Flight Dynamics Analysis Branch

End of Fiscal Year 2004 Report

Prepared by members of the Flight Dynamics Analysis Branch 

Applied Engineering and Technology Directorate

National Aeronautics and

Space Administration

Goddard Space Flight Center 

Flight Dynamics Analysis Branch, Code 595

Greenbelt, Maryland 20771

February 2005

NASA/TM—2005–212777 

NASA/TM—2005–212777

Flight Dynamics Analysis Branch End of Fiscal Year 2004 Report
FDAB End of FY 2004 Report iii

ABSTRACT

This report summarizes the major activities and accomplishments carried out by the Flight 

Dynamics Analysis Branch (FDAB), Code 595, in support of fl ight projects and technology 

development initiatives in Fiscal Year (FY) 2004. The report is intended to serve as a summary of 

the type of support carried out by the FDAB, as well as a concise reference of key accomplishments 

and mission experience derived from the various mission support roles. The primary focus 

of the FDAB is to provide expertise in the disciplines of fl ight dynamics including spacecraft 

navigation (autonomous and ground based); spacecraft trajectory design and maneuver planning; 

attitude analysis; attitude determination and sensor calibration; and attitude control subsystem 

(ACS) analysis and design. The FDAB currently provides support for missions and technology 

development projects involving NASA, other government agencies, academia, and private industry.
iv FDAB End of FY 2004 Report

TABLE OF CONTENTS

1.0 Introduction........... ..................................................................................................................1

2.0 Flight Project Support ............................................................................................................3

2.1 Development Missions ...............................................................................................3

 2.1.1 Aquarius ....................................................................................................3 

 2.1.2 Earth Observing System (EOS) Constellation Management ....................3 

 2.1.3 InFocus .....................................................................................................5

 2.1.4 Gamma Ray Large Area Telescope (GLAST) ..........................................6 

 2.1.5 Global Precipitation Mission (GPM) ........................................................7

 2.1.6 Geostationary Operational Environmental Satellite (GOES) – N ............8

 2.1.7 Hubble Robotic Vehicle (HRV) ................................................................9

 2.1.8 James Webb Space Telescope (JWST) ...................................................10

 2.1.9 Lunar Reconnaissance Orbiter (LRO) ....................................................11

 2.1.10 Magnetospheric Multiscale (MMS) Mission ..........................................12

 2.1.11 Solar Dynamics Observatory (SDO) ......................................................12

 2.1.11.1 SDO Trajectory Design ........................................................13

2.1.11.2 SDO Attitude Analysis .........................................................13

 2.1.12 Space Technology 5 (ST5) ......................................................................14

 2.1.13 Space Technology 7 (ST7) Disturbance Reduction System (DRS) ........15

 2.1.14 Swift .......................................................................................................16

 2.1.15 Time History of Events and Macroscale Interactions 

 during Substorms (THEMIS) .................................................................17

2.2 Operational Missions ................................................................................................17

 2.2.1 EOS Aura ................................................................................................17

 2.2.2 Gravity Probe-B (GP-B) .........................................................................19

 2.2.3 Hubble Space Telescope (HST) Two-Gyro System (TGS) ....................20

 2.2.4 LandSat-7 ................................................................................................20

 2.2.5 Rossi X-Ray Timing Explorer (RXTE) Tracker Anomaly .....................21

 2.2.6 Tropical Rainfall Measuring Mission (TRMM) .....................................22

 2.2.6.1 TRMM Reengineering ...........................................................22

2.2.6.2 TRMM Reentry Planning ......................................................23

2.3 Flight Dynamics Facility (FDF) ...............................................................................24

 2.3.1 FDF Overview ........................................................................................24

 2.3.2 Attitude Operations .................................................................................24

 2.3.3 Expendable Launch Vehicle (ELV) Support ...........................................25

 2.3.4 Human Spacefl ight Support ....................................................................26

 2.3.4.1 STS Support ...........................................................................26

2.3.4.2 ISS Support ............................................................................26

 2.3.5 Maneuver Operations .............................................................................27

 2.3.6 Metric Tracking Data Evaluation ...........................................................27

 2.3.7 Orbit Operations .....................................................................................27

 2.3.8 Software Maintenance ............................................................................28

 2.3.9 Sustaining Engineering Activities ..........................................................29

3.0 Study Mission Support .........................................................................................................31

3.1 Integrated Mission Design Center (IMDC) ..............................................................31

3.2 Autonomous NanoTechnology Swarm (ANTS) ......................................................31
FDAB End of FY 2004 Report v

3.3 Constellation X Formation Flying Mission ..............................................................32

3.4 Dark Universe Observatory (DUO) Science Observation Analysis .........................33

3.5 Extrasolar Planet Imager Coronagraph (EPIC) ........................................................33

3.6 Geospace Electrodynamic Connections (GEC) .......................................................33

3.7 Glory......... ................................................................................................................34

3.8 Laser Interferometer Space Antenna (LISA) ...........................................................34

3.9 Organics Origins Observatory (OOO) .....................................................................37

3.10 Solar Sentinels ..........................................................................................................37

3.11 Sub-millimeter Probe for Evolution of Cosmic Structure (SPECS) ........................37

3.12 Space Infrared Interferometric Telescope (SPIRIT) ................................................38

3.13 Terrestrial Planet Finder (TPF) .................................................................................38

3.14 Venus Sounder for Planetary Exploration (VESPER) ..............................................40

4.0 Technology Development ......................................................................................................41

4.1 Advanced Attitude Determination and Sensor Calibration ......................................41

4.2 Advanced Navigation Concepts ...............................................................................42

4.3 Space Science Mission Offi ce (SSMO) Ground Attitude 

 System Reengineering ..............................................................................................42

4.4 Global-Positioning-System-Enhanced Onboard Navigation 

 System (GEONS) .....................................................................................................43

4.5 GPS-Based Navigation for High Earth Orbits .........................................................44

4.6 Formation Flying Technology ..................................................................................45

 4.6.1 Earth-Orbiting Formation Control ..........................................................46

 4.6.1.1 Formation Navigation, Control, and Mission 

 Design Algorithms .................................................................46

 4.6.1.2 “Virtual Rigid Body” (VRB) Satellite Formation 

 Control Technology Using Relative Vehicle Dynamics ........47

 4.6.2 Earth-Orbiting Formation Design ...........................................................47

 4.6.2.1 Pseudospectral Methods for Guidance Law 

 Development for Optimal Design of Formations ..................47

 4.6.3 Fault-Tolerance, Collision Avoidance, and Formation Safety ................48

 4.6.3.1 Fault Detection, Identifi cation, Reconstruction, 

 and Fault-Tolerant Estimation for a Satellite and 

 Satellite Cluster ......................................................................48

 4.6.3.2 Collision Avoidance and Safe Mode for 

 Satellite Formations ...............................................................49

 4.6.4 High-Altitude Relative Navigation .........................................................49

 4.6.4.1 Mitigation of the Impact of Sensing Noise on 

 the Precise Formation Flying Control Problem .....................50

 4.6.4.2 Assessment of Intersatellite Measurements for Precise 

 Relative Navigation of HEO Satellite Formations .................50

 4.6.4.3 Precise Relative Navigation for High Earth 

 and Libration Point Missions .................................................51

 4.6.4.4 Sensing and Estimation Methods for Relative 

 Navigationi and Attitude Determination of Large 

 Satellite Formations ...............................................................51

 4.6.4.5 Relative Navigation of Formations of 

 High-Earth-Orbiting Satellites Using Dual 

 Frequency Civilian GPS Technology .....................................52
vi FDAB End of FY 2004 Report

 4.6.5 Libration Point Control ...........................................................................52

 4.6.5.1 Libration Point Mission Formation Control ..........................53

4.6.5.2 Modelling and Control of Libration Point 

 Satellite Formations ...............................................................53

 4.6.6 Libration Point Formation Design ..........................................................54

 4.6.6.1 Libration Point Formation Design .........................................54

4.7 Mission Formulation ................................................................................................55

4.8 Solar Sails. ................................................................................................................56

4.9 Magnetometer Navigation Experiment Onboard the WIRE Spacecraft ..................56

5.0 Branch Infrastructure ..........................................................................................................59

5.1 Best Practices for Orbit Analysis, Design, Navigation, and Control .......................59

5.2 Commercial-Off-The-Shelf (COTS) Software Management ...................................59

5.3 Generator Tool Enhancements .................................................................................60

5.4 Goddard Mission Analysis Tool (GMAT) ................................................................60

5.5 FDAB Web Page and Tools ......................................................................................61

5.6 In-House Navigation Systems Development ...........................................................62

6.0 Employee Development ........................................................................................................63

6.1 New Employee Profi les ............................................................................................63

6.2 Profession Intern Program (PIP) ..............................................................................63

 6.2.1 PIP Level I: Evaluation of Analytical Solutions for an 

 Elliptical Relative Motion Problem (Rivers Lamb) ...............................63

 6.2.2 PIP Level I: The Effects of Attitude Maneuvers on the 

 MMS Formation (Dean Tsai) ..................................................................64

6.3 Cooperative Education Program ..............................................................................65

 6.3.1 Edwin Dove (Pennsylvania State University) ........................................65

 6.3.2 Stephanie Gil (Cornell University) .........................................................65

7.0 Outreach Activities.. ..............................................................................................................67

7.1 SAMPEX University Operations .............................................................................67

7.2 TableSat....... .............................................................................................................67

8.0 Interagency Activities ...........................................................................................................69

8.1 NASA Technical Standards Program .......................................................................69

8.2 Global Positioning System (GPS) Modernization ...................................................69

8.3 NASA Engineering And Safety Center (NESC) Support .........................................70

 8.3.1 Space Shuttle Recurring Anomalies Review ..........................................71

8.4 Low-Thrust Working Group .....................................................................................72

Appendix A: Conferences and Paper Abstracts ...........................................................................73

Appendix B: Reviews Supported .................................................................................................83

Appendix C: Acronyms and Abbreviations .................................................................................85
FDAB End of FY 2004 Report vii

LIST OF FIGURES

Figure 2-1 The ESMO Afternoon Constellation Confi guration ...................................................3

Figure 2-2 CCS display ................................................................................................................4

Figure 2-3 InFocus readying for launch .......................................................................................6

Figure 2-4 Cumulated Earth coverage for 7 days as a function of the starting 

 time for the different control boxes ............................................................................7

Figure 2-5 A rendition of the HRV attached to the HST ..............................................................9

Figure 2-6 Apoapsis/Periapsis Altitudes with +/- 10 km Control ..............................................11

Figure 2-7 ST7 Mission Representation ....................................................................................16

Figure 2-8 WRS Error during Ascent Relative to Control Box Limits ......................................18

Figure 2-9 Inclination Adjust Maneuver Plan ............................................................................18

Figure 2-10 AutoFDS ...................................................................................................................22

Figure 3-1 Pointing and Alignment Overview for the Constellation X Formation 

Flying Mission .........................................................................................................32

Figure 3-2 Link Acquisition Order for Scan Acquisition Strategy ...........................................35

Figure 3-3 A Typical Scan Time History ....................................................................................35

Figure 3-4 Link Acquisition Order for Defocus Acquisition Strategy .......................................36

Figure 3-5 A Typical Defocus Time History ..............................................................................36

Figure 3-6 Location of ACS Actuators and Sensors (courtesy of Timothy Ho) .......................39

Figure 4-1 Geometry for reception of GPS signals by a HEO spacecraft. 

 Side-lobe signals are weaker, but can still contribute to GPS 

 observability for HEO users. ....................................................................................44

Figure 4-2 Mission Formulation Earth-Moon Libration Orbit Stationkeeping Analysis ...........55

Figure 4-3 MAGNAV Performance during an Attitude Maneuver ............................................57

Figure 5-1 GMAT Screen Capture .............................................................................................61

Figure 7-1 TableSat ....................................................................................................................67

Figure 7-2 TableSat demonstration during “Inspire the Next Generation” Day at GSFC .........68
viii FDAB End of FY 2004 Report
FDAB End of FY 2004 Report 1

1.0 INTRODUCTION

This is the sixth annual report produced by members of the Flight Dynamics Analysis Branch 

(FDAB) at the Goddard Space Flight Center (GSFC). The Branch is responsible for providing 

analytic expertise for trajectory and attitude systems. This includes dynamics and control 

analyses and simulations of space vehicles. The Branch creates and maintains state-of-the-art 

analysis tools for mission design, trajectory optimization, orbit analysis, navigation, attitude 

determination, and controls analysis. The Branch also provides the expertise to support a wide 

range of fl ight dynamics services, such as spacecraft mission design, on-orbit sensor calibration, 

and launch/early orbit operations. An active technology development program is maintained, 

with special emphasis on developing new techniques and algorithms for autonomous orbit/

attitude systems and advanced approaches for trajectory design. Specifi c areas of expertise 

resident in the FDAB are:

 • Attitude and trajectory analysis and control design

 • Control/structure interaction analysis

 • Mission (attitude & trajectory) planning

 • Estimation techniques

 • Vehicle autonomy

 • Constellation analysis

 • Flight dynamics model development

The FDAB also provides fl ight dynamics operations services through its Flight Dynamics 

Facility (FDF). This facility supported fl ight dynamics computations for more than twenty 

spacecraft in Fiscal Year (FY) 2004. Operational services include orbit determination, 

acquisition data generation for the space and ground networks, tracking data evaluation, attitude 

determination and maneuver planning support. The FDF also supports Expendable Launch 

Vehicle (ELV) operations, International Space Station (ISS) orbit determination and Space 

Transportation System (STS) fl ight operations.

The FDAB is a branch in the Mission Engineering and Systems Analysis (MESA) Division 

(Code 590). The MESA division is responsible for providing strong mission-enabling leadership 

for a broad range of advanced science missions. In addition, many planned future missions will 

rely on highly integrated observatories in which the spacecraft functions and performance cannot 

be separated from the instrument and science functions and performance. The MESA division 

has the charter and the critical mass of people and skills to provide leadership in these areas. 

Within the division, the FDAB’s alliance with mission system engineers is a strong benefi t to 

the infusion of fl ight dynamics technologies into new mission concepts, enabling the branch’s 

mission designers to meet the needs of mission formulation study teams.

This document follows an outline similar to one used in past annual reports. It summarizes the 

major activities and accomplishments performed by the FDAB in support of fl ight projects 

and technology development initiatives in FY 2004. The document is intended to serve as both 

an introduction to the type of support carried out by the FDAB, as well as a concise reference 

summarizing key analysis results and mission experience derived from the various mission 
2 FDAB End of FY 2004 Report

support roles assumed over the past year. The FDAB engineers that were involved in the various 

analysis activities within the Branch during FY 2004 prepared this document. Where applicable, 

these staff members are identifi ed and can be contacted for additional information on their 

respective projects.

Among the major highlights by engineers in the FDAB during FY 2004 are:

 • Successful branch support for the launch and early operations of the Aura spacecraft.

As part of this support, the branch designed and implemented orbit-raising maneuvers.

 • Successful transition of FDF management to the FDAB. Prior to January 2004, the 

FDF operations were the responsibility of the Consolidated Space Operations Contract 

(CSOC) under management by the Goddard Mission Services Program Offi ce. In FY 

2004, FDF operations were transitioned to the Mission Operations & Mission Services 

(MOMS) contract and overall management responsibility for the facility transitioned to 

the FDAB.

 • Completion of the Solar Dynamic Observatory (SDO) preliminary design. The inhouse attitude control system analysis team and the fl ight dynamics team successfully 

presented their preliminary design and supporting analysis at the SDO Preliminary 

Design Review (PDR) in December, 2004. 

 • ST5 Team completes redesign activities. A new launch vehicle (Pegasus XL) was 

selected to deliver ST5 to orbit. As a result, the ST5 team re-designed an orbit and 

constellation scheme to satisfy the capabilities of the new launch vehicle 

 • Successful ST7 Dynamic Control System (DCS) critical design completed. Flight 

software builds were also delivered and mode transition strategies were completed.

 • GEONS wins the Federal Laboratory Consortium Mid-Atlantic Regional Award. The 

GEONS software package used for autonomous navigation also had two new releases 

in FY 2004. 

 • Hubble Robotic Vehicle concepts studied. Branch engineers played a key role in 

defi ning robotic servicing concepts for the Hubble Space Telescope. Simulations and 

early control concepts were developed to show the feasibility of robotic servicing. 
FDAB End of FY 2004 Report 3

2.0 FLIGHT PROJECT SUPPORT

2.1 DEVELOPMENT MISSIONS

2.1.1 AQUARIUS

Aquarius is an Earth System Science Program (ESSP) mission that plans to answer questions 

about the global cycle of water and the response of ocean circulation to climate change. The 

required mission lifetime is three years, with a goal of fi ve years.

FDAB personnel continued to provide analysis support for the Aquarius mission team. Coverage 

analysis was performed for the two 9-day repeating orbits at 596 and 630 km that fell within the 

allowable altitude span. Results showed that the 596 km orbit provided the desired coverage of 4 

observations of each grid point every 36 days while the 630 km orbit had several grid points that 

were only observed 3 times during the same period.

[Technical contact: Frank Vaughn]

2.1.2 EARTH OBSERVING SYSTEM (EOS) CONSTELLATION MANAGEMENT

FY 2004 has been a busy year for the Earth Sciences Mission Operations (ESMO) Project 

constellation management. Aura joined Aqua this year in ESMO’s Afternoon Constellation (AC); 

these two satellites anchor the two ends of the AC (see Figure 2-1). 

 Figure 2-1. The ESMO Afternoon Constellation Confi guration

Three new satellites will join the AC within the next calendar year. PARASOL, a CNES 

satellite, is scheduled to launch in December, 2004. CALIPSO, another CNES satellite, and 

JPL’s CloudSat will launch as dual payloads in April 2005. OCO will join the AC in 2008 and is 

expected to assume the lead position in front of Aqua. The six satellites will perform coincident 

Earth observations while fl ying in a loose constellation that crosses the equator at approximately 

13:30 (descending node). 
4 FDAB End of FY 2004 Report

Coordinating activities and sharing resources between missions becomes increasingly complex 

as the number of missions within the AC grows. The Constellation Coordination System 

(CCS), a web-based application for collaboration and data sharing, is a fi rst step in reducing the 

complexity of this type of constellation operations. The goal of the CCS is to make constellation 

coordination as routine and automated as possible. CCS provides the member missions of 

ESMO’s Morning (MC) and Afternoon Constellations with a tool to ensure constellation health 

and safety, to facilitate data exchange and coincident observations, and to allocate shared 

resources. 

The FDAB is responsible for defi ning the CCS requirements, software acceptance testing, and 

performing analysis with the system. The fi rst release was in May 2004; this release incorporated 

the capabilities of the ES Collaborator for continued use by members of the MC as well as 

added capabilities for the AC. The CCS checks constraints and monitors the satellites’ positions 

within their control boxes. It detects when constraints are violated, when control box limits 

are exceeded, and when a satellite might have a close approach with another AC satellite. CCS 

performs automated analyses and sends the results to any affected satellite’s fl ight operators, 

who can resolve any potential problems. Figure 2-2 shows a CCS display containing the MC 

visualization of control boxes and groundtracks. 

Figure 2-2. CCS display

CCS Release 1 was used for Aura’s launch and ascent and for monitoring the inclination 

maneuvers that Aqua and Aura performed in Fall 2004. It has also supported CALIPSO/CloudSat 

long-term simulations and will be a critical tool during the three AC launches next year. 

Release 2 is scheduled for delivery to operations in October 2004. This release will include the 

capabilities to read, convert, and output new product formats needed by PARASOL, CALIPSO 

and CloudSat, and to provide visualizations of the AC in addition to the MC. 

[Technical contact: Karen Richon]
FDAB End of FY 2004 Report 5

2.1.3 INFOCUS

The FDAB has supported pointing system development and fl ight operations of the InFocus 

Telescope Experiment since 1999. This experiment is a nine-meter focal-length imaging Xray telescope designed to observe celestial targets from a balloon gondola at altitudes greater 

than 40 km. The telescope had its fi rst fl ight in July, 2001, onboard a stratospheric balloon 

and used an azimuth/elevation pointing system that had been modifi ed from a smaller and 

lower resolution telescope. To achieve InFocus’s desired pointing accuracy of one arcminute, 

a star camera sent images to the ground that were used in identifying the pointing error and 

commanding corrections to the closed loop pointing control, which was controlled by sensors of 

the local magnetic and g fi elds. Unfortunately, higher-than-normal winds at the observing altitude 

continuously excited the swinging of the gondola from the load train. These oscillations could 

not be dampened suffi ciently to read the star camera, so very little data was obtained, other than 

demonstrating that the telescope was working. 

A more robust system was clearly needed for a telescope of this size under these disturbance 

conditions. A design effort led to upgraded performance of the pointing system, including the 

pointing algorithms, software, computer hardware, and actuators, in preparation for the next 

fl ight. Members of the FDAB were part of an engineering team in this effort. The basic azimuth/

elevation approach was kept, and a new control loop to make small angular adjustments about the 

remaining axis, cross elevation, was added to eliminate the source of the largest pointing error 

seen on the fi rst fl ight, namely that caused by the inadequacy of the azimuth control loop (at high 

elevation) to cancel the rotation of the gondola due to swinging from the balloon load train. The 

cross elevation approach used actuators that continuously adjusted the lengths of two of the three 

straps from which the gondola was suspended. Also, plans were made to close the loop around 

the star camera and the gyros mounted to the gondola base. Because pointing during the daytime 

was desired during the 24-hour mission, GPS attitude sensing was incorporated and was based on 

the Pivot GPS receiver (see section 4.5 for more discussion on the Pivot receiver).

The InFocus Balloon payload was fl own twice from Fort Sumner, New Mexico, in FY 2004. 

Branch members supported fi eld operations for the fi rst fl ight. During the fi eld operations several 

signifi cant revisions were made on the pointing system design, including in-fi eld implementation 

of a star camera/gyro control mode to complement the GPS pointing. The star camera was a 

piggyback experiment camera from the University of Pennsylvania designed to accommodate 

daytime star tracking. After extensive fi eld testing and weather delays, the fi rst InFocus fl ight 

was launched on May 31, 2004. Unfortunately, shortly after launch the telescope elevation drive 

was damaged from high loads after a hold-down cable was pyrotechnically released. The fl ight 

was terminated after a few hours of attempting to command a fi x. The cause of the anomaly was 

further disguised by the damage caused by the parachuting of the gondola onto rocky terrain. 

Nevertheless, the principal investigator and his science team decided to return for a second 

campaign in August and September. FDAB members did not travel to the fi eld but provided 

consultation support particularly for gyro alignment. The fi nal confi guration, having been greatly 

modifi ed throughout the previous year, fl ew successfully on September 17, 2004, with long 

observations of signifi cant X-ray targets, the results of which are now being studied. Despite the 

success, once again, the gondola and telescope suffered severe damage on landing. Nevertheless 

the science team tentatively plans to fl y InFocus within two years on a long duration balloon.
6 FDAB End of FY 2004 Report

Figure 2-3. InFocus readying for launch 

[Technical contact: Dave Olney]

2.1.4 GAMMA RAY LARGE AREA TELESCOPE (GLAST)

 http://glast.gsfc.nasa.gov/

GLAST is planned for launch in February, 2007. During its mission lifetime, GLAST will 

perform a full-sky survey of the gamma ray fi eld and will repoint to observe gamma ray bursts. 

Spacecraft orbit determination will be performed using a redundant pair of General Dynamics 

Viceroy GPS receivers.

The FDAB is involved in orbit and attitude analysis, design, operations, and on-orbit validation 

of the spacecraft. FDAB provided TDRSS and ground station view period analyses. Analysis was 

performed to show that Differenced One-Way Doppler (DOWD) can be used to validate the GPS 

receivers. GLAST orbital decay profi les were provided for altitudes in the range of 565 km to 

600 km to aid in analysis of Kapton erosion rates. FDAB also worked with the Flight Operations 

Team (FOT) to design fl ight dynamics software for the MOC.

[Technical contact: Mark Woodard]
FDAB End of FY 2004 Report 7

2.1.5 GLOBAL PRECIPITATION MISSION (GPM)

 http://gpm.gsfc.nasa.gov/

GPM is an international cooperative constellation of precipitation-measuring satellites. GPM will 

measure the global 4-dimensional variability of rainfall, latent heating, and the micro-physics 

of the variability. This information will be used to improve the prediction of climate change, 

weather, fresh water resources, and severe storms. To fulfi ll its mission in a cost-effective 

manner, the GPM project envisions using resources from already or soon-to-be launched 

satellites with suitable instruments (radiometers) for rainfall measurement. The program also 

aims to improve predictions of the Earth’s climate, the weather, and some components of the 

global water cycle. The FDAB’s contributions to the mission are in the areas of trajectory design, 

mission analysis, and attitude determination and control for the GPM primary spacecraft.

A major FDAB effort in the past year has been determining an optimal control box with respect 

to the following objectives: (1) minimizing orbit altitude variation; (2) minimizing delta-V; and 

(3) maximizing radiometer and radar coverage. The fi nal goal of this study is to help the science 

team choose a control box size that will provide the maximum science return while satisfying the 

mission constraints, such as power and thermal constraints.

Figure 2-4. Cumulated Earth coverage for 7 days as a function 

of the starting time for the different control boxes

Other orbit-related analyses that the FDAB has performed over the past year for the GPM Project 

include optimization of the GPM constellation for science; TDRSS coverage during insertion, 

descent, and mission orbit phases; ground operations concept; mission lifetime drag studies; 

radar footprint coverage analysis; and autonomous orbit maintenance strategies.

Another major FDAB effort is the design and development of GPM’s ACS, which will be fl own 

onboard as part of the fl ight software. The ACS consists of the logic and algorithms required 

to keep the spacecraft within its pointing requirements for each control mode throughout the 

mission’s lifetime. In FY 2004, the analysis team worked with the Project and other subsystems 
8 FDAB End of FY 2004 Report

to develop a design that will meet all mission requirements, designed the control modes and 

gains, and began the stability analysis for each mode. The team also provided feedback to the 

Project on requested information and studies, such as actuator sizing, sensor confi guration and 

location, slew requirements, error budgets and other attitude related analyses. The culmination of 

the attitude team’s work is an algorithms document that software personnel will use to integrate 

the ACS into the fl ight software, and an ACS requirements and specifi cations document, which 

references all the ACS-derived requirements and design practices that went into the ACS design.

[Technical contacts: Chad Mendelsohn, Joseph Garrick]

2.1.6 GEOSTATIONARY OPERATIONAL ENVIRONMENTAL SATELLITE (GOES) – N

The GOES-N launch is planned for the fi rst quarter of 2005. Unlike previous GOES missions, 

the FDF will not have primary support for launch and early orbit (L&EO) fl ight dynamics (FD) 

activities and will instead serve as consultants to the GOES Project while Boeing Satellite 

Systems (BSS) performs the FD work for L&EO.

The GSFC FD Team has been preparing for this role by reviewing the nominal BSS profi le and 

performing any mission analysis, such as ground station coverage and ascent profi le validation, 

that is requested by the GOES Project. Task personnel have worked with the Network Support 

Manger to help secure the Universal Space Network (USN) as a backup to GOES-N’s primary 

ground network, JPL’s DSN (26-meter Subnet). Telemetry and command services will be supplied 

to the BSS Flight Dynamics System (FDS) at Suitland Spacecraft Operations Control Center 

(SOCC) and tracking data will be supplied to the FDF. The FDF will incorporate both the DSN 

and USN data into “shadow” orbit determination solutions that will be available to BSS on 

request. While the FDF will perform orbit determination at GSFC, other members of the FDF team 

will be resident at SOCC to monitor BSS FDS operations and serve as consultants to the Project.

Following L&EO support, which will cover about 24 days, the FDF will become prime for orbit 

determination and acquisition data generation and delivery during the GOES-N Post Launch 

Testing (PLT) period, which covers about 45 days. FDF will aid in several of the PLT scenarios 

as the NOAA Orbit and Attitude Tracking System (OATS) undergoes its fi nal checkout. At the 

completion of testing, OATS will be able to assume full responsibility for GOES-N FD operations.

FDF has one additional responsibility on this mission. A new DSN frequency ranging system is 

being installed at the NOAA Command and Data Acquisition station at Wallops Island, Virginia. 

The FDF has been tasked to help certify the operational integrity of this system.

[Technical contact: Robert DeFazio]
FDAB End of FY 2004 Report 9

2.1.7 HUBBLE ROBOTIC VEHICLE (HRV)

HRV was conceived when NASA decided, after the Columbia accident, not to use the Space 

Shuttle for a fourth Hubble Space Telescope (HST) servicing mission. The HRV’s mission is 

to autonomously rendezvous with, grapple via a robotic appendage, and berth with the Hubble 

Space Telescope. Upon completion of a successful berthing to the aft of HST, the HRV will 

attempt a complex set of servicing tasks intended to extend the usable lifetime of the telescope. 

These services include battery augmentations, gyro replacement, Cosmic Origins Spectrograph 

(COS) instrument replacement, and Wide Field Camera 2 installation. When servicing is 

complete, the Ejection Module (EM) component of the HRV will separate from HST and deorbit. The compact Deorbit Module (DM), which remains attached to HST, will ultimately be 

used to dispose of the telescope some time in the next decade.

Figure 2-5. A rendition of the HRV attached to the HST

The autonomous rendezvous and capture (AR&C) relies upon a suite of relative navigation 

sensors, mostly unproven for this application. The system requires two independent sensors in 

each of the various operational ranges (relative distances from HST). The baseline compliment 

includes Optech’s Relavis Laser Detector and Ranging (LIDAR), Sandia’s HST Laser Dynamic 

Range Imager (HLDRI), Lockheed’s camera-based Natural Feature Image Recognition (NFIR) 

and Enhanced Auto-track Computer Vision System (EAVCS).

The servicing will be accomplished using a dual-appendage dexterous robot, originally designed 

and built by the Canadian based MacDonald-Dettwiler Robotics (MDR), and a suite of mission 

specifi c tools. The Special Purpose Dexterous Manipulator (SPDM) was originally built for 

NASA and intended to be used in conjunction with the International Space Station’s remote 

manipulator. MDR will also be the manufacturer of the custom Grapple Arm (GA), based on a 

modifi cation of the Shuttle Remote Manipulator design, that will autonomously capture HST.
10 FDAB End of FY 2004 Report

Due to the predicted rate of decay in HST’s battery capacity, a launch date of Decmeber 2007 

has been selected for the HRV– less than four years from project inception. In order to meet the 

mission’s signifi cant technical challenges and aggressive schedule, the HRV project has recruited 

a large number of team members from the public and private sections. They include but are not 

limited to: GSFC, JSC, MSFC, Lockheed-Martin Services, Draper Labs, MDR, Sandia National 

Laboratories, Orbital Sciences Corp., Swales Aerospace, Jackson & Tull Engineering, and 

University of Maryland.

The FDAB has been involved with this mission since its inception. At the very early stages, Code 

595 has provided orbit decay analysis, tumble rate predictions (assuming an uncontrolled Hubble), 

and AR&C feasibility studies. Code 590 personnel also provided the GNC designs for the strawman concept and participated on the source evaluation board for the primary contractor selection.

The current responsibilities for the FDAB include the trajectory planning, complete GNC design 

of the EM, verifi cation of the robotic tasks servicing dynamics, and mission GNC performance 

analysis and verifi cation. To address these tasks Code 595 personnel have developed high 

performance simulations of the vehicle dynamics and control. The Freespace simulation 

environment is a GSFC-developed tool that provides advanced simulation features such as 128-

bit precision, multi-processing, advanced integrators, a MATLABTM compatable script parser, 

and scene graph visualization using OpenGL PerformerTM and hard real-time capability. Current 

plans are to evolve this system, with its high-fi delity HRV models, into a component of the 

hardware-in-the-loop test lab, man-in-the-loop trainer, and HRV ground system.

[Technical Contact: Steve Queen]

2.1.8 JAMES WEBB SPACE TELESCOPE (JWST)

 http://www.jwst.nasa.gov/

JWST is planned to be launched in 2011 to the Sun-Earth L2 libration point. JWST just recently 

completed its Mission, Spacecraft and Ground System Requirements Review (SRR). In addition, 

a Flight Dynamics Peer Review was held in August, 2004. 

A number of design, requirement, and operations-concept changes have been incorporated since 

the original Northrop Grumman proposal:

 • Increased number of stationkeeping maneuvers to eight per revolution (every 22 days)

 • New sun shield design – smaller, less solar torque

 • Requirement for only one momentum unload within each tracking arc

 - Approximately 11-day frequency

 - Enables accurate OD without the use of accelerometer

 - Requirement placed on STScI (observation scheduling)

 • Requirement for telemetry on spacecraft attitude and propulsion system to FDF

 - Used for momentum unload and SRP modeling and calibration

 • Requirement for reorientation of spacecraft prior to momentum unloads

 - Minimized stationkeeping delta-V
FDAB End of FY 2004 Report 11

The changes have led to a robust design and ops concept that meet all mission requirements. The 

fuel mass budget also is consistent with the current operations concept.

A number of important issues still remain to be resolved. The fi rst is the issue of spacecraft 

venting. Instrument venting will affect early orbit determination and will induce torques that will 

increase the frequency of momentum unloads. The effects and design impacts of this venting are 

still being analyzed. The second issue is the desire not to have a burn towards the Sun. This has 

been accomplished for all but the fi rst correction maneuver. The JWST FD team will perform 

trade studies for the fi rst maneuver because the burn constraint affects launch opportunities and 

fuel mass. The last issue is the mission orbit size. No current requirement limits the size of the 

orbit about the Sun-Earth L2 point. A current trade team is being formed to analyze the impacts of 

restricting the mission orbit size. This trade will also affect launch opportunities and/or fuel mass.

[Technical Contact: Mark Beckman]

2.1.9 LUNAR RECONNAISSANCE ORBITER (LRO)

 http://centauri.larc.nasa.gov/lro/ 

LRO will be the fi rst US mission to the moon since the 1997 Lunar Prospector mission. The current 

LRO baseline is a mean 50-km circular polar orbit. LRO has just released an Announcement of 

Opportunity (AO) for instruments. It is expected that three to fi ve instruments will be selected.

A key design criterion for LRO is the altitude control box. Mean altitude varies due to lunar nonspherical gravity effects. The FDAB has designed a control algorithm that optimizes fuel usage while 

achieving a desired altitude control constraint. The required fuel mass to meet constraints of +/-5, 10, 

15 and 20 km has been developed. Figure 2-6 shows the altitude of LRO for a +/- 10 km control.

Figure 2-6. Apoapsis/Periapsis Altitudes with +/- 10 km Control

Orbit determination for LRO will be challenging. At 50 km altitude, lunar gravity is the leading 

source of orbital uncertainty. Based upon current tracking systems and models, LRO is expected 

to achieve a total position uncertainty of 500 meters with 18 meters of that being a radial 

uncertainty to the lunar surface.

[Technical Contact: Mark Beckman, David Folta]
12 FDAB End of FY 2004 Report

2.1.10 MAGNETOSPHERIC MULTISCALE (MMS) MISSION

 http://stp.gsfc.nasa.gov/missions/mms/mms.htm.

MMS is part of the Earth Sun System program, one of the science themes of NASA’s Science 

Mission Directorate. The major focus of the Sun-Earth Connection program is investigating the 

physical processes that link the Sun and the Earth. MMS is a four-spacecraft solar-terrestrial 

probe designed to study magnetic reconnection, charged particle acceleration, and turbulence 

in the key boundary regions of the Earth’s magnetosphere. An Announcement of Opportunity 

for the instrument complement and principle investigator teams was released in January 2003. 

Two proposal teams responded and in September 2003, both teams were selected for further 

refi nement of their mission concept. Final selection of one team is expected in early 2005. More 

details about the mission can be found at the Web site provided above. 

During 2004, both proposal teams requested technical assistance in matters related to the 

trajectories. Branch personnel were precluded, due to the proposal-process rules, from proposing 

a trajectory design but were permitted to provide answers to specifi c technical questions from 

the proposal teams. After the fi nal proposals were submitted, branch personnel participated in 

a technical review of the proposals, and provided comments that the advisory panel used in 

developing its report.

The MMS navigation team delivered Magnetospheric Multiscale Mission Phase 2; Navigation 

Performance Analysis, which provides a thorough analysis of the absolute and relative 

navigation accuracy achievable for the MMS Phase 2 formation using ground station range 

and two-way Doppler measurements, GPS pseudorange measurements, cross-link range 

measurements, and various combinations of these different measurement types. The team also 

delivered Magnetospheric Multiscale Mission Phase 4; Navigation Performance Analysis, which 

provides a thorough analysis of similar candidate navigation scenarios that are consistent with 

the use of the proposed Inter-spacecraft Ranging and Alarm System (IRAS). This work identifi es 

and compares several ground-based and onboard navigation support scenarios that can satisfy 

the absolute and relative position accuracy requirements to meet the MMS Phase 2 and Phase 4 

science objectives. This work provides a foundation for the selection of the navigation system by 

the MMS fl ight project in the future. The team wrote and presented the technical paper “Relative 

Navigation Strategies for the Magnetospheric Multiscale Mission” at the 18th International 

Symposium of Flight Dynamics held in Munich Germany October 11-15, 2004. This paper 

summarized the results of several navigation approaches for Phases 1 and 2 of the MMS mission 

that the team has performed.

 [Technical Contacts: Charles Petruzzo, Russell Carpenter]

2.1.11 SOLAR DYNAMICS OBSERVATORY (SDO)

The SDO mission, part of the Living With a Star Program, is slated for launch in 2008. It will 

observe the Sun with three instruments from geosynchronous orbit over a period of fi ve years. 
FDAB End of FY 2004 Report 13

2.1.11.1 SDO TRAJECTORY DESIGN

The trajectory team has planned a preliminary L&EO profi le to help answer many questions 

from spacecraft subsystem designers. Although the launch vehicle has not been selected, the 

decision will be between a Delta IV and an Atlas V and is expected well before the spacecraft 

CDR in April, 2005. Other mission analysis studies such as high gain antenna visibility, omni 

antenna coverage, star tracker interference, and lunar shadow occurrences and durations have 

been performed to answer project questions and points of interest.

In addition to mission analysis, the SDO trajectory team is heavily involved in refi ning the 

critical design of the Flight Dynamics System (FDS). This system, which is mainly resident 

in the MOC, will be used to perform most trajectory-related computations in all phases of the 

mission. Orbit determination will be performed by the FDF at Goddard. The FDF is the center of 

orbit determination expertise at GSFC and will provide orbit solutions to the SDO FDS/MOC. 

Three documents describe the FDS design and interface agreements. The SDO FDS System 

Description and Design Document maps the SDO FDS Level 4 requirements into the FDS 

software. Any requirements, which will necessitate software modifi cations or new development, 

are noted. Also, the inputs and outputs related to each required task are documented. The SDO 

FDS to Ground System Interface Control Document (ICD) details the formats and delivery 

information for all FDS products. The SDO FDS/MOC to FDF Interface Agreement Document 

(IAD) details functions and deliverables between the FDS/MOC and the FDF. Drafts of all 

three documents were completed by the end of FY 2004 and will be boarded with the project’s 

Confi guration Control Board (CCB) before the Project CDR.

2.1.11.2 SDO ATTITUDE ANALYSIS

SDO provides a wealth of engineering challenges from an ACS perspective: the need for highly 

stable pointing accuracies of 1-2 arcseconds with respect to the Sun and the need to guarantee 

smooth transitions between inertial sensors and Sun pointing guide telescopes are two examples 

of the problems being solved by FDAB engineers.

The fall of 2003 saw typical linear analysis and nonlinear simulation combined with fl ight 

software interface efforts and deployables reviews in preparation for the December, 2003, PDR. 

A trade study for safe-hold mode resulted in a gyroless controller design for safe-hold. Flight 

software requirements defi nitions and algorithms, including sensor data processing, controllers 

and estimators, and high-accuracy ephemeris, have been in constant development and refi nement 

over the course of the year. Most recently, fl ight software engineers have worked with analysts to 

defi ne telemetry packets and some preliminary fault detection and correction schemes. 

A high-fi delity (HiFi) simulator has been developed using the Simulink development tool. This 

HiFi serves a dual purpose: to provide time-domain simulations as verifi cation of all algorithms 

and analyses and to establish Real-Time Workshop models from which the core ACS control 

algorithms may be automatically converted to fl ight code.
14 FDAB End of FY 2004 Report

The analysis team supported discussions concerning GNC-related hardware, including the 

propellant tank and propellant management device, the instrument guide telescopes, star trackers, 

reaction wheels, and other GNC items. Component specifi cations and statements-of-work 

were written and sent out, and analysts participated in the instrument interface working group 

meetings in May, 2004, and August, 2004, to assist with the extremely complex pointing budget 

required for such stringent goals.

ACS analysts provided substantive assistance on the topic of high-frequency dynamics (i.e., 

jitter). FDAB analysts aided the development of requirements at the Observatory system level, 

provided estimates that prove jitter requirements will be met, and supported other subsystems 

(e.g., mechanical, high-gain antennas) both in defi nition of their requirements and in forming 

performance estimates. SDO instruments will be highly sensitive to jitter—pointing stability/

jitter has been one of the top fi ve driving requirements throughout SDO development—so 

detailed mechanical models and end-to-end dynamical analyses are required to guarantee 

successful performance.

[Technical contacts: Robert L. DeFazio, Scott R. Starin]

2.1.12 SPACE TECHNOLOGY (ST5)

 http://st5.gsfc.nasa.gov/

ST5 is a mission in the New Millennium Program and NASA’s fi rst experiment in the design 

of miniaturized-satellite constellations. The mission will last 90 days. During this time the 

constellation of three spin-stabilized spacecraft will validate new technology for spacefl ight 

while demonstrating formation fl ying capabilities. Technologies to be validated include a 

miniature cold gas thruster, an x-band transponder, fl exible interconnects, variable-emissivity 

coatings, ultra lower-power logic, autonomous constellation management ground software, and 

various technological improvements embedded in the spacecraft itself. 

In January, 2004, Orbital Sciences Corp.’s Pegasus XL launch vehicle was selected to deliver 

ST5 to orbit. The performance of the Pegasus XL is dramatically less than what the mission 

had originally planned to receive from its launch vehicle. Therefore the GNC team identifi ed an 

entirely new orbit regime to accommodate the ST5 mission. Numerous iterative consultations 

with the project’s science team and systems engineering team resulted in redefi ned science and 

mission requirements, eventually driving the design of the mission to its current orbit. 

The ST5 GNC team evaluated the new mission requirements and re-designed an orbit and 

constellation scheme to satisfy those new requirements. ST5 has a 300 x 4500 km orbit with 

a sun-synchronous inclination of 105.6°. A 06:00 GMT descending-node crossing time was 

selected to keep the orbit in full sun for the duration of the mission.
FDAB End of FY 2004 Report 15

In 2004, the following reviews were supported by the ST5 GNC team:

 • Orbital / KSC Technical Interface Meeting, January 15, 2004

 • Delta-CDR, July 21-22, 2004

 • Mission Operations Review, September 14-15, 2004

 • Orbital / KSC Mission Interface Working Group conference, September 30, 2004

The ST5 GNC team has developed a maneuver plan to validate onboard thrusters and deploy the 

constellation to two predefi ned formations over the 90-day mission. This plan will obviate the 

need to precess the attitude of each spacecraft before and after each orbit maneuver, which will 

simplify operational support and ultimately save propulsion. 

[Technical Contact: Marco Concha, Mark Woodard]

2.1.13 SPACE TECHNOLOGY 7 (ST7) DISTURBANCE REDUCTION SYSTEM (DRS)

 http://nmp.jpl.nasa.gov/st7/

The ST7 DRS is a project within the New Millennium Program with a mission objective to test two 

advanced technologies: Gravitational Reference Sensor (GRS) and colloidal micronewton thrusters 

(CMNT). ST7 is scheduled to fl y in 2008 as an instrument package aboard ESA’s SMART-2: 

LISA Pathfi nder spacecraft, which will orbit around the Sun-Earth L1 Lagrange point. Technical 

objectives of this mission include validating that a test mass follows a trajectory determined by 

gravitational forces within 3x10-14 x (1+(f/3 mHz)2

) m/(s2√Hz), and obtaining spacecraft position 

control to an accuracy of less than 10 nm/√Hz within the measurement band of 1-30 mHz. 

ST7 is a joint venture consisting of JPL, Stanford University, Busek Co., Inc., and GSFC. The 

responsibilities of the FDAB to the project include the development of the Dynamics Control 

System (DCS) that controls the spacecraft position and attitude to establish drag-free motion of the 

test masses within the GRS units, development of a full nonlinear dynamic model of the spacecraft 

and test masses (Hi-fi delity simulation model), and generation of fl ight code for the DCS. 

ST7 consists of two GRSs with internal free-fl oating cubic test masses, designed to follow 

gravitational trajectories, and two clusters of four thrusters for spacecraft translational and 

rotational control. The DCS is responsible for using star-tracker data and GRS data to generate 

commands, which are DCS-mode dependent, for the thrusters. Five operational modes exist 

within the DCS: attitude-only mode, accelerometer mode, initial drag-free mode, interim drag-free 

mode, and full-drag free or science mode. In the science mode, the DCS centers the spacecraft in 

translation about the reference test mass and centers the spacecraft in the transverse axis about the 

non-reference test mass using spacecraft rotation in the measurement band. Control for test masses’ 

relative attitude and non-reference test mass’s position in the sensitive axis is provided by the GRS 

suspension loop. A representation of the ST7 mission is shown in fi gure 2-7.
16 FDAB End of FY 2004 Report

Figure 2-7. ST7 Mission Representation

During FY 2004, the FDAB accomplishments include:

 • Delivery of DCS Flight Software Builds 0.1, 1.0, and 2.0.

 • Developed and tested mode transition strategies.

 • Completed controller designs.

 • Presented papers on ST7 at GSFC Flight Mechanics Symposium, AIAA Guidance 

Navigation & Control Conference in Providence, RI, and the 49th Annual SPIE 

Conference.

 • Successfully held DCS CDR at GSFC.

 • Supported other ST7 subsystem CDRs.

[Technical Contact: Oscar Hsu]

2.1.14 SWIFT

 http://swift.gsfc.nasa.gov/

Swift was launched in November of 2004. The FDF will provide support to the Swift mission 

during the fi rst week of operations. FDF support will include delivery of Swift ephemerides, 

local oscillator frequency reports, and acquisition data for the Space Network (SN). These 

products are made available to the Swift MOC via the FDF Product Center Web site. Detailed 

requirements between the FDF and the Swift project are documented in the Memorandum of 

Understanding (MOU) between the FDF and the Swift MOC. 

FDF performed C-band radar site selection and coverage analysis to augment SN tracking 

support during the early orbit period. C-band radar sites ASCQ, KMRQ and KPTQ have the best 

Swift coverage after separation and will provide angle and range tracking data on launch day for 

critical initial orbit determination and ephemeris generation.

FDF has supported pre-launch testing with the SN as well as two interface tests with the MOC. 

Past and future simulations include the support of nominal and contingency L&EO periods. FDF 

has also consulted on fl ight dynamics issues of relevance to FOT operations.

[Technical Contact: Mark Woodard]
FDAB End of FY 2004 Report 17

2.1.15 TIME HISTORY OF EVENTS AND MACROSCALE INTERACTIONS DURING SUBSTORMS (THEMIS)

 http://sprg.ssl.berkeley.edu/themis/Flash/THEMIS_fl ash.htm

The THEMIS mission is a NASA Explorer Program mission set to launch in mid-2006. The 

THEMIS spacecraft is being built by Swales Aerospace under contract to the University of 

California Berkeley. THEMIS is a formation of fi ve spacecraft in various highly elliptical Earth 

orbits. The fi ve probes will have apogee radii of 10 to 30 Re

 (Earth radius). The periods of the 

probes will be one, two and four days, allowing the probes to align at apogee during conjunction.

The FDAB is providing consultation and software support to the THEMIS project. This support 

includes orbit determination, maneuver planning and attitude determination software and training 

UCB personnel in its use. FDAB personnel also serve on the NASA Review Panel evaluating 

THEMIS progress.

THEMIS completed their CDR and subsystem peer reviews in 2004.

[Technical Contact: Mark Beckman, Robert DeFazio, Richard Harman]

2.2 OPERATIONAL MISSIONS

2.2.1 EOS AURA

 http://eos-aura.gsfc.nasa.gov/

The Aura spacecraft successfully launched from the Western Test Range aboard a Delta 7920 

rocket on 15 July 2004 at 10:01:59.364 GMT. Aura is 3-axis stabilized and operates in a 

near-circular, 705-km altitude, sun-synchronous polar orbit with ascending nodal crossings 

at 1:45pm +/- 15 min solar mean local time (MLT). Aura is fl ying in the ESMO Afternoon 

Constellation behind EOS Aqua and is positioned such that Aqua’s nadir FOV intersects the 

Aura’s atmospheric limb FOV. This viewing intersection imposed two additional requirements 

on Aura’s orbit: a separation of 8-15 minutes later than Aqua in MLT, with a goal of 8 minutes, 

and a separation of 15-22 minutes later in along-track, with a goal of 15 min. The FDAB has 

responsibility for all Aura fl ight dynamics work until mid-November 2004, when the FOT will 

take over routine operations; FDAB personnel will continue to be responsible for maneuver 

planning and calibration and will be available for contingency support throughout the six-year 

mission lifetime. The FDF will also continue to provide orbit determination services for the 

duration of the mission. 

In FY 2004, FDAB provided both pre- and post-launch support for Aura. Pre-launch activities 

included performing attitude and orbit analyses, presenting at mission-level reviews, testing the 

Aura Flight Dynamics System (FDS), participating in mission simulations and readiness tests, 

and the drafting and updating of various requirements and documents. L&EO operations support 

is being provided in four key areas: maneuver planning and calibration, attitude determination 

and calibration, product generation, and orbit determination. 
18 FDAB End of FY 2004 Report

Maneuver support has consisted of ascent and inclination maneuver planning. The maneuver 

team planned the 6 orbit-raising maneuvers, which moved Aura from its injection orbit to its 

mission orbit rendezvous with Aqua. To better predict maneuver performance, the maneuver 

planning employed lessons-learned from Aqua’s ascent; in particular, using the effects of orbital 

position and solar-array angle on thruster duty cycles. The maneuvers were very repeatable and 

were each calibrated to within the stated accuracy of the control system. Once Aura achieved 

mission orbit the two spacecraft had an ascending node MLT separation of 8.25 min and an 

along-track separation of 15.74 min, well within the stated requirement. Figure 2-8 shows the 

ground-track error relative to the control box limits throughout the ascent maneuver phase. 

Figure 2-8. WRS Error During Ascent Relative to Control Box Limits

Aqua completed a series of inclination maneuvers in the Fall 2004. To maintain proper 

constellation confi guration, the Aura maneuver team planned 4 maneuvers designed to match 

Aqua’s inclination adjustment and to minimize semi-major axis changes. Figure 2-9 shows the 

Aqua and Aura inclination change plans. 

Figure 2-9. Inclination Adjust Maneuver Plan
FDAB End of FY 2004 Report 19

The attitude team has performed various calibrations, improvements, and analyses to date. 

Determining coarse magnetometer biases improved the yaw-pointing performance in Earth 

Point Mode by 7-10°. Fine magnetometer calibration assessed and showed the effects of induced 

magnetic fi elds caused by internal power loads. Gyro alignment and scale factor calibration 

was completed with data from dedicated attitude maneuvers. Star tracker calibration revealed 

the relative alignment between the two trackers to be ~60 arcseconds different from pre-launch 

alignment due to launch shock and ground alignment measurement limitations. The team 

will provide updates for onboard gyro and star tracker parameters if necessary. Emergency 

support for roll-rate phasing requirement in Sun Point Mode was quickly provided to address 

new science instrument thermal requirements. Attitude histories were provided to the thermal 

engineers to help improve their instrument models. The calibration of a science instrument’s 

gyros was not completely successful due to the observed instrument gyro performance 

characteristics. An investigation of stars with large position residuals in onboard attitude 

determination exposed problems with the onboard and ground star catalogs for Aura (and Aqua). 

In a particular case examined, a variable star, faint in the visual magnitude (Mv) passband but 

relatively bright in the star tracker passband, was close enough to the onboard catalog star to 

offset the observed position of the catalog star by 41 arcseconds. Analysis showed that up to 10% 

of the onboard catalog stars (~330 stars) could suffer to varying degrees from similar effects. The 

effect on Aura onboard attitude determination is still under investigation. 

The products team used the FDS in the EOS MOC to generate the planning and scheduling data 

for the FOT and instrument teams as dictated by the FDS requirements. Collision avoidance 

computations were obtained from US Stratcom and evaluated by the FD team throughout the 

ascent and inclination-adjust phases. The products team also provided training on routine FDS 

operations for the FOT. 

[Technical contacts: Lauri Newman, David Tracewell]

2.2.2 GRAVITY PROBE-B (GP-B)

GP-B is a relativity gyroscope experiment that was developed by NASA and Stanford University 

to test two unverifi ed predictions of Albert Einstein’s general theory of relativity. GP-B launched 

successfully from Vandenberg Air Force Base on April 20, 2004. FDAB support was provided 

through the FDF.

FDF and FDAB personnel worked with the GP-B team to defi ne the FDF’s role and 

responsibilities for GP-B. FDF participated in pre-launch simulations, provided launch support, 

and provided OD and acquisition data to the GP-B MOC. During early orbit operations, the 

FDF confi rmed an orbit perturbation that was later determined to be caused by excess spacecraft 

venting. SN center frequency updates were provided after GP-B began having acquisition 

problems after launch. The FDF provided extended orbital support during GP-B’s initialization 

and orbit check-out phase due to the anomalistic venting on-board the spacecraft and problems 

with gyro spin-up. Additional support included orbit determination, updating the GN and SN 

with daily acquisition data updates, and providing one-line summaries for GP-B MOC planning. 
20 FDAB End of FY 2004 Report

The FDF recently provided orbital updates due to stale two-line elements (TLE) caused by GP-B 

orbit perturbation. The FDF provided updated GN acquisition data after reports of excessive data 

loss due to the TLE inaccuracies. In addition, the FDF sent GP-B MOC FDF orbital solution for 

comparison to GPS solutions.

The FDF continues to monitor GP-B as a part of its routine operation.

[Technical Contact: Anne DeLion]

2.2.3 HUBBLE SPACE TELESCOPRE (HST) TWO-GYRO SYSTEM (TGS)

 https://edocs1.hst.nasa.gov/

The HST Project and Lockheed Martin have nearly completed a pointing control system for HST 

which requires only two gyros. In development for one year, the TGS may become necessary; 

only three of the original six gyroscopes of the Rate Sensing Units are still working (a fourth 

is demonstrating an unstable bias). The TGS comprises a sequence of sub-mode controllers 

- progressing from magnetometers (M2G) to star trackers (T2G) to, fi nally, the fi ne guidance 

sensors (F2G). Rate estimates for the missing third axis are derived from these attitude sensors. 

The TGS is expected to provide a pointing stability of 10-20 milliarcseconds, compared to the 

current 7. The controllers show adequate single axis stability margins of 9 dB and 30 deg. A 

set of enhancements, such as operating with a single fi ne guidance sensor and modifying F2G 

acquisition logic for increased robustness against guide star loss-of-lock, will be studied in the 

upcoming “phase 2”. 

Final algorithms will be delivered to the Lockheed Flight Software Group by Oct 15, 2004. An 

on-orbit test of the TGS is planned for February 2005. Investigation into the feasibility of a onegyro system is beginning. FDAB personnel are working closely with Lockheed Martin and HST 

Project personnel to develop these algorithms. 

[Technical Contact: Michael Femiano]

2.2.4 LANDSAT-7

 http://landsat7.usgs.gov/index.php

LandSat-7, launched in 1999, is a three-axis-stabilized, Earth-observing spacecraft in a circular, 

Sun-synchronous, near-polar orbit at a nominal altitude of 705 km. The design mission lifetime is 

fi ve years. LandSat-7’s orbit is a prime Earth-observing orbit; other missions in that orbit include 

EOS Terra and EO-1. One of LandSat-7’s three gyros on indicated a possible failure in the near 

future. On May 5, 2004, the USGS decided that the safest course of action was to turn off the 

failing gyros and switch to the redundant gyros to continue taking science data. A major concern 

was that if another gyro failed, then it might not be possible to lower the spacecraft out of the 

705-km constellation. The spacecraft would then be taking up valuable “real-estate” in the orbit 

and it may become a collision hazard for other spacecraft.
FDAB End of FY 2004 Report 21

At the request of USGS, the FDAB performed a brief analysis to determine how much to lower 

Landsat-7’s altitude to safely move it out of its orbit. The original desire had been to drop Landsat-7 

about 5 km in altitude to effect possible repairs to the spacecraft and then restore it to its nominal orbit. 

The analysis, however, showed that it would require a decrease of almost 20 km to remove LandSat-7 

completely from its science orbit. At the time results were presented, a 20km decrease in altitude was 

thought to be unfeasible.

A later analysis request from ESMO studied the no-burn orbital decay rate of LandSat-7. An orbit 

propagated for one year with no drag modeled approximated the spacecraft staying in its nominal orbit 

with ground track control. A second propagation was made with drag modeled and no ground track 

control. Comparison of the two propagated orbits showed that Landsat-7 would be safely out of the 

705-km orbit range in about 5 months. If Landsat-7’s orbit were allowed to decay in this way, then the 

orbit should be monitored for close approaches with other sun-synchronous spacecraft during those 5 

months. Any spacecraft in danger of colliding with Landsat-7 would have to take evasive action.

The FDAB also assembled a brainstorming team to explore new ways of continuing the mission and 

to decommission the spacecraft when necessary. The team came up with about a dozen concepts. Cost 

and schedule reduced the concepts down to deriving rates using the Earth sensor, magnetometer or the 

coarse Sun sensors. A software module will be developed that will continually derive the rates from 

the selectable sensors and be monitored from the ground. This derived rate can be switched into any 

control mode on the spacecraft. 

[Technical contacts: Dave Mangus, Robert DeFazio, Karen Richon]

2.2.5 ROSSI X-RAY TIMING EXPLORER (RXTE) TRACKER ANOMALY

RXTE observes various high-energy sources, with a large angle slewing and 1-arcsecond attitude 

control system. The primary attitude references for this ACS are two CT-601 star trackers from Ball 

Aerospace. Since RXTE’s launch in 1995, the trackers have performed well even with some initial 

loss-of-track anomalies that occurred immediately after launch and were subsequently repaired in 

fl ight software. 

Recently one tracker has, on at least six occasions, exhibited spurious detections, which are 

indistinguishable from real star measurements, that appear in a single CCD column and are one 

arcminute wide. These readings are from tracker slots operating in ‘search’ mode rather than ‘directed 

track’ mode, the mode used for Kalman fi lter updates in Fine Pointing.

While the anomalous detections can affect the centroid calculation of a legitimately tracked star, 

they only minimally interfere with the essential attitude determination process and may, with further 

investigation, prove to be supressable with fl ight software fi lters. Spacecraft pointing capabilities 

are unaffected at present. Star-mapping activities in ground software have been disrupted by 

the anomalous data, as they are reliant on ‘search mode’ telemetry. The cause is unknown; one 

possibility is radiation damage to the CCD resulting in an increased charge transfer ineffi ciency. The 

investigations continue, with the participation of personnel from FDAB and other organizations.

[Technical Contact: Michael Femiano]
22 FDAB End of FY 2004 Report

2.2.6 TROPICAL RAINFALL MEASURING MISSION (TRMM)

 http://trmm.gsfc.nasa.gov/

TRMM is a joint mission between NASA and the Japan Aerospace Exploration Agency (JAXA) 

and is designed to monitor and study tropical rainfall. TRMM was launched in November, 1997.

2.2.6.1 TRMM REENGINEERING

The purpose of the TRMM re-engineering effort was to move most of the fl ight dynamics 

(FD) functions into the TRMM MOC using both COTS and GOTS software packages. 

TRMM’s reengineering effort led to automated FD functions and streamlined operations, both 

of which reduced the overall satellite operations costs and increased the system’s reliability. 

The Autonomous Flight Dynamics System (AutoFDS) was used to automate FD functions for 

TRMM. The products are scheduled in AutoFDS and automatically generated using tools such as 

FreeFlyer, Matlab, and Excel. Products include station contacts, TDRS contacts, node crossing, 

shadow times, maneuver planning, etc. 

Figure 2-10. AutoFDS

COTS applications were used for the new TRMM FDS, as this is standard for most Earth 

Observing System (EOS) missions. The TRMM reengineering effort used FreeFlyer for 

planning and maneuver products generation and Matlab for attitude products generation. The 

Quality Assurance (QA) tool was used for the QA of all fl ight dynamics products generated by 

TRMM AutoFDS. The transition to the new TRMM AutoFDS in the MOC was accomplished 

in three phases to minimize risk to mission operations support. Phase 1 consisted of moving 

the scheduling/planning functions into the MOC while Phase 2 and 3 consisted of moving the 

maneuver and attitude functions respectively. 
FDAB End of FY 2004 Report 23

The TRMM AutoFDS went through the acceptance, integration, and parallel operations testing 

that allowed the system to be certifi ed for operations support. A Real-time Attitude Determination 

System (RTADS) front-end socket connection (TPOCC server) was also developed and installed 

in the MOC computers. This connection allows the TPOCC telemetry data to be properly 

placed in the appropriate arrays and later ingested by RTADS. A version of the Multimission 

Three-Axis-Stabilized Spacecraft (MTASS) attitude determination system was also developed 

and installed in the TRMM MOC. An Operational Readiness Review was held on December 

8, 2003 before the new TRRM AutoFDS system was accepted and approved for operations. 

Since January 6, 2004, the TRMM AutoFDS system has successfully provided Flight Dynamics 

support in a lights-out environment. 

[Technical Contact: Osvaldo O. Cuevas]

2.2.6.2 TRMM REENTRY PLANNING

FDAB personnel continued the development of a controlled reentry plan for the TRMM spacecraft. 

In January 2004, a MESA-led independent evaluation of TRMM’s controlled reentry reliability 

showed that TRMM could continue science operations for two more years without reducing its 

reentry reliability. The solar array drive was identifi ed as a credible single point failure. In response 

to this and to concerns about the approximately three-year-long descent phase, the GNC team 

investigated different solar array confi gurations and discovered that an “X-wing” confi guration 

(arrays at ± 45 degrees) would reduce the descent time to about two years and also eliminate the 

solar array drive single point failure. The GNC team started to prepare for controlled reentry in 

March, 2004, but this was complicated by the failure of the –Y array in the spring of 2004.

The FDAB team supported a GNC peer review of the reentry plan in June, 2004. The 

team presented a mature reentry plan, contingency fl owcharts and procedures, nominal 

and contingency burn plans and orbital analysis, and a well-validated simulator to perform 

simulations with the new solar array confi guration. The team solved algorithm and modeling 

problems in various simulators, updated the Solar Pressure and Aerodynamic Drag (SPAD) 

model of TRMM, solved the hangoff and attitude drift errors appearing in the thruster 

modes, and created test procedures, new telemetry plots, and commit and abort criteria. Orbit 

maintenance maneuvers were discontinued in July 2004 to start the drag-down phase of the 

reentry plan, but after negotiation with NASA, NOAA provided funding to continue operations 

through January 1, 2005, in order to provide data during the 2004 hurricane season; orbit 

maintenance maneuvers resumed in August, 2004. Reentry simulation support has begun 

and FDAB personnel have developed and provided products in support of those simulations. 

Preparations are also in work for support of a Code 300 review in late 2004 or early 2005.

In early 2005, the National Academy of Sciences will provide an evaluation of the value of the 

TRMM data versus the hazards of an uncontrolled reentry and make a recommendation either to 

continue the science mission or proceed with preparations for a controlled reentry. If the decision 

is made to end the science mission in January, the earliest that the fi nal reentry operation would 

begin is July 2006 according to current estimates.

[Technical contacts: Frank Vaughn, Steve Andrews]
24 FDAB End of FY 2004 Report

2.3 FLIGHT DYNAMICS FACILITY (FDF)

2.3.1 FDF OVERVIEW

Goddard’s FDF is a multi-mission operations facility that provides routine orbit, attitude and 

network support. Located in Goddard’s building 28, the FDF has supported Goddard fl ight 

projects for more than 30 years. The FDF often provides operational services to non-Goddard 

projects as well, including launch support for both expendable boosters and the Space Shuttle, 

navigation support to National Oceanographic and Atmospheric Administration (NOAA) 

missions, and network acquisition data for non-Goddard NASA fl ight projects.

Prior to 2004, the FDF was operated under the Consolidated Space Operations Contract (CSOC) 

and was managed at Goddard by the Mission Services Program Offi ce. In 2004, management 

responsibility for the FDF transitioned to the FDAB and contractor support for the facility is now 

obtained from the new Mission Operations Mission Services (MOMS) contract. This represents 

a signifi cant change and was accomplished successfully with no interruption in service to 

operational missions. 

Many challenges exist with the FDF. Cost reduction in operations is a major driver in 

reengineering operational processes as well as hardware and software systems. In 2004, attention 

was given to hardware upgrades and assuring security needs were met. In 2005, more attention 

will be given to retiring old software systems and initiating reengineering activities, especially 

with regard to the attitude support operations in the FDF.

Work within the facility is organized by functional area: attitude operations, orbit operations, 

expendable launch vehicle support, human spacefl ight support, maneuver support, tracking data 

evaluation, software maintenance, and sustaining engineering activities. Accomplishments in 

each of these areas are discussed in the sections that follow.

[Technical Contacts: Tom Stengle, Sue Hoge]

2.3.2 ATTITUDE OPERATIONS

The FDAB wrote the Statement of Work (SOW) and discussed the Task Implementation Plan 

(TIP) to ensure the FDF would provide the required attitude operations services. A task manager 

in FDAB worked closely with the Attitude Operations task leader throughout the year; the task 

support was excellent. Monthly task status meetings addressed monthly accomplishments, 

performance metrics, mission anomaly resolution, and other items. The SOW for 2005 was 

written. This task provided attitude determination, calibration, and product generation support for 

the ERBS, UARS, ACE, RXTE, SOHO, Wind, and Polar missions.

[Technical Contact: Mark Woodard]
FDAB End of FY 2004 Report 25

2.3.3 EXPENDIBLE LAUNCH VEHICLE (ELV) SUPPORT

The FDF ELV Support Task has successfully supported 15 missions since the beginning of the 

MOMS contract. Mission support includes generation and transmission of pre-mission acquisition 

data and planning products, and real-time acquisition updates based on processing of inertial 

guidance data and tracking data during fl ight. The missions supported to date are listed below:

ELV LAUNCH LOG (2004)

 DATE/EPOCH (Z) LAUNCH

 1 January 11, 2004

 011/04:13:00.000 Sea Launch/Estrela doSul (SL-19)

 2 February 5, 2004

 036/23:46:02.651 Atlas IIAS/AMC-10 (AC-165)

 3 February 14, 2004

 045/18:50:00.948 Titan/IUS B-39 (DMSP-22)

 4 March 13, 2004

 072/05:40:00.844 Atlas IIIA/MBSAT (AC-202)

 5 April 16, 2004

 107/00:45:00.306 Atlas/Superbird-6 (AC-163)36B

 6 April 20, 2004

 111/16:57:23.754 Delta/Gravity Probe -B 

 7 May 4, 2004

 125/12:41:59.000 Sea Launch/DirecTV (SL-21)

 8 May 19, 2004

 140/22:22:00.513 Atlas IIAS/AMC-11 (AC-166)36A

 9 May 20, 2004

 141/17:47:03.310 Taurus/ROCSAT

 10 June 29, 2004

 181/03:58:59.000 Sea Launch/SL-20 Telstar-18

 11 July 15, 2004

 197/10:01:59.344 Delta II/AURA (WR)

 12 July 29, 2004

 211/17:18:00.000 P-3/ARROW FT-1 (drop)

 13 August 3, 2004

 216/06:15:56.537 Delta II/Messenger

 14 August 26, 2004

 239/17:09:00.000 P-3/ARROW FT-2 (drop)

 15 August 31, 2004

 244/23:17:00.717 Atlas/NROL-1 (AC-167)

[Technical Contacts: Frank Vaughan, Michael Mesarch]
26 FDAB End of FY 2004 Report

2.3.4 HUMAN SPACEFLIGHT SUPPORT

The FDF supports both the Space Transportation System (STS) and the International Space 

Station (ISS). For both the STS and ISS programs, FDF personnel continued to evaluate potential 

risks to mission support and, as risks were identifi ed, developed plans to mitigate those risks. 

Support items under continuous risk review include mission support personnel development and 

training, and FDF hardware and software diversity, redundancy, and reliability. 

2.3.4.1 STS SUPPORT

During FY 2004, the FDF supported the STS Program’s Return-to-Flight (RTF) efforts, which 

included full-up simulations with external mission support elements and both the Ground 

Network (GN) and Space Network (SN). These simulations exercised FDF pre-mission and 

launch support procedures. FDF personnel developed and conducted internal and FDF/SN-only 

profi ciency simulations, as well as joint ascent-abort simulations with JSC. The simulations 

were designed to train new FDF Space Shuttle support personnel, as well as to rigorously 

exercise FDF and SN contingency procedures not typically exercised during the full-up 

network simulations. The JSC Flight Design and Dynamics Division levied a new requirement 

on the FDF by requesting that TDRS beam angle displays be provided via the Internet during 

Emergency Mission Control Center activation periods. This effort involved the development 

of new Space Shuttle display capabilities and is still on-going. FDF personnel also participated 

in integrated networks RTF meetings and reviewed STS program documentation, and provided 

input as needed. Personnel also supported the Network Support Group (NSG) meetings at JSC in 

March, 2004, and September, 2004.

2.3.4.2 ISS SUPPORT

The FDF supported two Soyuz crew rotation missions to the ISS; Soyuz 7S launched in October, 

2003, and Soyuz 8S launched in April, 2004. The FDF also began preparations for supporting 

the Soyuz 9S mission, which is scheduled for launch in early FY 2005. FDF personnel supported 

several ISS orbit reboosts throughout the year, as well as testing of the United States’s very high 

frequency (VHF)-1 and VHF-2 emergency communication systems. The fi rst and only planned 

test of the VHF-2 system, performed in September, 2004, was successful and received pre-test 

approval from the FAA due to potential interference with commercial aviation. The JSC ISS 

personnel requested that the FDF analyze results from a test of the 150-megabit-per-second 

(mbps) K-band communication system; FDF presented the analysis results at the September 

2004 NSG meeting. FDF personnel participated in teleconferences about ISS Backup Control 

Center operations and developed new FDF support procedures based on those discussions. The 

FDF continued to evaluate ISS tracking data and provided the networks with weekly localoscillator-frequency reports. FDF personnel also reviewed documentation and participated in 

meetings to discuss support of the ESA’s Autonomous Transfer Vehicle (fi rst launch to ISS is 

planned for late 2005) and Japan’s H-II Transfer Vehicle.

[Technical Contacts: John Lynch, Chad Mendelsohn]
FDAB End of FY 2004 Report 27

2.3.5 MANEUVER OPERATIONS

The FDF Maneuver Support Task, planned and monitored orbit maneuver operations on a 

complement of NASA spacecraft including WIND, POLAR, SOHO, Aqua, and ACE. The task 

also helped to troubleshoot anomalies occurring during orbit maneuvers. Since January, 2004, 

the task has performed the two maneuvers for WIND, three for SOHO, three for ACE, and one 

for Aqua. These maneuvers can generally be classed as station keeping or orbit maintenance 

maneuvers. Task personnel also supported recovery from a SOHO anomaly that occurred during a 

SOHO attitude maneuver. In that case, recovering from the anomaly involved an orbit adjustment.

[Technical Contacts: Robert DeFazio, Dave Quinn, Rivers Lamb]

2.3.6 METRIC TRACKING DATA EVALUATION

This task provides tracking network validation and calibration, STS support, ELV support, space 

mission support, and new tracking antenna certifi cation support for missions supported by and 

tracking systems utilized by the GSFC FDF. 

[Technical Contacts: Greg Marr, Sue Hoge]

2.3.7 ORBIT OPERATIONS

FDF Orbit Operations supported over forty missions, which ranged from suborbital balloon 

missions to Earth-orbiting missions to libration point missions, in FY 2004. The Orbit group 

has continued providing excellent support to all fl ight projects while undergoing a signifi cant 

contract change. They provide thousands of products each year, such as orbit determination (OD) 

products, station coverages, and various reference fi les, that require a high degree of automation 

and expertise when that automation fails. In addition to all its standard products and services, 

FDF Orbit group provided its expertise to Hubble end-of-life planning, launch support for EOS 

Aura and Gravity Probe-B (GP-B), TDRS relocation efforts, and UARS SN coverage. 

Task personnel received special requests from both the Hubble Space Telescope (HST) and the 

FDAB for HST end-of-life planning. The requests included a listing of HST’s defi nitive accuracy 

achievements, orbital solution coeffi cient-of-drag values for the past four years, current year 

solve-for-drag correction terms, and the Extreme Ultraviolet Explorer early- and late-mission 

orbit vectors. These data are being used to characterize the predicted HST orbital decay for use in 

the future HST rendezvous effort.

Task personnel successfully supported the pre-launch, L&EO, and on-orbit activities for 

two major satellites this year: EOS Aura and NASA/Ames Research Center’s GP-B. The 

Aura support has been fl awless; products that are provided to the Aura MOC include orbit 

determination during all mission phases, acquisition-data generation on launch day, weekly localoscillator-frequency reports, and a number of reference fi les, i.e. drag coeffi cient updates and 

atmospheric models. FDF support of GP-B was due to end 30 days after launch, but Ames chose 

to extend that support to retain the FDF’s orbit expertise in orbit determination and prediction 

and network acquisition.
28 FDAB End of FY 2004 Report

The FDF also played a key role in the relocation of TDRSs 5, 7, 8, 9, and 10. This support involved 

planning and real-time support for 80 maneuvers, which were a combination of stationkeeping 

burns, north thruster fl ushings, and the actual relocation burns. Orbit personnel provided OD and 

acquisition data support for every maneuver; most maneuvers were supported in real time. For 

some maneuvers, task personnel performed collision avoidance analysis and assisted the White 

Sands Complex in choosing maneuver dates to assure spacecraft safety and performance.

The Upper Atmospheric Research Satellite (UARS) is an on-orbit mission that receives FDF 

support. UARS has been supported by two TDRS satellites since its launch in July 1991, but 

system failures have led to TDRS-coverage problems. Due to continued failures, a transition to a 

third TDRS was required for additional coverage. FDF personnel performed extensive interface 

and acceptance testing with external elements prior to the transition to the new TDRS.

 [Technical Contact: Karen Richon]

2.3.8 SOFTWARE MAINTENANCE

This task is responsible for the development and maintenance of the Flight Dynamics software 

used by the FDF in support of institutional space mission operations activities as well as 

maintenance of the FDAB R&D software tools to ensure consistency with the broader aerospace 

community practices. The fl ight dynamics software supports the following activities: attitude 

error analysis, prediction and determination; navigation, orbit prediction and determination, and 

error analysis; mission analysis; trajectory design and analysis; maneuver planning; acquisition 

data generation; and other mission planning tools.

The team’s main challenge for 2004 was to take over responsibility of FDF’s software 

maintenance from the previous contractor. The new team performed an inventory of all 

applications that needed maintenance and created the processes and procedures for performing 

the maintenance and confi guration management of those applications. An added diffi culty was 

the general lack of up-to-date documentation for the majority of the software. The maintenance 

plan created by the team lays the groundwork for continual maintenance task activities because 

software that is not properly maintained is a risk with very real consequences to the FDF’s 

operational environment. 

Following the maintenance plan has created good results. The team has begun the analysis for 

reducing the number of applications on the inventory list. A confi guration plan has been created, 

as well as specifi cations for a confi guration management system implementation. Plans have 

also been created for risk management, software maintenance and testing. The team responded 

to early challenges presented by the Tracking Data Formatting system and effectively researched 

and solved the problem, then created a plan to upgrade the system to eliminate future issues.
FDAB End of FY 2004 Report 29

Another challenge for the team is the requirement that the facility upgrade to a Hewlett-Packard 

operating system version that is supported by the vendor. The facility currently makes wide use 

of HP UX 10.2 and must upgrade to 11.i. As a result, all of the applications maintained in the 

FDF must be analyzed, tested, and rebuilt to be maintainable under the new OS. The upgrade of 

the operating system presents a further challenge to maintenance of the tracking data databases, 

as the version of Oracle in use is no longer supported and will not run on the newer OS, while the 

newer version of Oracle will not execute on the older OS. The team has been involved heavily 

in analyzing and creating the plans to perform these upgrades with minimal impact to the user 

community.

[Technical contact: Felipe Flores-Amaya]

2.3.9 SUSTAINING ENGINEERING

The FDAB took over management of the FDF beginning January 2004. An assessment was 

done of the condition of the computing systems within the facility at the time of the contract 

change. Based on that assessment, several upgrades and system changes were implemented. 

The Fiber Distributed Data Interface (FDDI) ring was removed, the network was rebalanced 

to provide better communications, and an open IONet connection was established. The entire 

facility hardware and software was place under a rigorous confi guration management process. 

A re-engineering plan was developed and will be implemented in 2005.

[Technical contact: Sue Hoge]
30 FDAB End of FY 2004 Report
FDAB End of FY 2004 Report 31

3.0 STUDY MISSION SUPPORT

3.1 INTEGRATED MISSION DESIGN CENTER (IMDC)

 http://imdc.gsfc.nasa.gov/

The IMDC is a human and technology resource dedicated to innovation in the development of 

advanced space mission design concepts to increase scientifi c value for NASA and its customers. 

The IMDC provides specifi c engineering analysis and services for mission design and provides 

end-to-end mission design products.

The FDAB provides its engineering expertise in the areas of trajectory design and attitude 

control. The trajectory engineers provide critical mission-specifi c analysis and design for mission 

trajectories. Attitude control engineers provide expertise in the refi nement of ACS requirements, 

sensor selection, actuator sizing, component placement and specifi cation, control modes design, 

and risk assessment. Engineers also identify “tall-poles” that require science requirement 

revisions. Many of these tall-poles are ACS-related such as formation sensing, tight attitude 

requirements, and fuel constraints. ACS engineers also provide critical cost analyses and trade 

studies to determine the lowest cost confi guration that will meet the science requirements. The 

innovative nature of the missions proposed by IMDC customers challenges the FDAB engineers 

to fi nd creative solutions to meet those missions’ science requirements.

Eleven mission studies, covering a wide range of mission types, were supported in FY 2004; 

these included low and high Earth orbits, Sun-synchronous, Molniya, Sun-Earth L2, Solar driftaway orbits, and formation fl ights. Some missions required point solutions while others required 

new technology concepts to achieve the science goals. Many of the formation-fl ight studies 

required innovative ways of solving the problems posed by the customers.

FDAB personnel also participated in human spacefl ight and Mars mission design workshops 

sponsored by the IMDC.

[Technical Contacts: Frank Vaughn, Michael Mesarch, Joseph Garrick]

3.2 AUTONOMOUS NANOTECHNOLOGY SWARM (ANTS)

 http://ants.gsfc.nasa.gov/

The ANTS advanced concept, proposed by GSFC’s Laboratory for Extraterrestrial Physics, 

envisions the use of a large number of small, autonomous spacecraft to explore the asteroid belt. 

The FDAB, in partnership with the University of Cincinnati and NASA/Langley Research Center, 

has performed analysis for the transfer trajectory and asteroid proximity operations phases.

[Technical contacts: Greg Marr, David Folta]
32 FDAB End of FY 2004 Report

3.3 CONSTELLATION X FORMATION FLYING MISSION

 https://conxproj.gsfc.nasa.gov

Constellation X is an x-ray telescope mission that will investigate black holes, Einstein’s Theory 

of General Relativity, galaxy formation, the evolution of the Universe, recycling of matter and 

energy, and the nature of “dark matter”. One design alternative being considered calls for two 

spacecraft fl ying in precise formation at the Earth/Moon-Sun L2 libration point. The spacecraft 

maintain a separation of 50 meters. Figure 3-1 shows the two spacecraft, the coordinate frames, 

the mirror focal point, and the actual image location. 

Figure 3-1. Pointing and Alignment Overview for the Constellation X Formation Flying Mission

Ideally, the center of the detector spacecraft, the mirror focal point, and the image location 

will coincide. The current control requirements are to maintain translation errors (in Y and Z) 

within ± 4mm and the relative position within ± 5 mm. The estimated relative positions must be 

accurate to within 0.25 mm. The individual spacecraft pointing control requirements are ±10 arcsec in pitch and yaw and ± 20 arc-sec in roll, the estimation requirements are 1.5 arc-sec in pitch 

and yaw and 10 arc-sec in roll.

Preliminary studies of the Constellation X formation fl ying concept have focused on 

characterizing the fuel and thruster requirements for the formation alignment and stationkeeping. The nominal science plan includes two formation re-orientation maneuvers per day, 

with an average maneuver size of 63 degrees. Additional studies characterizing the estimation 

problem have been initiated. The estimation system, in addition to estimating the individual 

spacecraft navigation states, must also estimate the location of the detector spacecraft with 

respect to the optics spacecraft. The estimation will involve the use of both RF and laser ranging 

systems simultaneously with a visual navigation system. The visual navigation system will 

include a star tracker, mounted on the detector spacecraft, that is capable of detecting both stars 

and ‘star-like beacons’ that will be placed on the optics spacecraft. An IMDC run in June 2004 

provided a high level, complete system description of the formation fl ying mission.

[Technical contacts: Julie Thienel, Rich Luquette]
FDAB End of FY 2004 Report 33

3.4 DARK UNIVERSE OBSERVATORY (DUO) SCIENCE OBSERVATION ANALYSIS

 http://duo.gsfc.nasa.gov/

FDAB personnel provided analysis support for the DUO mission proposal team by analyzing 

the effect of various orbit and attitude parameters on DUO observations of the Sloan (Northern) 

and Deep (Southern) fi elds. Each fi eld was modeled by a series of points in right ascension and 

declination on the celestial sphere. A dynamic model of the viewing geometry was developed 

using STK, which was driven by a Matlab script to generate and display visibility data for 

each point in each fi eld during a one-year time span. Analysis of this data helped determine 

when to schedule each point’s observation period in to order to avoid solar, lunar, South 

Atlantic Anomaly, Earth-limb grazing, and spacecraft latitude and attitude constraints. It also 

unexpectedly revealed that clocking the spacecraft roll angle in discrete increments of 60° in 

order to track the solar panels with the Sun while maintaining proper scan tracking geometry 

resulted in a portion of the Sloan fi eld being unobservable.

[Technical contacts: David Folta, Chad Mendelsohn, Frank Vaughn]

3.5 EXTRASOLAR PLANET IMAGER CORONAGRAPH (EPIC)

EPIC is a heliocentric mission designed to detect giant planets in other solar systems using 

its unique nulling coronagraph. The FDAB supported the GSFC Principal Investigator in the 

development of EPIC’s Discovery-Program proposal. The FDAB performed trade studies to 

determine the optimum mission orbit. Because of science viewing requirements, a Sun-Earth 

L2 libration point Halo orbit and an Earth-trailing heliocentric, or “drift-away”, orbit were the 

primary mission orbits considered. With regard to the choice of a mission orbit, it is important 

to note that EPIC must fi re its thrusters approximately every four days in order to unload 

momentum stored in on-board reaction wheels. The FDAB noted that if a Sun-Earth L2 orbit 

was chosen, then these frequent momentum dumps may adversely affect the orbit determination 

process, which is a great concern in this inherently unstable orbit. Based partly upon this 

information, a heliocentric drift-away orbit was chosen for EPIC. In addition to the trade 

studies and orbit determination analysis, the FDAB also analyzed launch vehicle requirements, 

generated nominal trajectory data, generated nominal ground coverage statistics, and determined 

spacecraft energy (delta-V) requirements.

[Technical contact: Steven Cooley, Greg Marr]

3.6 GEOSPACE ELECTRODYNAMIC CONNECTIONS (GEC)

 http://stp.gsfc.nasa.gov/missions/gec/gec.htm

The GEC mission is a multi-spacecraft mission managed by NASA’s Solar Terrestrial Probe 

Offi ce (STP) at GSFC. Currently in the formulation phase, GEC plans to use three or four 

spacecraft to study the Earth’s Ionosphere-Thermosphere (IT) system. While this region has 

been studied before, the coordinated use of multiple spacecraft will allow scientists to discover 

the spatial and temporal scales on which magnetospheric energy input to the IT region occurs, 

determine the spatial and temporal scales for the response of the IT system to this input of 

energy, and quantify the altitude dependence of the response.
34 FDAB End of FY 2004 Report

The second GEC Rapid Spacecraft Development Offi ce (RSDO) study was fi nished at the end of 

and Spectrum Astro. All three gave excellent presentations covering the two different options for 

GEC – fl ying three spacecraft with multiple dipping campaigns or fl ying four spacecraft without 

performing dipping campaigns.

Following the RSDO study, an effort was made to perform an independent optimization study 

of the GEC orbit. Using the same data that was given to the industry teams, FDAB personnel 

developed MATLAB scripts to optimize the GEC parking orbit with the requirement to complete 

ten, one-week dipping campaigns with perigee near 130 km (the original requirement). The 

complete range of launch vehicle performance data was analyzed, and it was determined that 

a 222 x 1525 km orbit was optimal as it maximized the dry mass available for the spacecraft 

subsystems and instrument payload. Further analysis was performed to assess the sensitivity of 

this optimal solution as a function of the number of dipping campaigns (varied from 8 to 12), the 

coeffi cient of drag (2.5 ± 10%), and propellant specifi c impulse (285 sec to 310 sec). The results 

of the optimization and sensitivity analyses were compiled in the paper “Orbit Optimization for 

the Geospace Electrodynamics Connections (GEC) Mission” and were presented at the AIAA/

AAS Astrodynamics Specialists Conference in Providence, RI in August of 2004.

Funding for GEC was halted late in FY 2004 following the refocusing of NASA priorities 

stemming from the Vision for Space Exploration (VSE). While the STP Offi ce and the science 

community remain committed to the realization of the GEC mission, it is unclear when study 

efforts will resume.

[Technical Contact: Michael Mesarch]

3.7 GLORY

FDAB personnel continued to provide analysis support for the Glory mission team. Analysis 

included validation of orbit requirements to meet mission goals, Sun angle calculations to 

determine the frequency of yaw maneuvers to track the Sun, and development of tools to 

generate and analyze Sun glint observation data for various attitude geometries.

[Technical contact: Frank Vaughn]

3.8 LASER INTERFEROMETER SPACE ANTENNA (LISA)

 http://lisa.gsfc.nasa.gov/

LISA is one of the fi rst gravitational science missions that will detect ripples in space-time itself. 

Gravity waves are detected by measuring the strain in space, i.e. the change in distance between 

detect change in distance between test masses which are located on three different spacecraft; 

these spacecraft are in heliocentric orbit. The orbits are chosen so that the three spacecraft form a 

roughly equilateral triangle, with its center located at a radius of 1 AU and 20 degrees behind the 

Earth. The 5-million-km arms and very quiet acceleration environment (3.5x10-15 2

LISA allow for the detection of gravity wave strains to a best sensitivity of 3x10-24

a set of masses separated by a great distance. LISA uses laser interferometric measurement to 

 m/s / Hz) of 

 strain/ Hz over 

FY 2004 with presentations from the three respondents – Astrium GmBH, Orbital Sciences Corp., 
FDAB End of FY 2004 Report 35

the measurement band of 0.1 mHz to 0.1 Hertz for a one-year observation. Stringent requirements 

-9 -9

spacecraft to ensure that the proper sensitivity for science measurements can be achieved.

The FDAB personnel supported LISA’s acquisition control and the design and analysis of 

Disturbance Reduction System (DRS) control. There are six optical links that need to be 

established before the constellation’s science operations can commence. Two acquisition 

strategies for establishing the laser links were developed. The fi rst strategy is based on a scanning 

approach. The width of the outgoing beam does not typically cover the position uncertainty 

of the receiving spacecraft, so a scan has to be performed to allow the receiving spacecraft to 

identify the orientation it has to assume to be able to illuminate the transmitting spacecraft. 

Overall, three scans have to be performed. Once a scan is complete, it uses an array of available 

sensors, with varying degrees of resolution, to lock in one laser link at a time. The order of 

the links, as they are established, is shown in Figure 3.2. An acquisition time history plot for a 

typical link is shown in Figure 3.3. 

Figure 3-2. Link Acquisition Order for Scan Acquisition Strategy 

Figure 3-3. A Typical Scan Time History

are placed on the rotational (8x10 rad/ Hz) and translational dynamics (10x10 m/ Hz) of each 
36 FDAB End of FY 2004 Report

The second strategy defocuses the outgoing laser beam by a factor of q to encompass the 

accuracy and alignment of the star tracker as well as orbital knowledge, and hence avoids the 

need for time-consuming scans. Because of potential stray light issues and the dim incoming 

beam, the local laser is turned off until the start of the heterodyne wavefront sensing. The order 

of the link establishment is different than the scan strategy, and it is shown in Figure 3.4. An 

acquisition time history plot for a typical link is shown in Figure 3.5. 

Figure 3-4. Link Acquisition Order for Defocus Acquisition Strategy

Figure 3-5. A Typical Defocus Time History

A Kalman fi lter, which uses star tracker information as well as gravitational sensor acceleration 

data, is used to estimate attitude errors during the time it takes to scan, achieve phase locking, 

and to obtain heterodyne wavefront tilt measurements. Both strategies are sequential, in which 

one one-way link is established at a time. The process for the single-link acquisition is initiated 

from ground command and then accomplished autonomously. Constellation-level models and 

simulations with refi ned DRS controls have been developed and used to assess the effi ciency of 

both proposed strategies.

[Technical contacts: Peiman G. Maghami]
FDAB End of FY 2004 Report 37

3.9 ORGANICS ORIGINS OBSERVATORY (OOO)

The OOO, a Discovery Program proposal, is a Sun-Earth L2 libration-point mission concept that 

is being led by GSFC’s Laboratory for Extraterrestrial Physics. The FDAB has analyzed launch 

vehicle requirements, generated nominal trajectory data, analyzed spacecraft fuel requirements, 

and performed OD error analysis.

[Technical contacts: Steven Cooley, Greg Marr]

3.10 SOLAR SENTINELS

 http://lws.gsfc.nasa.gov/sentinels.htm

The Solar Sentinel mission concept, proposed by GSFC’s Laboratory for Extraterrestrial Physics 

as part of the Living With A Star Program, plans to study the connection between solar phenomena 

and geospace disturbances. The current orbit design calls for multiple spacecraft launched on the 

same launch vehicle to make use of Venus fl y-bys to place the spacecraft in different heliocentric 

orbits. The FDAB has performed trajectory design analysis in support of this concept.

[Technical contacts: David Folta, Greg Marr, John Downing]

3.11 SUB-MILLIMETER PROBE FOR EVOLUTION OF COSMIC STRUCTURE (SPECS)

 http://space.gsfc.nasa.gov/astro/specs/

In the spring of 2003, NASA issued a request for proposals for a series of Vision Mission 

studies, which are intended to examine the justifi cation for mounting challenging long-term 

missions of potential interest to the agency and to determine the key technical capabilities that 

would have to be in place to assure success. One of these studies called for an investigation of 

a kilometer-baseline far-infrared and submillimeter interferometer in space. The SPECS Vision 

Mission proposal was funded in May, 2004. The SPECS project consists of a science team, 

an engineering team, and a smaller core group that belongs to both teams and assures rapid 

exchange of information between them. 

The science team examined what capabilities an interferometer would need to assure that 

currently unattainable astrophysical or cosmological observations will be made possible. The 

engineering team translated these capabilities into hardware and software requirements and has 

sought to identify the key technical hurdles to be overcome. The science team reconsidered the 

capabilities when the technological hurdles seemed excessive and supplied the engineering team 

with an alternative set of requirements that will still yield appreciable advances. This back-andforth exchange has led to agreement on a set of key scientifi c objectives and a corresponding 

preliminary interferometer architecture. The team is currently studying this architecture in greater 

depth to identify the major technological problems it may entail. 

The current concept envisions SPECS as a basic confi guration of two light collectors – 

telescopes – relaying far-infrared and sub-millimeter radiation to a central beam combiner with 

an angular resolution of 50 mas, comparable to that obtained with the HST (Hubble Space 

Telescope). The wavelength range for SPECS will be 40 - 640 microns and is expected to span 
38 FDAB End of FY 2004 Report

a gap that other missions, such as HST, JWST, and ALMA, will not study. Since SPECS will be 

located at the Sun-Earth L2 Lagrangian point, this angular resolution requirement calls for the 

baseline (separation between collector spacecraft) to vary between 20 and 500 meters.

Several signifi cant problems are currently being examined including the use of tethers for 

relative position control, active cooling systems capable of maintaining all elements of the 

optical at 4° Kelvin, and advanced metrology systems capable of delivering the degree of 

precision and accuracy required for mission success.

[Technical Contact: Dave Quinn]

3.12 SPACE INFRARED INTERFEROMETRIC TELESCOPE (SPIRIT)

The FDAB recently began a comprehensive effort to design trajectories for the SPIRIT mission, 

which was selected in July 2004 for further study under an Origins Program NASA Research 

Announcement (NRA). SPIRIT, led by GSFC, is an interferometric mission with a large SunEarth L2 libration point mission orbit. The FDAB will produce several years of launch window 

data using mission design techniques fi rst developed for the TRIANA and FKSI missions. 

The goal is to build upon this past work, which uses invariant manifold theory techniques, to 

further automate the process of generating nominal trajectories over a multi-year time frame. 

It is anticipated that the trajectory design refi nements developed here will be useful for all 

future libration point missions. In addition, the FDAB also plans to analyze launch vehicle 

requirements, generate nominal ground coverage statistics, determine spacecraft energy (delta-V) 

requirements, and develop contingency strategies for the SPIRIT mission. 

[Technical contacts: Steven Cooley, Greg Marr, Dave Quinn]

3.13 TERRESTRIAL PLANET FINDER (TPF)

 http://planetquest.jpl.nasa.gov/TPF/tpf_index.html 

TPF, one of the proposed missions under NASA’s Origins Program, will search for habitable 

extra-solar planets and life beyond Earth. Currently there are two promising architectures viable 

for extra-solar planet detection: visible-light coronagraph, and infrared interferometer. In April, 

2004, NASA decided to proceed with both architectures; JPL will lead the missions and GSFC 

will provide the telescopes. 

During FY 2004, a variety of dynamic analyses were done for the TPF Coronagraph (TPF-C) 

team. Figure 3-6 shows a plot of the deployed TPF-C observatory and the proposed actuator and 

sensor locations. 
FDAB End of FY 2004 Report 39

Figure 3-6. Location of ACS Actuators and Sensors (courtesy of Timothy Ho) 

To enable planet detection, the observatory must achieve one-billion-to-one image contrast, 

which translates to maintaining dynamic pointing stability in the sub-milliarcsecond level. 

Meeting these stringent stability requirements poses great engineering challenges and stretches 

current state-of-the-art technologies. A preliminary design of the pointing control system (PCS) 

for TPF-C has been developed to meet the stability requirements. The PCS topology combines 

a three-axis, inertially-stabilized attitude control system, an image motion control system that 

provides tighter control around pitch and yaw axes, and a vibration isolation system that reduces 

high frequency structural jitter. 

Once the PCS was defi ned, an integrated model was developed by incorporating dynamic models 

from various disciplines, including structures, optics, and controls. Such a model allows end-toend performance prediction from various disturbance sources. Estimates of rigid-body pointing 

error, image jitter motion, and wavefront error were computed using reaction wheel disturbances 

as inputs. In addition to the linear, frequency domain jitter analysis, a time-domain nonlinear 

simulation was also developed to evaluate the slew/settle performance of the observatory. 
40 FDAB End of FY 2004 Report

Results obtained from integrated modeling analysis and time simulations were presented at JPL’s 

Minimum Mission Review. The analysis results show that the point design (0.75 Hz bus-payload 

isolation, 2 Hz RWA isolation) meets both the image centration and contrast requirements. 

From the slew/settle simulation, the observatory was shown to meet the slew time requirement, 

although acquisition phase has not been properly modeled in the simulation. These benchmark 

results demonstrate that a properly designed system can meet the stringent performance 

requirements for TPF-C. The analysis can now proceed to explore various design options and 

simultaneously examine the effects of modeling uncertainty and actuator/sensor non-idealities.

[Technical contact: Kuo-Chia (Alice) Liu]

3.14 VENUS SOUNDER FOR PLANETARY EXPLORATION (VESPER)

The FDAB supported VESPER, which is a proposal mission in NASA’s Discovery Program and 

is led by GSFC’s Laboratory for Extraterrestrial Physics. VESPER will integrate key mission 

measurements with atmospheric models to investigate the coupled processes of chemistry and 

dynamics in the Venus middle atmosphere; the VESPER goal is to conduct a tightly focused 

study of the Venus atmosphere as part of a larger NASA program of comparative planetology. 

VESPER consists of a spacecraft and an atmospheric entry probe. The FDAB has analyzed 

launch vehicle requirements, generated nominal trajectory data, and analyzed potential probe 

impact locations for 2009 and 2010 launch opportunities.

[Technical contact: Greg Marr]
FDAB End of FY 2004 Report 41

4.0 TECHNOLOGY DEVELOPMENT

4.1 ADVANCED ATTITUDE DETERMINATION AND SENSOR CALIBRATION

The purpose of the advanced attitude determination and sensor calibration task is to improve 

the accuracy and effi ciency of both processes while taking into account any current and future 

mission requirements. In FY 2004, this task studied spinning spacecraft attitude issues and attitude 

determination effi ciency.

Algorithms were developed to better estimate attitude for spinning spacecraft. In the past, the 

requirements on spinning spacecraft ground attitude systems did not require the sophisticated 

algorithm development that is necessary for three-axis stabilized missions. Within the next two years, 

two missions consisting of spinning spacecraft, THEMIS and ST5, will launch with modest attitude 

sensors but with challenging attitude requirements. In many respects, spinning spacecraft attitude 

estimation and sensor calibration now require more sophisticated algorithms than those developed for 

three-axis stabilized missions. The ground attitude estimation studies led to two attitude estimation 

algorithms being developed for spinning spacecraft: pseudo-linear Kalman fi lter estimating the 

attitude and rate and an extended Kalman fi lter (EKF) using Markley variables. Two pseudo-linear 

algorithms were developed: q-fi lter and D-fi lter. The q-fi lter estimates the attitude quaternion and 

rate while the D-fi lter estimates the direction cosine matrix and rate. Both fi lters were successfully 

operated on simulated spinning spacecraft sensor data. The 7-state q-fi lter had the advantage of 

smaller state vector than the 12-state D-fi lter. However, the D-fi lter demonstrated improved attitude 

accuracy due to an inherently linear dynamics model as opposed to the pseudo-linear measurement 

model for the q-fi lter. The Markley variable EKF algorithm has been developed and will undergo 

testing in the next fi scal year. Upon completion of algorithm testing using simulated and fl ight data, 

the next step is to develop the spinning spacecraft sensor calibration algorithm. This step is expected 

to be completed in the fi rst quarter of FY 2006. 

The task also worked to improve the effi ciency of advanced attitude determination and sensor 

calibration. First, the Mission Three-Axis Stabilized Spacecraft (MTASS) software system was 

successfully integrated into the GMSEC system architecture. In the short term, this provides MTASS 

with a standard real-time interface that could either be used to just collect data for later processing or 

as the front-end for a Real-Time Attitude Determination System (RTADS). Second, an autonomous 

module has been added to the gyro calibration portion of MTASS. This module has been successfully 

tested using fl ight data. The immediate advantage for missions performing a signifi cant number 

of attitude maneuvers is that the need for special gyro calibration maneuvers decreases potentially 

to zero. The implemented sequential Davenport algorithm has the ability to update the latest gyro 

calibration parameters with the information from discrete maneuvers instead of needing to use all 

the maneuvers at once. The MTASS system is currently being moved to the Rossi X-Ray Timing 

Explorer (RXTE) control center with the eventual goal of being operated autonomously for ground 

attitude validation of the onboard attitude estimate as well as autonomously performing gyro 

calibration. A prototype system is expected to be completed in the early FY 2005 timeframe. FY 2005 

work on this task will concentrate on automating the Mission Spin Stabilized Spacecraft (MSASS) 

multi-mission attitude system as well as automating the MTASS sensor alignment calibration process.

[Technical contact: Richard R. Harman] 
42 FDAB End of FY 2004 Report

4.2 ADVANCED NAVIGATION CONCEPTS

 “Libration Point Navigation Concepts Supporting the Vision for Space Exploration”

This paper was presented at the American Astronautical Society’s Astrodynamics Specialists 

Meeting, in Providence, RI, and it examines the autonomous navigation accuracy achievable for a 

lunar exploration trajectory from a translunar libration point (L2) lunar navigation relay satellite, 

augmented by signals from GPS. The paper also provides a brief analysis comparing the libration 

point relay to lunar orbit relay architectures and discusses some issues of GPS usage for cis-lunar 

trajectories. This study indicates that accuracies of better than 1 km and 5 cm/sec may be feasible, 

which are quite promising in comparison with the trans-lunar post-maneuver results on the order 

of kilometers and dozens of centimeters-per-second achieved during Lunar Prospector using twoway Doppler from DSN 34- and 26-meter tracking sites. Since these are single-case results, the 

value of the actual errors in predicting real-world performance is somewhat reduced. Instead, one 

may view these results as a guideline for the range of accuracy that might be achievable. Although 

a case can be made for lunar orbiting constellations in support of long-term human and robotic 

lunar exploration, the authors believe that the Earth-Moon L2 Orbiter provides a great deal of 

capability with minimal investment as a starting point for a comprehensive lunar and planetary 

navigation and communications infrastructure beyond near Earth orbit.

 [Technical contact: Russell Carpenter]

4.3 SPACE SCIENCE MISSION OPERATIONS (SSMO) 

 GROUND ATTITUDE SYSTEM REENGINEERING

The Goddard SSMO Project operates fi ve missions at Goddard that observe various space science 

phenomena. The Active Coronal Explorer (ACE) orbits the libration point between the Earth and 

the Sun and observes the Sun’s corona. The SOHO spacecraft also orbits the libration point between 

the Earth and the Sun and is most known for observing solar fl are activity. The Rossi X-ray Timing 

Explorer (RXTE) orbits the Earth at an altitude of 500 km and observes x-rays, one of the highest 

energy waves, to investigate space phenomena. The POLAR spacecraft also orbits the Earth, but at 

an altitude of 1.6 Re at its apogee and 1.2 Re at perigee. This orbit allows the POLAR spacecraft to 

observe the poles for extended periods to explore the Aurora phenomena. Finally, the WIND spacecraft 

has modifi ed its orbit many times to explore the solar wind phenomena between the Sun and the Earth.

Each of these missions suffers from the same problem: age. The youngest mission, ACE, was 

launched in 1997. Each mission is nevertheless still called upon to operate without fail, and in 

the face of reduced budgets. This has led SSMO to look for ways to reduce its operating costs to 

remain within these lower budgets. 

Ground-based attitude determination accounts for a signifi cant portion of spacecraft operating 

costs. Reengineering of these systems to a more effi cient system is necessary to reduce operations 

and enable safe operation of the spacecraft into the future. A study was conducted of the missions 

mentioned above that documented the current architecture of the attitude system, detailed the 

operating procedures, and how diffi cult the system was to operate. A second study analyzed the 

current systems and determined which systems were candidates for reengineering, along with 

different paths to a new system. These two studies led to a categorization of reengineering needs.
FDAB End of FY 2004 Report 43

The reengineering of the ground attitude systems of SSMO will be a continual effort into the 

next year, with the focus being on ACE, RXTE and SOHO. In the case of the ACE mission, 

it was deemed that the level of complexity for routine operations was too high. The path of 

its reengineering effort is currently being examined. For the RXTE mission it was clear that 

the attitude system was very mature with moderately complex attitude operations. As a result, 

the system and its operation could be moved from the FDF to the RXTE MOC with minimal 

effort but with a signifi cant reduction in operations costs. The SOHO mission has an attitude 

system that, over the years, has had several independent pieces developed, but that do not all 

operate together. The reengineering approach for SOHO is to bring the different pieces together 

into a cohesive system and then potentially place the new system in the Payload Operations 

Control Center. The WIND and POLAR missions are slated to be decommissioned and would 

consequently not recover the cost of the reengineering.

 [Technical contacts: John M. Van Eepoel, Richard R. Harman]

4.4 GLOBAL-POSITIONING-SYSTEM-ENHANCED ONBOARD NAVIGATION SYSTEM (GEONS)

 http://geons.gsfc.nasa.gov

The GEONS team completed two new releases of GEONS during FY 2004. GEONS 2.1 

includes upgrades to celestial navigation for horizon sensor and sun sensor measurements from 

spinning spacecraft; a cold-start initialization procedure that uses GPS measurements in a batch 

form; and the capability to integrate user-provided formation control algorithms. GEONS 2.2 

includes a capability to model antenna offsets for spin-stabilized satellites; improvements to 

the cross-link measurement models, including explicit modeling of clock bias and drift for both 

one-way and two-way measurements; and modeling of antenna-offsets for multiple antennas 

on both transmitting and receiving satellites. In addition, the team completed the mathematical 

specifi cation for GEONS 2.3. This release was targeted for completion during FY 2004, but, due 

to contract transition issues, and a greater degree of diffi culty than anticipated for the software 

improvements in GEONS 2.2, has been delayed to approximately the end of calendar year 2004. 

GEONS 2.3 will include capabilities for processing one-way Doppler data from TDRS (i.e. 

TDRSS Onboard Navigation System, or TONS, capability); modeling ionospheric delay for lowEarth orbit users; and improvements in bias and state reset commands.

The GEONS software has been licensed to Orbital Sciences Corporation and to Ball Aerospace 

and Technologies Corporation. Ball is currently incorporating GEONS into the Cloud-Aerosol 

Lidar and Infrared Pathfi nder Satellite Observations (CALIPSO) to fl y in formation with Frenchbuilt Coalition for Environmentally Responsible Economies (CERES) instruments on the EOS 

Aqua satellite. The CALIPSO mission is managed by NASA’s Goddard Space Flight Center and 

implemented by NASA’s Langley Research Center for the NASA Earth System Science Pathfi nder 

(ESSP) program and collaborates with the French space agency Centre National d’Etudes Spatiales 

(CNES), Ball Aerospace and Technologies Corporation, Hampton University, and the Institut Pierre 

Simon Laplace in France. CALIPSO is scheduled for launch in 2005. Orbital Sciences incorporated 

an orbit determination package based on GEONS into OrbView-3, and is currently putting GEONS 
44 FDAB End of FY 2004 Report

in the Solar Radiation and Climate Experiment (SORCE), which is a NASA-sponsored satellite 

mission that will provide state-of-the-art measurements of incoming x-ray, ultraviolet, visible, 

near-infrared, and total solar radiation. GEONS has also been released to numerous contractor and 

grantee teams under NASA project releases. New agreements of this type in 2004 were with Broad 

Reach Engineering and Star Technologies.

GEONS also was nominated for two awards during 2004: the Space Technology Hall of Fame, 

and the Federal Laboratory Consortium Mid-Atlantic Regional Award. As of September, 2004, 

the GEONS team received word that they had won the latter.

 [Technical contact: Russell Carpenter]

4.5 GPS-BASED NAVIGATION FOR HIGH EARTH ORBITS

The FDAB has been a leader in technology development to enable autonomous navigation and 

formation fl ying for spacecraft in high Earth orbits. Recent advances in GPS receiver designs and 

signal processing capabilities now make it feasible to consider using GPS to provide autonomous 

onboard navigation for high altitude space missions. 

In the past, GPS applications for absolute and relative navigation have been limited to altitudes 

below ~3000 kilometers, where a conventional instantaneous GPS solution is always possible. 

GPS-based navigation can reasonably be expanded to geostationary and highly eccentric 

orbits extending to ~50 Re using a specially-designed GPS receiver coupled with an orbit 

determination fi lter to sequentially process the sparse pseudorange measurements. Figure 4-1 

illustrates the geometry for receiving GPS main and side-lobe signals in a high Earth orbit, when 

the spacecraft is sometimes above the altitude of the GPS constellation. 

Figure 4-1. Geometry for reception of GPS signals by a HEO spacecraft. Side-lobe 

signals are weaker, but can still contribute to GPS observability for HEO users.
FDAB End of FY 2004 Report 45

The FDAB is involved with several technology initiatives to advance capabilities for applying 

GPS to high altitude orbits through analytical studies, GPS receiver development, and 

hardware in-the-loop testing. The DATSIM and GEONS software tools provide a high fi delity 

measurement simulation capability that may be used to assess navigation performance in a wide 

range of orbital regimes using GPS and other measurement types. GPS receiver development 

support in the FDAB has focused on the PiVoT and the Navigator receivers. The PiVoT receiver 

was originally developed for LEO applications, but the FDAB has developed modifi cations 

that enable its operation above the GPS constellation, which provides the branch with a unique 

hardware-in-the-loop testing capability. Navigator is a new, fully spacefl ight qualifi ed HEO 

receiver optimized for fast signal acquisition and weak signal tracking. It acquires and tracks 

GPS signals with a carrier-to-noise ratio (C/N0

) as low as 25 dB-Hz, a signifi cant improvement 

over PiVoT and other receivers suitable for spacefl ight. A breadboard version of the receiver will 

be available for hardware-in-the-loop testing in early 2005. 

FDAB personnel participated in a study in MESA’s Formation Flying Test Bed (FFTB) to assess 

real-time GPS-based orbit determination accuracies obtainable in a range of high Earth orbits. 

The FFTB uses real-time, distributed software to integrate RF signal simulators, actual GPS 

receivers and/or cross-link transceivers, and fl ight processors to provide a real-time simulation 

environment for system- and component-level studies. In this study, actual measurements were 

recorded from GPS receivers and processed in real-time using the GEONS fl ight software. This 

study indicates that autonomous, onboard navigation using GPS is possible in a comprehensive 

set of high earth orbits. Initial results indicate position accuracies on the order of tens of meters 

are routinely possible in some of the higher orbits. Work is ongoing to conduct real-time tests of 

longer period orbits for the GOES and MMS Projects.

[Technical contact: Mike Moreau]

4.6 FORMATION FLYING TECHNOLOGY

Spacecraft formations are a subset of the global collection of multiple spacecraft missions, 

classifi ed as Distributed Space System (DSS). In general a DSS is a collection of two or more 

space vehicles designed to accomplish similar or shared objectives; an end-to-end (information) 

system consisting of two or more space vehicles, coordinated fl ight management, and an 

integrated infrastructure for data acquisition, storage, analysis, and distribution. In contrast a 

formation is comprised of multiple spacecraft with the ability to cooperatively detect, maintain, 

and agree on the appropriate maneuver to maintain a desired position and orientation. Formation 

fl ying is enabling technology required to maintain the relative separation, orientation, or position 

between or among the formation spacecraft.

Overall responsibility for DSS technology development resides with the Guidance, Navigation 

& Control Systems Engineering Branch of the MESA Division at GSFC. DSS/formation fl ying 

technology development is supported by personnel within the FDAB. The specifi c focus areas 

are Earth-orbiting Formation Control; Earth-Orbiting Formation Design; Fault-Tolerance, 

Collision Avoidance, and Formation Safety; High-Altitude Relative Navigation; Libration Point 

Formation Control; and Libration Point Formation Design. The progress for each topic during 

FY 2004 is summarized below. 
46 FDAB End of FY 2004 Report

4.6.1 EARTH-ORBITING FORMATION CONTROL

 [Technical Contact: Dave Quinn]

This subtopic covers all missions in which the gravitational infl uence of the earth is the primary 

external force. Applicability to other bodies is of minor interest. Disturbances include but are not 

limited to drag, solar radiation pressure, and non-primary gravitational bodies.

Below is the supervised research within this topic that is being completed under Cooperative 

Agreements. 

4.6.1.1 FORMATION NAVIGATION, CONTROL, AND MISSION DESIGN ALGORITHMS

 Principal Investigator: Jonathan P. How, Department of Aeronautics and Astronautics,

Massachusetts Institute of Technology, Cambridge, MA

Recent hardware-in-the-loop experiments performed on the NASA GSFC Formation Flying 

Testbed confi rmed that decentralized Carrier-phase Differential GPS (CDGPS) yields excellent 

position accuracies (~ 2cm) for close formations in LEO. These results suggest that CDGPS 

would be an attractive sensor for the relative navigation of the formation fl ying missions described 

in the NRA. However, there is a problem because the corresponding velocity estimate errors are 

small (<= 0.5mm/s) but have a signifi cant impact on the fuel cost of the LEO/HEO formations. 

Thus the objectives of this effort are: (1) Complete the analysis of the impact of the velocity 

errors (i.e., consider more general orbit confi gurations); (2) Investigate the fundamental limits 

of the CDGPS estimator and explore possible changes that might improve upon the accuracy 

of the current velocity estimates; (3) Identify sensing augmentation approaches that could be 

effi ciently added to the spacecraft to improve the velocity estimates; (4) Extend current control 

techniques to mitigate the effect of these velocity errors on the fuel cost. It is anticipated that these 

investigations would be performed on the various testbed at MIT and on the FFTB at GSFC.

FY 2004 Publications:

 A. G. Richards and J. P. How, “Analytical Performance Prediction for Robust 

Constrained Model Predictive Control,” AIAA Guidance, Navigation and Control 

Conference, Providence RI, August 2004. AIAA-2004-5110.

 J. P. How, T. Alfriend, L. Breger, and M. Mitchell, “Semimajor Axis Estimation 

Strategies,” presented at the 2nd International Formation Flying Symposium, Sept. 2004.

 M. Mitchell, L. Breger, J. P. How, and T. Alfriend, “Effects of Navigation Filter 

Properties on Formation Flying Control,” presented at the AIAA Guidance, Navigation 

and Control Conference, Aug.~2004. AIAA-2004-5024

 M. Mitchell, “CDGPS-Based Relative Navigation for Multiple Spacecraft,” S.M. Thesis, 

Massachusetts Institute of Technology, Dept. Aeronautics and Astronautics, June 2004.

 L. S. Breger, “Model Predictive Control for Formation Flying Spacecraft,” S.M. Thesis, 

Massachusetts Institute of Technology, Dept. Aeronautics and Astronautics, June 2004.
FDAB End of FY 2004 Report 47

4.6.1.2 “VIRTUAL RIGID BODY” (VRB) SATELLITE FORMATION CONTROL TECHNOLOGY

USING RELATIVE VEHICLE DYNAMICS

 Principal Investigator: Robert M. Sanner, Department of Aerospace Engineering 

University of Maryland, College Park, MD

This research will extend the VRB control paradigm for formations of satellites, developed under 

a previous NASA grant. In particular, we will reformulate the methodology so as to be applicable 

for relative referenced formations, as opposed to the inertial referenced formations, assumed in 

our current model. This new capability will be added to our formation fl ying simulation facility, 

and its performance will be evaluated on baseline Earth-orbiting mission concepts identifi ed 

in the NRA. The accuracy of the new algorithm will be evaluated, and compared with our 

previous designs. The control synthesis technique will also be extended to incorporate additional 

robustness and fault tolerance features, both for parametric uncertainty in the spacecraft 

dynamics, sensors and actuators, as well as for stochastic perturbations arising in the vehicle’s 

environment and sensing system. Additional, and more realistic, actuator and sensor models will 

be incorporated, and the control formulation extended to include these new models.

FY 2004 Publications:

 R. M. Sanner, and D. K. Proffen, “Virtual Rigid Body (VRB) Satellite Control with 

Formation Preserving Cross-Coupling,” 2nd Intl Symp on Formation Flying Missions & 

Technologies, Arlington VA, Sept 2004 (in preparation for submission to AIAA Journal of 

Guidance, Control & Dynamics).

4.6.2 EARTH-ORBITING FORMATION DESIGN

 [Technical Contact: Steven Hughes]

This topic covers all aspects of mission design and guidance for Earth orbiting formations 

including LEO and HEO. This research effort investigates formation design approaches and 

optimal guidance and maneuver planning. We have used Magnetosphere Multiscale Mission 

(MMS) as a benchmark problem and are applying new trajectory design methods to provide orbit 

solutions for MMS.

Below is the supervised research within this topic that is being completed under Cooperative 

Agreements. 

4.6.2.1 PSEUDOSPECTRAL METHODS FOR GUIDANCE LAW DEVELOPMENT

FOR OPTIMAL DESIGN OF FORMATIONS

 Principal Investigator: Anil V. Rao, The Charles Stark Draper Laboratory, 

555 Technology Square. Cambridge MA 02139. 

 

The objectives of this research effort are as follows: (1) to develop a unifi ed numerical approach 

for minimum-fuel trajectory design and guidance for satellites fl ying in Earth-orbiting formation 

and (2) to gain insight into the underlying structure of the minimum-fuel mission designs using 

the obtained numerical results. The numerical methodology used in this research is the Gauss 

pseudo-spectral method for discretizing continuous-time optimal control problems. The expected 
48 FDAB End of FY 2004 Report

signifi cance of the results are (1) the development of an advanced approach in that the same 

methodology will be used for guidance as is used for optimal mission design and (2) an increase 

in the fundamental understanding of the key issues required for both trajectory planning and 

guidance of satellite formation fl ying.

4.6.3 FAULT-TOLERANCE, COLLISION AVOIDANCE, AND FORMATION SAFETY

 [Technical Contact: Russell Carpenter]

This is an interdisciplinary topic that includes all aspects of relative trajectory estimation and control 

in off-nominal circumstances, such as detected and undetected failures and signifi cant degradations 

of performance in sensors, actuators, communications systems, onboard processors or busses, etc. It 

also covers all aspects of predicting unplanned close approaches and any other anomalies that would 

require that the formation enter a stable “safe mode” of operations. Design of such “safe mode” 

formation confi gurations that would allow time for recovery operations without loss of the formation 

due to collision, dispersal, or other circumstances is of special interest. Algorithms for fault detection, 

identifi cation, and recovery are of interest, as are control and estimation architectures that enhance 

overall mission reliability via distribution or decentralization of the estimation, guidance, and/or 

control computations. Examples of planned NASA missions that could benefi t from the research 

include the NASA ST-5 Nanosat Constellation Trailblazer mission, Magnetospheric Multiscale 

(MMS) and Magnetospheric Constellation (MagCon) missions (the latter involving 50-100 nanosats) 

and the Laser Interferometric Space Antenna (LISA); and the European Space Agency DARWIN 

space infrared interferometer. In addition, techniques required for autonomous satellite formation 

fl ight have recently been demonstrated on-orbit by the Landsat-7/Terra (EO-1) Enhanced Formation 

Flying (EFF) experiment and the Gravity Recovery and Climate Recovery (GRACE) mission.

Below is the supervised research within this topic that is being completed under Cooperative 

Agreements 

4.6.3.1 FAULT DETECTION, IDENTIFICATION, RECONSTRUCTION, AND FAULT-TOLERANT ESTIMATION

FOR A SATELLITE CLUSTER

 Principal Investigator: Jason L. Speyer, Mechanical and Aerospace Engineering 

Department, University of California, Los Angeles

Over the last few years, powerful fault detection fi lters that generate geometrically constrained 

residuals have been developed. These fault detection fi lters are generalizations of previous fi lters 

to robust, time-varying, and decentralized fault detection fi lters. Due to the presence of system 

uncertainty, the residuals generated by the geometric properties of the fault detection fi lters are 

compromised. To enhance fault detection and identifi cation, sequential probability tests have been 

developed to process the residual. The output of these residual processors is a probability of the 

identifi cation of a fault. Furthermore, fault reconstruction processes have been developed to obtain 

the magnitudes of the faults. Fault detection fi lters, residual processors, and fault reconstruction 

processes should be designed together. This work applies these analytical redundancy schemes to 

single satellites and satellite clusters. Based on extensions of our fault detection, identifi cation, and 

reconstruction schemes, new methodologies are being developed for constructing fault-tolerant 

estimators for single satellites and decentralized fault-tolerant estimators for satellite clusters.
FDAB End of FY 2004 Report 49

FY 2004 Publications:

 Robert H. Chen, Hok K. Ngy, Jason L. Speyer and Lokeshkumar S. Guntur, Russell 

Carpenter, “Health Monitoring of a Satellite System” AIAA GNC 2004, Providence, RI.

 Gene M. Belanger, Slava AnanyevÝ , and Jason L. Speyer, David F. Chichka, J. Russell 

Carpenter, “Decentralized Control of Satellite Clusters Under Limited Communication” 

AIAA GNC 2004, Providence, RI.

4.6.3.2 COLLISION AVOIDANCE AND SAFE MODE FOR SATELLITE FORMATIONS

 Principal Investigator: Trevor W. Williams, Professor of Aerospace Engineering 

Co-Investigator: Gary L. Slater, Professor of Aerospace Engineering

The objective of this research is to develop techniques for collision prediction and avoidance 

for satellite formations in low-Earth orbit, and to derive useful “safe hold” confi gurations for 

them to enter under certain failure modes. The collision prediction problem is closely related 

to that of relative orbital navigation of the formation satellites, which in turn depends on the 

type(s) of sensor and data that are available. The research will therefore fi rst investigate the 

classes of sensors that exist for the formation fl ight relative orbital navigation problem, and 

the orbit determination performance that is obtainable with each. In addition, the low thrust 

electric propulsion that is typical of formation missions will severely limit the class of safe hold 

formations that are reachable.

FY 2004 Publications:

 G.L. Slater, S.M. Byram, T.W. Williams, “Collision Probabilities for Satellites in 

Formation Flight” AIAA GNC 2004, Providence, RI.

 Trevor Williams, Justin Register, and Gary Slater “Formation-Keeping Maneuver 

Dispersions and Safe Mode Insertion For Satellite Formation Flight” AIAA GNC 2004, 

Providence, RI.

4.6.4 HIGH-ALTITUDE RELATIVE NAVIGATION

 [Technical Contact: Mike Moreau]

Onboard formation fl ying and navigation techniques and systems are being investigated to 

provide new and improved capabilities to support relative navigation for Distributed Space 

Systems (DSS). This topic includes all aspects of relative orbit determination specifi cally 

targeted towards high Earth orbit (HEO) and libration point orbit (LPO) missions. Navigation 

algorithms of interest include, but are not limited to, those that perform relative and simultaneous 

navigation of multiple spacecraft using GPS beyond LEO, celestial navigation, very-highprecision relative ranging techniques using optical and radio frequency cross-links, and passive 

techniques such as refl ected GPS and angles-only relative state measurements.

Below is the supervised research within this topic that is being completed under Cooperative 

Agreements. 
50 FDAB End of FY 2004 Report

4.6.4.1 MITIGATION OF THE IMPACT OF SENSING NOISE ON THE PRECISE FORMATION FLYING

CONTROL PROBLEM

 Principal Investigator: K. T. Alfriend, Texas A&M University

The major error source for the control of precise formations in Earth orbit is the relative 

navigation error. Currently differential carrier phase GPS (DCGPS) is the preferred method 

for the relative navigation. The primary error is the in-track drift that results from an incorrect 

estimate of the semi-major axis (SMA) difference. The equations of motion indicate, and other 

research has shown, that the SMA estimate error is minimized if the radial/in-track velocity 

correlation coeffi cient, ρ, is (-1). However the real world results have shown that ρ -0.1. An 

analytic investigation that developed an approximate solution to the 4x4 Riccati equation for the 

planar relative motion was performed. The results showed that ρ -0.1 is the correct answer. The 

analytic approach showed that the high data rate was dominating the radial/in-track coupling that 

occurs at orbit rate. It also demonstrated a) the only effective way to reduce the SMA error is to 

reduce the process noise, and that physically attainable relative velocity measurements will only 

provide minimal improvement in the SMA estimate.

FY 2004 Publications:

 Mitchell, M., Breger, L., How, J. P. and Alfriend, K.T., “Effects of Navigation Filter 

Properties On Formation Flying Control,” Paper No AIAA 2004-5024, 2004 AIAA/AAS 

Astrodynamics Conference, Providence, RI, Aug. 2004.

4.6.4.2 ASSESSMENT OF INTERSATELLITE MEASUREMENTS FOR PRECISE RELATIVE NAVIGATION

OF HEO SATELLITE FORMATIONS

 Principal Investigator: Penina Axelrad, University of Colorado

The primary project objective is to evaluate relative navigation accuracy of satellite formations 

in high earth orbits, especially elliptical orbits. This includes modeling of measurement errors 

for direct and refl ected GPS and cross-link ranging measurements. Over the past year we have 

also pursued an investigation of linearized dynamic models applicable to this environment and 

the benefi ts of using these models for formation design and navigation fi lter state propagation. 

Geometrical methods for formation fl ying design based on the analytical solution to Hill’s 

equations have been previously developed and used to specify desired relative motions in 

near circular orbits. By generating relationships between the vehicles that are intuitive, these 

approaches offer valuable insight into the relative motion and allow for the rapid design of 

satellite confi gurations to achieve mission specifi c requirements. Prior work presents a similar set 

of geometrical relationships for formations in eccentric orbits. Several confi gurations are shown 

to illustrate how these relationships can be used to model the formation dynamics. Analysis of 

propagation errors due to the linearization and the formulation of a navigation fi lter based on this 

model are currently underway.

FY 2004 Publications: 

 C. Lane, P. Axelrad, Analysis of Formation Flying in Eccentric Orbits Using Linearized 

Equations of Relative Motion, 2nd International Symposium on Formation Flying, 

September 2004.
FDAB End of FY 2004 Report 51

4.6.4.3 PRECISE RELATIVE NAVIGATION FOR HIGH EARTH AND LIBRATION POINT MISSIONS

 Principal Investigator: Robert Bishop, University of Texas

The problem of autonomous navigation of multiple spacecraft in the vicinity of a libration 

point is under consideration. The strategy for the algorithm development is to employ extended 

Kalman fi lters (EKFs) as the basic computation unit supplemented by a hierarchical mixtureof-experts (HME) utilizing gating networks for regulation. The fi rst year emphasized the 

development of a single EKF capable of processing inertial measurement unit information 

aided by celestial navigation sensors and radiometric cross-links. Realistic sensor errors and 

environmental uncertainties were considered. The EKF performance was verifi ed through the 

use of monte carlo analysis and the estimation errors were quantifi ed. The sensor suite elements 

were compared in their respective abilities to contribute to the observability of the inertial state, 

relative state, and various bias and other error estimates. The fi rst year effort also includes a reformulation of the EKF to process lunar altimetry in addition to DSN and libration point sensors. 

This was in response to the recently announced Vision for Space Exploration which created a 

desire to consider formations in the Earth-Moon system in a fashion that supported a possible 

moon exploration mission to locate resources for future manned landings.

FY04 Publications: 

 P. Huxel and R. H. Bishop, “Navigation Algorithms for Formation Flying Missions,” 2nd 

International Symposium on Formation Flying Missions and Technologies, September 2004.

4.6.4.4 SENSING AND ESTIMATION METHODS FOR RELATIVE NAVIGATION AND ATTITUDE

DETERMINATION OF LARGE SATELLITE FORMATIONS

 Principal Investigator: Glenn Lightsey, University of Texas

Over the past 12-month period, three primary accomplishments have been attained. In the 

area of long baseline relative navigation, a navigation fi lter was implemented and tested 

using a hardware-in-the-loop GPS simulator at separation distances up to 500 km. It was 

determined that at distances up to 100 km, improvements in the relative navigation position 

solution could be achieved by processing the measurements centrally and providing detailed 

environmental models. Beyond 100 km, the measurements become suffi ciently independent 

that the improvements by differencing and modeling are marginalized. Separately, progress was 

made on a distributed real-time simulation test environment that can support an arbitrarily large 

number of vehicles. Although there were some security problems with networking simulators in 

different locations, most of these have been overcome and a real-time hardware demonstration 

using a constellation of more than 4 satellites with GPS receivers is expected soon. Also, attitude 

determination was combined with navigation in a 6N degree of freedom simulation (N is the 

number of vehicles in the simulation, which are modeled as rigid bodies). This capability was 

demonstrated using a 2 vehicle gravity gradient formation, and relative attitude estimation 

accuracy was quantifi ed using GPS receivers as sensors.
52 FDAB End of FY 2004 Report

FY 2004 Publications:

 E. G. Lightsey, “Relative Attitude Determination of Earth Orbiting Formations Using 

Global Positioning System Receivers,” 2nd International Symposium on Formation 

Flying and Mission Technologies, Sept. 15, 2004, Crystal City, VA.

 W. Bamford, “Navigation and Control of Large Satellite Formations,” Ph.D. Thesis 

Defense, The Univ. of Texas at Austin, May 28 2004, Austin, TX.

4.6.4.5 RELATIVE NAVIGATION OF FORMATIONS OF HIGH-EARTH-ORBITING SATELLITES

USING DUAL FREQUENCY CIVILIAN GPS TECHNOLOGY

 Principal Investigator: Mark Psiaki, Cornell University

Techniques are being developed to use civilian dual-frequency GPS signals for relative 

navigation of high-altitude Earth orbiting satellite formations. These navigation techniques will 

allow satellite formations to acquire and track GPS signals and perform relative navigation 

using differential carrier phase techniques. Progress has been made on receiver algorithm design 

for acquiring weak civilian L2 signals and on methods for processing/fi ltering GPS carrier 

phase observables for high precision relative orbit determination. FFT-based block processing 

acquisition methods have been developed and tested for L2 civilian signals with carrier-to-noise 

ratios as low as 9 dB-Hz, which enables side-lobe signal acquisition at altitudes ranging from 

geosynchronous out to 17 Re. The performance of double-differenced carrier phase differential 

GPS has been investigated for relative orbit determination. We have found that doubledifference integer ambiguity resolution techniques should be feasible for these applications if the 

formation’s spacecraft carry properly designed receivers.

FY 2004 Publications:

 Psiaki., M.L., Winternitz, L.B., and Moreau, M.C., “FFT-Based Acquisition of GPS L2 

Civilian CM and CL Signals”, Proceedings of the ION GNSS 2004, Sept. 21-24, 2004, 

Long Beach, CA.

4.6.5 LIBRATION POINT CONTROL

 [Technical Contact: Rich Luquette]

This subtopic covers all missions in which the gravitational infl uence of at least two major 

bodies plays a signifi cant role, so that approximations of the three-body problem of Lagrange 

are applicable. Of major interest are missions in large repeating trajectories around the co-linear 

equilibrium points surrounding the secondary body, and in particular, the Sun-Earth/Moon 

system is of interest. Control of “deep-space” missions, in which the sun may be considered 

as the central body, is of secondary interest, but approaches that are equally applicable to both 

“deep space” missions and either or both of the above subtopics are of special interest.

Below is the supervised research within this topic that is being completed under Cooperative 

Agreements. 
FDAB End of FY 2004 Report 53

4.6.5.1 LIBRATION POINT MISSION FORMATION CONTROL

 Principal Investigator: S.N. Balakrishnan, University of Missouri-Rolla (UMR)

Co-Investigator: Henry Pernicka, University of Missouri-Rolla

Since receipt of funding under the NASA GSFC Formation Flying NRA, efforts at the University 

of Missouri-Rolla (UMR) have focused on various aspects of formation control. Both continuous 

and discrete control strategies have been developed, initially applied to a pair of spacecraft in a 

Leader-Follower confi guration. The efforts in discrete control quantify at what formation size 

and allowed deviation that the formation design becomes feasible (given a maneuver “threshold,” 

defi ned as the smallest V that can be reliably executed). The efforts in continuous control have 

used a new method developed at UMR known as the “Theta-D” technique to control the relative 

motion of a pair of spacecraft. We have also come up with a virtual architecture for multiple 

spacecrafts and have tested the concept with a 4 spacecraft formation. In addition to the PI and 

Co-PI, two graduate students and one post-doctoral student are assisting with this research. 

FY 2004 Publications:

 Xin, Ming, Dancer, M. W., Balakrishnan, S.N., and Pernicka, H.J. “Stationkeeping of an 

L2

 Libration Point Satellite with – D Technique,” American Control Conference, 

Boston, MA, June 30-July 2, 2004. 

 Xin, Ming, Balakrishnan, S.N. and Pernicka, H. “Deep-Space Spacecraft Formation 

Flying Using – D Control,” AIAA Guidance, Navigation, and Control Conference, 

Providence, Rhode Island, August 16-19, 2004, paper AIAA 2004-4784.

4.6.5.2 MODELLING AND CONTROL OF LIBRATION POINT SATELLITE FORMATIONS

 Principal Investigator: S. R. Vadali, Texas A&M University

Co-Investigator: K. T. Alfriend, Texas A&M University

The investigation develops new dynamic modeling and control techniques for the Sun-Earth/Moon 

libration point formations. Research develops control laws for relative and absolute motion, during 

science modes and for reconfi guration. The emphasis of this investigation is the development of 

impulsive control laws that use thrust intermittently for formation keeping as well as maneuvering. 

Utilization of solar radiation pressure for orbit control is considered, requiring a combined study of 

the attitude as well as orbit dynamics (6-DOF). A novel approach to reference trajectory generation, 

valid for formation slewing as well as reconfi guration, using the concept of eigen-axis rotations are 

developed. The technique converts the formation control to an attitude control problem and can be 

utilized for large or small formations. A concept for balancing the fuel consumption among all the 

subapertures is developed to increase the mission duration as well as the image quality. Nonlinear 

control techniques that do not require linearization about a reference trajectory is investigated. Besides 

using impulsive thrust, orbit control using internal mass movement techniques is also considered.

FY 2004 Publications:

 Vadali, S. R., Bae, H.-W., and Alfriend, K. T., “Design and Control of Libration Point 

Satellite Formations”, 2004 AAS/AIAA Space Flight Mechanics Meeting, Maui, HI, 

February 2004, Paper No. AAS 04-161.
54 FDAB End of FY 2004 Report

4.6.6 LIBRATION POINT FORMATION DESIGN

 [Technical Contact: David Folta]

This subtopic covers all missions near libration points where the dynamics of the gravitational 

infl uence of two major bodies plays an important role. Beginning with approximations of the 

circular restricted three-body problem of Lagrange to the use of full ephemeris modeling and 

modeling of all third body perturbation, this topic analyzes the impacts of design for formations 

in these regions. These orbits include both co-linear (L1

 and L2) lissajous and halo orbit classes 

and bifurcations into associated orbits of equilibrium points surrounding the Sun-Earth/Moon 

system. Control of “deep-space” missions, in which the sun may be considered as the central 

body, is of secondary interest in this NRA, but approaches that are equally applicable to both 

“deep space” missions and either or both of the above subtopics are of special interest.

Below is the supervised research within this topic that is being completed under Cooperative 

Agreements. 

4.6.6.1 LIBRATION POINT FORMATION DESIGN

 Principal Investigator: K.C. Howell, Purdue University

 Co-Investigator: B. Marchand, Purdue University

Upon receipt of funding under the NASA GSFC Formation Flying NRA, efforts at Purdue 

University and GSFC have focused on various aspects of how to best design formations to 

minimize the control efforts and to analyze the use of dynamical systems, central manifolds for 

example, for initialization. The optimization of the design of a formation can be improved by 

incorporating dynamical relationships representing the evolution of the families of solutions in 

libration orbits. Combined with full modeling, a high fi delity system is produced which permits 

the analyst to accurately determine the control cost of maintenance of the orbit as well as the 

formation. The use of dynamics relationships and input/output feedback linearization has been 

used to develop control strategies applied to a formation consisting of multiple (6-30) spacecraft 

in various pointing directions. These efforts quantify the formation orbit and design that allowed 

minimal deviation that meet the driving optical-plane science requirements. The design efforts 

used dynamical system methods (Floquet and others) developed at Purdue and at GSFC. We 

designed an architecture for a multiple formation (MAXIM and Stellar Imager) and have tested 

the concept with a 7 spacecraft formation. In addition to the PI and Co-PI, two graduate students 

are assisting with this research. 

FY 2004 Publications:

 B.G. Marchand and K.C. Howell, “Formation Flight Near L1 and L2 in the Sun Earth/

Moon Ephemeris System Including Solar Radiation Pressure,” AAS/AIAA Astrodynamics 

Specialists Conference, Big Sky, Montana, August 3-7, 2003, Paper No. AAS03-596.

 D.C. Folta, K.Hartman, K.C. Howell, B.G. Marchand, “Formation Control of the 

MAXIM L2 Libration Orbit Mission”, AIAA/AAS Astrodynamics, Guidance, 

Navigation, and Control Conference, Providence, Rhode Island, August 16-19, 2004.
FDAB End of FY 2004 Report 55

 K.C. Howell and B.G. Marchand, “Control Strategies for Formation Flight in the Vicinity 

of the Libration Points,” AIAA/AAS Space Flight Mechanics Conference, Ponce, Puerto 

Rico, Feb. 9-13, 2003. AAS Paper 03-113.

4.7 MISSION FORMULATION

This effort provided technology enhancements to address three basic areas important to GSFC in 

support of all missions and future space architectures: support for Project or PI mission design requests, 

innovative orbit designs, and the application of new algorithms to our ground support software.

Over the last several years, the FDAB has provided projects with support for the study and 

analysis of current and future missions. The primary areas supported were projects or PIs that 

request FDAB support and to provide mission formulation in advance to enable the FDAB 

to respond to future needs of both Earth and Space Science. FDAB personnel applied past 

development results to the defi nition of new classes of orbits and computed the trajectory and 

cost (delta-V, mass, launch vehicle, etc). An example of this is the assessment of the insertion 

and station keeping costs associated with a mission to any one of the Earth-Moon libration points 

(see Figure 4-2). 

Figure 4-2. Mission Formulation Earth-Moon Libration Orbit Stationkeeping Analysis

FDAB provided support to missions and proposals such as DUO, SIRA, Maxim, Swarm/IT, 

and the Lunar Initiative. These analysis efforts resulted in analysis that comprised coverage 

analysis, optimization of orbits for best science collection, formation design, formation control, 

minimization of Delta V/fuel, sun glint, to name a few.
56 FDAB End of FY 2004 Report

Innovative orbit designs provide both pure research and applications of previous investigations 

to support GSFC projects and scientists. The FDAB investigated libration gateways, formation 

confi gurations that minimize maintenance requirements, transfers and stationkeeping of Earthmoon libration orbits, and new orbits in the Earth-moon region. The research into these areas of 

orbit design is new and is performed on a limited basis. GSFC is a leader in these areas and the 

work proposed here is important for maintaining our expertise.

Ground Algorithms/Software applications ensured that new mission design techniques and 

software are verifi ed and used effectively. The advantage of previous software utilities is that 

these can now be easily updated or upgraded to include the research efforts stated above. The 

development of the Goddard Mission Analysis Tool (GMAT) open source software continued so 

that the FDAB can meet the demands of mission formulation efforts. 

[Technical contacts: David Folta, Frank Vaughn, and Steven Hughes]

4.8 SOLAR SAILS

FDAB continues to participate in the New Millennium Program’s Space Technology 9 (ST9) 

Solar Sail technology validation mission concept studies. The FDAB, in conjunction with 

GSFC’s Mission Applications Branch, developed a medium-fi delity Matlab-based tool that will 

be used to perform preliminary mission design analysis for low thrust missions. GEODYN is 

being investigated for navigation-related analysis under low thrust conditions.

The FDAB is working closely with the GSFC Solar Sail team, the MSFC In-Space Propulsion 

team, JPL and Langley to defi ne an ACS that uses standard and sail actuator systems. The 

FDAB also developed and validated a low-fi delity coupled ACS and orbit simulator to trade 

controllability with orbit maneuvering. With heavy FDAB support, the teams are developing 

solar sail validation and verifi cation concepts and addressing any scalability concerns for various 

Earth orbit missions.

[Technical contacts: Dave Mangus, Steven Cooley, Greg Marr]

4.9 MAGNETOMETER NAVIGATION (MAGNAV) EXPERIMENT ONBOARD

THE WIRE SPACECRAFT

The MAGNAV algorithm ran as a fl ight experiment as part of the Wide Field Infrared Explorer 

(WIRE) Post-Science Engineering Testbed. Initialization of MAGNAV occurred on September 4, 

2003. The WIRE spacecraft was designed as a four month infrared survey of the universe. WIRE 

was launched in March, 1999, but was unable to carry out its primary science mission. Since all 

the non-instrument systems continued to work, WIRE became a test-bed for science opportunities, 

technology infusion, risk management, educational outreach, and training. MAGNAV ran 

successfully as an in-fl ight technology experiment onboard WIRE. The experiment validated 

MAGNAV as a low cost approach to autonomous navigation that uses existing, reliable sensors.

MAGNAV is designed to autonomously estimate the spacecraft orbit, attitude, and rate using 

magnetometer and sun sensor data. Since the Earth’s magnetic fi eld is a function of time and 
FDAB End of FY 2004 Report 57

position, the differences between the computed magnetic fi eld and the measured magnetic fi eld 

components, as measured by the magnetometer, are a function of the spacecraft trajectory and 

attitude errors. Therefore, these errors are used to estimate both trajectory and attitude. In addition, 

the time rate of change of the magnetic fi eld vector is used to estimate the spacecraft rotation 

rate. The estimation of the attitude and trajectory is augmented with the rate estimation into an 

Extended Kalman fi lter blended with a pseudo-linear Kalman fi lter. Sun sensor data improves the 

accuracy and observability of the attitude and rate estimates. MAGNAV was loaded in the WIRE 

onboard computer as a separate task running in step with the attitude control system.

During the experiment WIRE underwent a series of maneuvers and control mode transitions; 

a period of maximum solar activity and the eclipse season occurred also during the testing. 

MAGNAV operated during all the events and converged successfully every time it was restarted 

throughout the experiment. Figure 4.3 shows an example of the results obtained from MAGNAV 

during the experiment. Figure 4-3(a) shows the MAGNAV attitude estimates and the star tracker 

based onboard attitude estimates during a maneuver, Figure 4-3(b) shows one axis of the rotation 

rate during the maneuver, Figures 4-3(c) and 1(d) show the orbit estimation errors. 

Figure 4-3. MAGNAV Performance during an Attitude Maneuver

Overall, the average attitude accuracies were between 1 and 2 degrees, the average rate 

accuracies ranged between 0.003 deg/sec to 0.008 deg/sec, and the average position accuracies 

ranged between 45 and 60 km. The position accuracies, in particular, were somewhat higher than 

anticipated, possibly from errors in time tags.

Future tests with MAGNAV are planned. Additional testing will help to identify sources of error 

and improve the overall navigation accuracy. The MAGNAV algorithm will then be coupled 

with the onboard coarse control algorithm to maintain WIRE in a zenith, sun-pointing attitude. 

MAGNAV is viable as an autonomous, low cost back-up algorithm, an initialization algorithm, 

or possibly as a prime navigation algorithm for a future mission with coarse requirements.

[Technical Contacts: Julie Thienel, Richard Harman]
58 FDAB End of FY 2004 Report
FDAB End of FY 2004 Report 59

5.0 BRANCH INFRASTRUCTURE

5.1 BEST PRACTICES FOR ORBIT ANALYSIS, DESIGN, NAVIGATION, AND CONTROL

Due to recommendations by the Columbia Accident Investigation Board, the FDAB has begun 

an effort to identify and record practices essential to mission success by documenting its 

practices for orbit analysis, design, navigation, and control. In general, these methods are already 

in use within the branch and will be used as guidelines for future orbit work. Project review 

boards will verify that these practices are being followed. 

All phases of spacefl ight missions are covered, from preliminary mission analysis to spacecraft 

end-of-life. FDAB’s set of best practices primarily includes topics that arise during mission 

development as well as some operations topics. Nevertheless, the FDAB will use AIAA’s 

“Satellite Mission Operations Best Practices”, April, 2003, (available at http://www.aiaa.org/

tc/sos/bp/Ops_Best_Practices.PDF) as its baseline of best practices for any mission operations 

phase. The FDAB Best Practices document will be expanded as new experiences provide new 

insights and as growing familiarity with the document identifi es currently accepted practices that 

are overlooked in the latest version text.

[Technical Contact: Charles Petruzzo]

5.2 COMMERCIAL-OFF-THE-SHELF (COTS) SOFTWARE MANAGEMENT

The FDAB led the effort to consolidate COTS software licenses for Analytical Graphics, Inc. 

(AGI) STK at GSFC. STK is used heavily in the FDAB and FDF for feasibility studies, prelaunch analysis, launch and on-orbit operations support. STK is also critical to many operational 

missions managed by ESMO and SSMO. Future missions, such as SDO, ST5, GPM and LRO, 

plan to use STK for their pre-launch and operations mission phases, and the demand for STK 

continues to grow as AGI adds new modules and capabilities to its software. STK’s capabilities 

are outstanding, but the cost is somewhat prohibitive for many missions and organizations 

so some, as a cost-saving measure, have declined to pay maintenance for their licenses. This 

approach has its problems, as AGI does not provide technical support for un-maintained licenses 

(a standard practice in the COTS world) and some missions that dropped their STK maintenance 

now fi nd that they need to upgrade to necessary capabilities. Approximately 85 licenses were 

purchased over the last four years, but about 55-60 actually kept up-to-date in maintenance. 

A second cost issue is few-license purchases versus multiple-license purchases. Most 

organizations purchase licenses separately or a few at a time, which precludes them from 

multiple-license discounts. The FDAB, which maintains 30 licenses for the basic STK modules 

and varying numbers of specialty-module licenses, benefi ts heavily from the multiple license 

discount, saving approximately 30% over the cost of single-license purchase and renewal. The 

FDAB plans to bring the FDF licenses under the FDAB’s STK license maintenance scheme; this 

plan was also expanded to include the primary users of STK in the ESMO and SSMO MOCs. 

These licenses constitute the majority of active STK use at GSFC. 
60 FDAB End of FY 2004 Report

The FDAB worked closely with SSMO and ESMO to determine the current and projected 

use of STK for their respective organizations and to determine the funding available to put a 

consolidated license scheme in place. After negotiating with AGI, the GSFC group settled on a 

consolidation and upgrade of 55 basic STK licenses along with an increase in the numbers of 

licenses for in-demand modules such as the Advanced Visualization and Attitude. The licenses 

will be available to SSMO & ESMO MOCs, the IMDC, FDAB and FDF through the open and 

closed networks. Plans for systems administration management and IT security requirements are 

being formulated now.

Future plans include integrating other GSFC organizations into the consolidation who have 

expressed interest in using STK, such as AETD’s Software Engineering Division, the Mechanical 

Engineering Division, Networks Engineering Division, the Earth Sciences Directorate and the 

Space Sciences Directorate, and even the Public Affairs Offi ce. Negotiations will begin next year 

with AGI in pursuit of a site license for GSFC, as well as a multi-year maintenance agreement 

for STK products. 

[Technical Contact: Karen Richon]

5.3 GENERATOR TOOL ENHANCEMENTS

The FDAB and Purdue University completed major upgrades to the Generator software. 

Generator, developed at Purdue, is a powerful trajectory design tool that uses invariant manifold 

theory techniques in conjunction with a sophisticated two-level differential correction scheme to 

generate libration point trajectories. Generator and its JPL software counterpart, LTOOLS, have 

a proven track record and have successfully been used to design trajectories for both TRIANA 

and the recently completed JPL GENESIS mission. Generator is currently being used at GSFC to 

develop trajectories for the SPIRIT Origins proposal. 

Two main enhancements to Generator were completed in FY 2004. First, a new J2 geopotential 

capability was added to both the force model and the differential corrector. Second, a set of 

enhancements, intended to allow more effi cient use of Generator to design Earth-Moon libration 

point trajectories, were developed. GSFC had previously used Generator to design mainly SunEarth libration point orbits. With this new capability, Generator will be now used to develop 

mission concepts for the Exploration Vision program.

[Technical contact: Steven Cooley]

5.4 GODDARD MISSION ANALYSIS TOOL (GMAT)

GMAT is an advanced mission analysis system currently under development at GSFC in 

partnership with private industry. The primary technical objective of the GMAT development 

effort is to provide a mission analysis system that meets design needs that are not met by current 

GOTS or COTS products. GMAT has been designed, from the beginning, to perform mission 

optimization and to interface with external optimization systems. Hence GMAT will enable 

mission analysts to provide fl ight projects with the best possible orbit design to maximize the 

science return of complex missions and to clarify the relationships between specifi c mission 

constraints and science performance. GMAT will employ the use of automated optimization 
FDAB End of FY 2004 Report 61

and search techniques that will enable one analyst or a small group of analysts to perform 

rapid trade studies in the mission design process. GMAT can already model the dynamics of 

distributed spacecraft systems as no other existing system can. The equations of motion for 

multiple spacecraft missions can be integrated separately or as a coupled dynamic system. 

This is essential for many missions and also provides a signifi cant speed advantage. GMAT 

has been designed to allow global epoch synchronization that synchronizes objects in time 

according to several rules that can be chosen by the user. Current systems either post-process 

data or require using a common integrator time step for all objects. The secondary objective of 

the GMAT project is to provide a fl exible and modular system that is open source, to facilitate 

interoperability and reuse and to reduce cost, in the spirit of the One NASA initiative. Due to the 

open nature of GMAT, models and algorithms can be used by multiple projects and, if necessary, 

project specifi c changes can be made effi ciently by employing appropriate experts. The GMAT 

effort is intended to foster active involvement from the private sector and academia, encourage 

collaborative funding from multiple government agencies and the private sector, and to promote 

the transfer of technology from government-funded research to the private sector. Below is a 

screen capture of GMAT in its current form.

Figure 5-1. GMAT Screen Capture

[Technical contacts: Steven Hughes, David Folta]

5.5 FDAB WEB PAGE AND TOOLS

 http://fdab.gsfc.nasa.gov

The FDAB Web site Maintenance updated the Web site to make it current and included 

additional information, such as lunar mission design material. This task is ongoing but the 

updates to the site included incorporating information from the FY 2003 FDAB End of Year 

Report and updating the personnel list. 

[Technical contact: Oscar Hsu]
62 FDAB End of FY 2004 Report

5.6 IN-HOUSE NAVIGATION SYSTEMS DEVELOPMENT

An in-house navigation systems development effort has been performed by FDAB engineers 

to maintain and enhance ground-based navigation systems such as the Goddard Trajectory 

Determination System (GTDS). In this fi scal year, a major effort has been focused on the 

development of a sophisticated user interface and graphics capabilities (GUI) for GTDS with the 

support of Code 583 software engineers. 

Version 1.1 of this GTDS GUI has been completed and is planned for delivery to GTDS users 

by December 31, 2004. This version includes basic user interface functions and 2-D graphics 

capabilities for ephemeris generation (EPHEM), ephemeris comparison (COMPARE), and 

differential correction (DC). The latest PC version of GTDS available for operations is integrated 

into this version.

The next version of GTDS GUI will include more complex functions of user interface, the 

updated version of GTDS and 3-D graphics capabilities. 

[Technical Contacts: Son Truong, Joseph Toth]
FDAB End of FY 2004 Report 63

6.0 EMPLOYEE DEVELOPMENT

6.1 NEW EMPLOYEE PROFILES

Dean C. Tsai joined the FDAB on February 9, 2004. He received his B.S. degree in Mechanical 

Engineering from University of California at Berkeley in December 2003. During his undergraduate 

years, he participated in the development of Joint Strike Fighter (JSF) during his internship at Pratt & 

Whitney in 2002; he participated in the integration and testing of the Mars Exploration Rover (MER) 

during his Co-op at Jet Propulsion Laboratory in 2003. Dean is currently developing the satellite 

simulation for the Magnetosphere Multiscale mission (MMS) as his Professional Intern Program 

(PIP) project. He is also supporting the ground data processing for the Wire/Magnav experiment and 

the formation control studies for Constellation-X.

Kevin Berry joined the FDAB on August 23, 2004. He received his B.S. degrees in Applied 

Mathematics and Mathematical Physics from the California State University at Northridge in 

June 2004. Since his arrival, Kevin has been busy learning the workings of the Satellite Tool Kit 

(STK) software by attending a full day training class and executing all of the available tutorials. 

He has successfully re-run several previous scenarios for the Solar Dynamic Observatory (SDO) 

in STK and was able to duplicate previous results. STK, plus other software tools, will be used 

in supporting calculations of the orbit circularization profi le of SDO. Kevin will be working on 

software modeling of the propulsion system of a mono-propellant spacecraft for his PIP I project

Leigh Janes returned to the FDAB on August 23 2004. She fi rst started working in the Branch as a 

co-op in June 2000 and earned her B.S. in Aerospace Engineering from Purdue University in May 

2004. Leigh is currently performing analysis for JWST’s transition orbit for her PIP I Project.

6.2 PROFESSION INTERN PROGRAM (PIP)

The PIP is a developmental program designed to acquaint entry-level professional with NASA and 

GSFC missions and operations, integrate them into the workforce as quickly as possible, and prepare 

them for more complex and responsible duties that they can perform with increasing independence. 

Required program activities include an Individual Development Plan (IDP) prepared for each intern 

by the supervisor, establishment of a mentor relationship with an experienced staff member, various 

orientation activities, formal and on-the-job training, and completion of a PIP project, which the intern 

describes in a written report and oral presentations given in Levels I and II to a panel of evaluators.

6.2.1 PIP LEVEL I: EVALUATION OF ANALYTICAL SOLUTIONS FOR AN ELLIPTICAL RELATIVE

MOTION PROBLEM (RIVERS LAMB)

As part of the New Millennium Program, the Space Technology 5 (ST5) mission is designed 

to prove several new technologies onboard three identical spacecraft. These spacecraft were to 

be deployed into a string of pearls confi guration in a Geosynchronous Transfer Orbit (GTO). 

Understanding the relative motion problem is critical for deployment from the launch vehicle as 

well as for maneuver planning. While the relative motion problem is well understood for circular 

orbits, motion in this highly elliptical regime is more challenging. The goal was to fi nd an 

analytical solution to the elliptical relative motion problem since a thorough numerical analysis 

can be time consuming and ineffi cient.
64 FDAB End of FY 2004 Report

Two different analytical solutions were researched, implemented, and compared to a 

benchmarked numerical model. Neither solution, however, produced completely satisfactory 

results for the highly elliptical orbit case. In the meantime, the ST5 mission profi le changed with 

the commitment to a Pegasus XL launch vehicle. In this new orbit regime, an analytical solution 

became more acceptable due to the change in relative motion dynamics at the signifi cantly 

lower eccentricity. For future analyses in this orbit regime, it will be possible to use either this 

acceptable analytical solution or a numerical solution.

(Rivers Lamb has been a full-time Goddard employee since August 2003. Prior to that time, he 

was a Co-op student within the Branch. He received his B.S. degree in Aerospace Engineering 

from Virginia Tech.)

6.2.2 PIP LEVEL I: THE EFFECTS OF ATTITUDE MANEUVERS ON THE MMS FORMATION (DEAN TSAI)

The main objective of the MMS mission is to further study the Earth-Sun magnetosphere. The 

mission consists of four spinning spacecraft fl ying in tetrahedron formation to capture the spatial 

and temporal dynamics of the magnetosphere. One of MMS’s challenges is to design, for each 

spacecraft, an optimal orbit that minimizes the number of maintenance maneuvers that are 

required during the science phase. While the fl ight dynamics team has spent tremendous efforts 

in designing the optimized orbits, little effort has gone towards thruster arrangement designs 

and maneuver scheme designs. The objective of this PIP project was to look at the feasibility 

of individual spacecraft reaching its optimized orbit while subject to a particular thruster 

arrangement design, maneuver scheme, and environment perturbations. 

The project has the following components:

 1. Develop a Low Fidelity Simulation for MMS spacecraft

 The simulation features spinning dynamic propagation, sensor noise models, a 

maneuver execution scheduler, a bang-bang attitude controller, a thruster model, 6DOF 

orbit propagation, and various orbit perturbation models. The simulation has enough 

complexities for orbit errors and maneuver scheme trade studies. It also has a generic 

framework that will allow it to become a high fi delity simulation for operations. 

 2. Adopt a Thruster Arrangement and a Nominal Maneuver Scheme

 A reorient-and-burn maneuver scheme has been adopted as the nominal scheme. 

It requires an individual spacecraft to reorient its spin axis before performing orbit 

maneuvers. An advantage of this scheme is thruster arrangement simplicity. Several 

thruster arrangements have been considered, and the nominal thruster arrangement design 

satisfi es the attitude performance requirements. 

 3. Create the Formation Initialization Maneuver Sequence

 The fl ight dynamics team has designed the MMS’s orbit in terms of instantaneous deltaV. A Matlab optimization algorithm is used to translate the instantaneous delta-Vs to 

fi nite burns. The 10-km (inter-spacecraft separation distance) tetrahedron initialization is 

used as the main test case.

 4. Evaluate the Performance of the Nominal Maneuver Sequence

 Post-maneuver states are examined in the context of evaluating formation integrity. 

The deviation of semi-major axis is the primary performance indicator because semimajor axis is crucial for period-matching between spacecraft.
FDAB End of FY 2004 Report 65

This PIP I project was successfully completed on August 04, 2004. It demonstrated that the 

MMS simulation has the capability of executing a maneuver sequence and generating data for 

post-maneuver performance studies. The results of the test case showed the nominal maneuver 

scheme and thruster arrangement designs introduce excessive orbit errors during the tetrahedron 

initialization. These results have triggered a series of studies, now underway, on alternative 

maneuver scheme and thruster arrangement designs.

(Dean Tsai started at Goddard in February, 2004. He received his B.S. degree in Mechanical 

Engineering from University of California.)

6.3 COOPERATIVE EDUCATION PROGRAM

The Cooperative Education Program integrates academic study with full time meaningful 

professional experience. This allows the students, through study and work experience, to enhance 

their academic knowledge, personal development, and professional preparation.

6.3.1 EDWIN DOVE (PENNSYLVANIA STATE UNIVERSITY)

Edwin Dove started his fi rst cooperative education (“co-op”) rotation in January, 2004, and is 

the Pennsylvania State University’s fi rst co-op student in the FDAB. His rotation lasted one year, 

instead of the standard one semester or summer, and he completed projects in both the attitude 

and orbit sides of the FDAB.

The fi rst half of his rotation was in the orbit group. He created a comparative analysis between 

several orbital lifetime prediction programs, such as STK/Lifetime and GTDS. The purpose of 

the analysis was to fi nd a possible replacement for PC-Lifetime, one of the FDAB’s in-house 

analytical lifetime prediction programs. He presented the results of his analysis at the 2004 

STK Users’ Conference in Chantilly, Virginia. He found working in the orbit group to be a good 

educational experience and a lot of fun.

He worked in the attitude group during the second half of his co-op rotation. He learned 

Simulink, increased his knowledge of Matlab, generated a summary of the thruster modes (deltaV and delta-H) for Solar Dynamic Observatory (SDO), updated SDO’s Simulink thruster models, 

updated duty cycle analysis for SDO, and learned stability analysis related to SDO. As with his 

orbit group work, he learned new programs and experienced the engineering life of Goddard.

Edwin will return to Penn State in January 2005 to complete his fi nal semester and will graduate 

in Spring 2005. He hopes to return to the FDAB full-time after graduation.

6.3.2 STEPHANIE GIL (CORNELL UNIVERSITY)

Stephanie Gil is a junior majoring in mechanical/aerospace engineering at Cornell University. 

This is her fi rst co-op rotation, which began in September, 2004, and will end in January, 2005, at 

NASA Goddard. She is working in the attitude group on the Solar Sail project. In FY 2004, she 

analyzed the effects that sinusoidal-shaped wrinkles on the sails have on the force imparted on the 

sails by solar pressure. Using the results of this analysis, she compared the force expected on a sail 

with no wrinkles versus a sail with wrinkles. This work helped produce an understanding of the 

Solar Sail spacecraft’s actual behavior as a function of wrinkle size and sun incidence angle.
66 FDAB End of FY 2004 Report
FDAB End of FY 2004 Report 67

7.0 OUTREACH ACTIVITIES

7.1 SAMPEX UNIVERSITY OPERATIONS

The University of Maryland’s Aerospace Engineering Department completed its fi nal year 

of fl ight dynamics operations support for the Solar Anomalous and Magnetospheric Particle 

Explorer (SAMPEX) spacecraft. This activity was brought to a close with the end of SAMPEX 

science operations in the summer of 2004. For fi ve years, a team of University of Maryland 

undergraduate and graduate students provided spacecraft orbit determination, attitude 

determination, attitude sensor analysis, and fl ight dynamics product generation. This effort was 

sponsored and supported by the FDAB, which provided consultation support as needed and 

periodically reviewed the overall program status. This was a very successful outreach initiative 

and gave the student team practical experience and training in spacecraft fl ight dynamics 

computations, the use of several commercial ground support tools, and analysis of fl ight data. 

One of the current FDAB employees, Oscar Hsu, was an early member of the University of 

Maryland student team prior to his employment with NASA. 

[Technical Contact: Thomas Stengle]

7.2 TABLESAT

TableSat is an interactive, single-axis spacecraft simulator designed as a tool for demonstrating and 

teaching the process and challenges of designing attitude control systems. It is composed of a 15” 

diameter disc, balanced on a center spindle, with four coarse sun sensors, a three-axis magnetometer, 

and a single axis gyro for sensors; two 12-volt computer fans for actuators; wireless Ethernet for 

communications; a battery pack for power; and an onboard fl ight processor (see Figure 7.1). 

Figure 7-1. TableSat
68 FDAB End of FY 2004 Report

The table was originally developed as a demonstration tool for the FDAB’s “Attitude Control 

Systems for Non-ACS Engineers” course, but its uses were expanded after receiving positive 

feedback from class participants. It has been used to explain the fundamentals of controls 

and control systems to middle- and high-school students. It was also demonstrated to several 

undergraduate classes at the University of Maryland’s Aerospace Engineering Department. 

TableSat is currently being upgraded, with help from the University of Maryland, to better serve 

as a demonstration tool for undergraduate students in linear controls classes. TableSat now has a 

faster fl ight processor, larger fans, a more powerful battery, and a new communications system. 

The TableSat fl ight code has been rewritten to include more functionality, including variable 

control, estimation, and actuation rates; onboard state estimation; and three types of actuation: 

continuous, bang-bang, and pulse-width modulation. The user can either test controllers using a 

Simulink block diagram or load controllers and state estimators directly to the fl ight processor. A 

Matlab Graphical User Interface (GUI) is currently being developed to allow users to easily vary 

different TableSat parameters. 

Figure 7-2. TableSat demonstration during “Inspire the Next Generation” Day at GSFC

[Technical Contact: Missie Vess]
FDAB End of FY 2004 Report 69

8.0 INTERAGENCY ACTIVITIES

8.1 NASA TECHNICAL STANDARDS PROGRAM

 http://www.ccsds.org/

 http://standards.gsfc.nasa.gov/

The FDAB supports the NASA Technical Standards Program by contributing to the work of the 

GSFC standards program, the NASA Data Standards Steering Council (DSSC), and the Consultative 

Committee for Space Data Systems (CCSDS). The GSFC standards program aims to expand the 

scope of best practices, and to develop an agency-endorsed database of preferred technical standards 

for NASA. The DSSC is the hub of the NASA Data Systems Standards Program and is sponsored 

by NASA Headquarters. The CCSDS is an international organization of space agencies interested in 

mutually developing standard data-handling techniques to reduce cost, risk and development time and 

to promote enhanced interoperability and cross-support. 

In FY 2004, FDAB personnel participated in the CCSDS navigation workshops that were hosted by 

the Computer Sciences Corporation, in Lanham, Maryland, during October, 2003, and the Canadian 

Space Agency facility at Saint Huber, Canada, in May, 2004. 

During the fi rst quarter of calendar year 2004, the navigation working group completed another agency 

wide review of the Orbit Data Message (ODM) Red Book, and conducted exercises with NASA, DLR, 

and ESA to exchange orbit parameters and ephemeris messages, which is a requirement to qualify the 

document as a formal CCSDS Recommendation (standard). In September 2004 the CCSDS management 

council announced its formal approval establishing the ODM as an accepted Recommendation. 

FDAB personnel continued discussions, via email and tele-conferences, to advance and revise 

documentation for attitude data messages, tracking data message, Space Assigned Numbers Authority, 

Security, and external interfaces. Comments were provided to the CCSDS Cross Support Services 

(CSS) tracking service white book. Also, CSS personnel are investigating use of streaming media for 

tracking data transmission, and the navigation working group is investigating whether this concept 

will effect the defi nition of a tracking data standard. Updated white book versions were completed 

for attitude data and tracking data messages, and these documents are currently under review by the 

working group. Future work will include completion of formal standards for attitude and tracking data 

exchange and description of XML formats for attitude, orbit and tracking data messages.

[Technical contact: Felipe Flores-Amaya]

8.2 GLOBAL POSITIONING SYSTEM (GPS) MODERNIZATION

The GPS, a space-based radio-navigation system providing highly accurate position, velocity, and 

time information, was developed in the 1970s and 80s by the U.S. Department of Defense. NASA 

uses GPS for a wide range of navigation, timing, attitude determination, and scientifi c applications. 

With very few exceptions, the GPS signals available to users have remained essentially unchanged 

since the fi rst GPS satellite was launched in 1978. There are two L-band carrier signals used for 

navigation: L1 at 1575.42 MHz and L2 at 1227.60 MHz. There is a Coarse Acquisition (C/A) code 
70 FDAB End of FY 2004 Report

on the L1 frequency that is available to anyone, as well as a Precision (P(Y)) code available to 

authorized (military) users on L1 and L2. The great leaps in digital communications technology 

since the early 1980s have led to a push to modernize the GPS constellation in order to incorporate 

more modern signal structures and expand the level of services provided to civil users, who now 

greatly outnumber the military users for whom the system was originally developed.

A number of new capabilities will be available to civil users such as NASA after the launch of the 

fi rst in a series of “modernized” GPS satellites in 2005. First, a new “precision” civil signal is being 

added on the L2 carrier that will allow civil users to directly measure and correct for ionospheric 

errors by tracking signals on both L1 and L2. Furthermore, the new L2C signal has better crosscorrelation properties than the C/A signal and has a component that is not modulated by a data 

message. This makes the new signal advantageous for weak signal tracking applications, such as the 

capabilities being developed in NASA’s Navigator GPS receiver. In 2007, GPS satellites will include 

a third navigation signal, L5 at 1176.45 MHz, which is being developed to meet the specifi c needs of 

aviation users. These new capabilities onboard the GPS satellites coupled with improvements to the 

GPS ground segment will signifi cantly improve the performance of GPS for civil users. 

The Air Force is also currently conducting detailed architecture studies for GPS III, the next series 

of GPS satellites that will begin launching early in the next decade. The GPS III program will 

include a number of new improvements to both the ground and space segments of the GPS system, 

including a cross-link ranging system that will allow near real-time satellite ephemeris and clock 

updates to be transmitted to users, a new integrity signal, critical for aviation users, that will provide 

real-time information regarding satellite anomalies or degradations in service, and a modernized 

navigation signal on the L1 carrier that will be compatible with the new European Galileo Satellites. 

To ensure their navigation needs are met over the next decades, NASA and other civil agencies 

have an important role on the GPS III team. Specifi cally NASA has responsibility to help defi ne the 

GPS system requirements for space users and has incorporated changes into the GPS III System 

Specifi cation that, for the fi rst time, spell out signal power and availability requirements for space 

users. The modernization of GPS will mean improved navigation performance for all Earth-orbiting 

spacecraft, particularly missions in high Earth orbits. 

[Technical contact: Mike Moreau]

8.3 NASA ENGINEERING AND SAFETY CENTER (NESC) SUPPORT

 http://nesc.nasa.gov

NESC was formed in the wake of the Space Shuttle Columbia accident to serve as an independent 

technical resource for NASA managers and employees. The objective of the NESC is to improve 

safety by performing in-depth independent engineering assessments, testing, and analysis to 

uncover technical vulnerabilities and to determine appropriate preventative and corrective actions 

for problems, trends or issues within NASA’s programs, projects, and institutions.

FDAB personnel have been supporting the NESC Guidance, Navigation, and Control Super 

Problem Resolution Team (GNC SPRT) in numerous capacities ranging from core members to 

technical-team support members. There are fourteen FDAB members on the GNC SPRT: one 
FDAB End of FY 2004 Report 71

senior engineer who serves as the core team member, ten engineers who serve as sub-discipline 

experts, and three junior engineers serving as technical-team support members.

During FY 2004, the FDAB personnel have been involved with the following NESC GNC SPRT 

activities:

 • Face-to-Face Meeting at the AIAA Guidance, Navigation, and Control Conference in 

Providence, RI.

 • Past SPRT Support

 - MER, Calipso, International Space Station (ISS) Control Moment Gyro Anomaly

 • Current SPRT Support 

 - Independent Technical Assessment/Investigations: ISS & Shuttle Recurring 

Anomalies, Orbiter Repair Manuever, Genesis Re-entry Observation 

 - Consultations: Cassini Orbit Insertion, Cassini-Huygens Probe Entry, Genesis, 

Shuttle Reentry/Aero Flight Control Technical Interchange Meeting, Hubble 

Space Telescope System Health

8.3.1 SPACE SHUTTLE RECURRING ANOMALIES REVIEW

The Space Shuttle Recurring Anomalies review effort includes engineers from the NASA 

centers and from private industry. The review effort is intended to apply independent technical 

resources to Shuttle problems, uncover technical vulnerabilities, and perform independent 

engineering trend analysis and risk assessment. The teams are mechanisms (dynamic mechanical 

systems, actuators, and pyrotechnics), structures (static mechanical systems, thermal protection, 

materials),fl uids, propulsion, electrical /avionics, software, and human factors. The teams 

perform a structured review of existing Shuttle anomaly reports, along with further searches of 

the Shuttle’s Problem Reporting and Corrective Action Database. All of the identifi ed issues are 

documented and reported to the NESC Systems Engineering Offi ce. 

The electrical/avionics team, in particular, is tasked with the review of all the Shuttle guidance, 

navigation, and control issues along with all the electrical issues. This includes wire splices, 

connector savers, metastability, particle and debris sealed devices, servo valve oscillations, gyros, 

star trackers, IMU, single event upsets, pyro fi ring failures, Kapton wiring, shuttle and SRB 

umbilical, CE-07 trending, bent connector pins, crimping processes, exceptions to standard repairs, 

microswitch contacts, issues with ET doors, single-use cables, capacitor and power supplies, water 

spray blower motor, fl ash evaporator, redundancy, fl ood-light seals, insulation, staking of screws 

with potting compound, AC motor valve, corrosion, EVA and ground operations. 

GNC-specifi c issues that have been documented to date relate to problems with the IMU, 

the solid rocket booster gyros, and the star trackers. The items with the highest criticality 

are the IMU and gyro issues. Problems related to wiring, lubricants, shipping, restraint drift, 

accelerometer bias, power supply issues, noisy/high rate/spikes/instability in output, spin motor 

rotation detector issues, test failures, electrical/bent pin issues, and metal issues have been 

documented and reported. The Shuttle review effort will end in October, 2004, and will be 

followed by a similar review effort for the International Space Station.

[Technical contact: Dave Mangus, Oscar Hsu, Julie Thienel]
72 FDAB End of FY 2004 Report

8.4 LOW-THRUST WORKING GROUP

GSFC continued its participation in the interagency Low Thrust Working Group. The working 

group, funded by NASA HQ and managed by MSFC, is developing a new state-of-the-art suite 

of low-thrust tools. The fi ve tools, called MALTO, Mystic, OTIS, SNAP, and Copernicus, will 

meet the needs of our internal and external customers, who are planning ever more complex 

missions that require low-thrust propulsion. The tools are also designed to be compatible with 

each other. GSFC will receive preliminary versions of the tools in early FY 2005 and will 

participate in Beta testing. The target release date for Version 1.0 of these tools is at the end of 

FY 2005. Academia and industry will have, to the maximum extent possible, access to the tools 

in this suite for use in research and business.

The working group has held three yearly Technical Interchange Meetings (TIMs). GSFC 

personnel participated in the recent 2004 NASA Intercenter Low-Thrust (LT) TIM held at JPL in 

August, 2004. The next LT TIM, which coincides with the planned release of the suite of tools, 

will be held at MSFC in September, 2005.

[Technical contact: Steven Cooley]
FDAB End of FY 2004 Report 73

APPENDIX A: CONFERENCES AND PAPER ABSTRACTS

Given below are abstracts from professional papers and technical presentations that were 

prepared and delivered in FY 2004 by branch members.

JOURNAL ARTICLES

2004 CLASSICAL AND QUANTUM GRAVITY, VOLUME 21, S635-S640, FEBRUARY, 2004

“Pointing Acquisition and Performance for the Laser Interferometry Space Antenna Mission,” 

Hyde, Maghami, Merkowitz

ABSTRACT: The laser interferometer space antenna (LISA) mission, a space-based 

gravitational wave detector, uses laser metrology to measure distance fl uctuations 

between proof masses aboard three spacecraft. Each spacecraft has two incoming 

and two outgoing laser beams for a total of six laser links. These links are 

established sequentially at the start of the mission, and the spacecraft control 

systems must aim their lasers at each other with pointing motions less than 8 nrad/

Hz-1/2 in the frequency band 1100 mHz. The process for acquiring the laser links 

as well as the simulated performance is described.

CONFERENCES

NASA/GODDARD SPACE FLIGHT CENTER FLIGHT MECHANICS SYMPOSIUM, GREENBELT, MARYLAND, 

OCTOBER 28-30, 2003

“Nonlinear Observers for Gyro Calibration,” Thienel, Sanner

ABSTRACT: Nonlinear observers for gyro calibration are presented. The fi rst observer estimates 

a constant gyro bias. The second observer estimates scale factor errors. The third 

observer estimates the gyro alignment for three orthogonal gyros. The convergence 

properties of all three observers are discussed. Additionally, all three observers are 

coupled with a nonlinear control algorithm. The stability of each of the resulting 

closed loop systems is analyzed. Simulated test results are presented for each system.

“Applications of a Semiparametric Statistical Method to Spacecraft Sensor and Calibration Data,” 

Kedem, Thienel, Harman

ABSTRACT: A semiparametric statistical method is applied to spacecraft sensor data. The 

method stipulates a reference distribution and deviations from it and the problem 

is to estimate the reference distribution and the distorted distributions from all 

available data. That is from the combined data obtained from all the sources under 

consideration. The problem can be solved by assuming a distortion form and 

independent data.
74 FDAB End of FY 2004 Report

“Gyroless Attitude and Rate Estimation Algorithms for the FUSE Spacecraft,” 

Harman, Thienel, Oshman

ABSTRACT: The Far Ultraviolet Spectroscopic Explorer (FUSE) is equipped with two ring 

laser gyros on each of the spacecraft body axes. In May 2001 one gyro failed. 

It is anticipated that all of the remaining gyros will also fail, based on intensity 

warnings. In addition to the gyro failure, two of four reaction wheels failed in late 

2001. The spacecraft control now relies heavily on magnetic torque to perform 

the necessary science maneuvers and hold on target. The only sensor consistently 

available during slews is a magnetometer. This paper documents the testing 

and development of magnetometer-based gyroless attitude and rate estimation 

algorithms for FUSE. The results of two approaches are presented, one relies on a 

kinematic model for propagation, a method used in aircraft tracking, and the other 

is a pseudo-linear Kalman fi lter that utilizes Euler’s equations in the propagation 

of the estimated rate. Both algorithms are tested using fl ight data collected over 

a few months after the reaction wheel failure. Finally, the question of closedloop stability is addressed. The ability of the controller to meet the science slew 

requirements, without the gyros, is analyzed.

“Formation Tetrahedron Design for Phase I of the Magnetospheric Multiscale Mission,” Hughes

ABSTRACT: The Magnetospheric Multiscale Mission (MMS) is a NASA mission intended 

to make fundamental advancements in our understanding of the Earth’s 

Magnetosphere. There are three processes that MMS will study including magnetic 

reconnection, charged particle acceleration, and turbulence. There are four phases 

in the nominal mission and this work addresses some of the outstanding issues in 

phase I. The nominal Phase-I orbit is a 1.2 x 12 Re

, highly elliptic orbit with four 

spacecraft nominally forming a regular tetrahedron. In this paper we investigate the 

relative dynamics of the four MMS spacecraft about an assumed reference orbit. 

There are several tetrahedron dimensions required in Phase I of the mission and in 

this work we design optimal tetrahedrons for the 10 km baseline. The performance 

metric used in the optimization process is directly related to the science return, 

and is based on an extension of previous work performed by Glassmeier. The 

optimizer we use is a commercially available Sequential Quadratic Programming 

(SQP) routine. Multiple optimal solutions are found, and we characterize how the 

performance of the formation varies between different regions of the reference orbit.

“Disturbance Reduction Control Design for the ST7 Flight Validation Experiment,” 

Maghami, Hsu, Markley, Houghton

ABSTRACT: The Space Technology 7 experiment will perform an on-orbit system-level 

validation of two specifi c Disturbance Reduction System technologies: a 

gravitational reference sensor employing a free-fl oating test mass, and a set of 

micro-Newton colloidal thrusters. The ST7 Disturbance Reduction System is 

designed to maintain the spacecrafts position with respect to a free-fl oating test 
FDAB End of FY 2004 Report 75

mass to less than 10 nm/vHz, over the frequency range of 1 to 30 mHz. This paper 

presents the design and analysis of the coupled, drag-free and attitude control 

systems that close the loop between the gravitational reference sensor and the 

micro-Newton thrusters, while incorporating star tracker data at low frequencies. 

A full 18 degree-of-freedom model, which incorporates rigid-body models of the 

spacecraft and two test masses, is used to evaluate the effects of actuation and 

measurement noise and disturbances on the performance of the drag-free system. 

AAS GUIDANCE AND CONTROL CONFERENCE, BRECKENRIDGE, COLORADO, FEBRUARY 4-8, 2004

“Nonlinear Observers for Gyro Calibration,” Thienel, Sanner 

ABSTRACT: Nonlinear observers for gyro calibration are presented. The fi rst observer estimates 

a constant gyro bias. The second observer estimates scale factor errors. The third 

observer estimates the gyro alignment for three orthogonal gyros. The observers 

are then combined. The convergence properties of all three observers, and the 

combined observers, are discussed. Additionally, all three observers are coupled 

with a nonlinear control algorithm. The stability of each of the resulting closed 

loop systems is analyzed. Simulated test results are presented for each system.

“Orbit Design for Phase I and II of the Magnetospheric Multiscale Mission,” Hughes

ABSTRACT: The Magnetospheric Multiscale Mission (MMS) is a NASA mission intended 

to make fundamental advancements in our understanding of the Earth’s 

magnetosphere. There are three processes that MMS is intended to study including 

magnetic reconnection, charged particle acceleration, and turbulence. There are 

four phases of the MMS mission and each phase is designed to study a particular 

region of the Earth’s magnetosphere. The mission is composed of a formation of 

four spacecraft that are nominally in a regular tetrahedron formation. In this work, 

we present optimal orbit designs for Phase I and II. This entails designing reference 

orbits such that the spacecraft dwell-time in the region of interest is a maximum. 

This is non-trivial because the Earth’s magnetosphere is dynamic and its shape 

and position are not constant in inertial space. Optimal orbit design for MMS also 

entails designing the formation so that the relative motion of the four spacecraft 

yields the greatest science return. We develop performance metrics that are directly 

related to the science return, and use Sequential Quadratic Programming (SQP) to 

determine optimal relative motion solutions. While designing for optimal science 

return, we also consider practical constraints such as maximum eclipse time and 

minimum inter-spacecraft separation distances. Data are presented that illustrates 

how long we can ensure that the formation remains in the relevant region of the 

Earth’s magnetosphere. We also draw general conclusions about where in the orbit 

acceptable tetrahedron confi gurations can be provided and for how long.
76 FDAB End of FY 2004 Report

AAS/AIAA SPACE FLIGHT MECHANICS MEETING, WAILEA, HAWAII, FEBRUARY 8-12, 2004

“Use of Invariant Manifolds for Transfers between Three-Body Systems,” 

Howell, Patterson, Beckman, Folta 

ABSTRACT: The Lunar L1 and L2 libration points have been proposed as gateways granting 

inexpensive access to interplanetary space. To date, only individual solutions to 

the transfer between three-body systems have been found. The methodology to 

solve the problem for arbitrary three-body systems and entire families of orbits 

does not exist. This paper presents the initial approaches to solve the general 

problem for single and multiple impulse transfers. Two different methods of 

representing and storing 7-dimensional invariant manifold data are presented. 

Some particular solutions are presented for the transfer problem, though the 

emphasis is on developing methodology for solving the general problem.

ASTRONOMICAL TELESCOPES AND INSTRUMENTATION, GLASGOW, SCOTLAND, JUNE 21-25, 2004

“Pointing Control System Design and Performance Evaluation of TPF Coronagraph,” 

Liu, Blaurock, Mosier

ABSTRACT: The Terrestrial Planet Finder (TPF) project aims to detect and characterize extrasolar Earth-like planets. The coronagraph telescope is one of the two mission 

concepts being studied. To reject the star fl ux and detect the planet fl ux in the 

visible light range, the coronagraph telescope must achieve a rejection ratio on the 

order of a billion to one. Dynamic jitter, introduced by environmental and onboard mechanical disturbances, degrades the optical performance, as characterized 

primarily by contrast ratio. The feasibility of using passive vibration isolation 

combined with active attitude and line-of-sight (LOS) control systems to stabilize 

the spacecraft and the optical components to the requisite level is being studied. 

The telescope is also required to slew between targets or rotate around the LOS. 

The slew mode control law must be designed to balance the need for effi cient 

large-angle maneuvers while simultaneously avoiding the excitation of fl exible 

modes in order to minimize settling time.

 

 This paper provides an overview of the current control design concept and 

sensor/actuator topology for TPF Coronagraph and illustrates the fi ne pointing 

performance of the telescope. This performance is primarily a function of the 

rejection of high-frequency dynamic disturbances, in this case due to reaction 

wheel disturbance forces/torques transmitted through the passive isolation stage. 

Trade studies between isolator force rejection and disturbance level reduction 

via wheel redesign are also presented to illustrate the requirements imposed on 

current technologies. Finally, the paper summarizes preliminary results on the 

slew/settle performance of the telescope. 
FDAB End of FY 2004 Report 77

“Requirements Formulation and Dynamic Jitter Analysis for the Fourier-Kelvin Stellar Interferometer,” 

Tupper, Liu, Blaurock, Bolognese, Howard, Danchi 

ABSTRACT: The Fourier-Kelvin Stellar Interferometer (FKSI) has been proposed to detect and 

characterize extra solar giant planets. The baseline confi guration for FKSI is a twoaperture, structurally connected nulling interferometer, capable of providing null depth 

less than 10-4 in the infrared. The objective of this paper is to summarize the process 

for setting the top level requirements and the jitter analysis performed on FKSI to date. 

The fi rst part of the paper discusses the derivation of dynamic stability requirements, 

necessary for meeting the FKSI nulling demands. An integrated model including 

structures, optics, and control systems has been developed to support dynamic jitter 

analysis and requirements verifi cation. The second part of the paper describes how the 

integrated model is used to investigate the effects of reaction wheel disturbances on 

pointing and optical path difference stabilities.

40TH AIAA JOINT PROPULSION CONFERENCE, FORT LAUDERDALE, FLORIDA, JULY 11-14, 2004

“Propulsion Options for the LISA Mission,” Cardiff, Marr

ABSTRACT: The LISA mission is a constellation of three spacecraft operating at 1 AU from the 

Sun in a position trailing the Earth. After launch, a propulsion module provides the 

DV necessary to reach this operational orbit, and separates from the spacecraft. A 

second propulsion system integrated with the spacecraft maintains the operational orbit 

and reduces non-gravitational disturbances on the instruments. Both chemical and 

electrical propulsion systems were considered for the propulsion module, and this trade 

is presented to show the possible benefi ts of an EP system. Several options for the orbit 

maintenance and disturbance reduction system are also briefl y discussed, along with 

several important requirements that suggest the use of a FEEP thruster system.

SPACE SYSTEMS OPTOMECHANICS AND DYNAMICS CONFERENCE, 49TH SPIE ANNUAL MEETING, 

DENVER, COLORADO, AUGUST 4-6, 2004

“Control Modes of the ST7 Disturbance Reduction System Flight Validation Experiment,” 

Maghami, Hsu, Markley, O’Donnell

ABSTRACT: Space Technology 7 (ST7) experiment will perform an on-orbit system-level validation of 

two specifi c Disturbance Reduction System technologies: a gravitational reference sensor 

employing a free-fl oating test mass and a set of micronewton colloidal thrusters. The ST7 

Disturbance Reduction System (DRS) is designed to maintain the spacecrafts position with 

respect to a free-fl oating test mass to less than 10 nm/vHz over the frequency range of 1 to 

30 mHz. This paper presents the overall design and analysis of the spacecraft drag-free and 

attitude controllers. These controllers close the loop between the gravitational sensors and 

the micronewton colloidal thrusters. There are fi ve control modes in the operation of the ST7 

DRS, starting with the attitude-only mode and leading to the science mode. The design and 

analysis of each of the control modes as well as the mode transition strategy are presented. 
78 FDAB End of FY 2004 Report

AIAA/AAS ASTRODYNAMICS SPECIALISTS CONFERENCE, PROVIDENCE, RHODE ISLAND, 

AUGUST 16-19, 2004

“Orbit Optimization for the Geospace Electrodynamics Connections (GEC) Mission,” Mesarch 

ABSTRACT: Part of NASA’s Solar Terrestrial Probe line of missions, the Geospace 

Electrodynamics Connections (GEC) mission will deploy a formation of three 

spacecraft to perform in-situ atmospheric research in the low IonosphereThermosphere region. These spacecraft will fl y together in a “string-of-pearls” 

formation with variable separations ranging from 10 seconds to one-quarter of 

an orbit at perigee. Over the course of its two-year mission, the three spacecraft 

will perform ten, 1-week dipping campaigns whereby they maneuver to lower 

their perigee to near 134 km. Using available launch vehicle performance data, 

an optimal parking orbit of 222 x 1525 km was found to maximize the dry mass 

available while providing enough propellant to perform the ten deep-dipping 

campaigns over its two-year mission. The results were used to create multivariable contour plots containing the orbit perigee, the orbit apogee, spacecraft 

dry mass, propellant mass, and T500 (a science data collection fi gure of merit 

that tabulates the cumulative time spent below 500 km). These plots illustrate 

how the mission can trade off science return relative to the cost in dry mass and 

propellant. Other optimal solutions such as minimum propellant or maximum 

T500 were found to either limit the science data collection or to be dry mass 

limiting, respectively. Sensitivity analyses were performed to fi nd new optimal 

(maximum dry mass) solutions if the number of campaigns changed, if the 

coeffi cient of drag (CD) were different, and if the propellant specifi c impulse 

were increased. A surprising result showed that the dry mass and T500 were both 

increased if the number of campaigns decreased. Changes in CD provided the 

expected results – raising CD lowered both the dry mass and T500 while lowering 

CD raised both the dry mass and T500. Increases in the propellant specifi c impulse 

had the expected outcome of raising the dry mass and lowering the propellant load 

but there was no change in the T500 fi gure of merit. The orbit optimization was 

performed parametrically using a MatlabTM script and validated using FreeFlyerTM, 

a commercial orbit analysis tool.

“Results of the Magnetometer Navigation (MAGNAV) Infl ight Experiment,” 

Thienel, Harman, Bar-Itzhack

ABSTRACT: The Magnetometer Navigation (MAGNAV) algorithm is currently running as 

a fl ight experiment as part of the Wide Field Infrared Explorer (WIRE) PostScience Engineering Testbed. Initialization of MAGNAV occurred on September 

4, 2003. MAGNAV is designed to autonomously estimate the spacecraft orbit, 

attitude, and rate using magnetometer and sun sensor data. Since the Earth’s 

magnetic fi eld is a function of time and position, and since time is known quite 

precisely, the differences between the computed magnetic fi eld and measured 

magnetic fi eld components, as measured by the magnetometer throughout the 
FDAB End of FY 2004 Report 79

entire spacecraft orbit, are a function of the spacecraft trajectory and attitude 

errors. Therefore, these errors are used to estimate both trajectory and attitude. In 

addition, the time rate of change of the magnetic fi eld vector is used to estimate 

the spacecraft rotation rate. The estimation of the attitude and trajectory is 

augmented with the rate estimation into an Extended Kalman fi lter blended with a 

pseudo-linear Kalman fi lter. Sun sensor data is also used to improve the accuracy 

and observability of the attitude and rate estimates. This test serves to validate 

MAGNAV as a single low cost navigation system which utilizes reliable, fl ight 

qualifi ed sensors. MAGNAV is intended as a backup algorithm, an initialization 

algorithm, or possibly a prime navigation algorithm for a mission with coarse 

requirements. Results from the fi rst six months of operation are presented.

“A Survey of Earth-Moon Libration Orbits: Stationkeeping Strategies and Intra-Orbit Transfers,” 

Folta, Vaughn

ABSTRACT: Cislunar space is a readily accessible region that may well develop into a prime 

staging area in the effort to colonize space near Earth or to colonize the Moon. 

While there have been statements made by various NASA programs regarding 

placement of resources in orbit about the Earth-Moon Lagrangian locations, there 

is no survey of the total cost associated with attaining and maintaining these 

unique orbits in an operational fashion. Transfer trajectories between these orbits 

required for assembly, servicing, and positioning of these resources have not 

been extensively investigated. These orbits are dynamically similar to those used 

for the Sun-Earth missions, but differences in governing gravitational ratios and 

perturbation sources result in unique characteristics. 

 We implement numerical computations using high fi delity models and linear and 

non-linear targeting techniques to compute the various maneuver delta-V and 

temporal costs associated with orbits about each of the Earth-Moon Lagrangian 

locations (L1

, L2, L3, L4, and L5). From a dynamical system standpoint, we speak 

to the nature of these orbits and their stability. We address the cost of transfers 

between each pair of Lagrangian locations 

“Formation Control of the MAXIM L2

 Libration Orbit Mission,” 

Folta, Hartman, Howell, Marchand

ABSTRACT: The Micro-Arcsecond X-ray Imaging Mission (MAXIM), a proposed concept for 

the Structure and Evolution of the Universe (SEU) Black Hole Imager mission, 

is designed to make a ten million-fold improvement in X-ray image clarity of 

celestial objects by providing better than 0.1 micro-arcsecond imaging. Currently 

the mission architecture comprises 25 spacecraft, 24 as optics modules and one 

as the detector, which will form sparse sub-apertures of a grazing incidence Xray interferometer covering the 0.3-10 keV bandpass. This formation must allow 

for long duration continuous science observations and also for reconfi guration 

that permits re-pointing of the formation. To achieve these mission goals, the 
80 FDAB End of FY 2004 Report

formation is required to cooperatively point at desired targets. Once pointed, the 

individual elements of the MAXIM formation must remain stable, maintaining 

their relative positions and attitudes below a critical threshold. These pointing and 

formation stability requirements impact the control and design of the formation. 

 In this paper, we provide analysis of control efforts that are dependent upon 

the stability and the confi guration and dimensions of the MAXIM formation. 

We emphasize the utilization of natural motions in the Lagrangian regions to 

minimize the control efforts and we address continuous control via input feedback 

linearization (IFL). Results provide control cost, confi guration options, and 

capabilities as guidelines for the development of this complex mission.

“Pseudo-Linear Attitude Determination of Spinning Spacecraft,” Bar-Itzhack, Harman 

ABSTRACT: This paper presents the overall mathematical model and results from pseudo 

linear recursive estimators of attitude and rate for a spinning spacecraft. The 

measurements considered are vector measurements obtained by sun-sensors, CCD 

head star trackers, horizon sensors, and three axis magnetometers. Two fi lters 

are proposed for estimating the attitude as well as the angular rate vector. One 

fi lter, called the q-Filter, yields the attitude estimate as a quaternion estimate, and 

the other fi lter, called the D-Filter, yields the estimated direction cosine matrix. 

Because the spacecraft is gyro-less, Euler’s equation of angular motion of rigid 

bodies is used to enable the estimation of the angular velocity. A simpler Markov 

model is suggested as a replacement for Euler’s equation in the case where the 

vector measurements are obtained at high rates relative to the spacecraft angular 

rate. The performance of the two fi lters is examined using simulated data.

“Implicit and Explicit Spacecraft Gyro Calibration,” Bar-Itzhack, Harman 

ABSTRACT: This paper presents a comparison between two approaches to sensor calibration. 

According to one approach, called explicit, an estimator compares the sensor 

readings to reference readings, and uses the difference between the two to estimate 

the calibration parameters. According to the other approach, called implicit, the 

sensor error is integrated to form a different entity, which is then compared with 

a reference quantity of this entity, and the calibration parameters are inferred 

from the difference. In particular this paper presents the comparison between 

these approaches when applied to in-fl ight spacecraft gyro calibration. Reference 

spacecraft rate is needed for gyro calibration when using the explicit approach; 

however, such reference rates are not readily available for in-fl ight calibration. 

Therefore the calibration parameter-estimator is expanded to include the estimation 

of that reference rate, which is based on attitude measurements in the form of 

attitude-quaternion. A comparison between the two approaches is made using 

simulated data. It is concluded that the performances of the two approaches are 

basically comparable. Sensitivity tests indicate that the explicit fi lter results are 

essentially insensitive to variations in given spacecraft dynamics model parameters.
FDAB End of FY 2004 Report 81

“Linear State-Space Representation of the Dynamics of Relative Motion, Based on Restricted 

Three BodyDynamics,” Luquette, Sanner

ABSTRACT: Precision Formation Flying is an enabling technology for a variety of proposed 

space-based observatories, including the Micro-Arcsecond X-ray Imaging 

Mission (MAXIM), Stellar Imager (SI) and the Terrestrial Planet Finder (TPF). 

An essential element of the technology is the control algorithm, requiring a 

clear understanding of the dynamics of relative motion. This paper examines 

the dynamics of relative motion in the context of the Restricted Three Body 

Problem (RTBP). The natural dynamics of relative motion are presented in their 

full nonlinear form. Motivated by the desire to apply linear control methods, the 

dynamics equations are linearized and presented in state-space form. The stability 

properties are explored for regions in proximity to each of the libration points 

in the Earth/Moon - Sun rotating frame. The dynamics of relative motion are 

presented in both the inertial and rotating coordinate frames.

2ND INTERNATIONAL SYMPOSIUM ON FORMATION FLYING, CRYSTAL CITY, VIRGINIA, 

SEPTEMBER 14-16, 2004

“Formation Control for the MAXIM Mission,” Luquette, Leitner, Gendreau, Sanner

ABSTRACT: Over the next twenty years, a wave of change is occurring in the space-based 

scientifi c remote sensing community. While the fundamental limits in the spatial 

and angular resolution achievable in spacecraft have been reached, based on 

today’s technology, an expansive new technology base has appeared over the 

past decade in the area of Distributed Space Systems (DSS). A key subset of the 

DSS technology area is that which covers precision formation fl ying of space 

vehicles. Through precision formation fl ying, the baselines, previously defi ned 

by the largest monolithic structure which could fi t in the largest launch vehicle 

fairing, are now virtually unlimited. Several missions including the MicroArcsecond X-ray Imaging Mission (MAXIM), and the Stellar Imager will drive 

the formation fl ying challenges to achieve unprecedented baselines for high 

resolution, extended-scene, interferometry in the ultraviolet and X-ray regimes. 

This paper focuses on establishing the feasibility for the formation control of 

the MAXIM mission. MAXIM formation fl ying requirements are on the order 

of microns, while Stellar Imager mission requirements are on the order of 

nanometers. This paper specifi cally addresses: (1) high-level science requirements 

for these missions and how they evolve into engineering requirements; and (2) the 

development of linearized equations of relative motion for a formation operating 

in an n-body gravitational fi eld. Linearized equations of motion provide the 

ground work for linear formation control designs.
82 FDAB End of FY 2004 Report

18TH INTERNATIONAL SYMPOSIUM ON SPACEFLIGHT DYNAMICS, MUNICH, GERMANY, 

OCTOBER 11-15, 2004

 “Hardware-in-the-Loop Testing of Continuous Control Algorithms for a Precision FormationFlying Demonstration Mission,” Naasz, Burns, Gaylor, Higinbotham

ABSTRACT: A sample mission sequence is defi ned for a low earth orbit demonstration of 

Precision Formation Flying (PFF). Various guidance navigation and control strategies 

are discussed for use in the PFF experiment phases. A sample PFF experiment is 

implemented and tested in a realistic Hardware-in-the-Loop (HWIL) simulation using 

the Formation Flying Test Bed (FFTB) at NASA’s Goddard Space Flight Center.

“Exchange of Standarized Flight Dynamics Data,” 

Martin-Mur, Berry, Flores-Amaya, Folliard, Kiehling, Ogawa, Pallaschke

ABSTRACT: Spacecraft operations require the knowledge of the vehicle trajectory and attitude and also 

that of other spacecraft or natural bodies. This knowledge is normally provided by the Flight 

Dynamics teams of the different space organizations and, as very often spacecraft operations 

involve more than one organization, this information needs to be exchanged between 

Agencies. This is why the Navigation Working Group within the CCSDS (Consultative 

Committee for Space Data Systems) has been instituted with the task of establishing 

standards for the exchange of Flight Dynamics data. This exchange encompasses trajectory 

data, attitude data, and tracking data. The Navigation Working Group includes regular 

members and observers representing the participating Space Agencies. Currently the group 

includes representatives from CNES, DLR, ESA, NASA and JAXA. This Working Group 

meets twice per year in order to devise standardized language, methods, and formats for 

the description and exchange of Navigation data. Early versions of some of these standards 

have been used to support mutual tracking of ESA and NASA interplanetary spacecraft, 

especially during the arrival of the 2003 missions to Mars. The Navigation Working 

Group is currently in the process of developing a common Extensible Markup Language 

(XML) specifi cation for all the navigation messages. This paper provides a summary of 

the activities carried out by the group, briefl y outlines the current and envisioned standards, 

describes the tests and operational activities that have been performed using the standards, 

and lists and discusses the lessons learned from these activities. 

“Control of the Laser Interferometer Space Antenna,” Maghami, Hyde, Kim

ABSTRACT: The Laser Interferometer Space Antenna mission is a planned gravitational wave detector 

consisting of three spacecraft in heliocentric orbit. Laser interferometry is used to measure 

distance fl uctuations between test masses aboard each spacecraft to the picometer level over 

a 5 million kilometer separation. The Disturbance Reduction System comprises the pointing 

and positioning control of the spacecraft, electrostatic suspension control of the test masses, and 

point-ahead and acquisition control. This paper presents a control architecture and design for 

the Disturbance Reduction System to meet the stringent pointing and positioning requirements. 

Simulations are performed to demonstrate the feasibility of the proposed architecture.
FDAB End of FY 2004 Report 83

APPENDIX B: REVIEWS SUPPORTED

Below is a list of various reviews that were supported by FDAB personnel during FY2004.

APL Honeywell MIMU Failure Briefi ng

APL New Horizons/Pluto Attitude Determination Review

Aura Flight Dynamics Peer Reviews

Aura OD Peer Review

Dean Tsai PIP Review

FUSE gyro-less Flight Actual Review

FUSE gyro-less Flight Reading Review

GLAST Flight Software Critical Design Review

GLAST Ground System SDR Review

GLAST Mission Operations Center (MOC) Design Peer Review 

GLAST Orbital Lifetime Review

GLAST Pointing Knowledge Review

GLAST Pointing Knowledge Review, #2

GLAST Re-Entry Peer Review

GPM Peer Review

HRV DM SEB

HST 2-gyro Science Mode System PDR Review

HST 2-gyro Science Peer Review

HST Pointing Control System Review

INFOCUS Peer Review

JWST ISIM System Requirements Review

Messenger Mission Readiness Review 

New Horizons Mission Design Review

SDO Ground System Preliminary Design Review

SDO Mission Operations Center Peer Review

SDO Peer Review

Sentinels Science Defi nition Team Meeting

ST-5 Mission Design Review

ST7 HiFi Stimulation Tabletop

STEREO Mission CDR Single-Point Failures Review

STEREO Mission Operations Review

STEREO Review

Sun Solar Systems Connections Roadmap Meeting

Swift FOR Review Board

THEMIS Flight Dynamics Operations Peer Review

THEMIS Peer Review

THEMIS Preliminary Design Review
84 FDAB End of FY 2004 Report
FDAB End of FY 2004 Report 85

APPENDIX C: ACRONYMS AND ABBREVIATIONS

AAS American Astronomical Society

AC Afternoon Constellation

AC analog current

ACE Active Coronal Explorer

ACS attitude control system

AETD Applied Engineering and Technology Directorate

AGI Analytical Graphics, Inc.

AIAA American Institute of Aeronautics and Astronautics

ALMA Atacama Large Millimeter Array

ANTS Autonomous NanoTechnology Swarm

AO Annoucement of Opportunity

APL Applied Physics Laboratory

AR&C Autonomous Rendezvous and Control

AU Astronomical Unit

AutoFDS Autonomous Flight Dynamics System

BSS Boeing Satellite Systems

CALIPSO Cloud-Aerosol Lidar and Infrared Pathfi nder Satellite

CCB confi guration control board

CCD Charge Coupled Device

CCS Constellation Coordination System

CDA Command and Data Acquisition

CDGPS Carrier-phase Differential GPS

CDR critical design review

CERES Coalition for Environmentally Responsible Economies

CMNT colloidal micronewton thruster

CNES Centre National d’Etudes Spatiales

co-op Cooperative Education

COS Cosmic Origins Spectrograph

COTS Commercial-off-the-shelf

CSC Computer Sciences Corp.

CSOC Consolidated Space Operations Contract

CSS Cross Support Services

dB decibel

DCS Dynamics Control System

deg degree

DM De-orbit Module

DOF degree of freedom

DOWD differenced one-way doppler

DRS Disturbance Reduction System

DSN Deep Space Network

DSS Distributed Space System

DUO Dark Universe Observatory

EAVCS Enhanced Auto-track Computer Vision System
86 FDAB End of FY 2004 Report

EFF Enhanced Formation Flying

EKF extended Kalman Filter

ELV Expendable Launch Vehicle

EM Ejection Module

EO Earth Observing

EOS Earth Observing System

EPIC Extrasolar Planet Imager Coronagraph

ES Earth Science

ESA European Space Agency

ESMO Earth Sciences Mission Operations

ESSP Earth System Science Program

EVA Extra-Vehicular Activity

FAA Federal Aviation Administration

FD fl ight dynamics

FDAB Flight Dynamics Analysis Branch

FDF Flight Dynamics Facility

FDS Flight Dynamics System

FFTB Formation Flying Testbed

FOT fl ight operations team

FOV fi eld of view

FUSE Far Ultraviolet Spectroscopic Explorer

FY Fiscal Year

GEC Geospace Electrodynamic Connections

GEONS GPS-Enhanced Orbit Navigation System

GLAST Gamma Ray Large Area Telescope

GMAT Goddard Mission Analysis Tool

GMSEC Goddard Mission Services Evolution Center

GMT Greenwich Mean Time

GN Ground Network

GNC Guidance, Navigation, and Control

GOES Geostationary Operational Environmental Satellite

GOTS Government-off-the-shelf

GPB Gravity Probe B

GPM Global Precipitation Mission

GPS Global Positioning 

GRACE Gravity Recovery and Climate Recovery mission

GRS Gravitational Reference Sensor

GSFC Goddard Space Flight Center

GTDS Goddard Trajectory Determination System

GTO geostationary transfer orbit

GUI graphical user interface

HEO High Earth Orbit/ Highly Elliptical Orbit

HiFi High Fidelity

HLDRI HST Laser Dynamic Range Imager

HME Hierarchical mixture-of-experts
FDAB End of FY 2004 Report 87

HP Hewlitt-Packard

HQ Headquarters

HRV Hubble Robotic Vehicle

HST Hubble Space Telescope

Hz hertz

IAD Interface Agreement Document

ICD Interface Control Document

IMDC Integrated Mission Design Center

IMU Inertial Measurement Unit

ISS International Space Station

IT Ionosphere-Thermosphere

JPL Jet Propulsion Laboratory

JSC Johnson Space Center

JWST James Webb Space Telescope

km kilometer

KSC Kennedy Space Center

L&EO launch and early orbit

LEO Low Earth Orbit

LIDAR Laser Detector and Ranging

LISA Laser Interferometer Space Antenna

LPO Libration Point Orbits

LRO Lunar Reconnaisance Orbiter

LT Low Thrust

m meters

MagCon Magnetospheric Constellation

MagNav Magnetometer Navigation

mas milliarcsecond

mbps megabit-per-second

MC Morning Constellation

MDR MacDonald-Dettwiler Robotics

MESA Mission Engineering and Analysis Branch

min minute

MIT Massachusetts Institute of Technology

MLT mean local time

MMS Magnetospheric Multiscale Mission

MOC mission operations center

MOMS Mission Operations and Mission Services Contract

MOU Memorandum of Understanding

MSASS Mission Spin-Stabilized Spacecraft

MSFC Marshall Space Flight Center

MTASS Mission Three-Axis Stabilized Spacecraft software

Mv visual magnitude

NESC NASA Engineering and Safety Center

NFIR Natural Feature Image Recognition

NOAA National Oceanic and Atmospherics Administration
88 FDAB End of FY 2004 Report

NRA NASA Research Announcement

NSG Network Support Group

OATS orbit and attitude tracking system

OCO Orbiting Carbon Observatory

OD Orbit Determination

OOO Organics Origins Observatory

OS Operating System

PARASOL Polarization & Anisotropy of Refl ectances for Atmospheric Sciences coupled with 

Observations from a Lidar

PCS pointing control system

PDR preliminary design review

PI Principal Investigator

PIP Professional Intern Program

PiVoT Position-Velocity-Time

PLT post-launch testing

QA Quality Assurance

R&D Research and Development

Re Earth Radius

RSDO Rapid Spacecraft Development Offi ce

RTADS Real-Time Attitude Determination System

RTF Return to Flight

RXTE Rossi X-Ray Timing Explorer

s second

SAMPEX Solar Anomalous and Magnetospheric Particle Explorer

SDO Solar Dynamics Observatory

sma semi-major axis

SN Space Network

SOCC Spacecraft Operations Control Center

SOHO Solar and Heliospheric Observatory

SORCE Solar Radiation and Climate Experiment

SOW Statement of Work

SPAD Solar Pressure and Aerodynamic Drag

SPDM Special Purpose Dexterous Manipulator

SPECS Sub-millimeter Probe for the Evolution of Cosmic Structure

SPIE International Society for Optical Engineering

SPIRIT Space Infrared Interferometric Telescope

SPRT Super Problem Resolution Team

SRB Solid Rocket Booster

SRP solar radiation pressure

SRR System Requirements Review

SSMO Space Science Mission Offi ce

ST Space Technology

STEREO Solar-Terrestrial Relations Observatory

STK Satellite Tool Kit

STP Solar Terrestrial Probe
FDAB End of FY 2004 Report 89

STS Space Transportation System

TDRS Tracking and Data Relay Satellite

TDRSS TDRS system

TGS Two-Gyro system

THEMIS Time History of Events and Macroscale Interactions during Substorms

TIM Technical Interchange Meetings

TIP Task Implementation Plan

TPF Terrestrial Planet Finder

TPF-C Terrestrial Planet Finder Coronagraph

TRMM Tropical Rainfall Measuring Mission

UARS Upper Atmospheric Research Satellite

UCB University of California, Berkeley

UMR University of Missouri, Rolla

US Stratcom United States Strategic Command

USGS United States Geological Survey

USN Universal Space Network

VSE Vision for Space Exploration

VESPER Venus Sounder for Planetary Exploration

VHF very high frequency

VRB virtual rigid body

WIRE Wide-Field Infrared Explorer
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