-integrated, similar halves with dissimilar components: the RTCS-I and the Construction 

Barge. RTCS-I is designed to be self-sufficient on-orbit without the Construction Barge. When the RTCS-I and the 

Construction Barge are mated and completes into the final RTCS configuration, the on-orbit telescope construction 

can begin. 

Figure NM4-5: Mission Schedule

NM4 Assemble EML1 Robotic

Current Best 

Estimate Phase A-F 

($M, FY 10)

AR&C $60 

Robot (2 GA+2 dexterous pairs+tools) $1,330 

Servicer Bus $600 

Launch Vehicle $300 

Operations $150 

Everything Else $590 

Total Servicing Cost $3,030 
Notional Mission 5: Servicing of the Advanced Technology Large Aperture Space Telescope 

(ATLAST)-9.2m Observatory with Robots and Humans in HEO

Mission Study Objective

The Notional Mission 5 (NM5) study objective is to develop a Servicer design concept that enables humans and 

robots to refurbish the ATLAST-9.2m observatory after 10 years of operation at Sun-Earth L2 (SEL2). The servicing 

mission takes place in a Highly Elliptical Orbit (HEO) that can be accessed relatively easily from an orbit around 

Earth-Moon L1 (EML1) and by crew launching from Earth. The particular HEO designed for Notional Mission 5 is 

referred to as the L1 Orbit Trajectory Used for Servicing (LOTUS), since it has unique properties that facilitate the 

servicing mission profile treated in Notional Mission 5, in which an EML1 Lyapunov orbit is used as the staging 

location for the Servicer. The Servicer carries the robotic elements, tools, replacement hardware for the observatory, 

docking points for the observatory, and an airlock with consumables for seventeen cycles (replenishable). No crew 

habitat is used in this mission within the Earth-Moon system, so the crew mission duration was limited to 21 days.

Mission Overview

The NM5 flight segments include the Human/Robotic Telescope Servicer (HRTS), ATLAST-9.2m, the Orion crew 

module, and a servicing barge. The HRTS is the only element developed into a design concept for the NM5 study; 

all other flight segments are assumed to exist and be ready to support the mission.

The NM5 Concept of Operations is found in Figure NM5-1. At the start of the mission, the ATLAST-9.2m 

observatory is stationed at Sun-Earth L2 (SEL2) after nine years of on-orbit operation. The HRTS is launched on an 

Ares V heavy-lift launch vehicle for insertion into a Lyapunov orbit about EML1. After a successful checkout of the 

HRTS, ATLAST-9.2m transits back to the Earth-Moon system and inserts into the EML1 Lyapunov orbit occupied by 

the servicer. The servicer then performs AR&C with the observatory, which requires 10–30 m/s of ΔV and takes 1–3 

days. Next, the HRTS/ATLAST-9.2m stack performs a small maneuver (~10 cm/s) to insert itself into the LOTUS, 

bringing it to a rendezvous point with the crew vehicle ~23.5 days later. The crew vehicle launches approximately 20 

days after the servicer/observatory and inserts itself into the LOTUS. The crew vehicle then performs AR&C with the 

 Appendix F – Notional Mission Studies, Notional Mission 5: Servicing of the ATLAST-9.2m Observatory with Robots and Humans in HEO | 171

Figure NM5-1: Concept of Operations
172 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

HRTS/ATLAST stack, which requires ~1 day and ~30 m/s of ΔV on the part of the crew vehicle. Note that during 

this AR&C sequence, the HRTS/ATLAST stack is a passive, cooperative rendezvous target for the crew vehicle. 

After fifteen days of servicing, the crew vehicle separates from the stack and performs a deorbit maneuver to 

return home. The HRTS/ATLAST stack remains on the LOTUS and, under the influence of the Earth-Moon system 

dynamics, naturally returns to the vicinity of EML1 approximately 2 months after the crew vehicle departs. A few 

days prior to EML1 return, the observatory separates from the HRTS and performs a small maneuver to place it 

onto a trajectory that will exit the Earth-Moon system and return to SEL2. The HRTS simply reinserts itself onto the 

Lyapunov orbit about EML1 with a small maneuver and resumes station-keeping. The LOTUS free return is shown in 

Figure NM5-2. Figure NM5-3 shows LOTUS Servicing.

After approximately 10 years in orbit, a refurbishing barge will be launched with replacement units for the 

HRTS and ATLAST-9.2m, as well as consumables for the airlock. While an essential flight element of the HRTS is to 

perform more than one servicing mission, the barge was not developed into a design concept for this study. After 

HRTS refurbishment, ATLAST-9.2m returns to EML1 for a second servicing mission. This cycle will repeat at the 20-

year mark, and after the third servicing mission of ATLAST-9.2m, the HRTS will be disposed of in space. 

HRTS System Description

Figure NM5-4 provides an overview of the HRTS components while Figure NM5-5 shows an artist’s rendition of 

HRTS. The HRTS is a modular, serviceable, refuelable spacecraft with a dry mass of 31,870 kg (includes 30% 

contingency). The HRTS design accommodates two Autonomous Rendezvous and Capture (AR&C) phases: as the 

active vehicle in the AR&C of ATLAST-9.2m, and then as the passive, fully cooperative vehicle in the AR&C with the 

Orion crew module. 

The HRTS houses the robotic systems required for the servicing mission, human-rated grapple arms and 

dexterous robotic pairs, and robot toolboxes. Two 20 m grapple arms are used for the berthing activities and for 

translating the crew and large hardware elements across longer distances. Two 2 m dexterous robot arms are 

mounted as pairs on either side of a box called a node. They are used for complex, dexterous tasks and to assist 

the crew. The grapple arms can be operated autonomously (to enable the servicer to berth ATLAST), locally by the 

crew when Orion is docked, or via scripted autonomy or teleoperation from the ground. The dexterous robot pairs 

can be operated locally by the crew or from the ground. Both the grapple and dexterous arms have their avionics 

distributed along the arm that communicates with a Data Management Unit (DMU). The HRTS has eight Robot 

Mounting Points (RMP) that provide power and data interfaces to which either end of the grapple arm or one face of 

the node of the dexterous robot pairs can be attached. This architecture allows the grapple arms to move end-overend from RMP to RMP (the grapple arms have identical end-effectors at both ends to allow for this). The grapple 

arms can also maneuver the dexterous robot pairs around and provide power and data across the mounting 

interface.

Figure NM5-2: LOTUS Free Return Figure NM5-3: LOTUS Servicing
The HRTS has three Telescope Mounting Points that provide 4 kW of power to and a 40 Mbps data link from 

the observatory during servicing. The HRTS uses a voltage-regulated bus at 120 VDC with bidirectional converters 

for battery charge and discharge to provide the peak power of 11,087 W (includes 30% contingency). This power 

is provided by body-mounted (yet replaceable) arrays with a total area of 49.67 m2

 using Tj GaAS, 28% efficient 

cells. Each of the ten, 100 Ah Li-Ion batteries is by-pass switched to provide fault protection. The battery capacity is 

driven by the need to provide power to ATLAST-9.2m during eclipses, while the solar array is sized to accommodate 

the electrical propulsion system.

The HRTS propulsion system is comprised of both a chemical 

system and an electric propulsion system. The pressure regulated 

bi-prop chemical system is used for high thrust, short time-scale 

maneuvers and consists of one Main ΔV engine for orbit insertions 

(900 lbf/4000 N, Isp 310 sec), 4 auxiliary ΔV engines for attitude 

control during main engine firing (200 lbf/890 N, Isp 310 sec), 20 

Reaction Control Engines (5 lbf/22 N, Isp 310-320 sec) and 21 tanks 

of fuel, oxidizer, and pressurant. The electric propulsion system is 

used for station-keeping during the loiter phase only. It consists of 

4 Gridded Xenon-Ion thrusters (NEXT engine, 0.055 lbf/.24 N, Isp

4,100 sec—two located on the sun-facing side and two located on 

the anti-sun-facing side—and three tanks of Xenon. The total fuel 

load for both systems is 17,213 kg. Figure NM5-6 shows HRTS with 

ATLAST 9.2m.

The up-link data rate to the HRTS is 132 Kbps with a down-link 

rate of 160 Mbps. The communication system is comprised of two 

switchable 1.2 m Ka HGAs (2-axis gimbaled), two Ka omnis, four 

S-band omnis, four Ka transponders and four S-band transponders. 

The HRTS bus Attitude Control System (ACS) is three-axis 

stabilized in all modes. ACS components include star trackers for 

primary attitude determination, IRUs for angular and linear rate 

determination, and coarse sun sensors for sun pointing mode. 

Rotation and translation actuation is performed using thrusters.

 Appendix F – Notional Mission Studies, Notional Mission 5: Servicing of the ATLAST-9.2m observatory with robots and humans in HEO | 173

Figure NM5-5: HRTS

Figure NM5-4: HRTS Components
174 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

I&T and Schedule

With a Phase A start assumed in January 2028, the HRTS would be 

scheduled to launch in 2036. The total integration and test duration 

is 4.3 years (including funded reserve). The AR&C system, robots, 

airlock, and orbital replacement instruments and units would be fully 

qualified prior to integration into the Servicer, and it is assumed that 

no additional testing of these is required. The mission schedule is 

shown in Figure NM5-7. 

Enabling Technology

At this time, the Ka Band transponders and omni antennas are at 

TRL 5, but are expected to be at least TRL 6 prior to 2020. Due to 

the extremely large sunshade and the possible impact to AR&C, 

a detailed plume study should be completed. The observatory 

contamination issue is of lesser concern. Thruster firing for 

attitude control could be optimized for station-keeping purposes if 

performed at the proper time.

Key Assumptions

The HEO orbit is strongly favored by astronauts due to a natural 

return to Earth’s proximity, and the LOTUS was specifically designed 

to return to EML1 naturally. In addition, this orbit maximizes the “onstation” time that the astronauts have to perform servicing.

This mission involves human activity; therefore critical systems are required to be dual-fault tolerant. Much time 

was spent discussing which systems are critical and what architecture to adopt to provide for two-fault tolerant 

systems (i.e., multiple active buses and internal redundancy). These decisions will need to be made by the project 

office on a system-by-system basis.

Figure NM 5-7: Mission Schedule

Figure NM5-6: HRTS with ATLAST 9.2m 

NM5 LOTUS Refurbish with Humans+Robots

Current Best 

Estimate Phase A-F 

($M, FY 10)

AR&C $60 

Robot Arms (2 GA+2 dexterous pairs) $1,230 

Payload (ORUs) $1,000 

Airlock+tools $300 

Servicer $760 

Launch Vehicle $300 

Operations $80 

Everything Else $990 

Total Servicing Cost $4,720 
 Appendix F – Notional Mission Studies, Notional Mission 6: Assembly of the 15.5 m ATLAST Observatory at SEL2 with Humans and Robots | 175

Figure NM6-1: Flight Segments

Notional Mission 6: Assembly of the 15.5 m ATLAST Observatory at SEL2 with Humans and 

Robots

Mission Study Objective

The objective of the Notional Mission 6 (NM6) study is to develop a Servicer design concept that provides a platform 

for robots and humans to work in concert to assemble a large observatory at SEL2. The Servicer carries the robotic 

elements and tools and accommodates the berthing of several observatory hardware transport barges and the crew 

vehicle/habitat/airlock stack during assembly. As it is assembled, the observatory is also mounted to the Servicer. 

The Servicer remains at SEL2 for 20 years following the deployment of the assembled observatory to provide a 

platform for human or robotic servicing of the flagship observatory or other missions.

Mission Overview

The NM6 flight segments include the Human and Robotic Telescope Construction Servicer (HRTCS), four Modular 

Propulsion System and Telescope (MPST) elements, a human habitation facility, an airlock, and the Orion crew 

module. Figure NM6-1 illustrates these flight segments, as well as the ATLAST observatory stowed in the MPSTs. 

The NM6 study focused on the design of the HRTCS segment. All other flight segments are used to drive the 

interface requirements on the Servicer and are assumed to exist and be ready to support the mission.

The NM6 Concept of Operations can be found in Figure NM6-2. The HRTCS is the servicing platform that 

supports the robotic and human construction of the observatory, and it houses the robotic tools and a quiver 

holding parts for the reconfigurable robot arms. The MPST is a spacecraft bus that transports observatory parts 

to SEL2, while the Orion spacecraft is used to transport the crew to and from the SEL2 halo orbit. An expandabletype habitat provides additional living space and perhaps radiation protection for the crew during orbital transfer. An 

airlock is required so that the crew can perform EVAs, and an Earth Departure Stage (EDS) is required to inject the 

Orion/Habitat/Airlock stack into the outbound trajectory towards the SEL2 halo orbit, after which the spent EDS is 

discarded. 

The HRTCS is launched into the SEL2 halo orbit on a heavy-lift launch vehicle, assumed to have performance 

characteristics commensurate with the current notional design for Ares V. Six months later, the first MPST launches 
176 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

into the SEL2 halo orbit on an upgraded Delta IV Heavy launch vehicle. MPST-2, -3, and -4 are launched at 

3-month intervals. Intervals between launches allow time to refurbish the launch pad and also serialize launch 

vehicle integration and payload preparation activities at the launch site. The 3-month allocation is driven by the 

dynamics of the SEL2 halo orbit, which has a minimum insertion ΔV every 6 months and a less desirable, but 

achievable, insertion ΔV halfway between the two minima. However, MPST-3 is the heaviest MPST and needs to 

travel to SEL2 on the lower insertion ΔV trajectory. 

The four MPSTs perform AR&C with the HRTCS, and the stacked configuration of HRTCS and MPSTs then 

waits for the human elements to arrive. As feasible, teleoperation of the robotic arms from the ground can be done 

to prepare for the telescope assembly during this period. The habitat, airlock, and Earth departure stage (EDS) are 

launched into LEO on an Ares V launch vehicle (or equivalent), followed by Orion, which is launched into LEO on an 

Ares I (or equivalent). In LEO, Orion performs AR&C with the habitat/airlock/EDS stack, at which point the habitat is 

inflated and checked-out. The habitat/airlock/EDS/Orion stack is then inserted into the outbound trajectory towards 

the SEL2 halo orbit by the EDS. The EDS is discarded after its fuel is depleted, which occurs while still well within 

the Earth-Moon system. After the spent EDS is discarded, Orion performs a short proximity operations maneuver to 

reposition itself on the opposite end of the habitat (previously occupied by the EDS).

The habitat/airlock/Orion stack performs AR&C with the HRTCS on the SEL2 halo orbit. Humans and robots 

then work in concert for 39 days to assemble the ATLAST-15.5 m observatory. Large-element mechanical assembly 

tasks are completed using two 20 m grapple arms teleoperated by the crew on-site and occasionally from the 

ground. Complex or dexterous tasks are completed in a series of 17 crew Extra-Vehicular Activities (EVAs) along 

with robot assistants equipped with a pair of 2 m arms. Once final testing is complete, the observatory is de-mated 

from HRTCS and deployed. The habitat/airlock/Orion stack then de-mates from HRTCS and transfers back to 

Earth. Shortly before Earth arrival, the habitat and airlock de-mate from Orion and the crew capsule performs a 

ballistic reentry. Using methods beyond our scope for study here, such as aerocapture, the habitat with airlock is 

kept in orbit for use during a future mission. The total duration of the manned mission is 79 days. The total duration 

of the assembly mission is 607 days. The HRTCS loiters in SEL2 for 20 years, discarding and properly disposing of 

the MPSTs as their fuel is depleted. 

Figure NM6-2: NM6 Concept of Operations (Observatory Assembly Phase)
Every 10 years, the HRTCS is serviced in 

preparation for the next planned upgrade of the 

ATLAST observatory. During servicing, HRTCS critical 

systems (e.g., solar arrays, propellant) are replaced 

as needed, and it receives additional MPSTs with 

Orbital Replacement Units (ORUs) for the upcoming 

observatory servicing mission. In addition, during the 

loiter phase (periods between ATLAST servicing), the 

HRTCS is available for use as a platform for any other 

assembly or servicing tasks in the SEL2 halo orbit. 

HRTCS System Description

Figure NM6-3 shows the HRTCS with robot arms 

stowed and Figure NM6-4 provides an overview of 

the HRTCS components. The HRTCS is a spacecraft 

with a dry mass of approximately 27,000 kg (includes 

30% contingency), designed to accommodate AR&C 

activities with the Orion/habitat/airlock stack and four 

MPSTs. In particular, the HTRCS is designed to be a 

passive, cooperative rendezvous target for the MPSTs, 

and the HRTCS/MPSTs stack is designed to be a 

passive, cooperative rendezvous target for the crew 

vehicle stack.

Two 20 m robotic arms are used for the berthing activities and large-scale assembly tasks. The HRTCS has 

six Robot Mounting Points (RMPs), and the robotic arms are able to move end-over-end using the RMPs. Two 2 m 

robotic arms assist the astronauts during EVAs. While the crew is sleeping, dexterous robots (a node and two 2 m 

arms) perform worksite preparation tasks using a combination of ground teleoperation and scripted autonomous 

tasks. The HRTCS robotic system has a total of 10 cameras to support teleoperation.

 Appendix F – Notional Mission Studies, Notional Mission 6: Assembly of the 15.5 m ATLAST Observatory at SEL2 with Humans and Robots | 177

Figure NM6-3: HRTCS with Robot Arms Stowed

Figure NM6-4: HRTCS Components/Launch and SEL2 Configurations
The observatory is assembled on the HRTCS 

turntable (6-meter diameter), which provides 500 W 

of power and a 40 Mbps data link to the observatory. 

The ATLAST spacecraft bus remains in an MPST with 

its solar array deployed and facing the sun, and is 

electrically connected to the HRTCS turntable. This 

allows the ATLAST solar array to provide 3,500 W of 

power to the observatory during construction and to 

control and checkout ATLAST components as they are 

assembled. This approach also reduces the power load 

on the HRTCS system to that of providing power just for 

itself (including robots and sensors) and an additional 

500 W of power to the observatory. Figure NM6-5 

shows the stacked configuration of the HRTCS/Orion/

Airlock with ATLAST.

The HRTCS uses a 120 V DC power system to 

provide the peak power of 4,431 W. This power is 

provided by two body-mounted arrays with a total 

area of 21.65 m2

. Two 100 Ahr LiIon batteries provide 

electrical power storage and incorporate by-switches 

for fault protection against dead cells. The HRTCS propulsion system is comprised of five ΔV engines and 16 RCS 

thrusters on Canfield gimbals. To fully utilize all available propellant and to increase options for thruster selection, 

the HRTCS assumes control of the RCS systems on docked MPSTs. An overview of the HRTCS and MPST orbital 

mechanics and required ΔVs can be found in Figure NM6-6. 

The up-link data rate to the HRTCS is 67 Mbps, and the down-link is 54 kbps. The communication system is 

comprised of two dual 2.0 m Ka high gain antennas (HGA) (2-axis gimbaled), two Ka omnidirectional antennas, two 

Ka transponders and four S-band transponders. The communication system has 1.1 Terabits of storage and can 

store nearly 6 hours of video, telemetry and housekeeping data. The avionics system uses three single-board voting 

computers and requires 67 units and 315 cards. All avionics, batteries and solar arrays are replaceable for servicing. 

With no Earth gravitational attraction and no orbital debris, the SEL2 halo orbit presents a significantly reduced risk 

of hypervelocity impacts. 

Figure NM6-6: Flight Dynamics/∆Vs

178 | Appendix – On-Orbit Satellite Servicing Study Project Report | October 2010

Figure NM6-5: HRTCS/Orion/Airlock with ATLAST
 Figure NM6-7: Mission Schedule

I&T and Schedule

In order to meet an assumed 2035 launch date, Phase A starts in 2026. The total integration and test duration is 

8.43 years (including funded reserve). The mission schedule is shown in Figure NM6-7 (TBS). 

Enabling Technologies

The Canfield gimbals provide improved range of motion that results in a significant reduction in the number of 

required thrusters. These gimbals are at TRL 5 and are expected to reach TRL 6 prior to Phase A for this mission.

Key Assumptions

This mission requires a launch vehicle capable of launching 32,715 kg to a SEL2 halo orbit insertion point. This 

falls between the upgraded Delta IV capacity (15,000 kg) and a notional Ares V capacity (60,000 kg). Heavy-lift is a 

necessary enabling technology for this mission, though the notional Ares V is not specifically required. A new launch 

vehicle offering intermediate launch mass capabilities could be used for this mission.

 Appendix F – Notional Mission Studies, Notional Mission 6: Assembly of the 15.5 m ATLAST Observatory at SEL2 with Humans and Robots | 179

NM6 SEL2 Refurbish with Humans+Robots

Current Best 

Estimate Phase A-F 

($M, FY 10)

AR&C (no PTU) $60 

Robot Arms (2 GA+2 dexterous pairs+tools) $1,340 

Servicer Bus $2,100 

Launch Vehicle $500 

Operations $240 

Everything Else $1,040 

Total Servicing Cost $5,280
“Where the willingness is great, the difficulties cannot be great.”

 Niccolò Machiavelli
National Aeronautics and Space Administration

Goddard Space Flight Center

Space Servicing Capabilities Project

Flight Projects Directorate

Greenbelt, MD 20771

http://servicingstudy.gsfc.nasa.gov/

NP-2010-08-162-GSFC