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Produced by the NASA Center for Aerospace Information (CASI)
Final Report Volume I

Executive Summary

D483-10012-1

Space Station

Systems Technology Study

Add-on Task

W7

(bASA-C3-171415) S pACB ST A :ICN SYSTEMS N85-22459

TECHNOLOGY STUDY (ACD-ON 1ASK). VOLUME 1:

esXECUTiYH SMf9ABY Pina1 FEport (Poainq

Aerospace Co., Huntsville, Ala.) 135 p Unclas

HC A%)6/NF Ail CSCL 22B G3/15 146ojIOE/AV4ff

February, 1985 SPECTRA RESEARCH SYSTEMS (SRS)

--S »;
D483-10012-1

SPACE STATION SYSTEMS TECHNOLOGY STUDY

(Add-on Tasid

Final Report

VOLUME 

^r EXECUTIVE SUMMARY

D493-10012-1

Conducted for NASA Marshall Space Flight Center

Under Contract Number NASS-34393

cl

C February 1985

C1

C Boeing Aerospace Company

C-1 Spectra Research Systems

I
D483-10012-1

FOREWORD

0

C)

Al

t

l

This Space Station Systems Technology Study add on task (Contract NAS8-34893 S/A 6)

was initiated in June 1984 and to be completed in February 1985. The study was conducted for the National Aeronautics and Space Administration, Marshall Space Flight

Center, by the Boeing Aerospace Company with Spectra Research Systems as a subcontractor. The study final report is documented in three volumes.

D483-10012-1 Vol. I Executive Summary

D483-10012-2 Vol. II Trade Study and Technology Selection Technical

Report

D483-10012-3 Vol. III Technology Advancement Program Plan

Mr. Robert F. Nixon was the Contracting Officer's Representative and Study Technical

Manager for the Marshall Space Flight Center. Dr. Richard L. Olson was the Boeing

study manager with Mr. Paul Meyer as the technical leader, and Mr. Rodney Bradford

managed the Spectra Research Systems effort. A listing of the key study team members

follows.

f

ii
iii

Subject

Study Manager

Technology Category

Autonomous Functional

Control

Attitude Control

Free Flier Controls

and Displays

Test Planning (SRS)

D483-10012-1

KEY TEAM MEMBERS

MSFC-Management Team

R. F. Nixon

H. E. Brown

P. D. Nacaise

F. Roe

Contractor Team

R. L. Olson

D. P Meyer

O. Bakken

M. H. Bantell

I Qualy-White

R. Bradford,

Management

I Cody

S. Montgomery

4
iv

D483-10012-1

TABLE OF CONTENTS

VOLUME I

1.0 INTRODUCTION

1.1 Technology Selections and Rationale

1.1.1 Autonomous Functional Control Rationale

l 1.1.2 Attitude Control Rationale

1.1.3 Controls and Displays for OMV, OTV and

Spacecraft Rationale

2.0 TECHNICAL SUMMARIES

2.1 Introduction

2.2 Autonomous Functional Control

2.2.1 Approach

2.2.2 Technical Discussion

2.2.3 Technology Candidate Comparisons

2.2.4 Conclusions

2.2.5 Technology Advancement Plans

2.3 Attitude Control Impact From Structural Dynamic Motions

2.3.1 Approach

2.3.2 Technical Discussion

2.3.3 Summary of Results

2.3.4 Conclusions and Recommendations

2.4 Controls and Displays for OMV, OTV and Spacecraft Servicing,

Flight Operations and Functional Operation

2.4.1 Approach

2.4.2 Technical discussion

2.4.3 Technology Candidate Comparisons

2.4.4 Conclusions and Recommendations

4

2.4.5 Technology Advancement Plans

F` l

Page

1

2

4

5

7

9

9

10

10

12

33

36

36

44

44

48

58

60

61

61

62

85

85

89
0

Ci

D483-10012-1

LIST OF FIGURES

No. Page

3

13

15

17

18

20

21

27

28

38

Study Plan Flow Diagram

Typical Guidance, Navigation and Control

Typical Space Station EPS Configuration

Typical Communication Subsystem Controller

Typical Data Management Subsystem Network Operating System

Typical Pumped Two-Phase Heat Transport System

Architecture for Subsystem Management

The Automated Decision Makers

Flow Chart for Integrating Controller Functions

Schedule for Space Station Subsystem Simulation Development Plan

Schedule fcr IC Expert System /Conventional Microprocessor

Software Interfaces

Schedule for Development of Compact Lightweight Interference

Processor for Space Applications

Definition of Symmetric/Anti-Symmetric Bending

Balanced Array Concept Astronaut Deployment for NASTRAN Analysis

Loads and Motions with Collocated Linear Controllers

Disturbance Model for Crew Activity

Preferred Berthing Configuration for Orbiter and Disturbance Impulse

Torsional Vibration Suppression Performance with CMG and Root or

Tip Mounted Dampers

Simulated Response of Root Mounted Torsional Damper for 20%

Damping— Tilt Actuator Locked Tx = 1000 N-M

Response of a Tip Mounted Torsional Damper Tuned for 15% Damping

Tilt Actuator Locked, Tx = 1000 N-M

Torsional Vibration Suppression Performance with CMG's,

Collocated Suntrack/Tilt Actuators

RCS (Resisto Jet) Control of Symmetric Bending Modes Response

to 1000 N-M-sec Torque in Pitch

Waffle Grid Solar Panel Structure

v

1.0-1

2.2-1

2.2-2

2.2-3

2.2-4

2.2-5

2.2-6

2.2-7

2.2-8

2.2-9

2.2-10

2.2-11

2.3-1

2.3-2

2.3-3

2.3-4

2.3-5

2.3-6

CK 2.3-7

C-1 2.3-8

c

2.3-9

c

2.3-10

2.3-11

c^

c

c

40

42

45

47

49

49

51

52

53

54

55

57
D483-10012-1

LIST OF FIGURES (continued)

Na Page

2.4-1 Mission Scenario Overview 65

2.4-2 Conceptual Workstation Configurations 83

2.4-3 Schedule for Development of WFOV/HUD 90

2.4-4 Schedule for High Performance Color Flat Panel LCD Display 92

2.4-5 Schedule for Small High Performance Color Programmable

Multifunction Switch 94

vi
D180-27935-1 yLIST OF TABLES

'No. Page

_ 1.1-1 Autonomous Functional Control Candidates Benefits/Cost

Ratios 6

1.1-2 Prioritized Autonomous Functional Control Technology

Candidates 6

2.2-1 Power Generation Autonomy Factors 16

2.2-2 Subsystem Modes 22

2.2-3 Subsystem Reconfigurations 23

_ 2.2-4 Subsystem State Change Factors 24

2.2-5 Integrating Controller Software Sizing and Timing 30

2.2-6 Integrating Controller Data Flow 31

2.2-7 Integrating Controller Benefits Estimate 34

` 2.2-8 Technology Advancement Cost Estimates 35

2.2-9 Resources for Space Station Subsystem Simulation

Deve:,jpment Plan 39

2.2-10 Resource Requirements for IC Expert System/Conventional

Microprocessor Software Interfaces 41

2.2-11 Resource Requirements for Development of Compact Lightweight

Interface Processor for Space Applications 43

2.4-! OMV Mission Scenario by Mission Phase 63/64

2.4-2 OMV Mission Scenario Functional Analysis 66-80

2.4-3 Display Technology Comparison 84

2.4-4 Qualitative Cost/Benefits of Technology 86

2.4-5 Quantitative Costs/Benefits/Risks of Technology 87/88

2.4-6 Resources for WFOV/HUD 91

2.4-7 Resource Requirements for High Performance Color Flat Panel

LCD Display 93

2.4-8 Resource Requirements for Small High Performance Color

-' Programmable Multifunction Switch 95

G

e

c

Ct vil
D483-10012-1

LIST OF ACRONYMS AND ABBREVIATIONS

ACCEL remote body station 1301

ACOR body station 100

ACS attitude control subsystem

AFB Air Force Base

Al artificial intelligence

APSTS Advanced Platform System Technology Study

ATP authorization to proceed

. , BAC Boeing Aerospace Company

BIT built in test

BITE built in test equipment

C& D controls and displays

CAD computer aided design

CAE computer aided engineering

CDG Concept Development Group

Cg center of gravity

CG and IM center of gravity and inertial momentum 

CGI computer generated imagery

CMG control moment gyro

GN2 nitrogren gas

-- CO2 carbon dioxide

CP co-pilot

f

l^

CPU

CRT

central processor unit

cathode ray tube

i DARPA Defense Advanced Research Projects Administration

do/ac direct current/alternating current

DEC Digital Equipment Company

deg/sec degrees per second

i_

DMS data management subsystem

DoD Department of Defense

C

viii
D483-10012-1

^e

i

1

i

EASY Engineering Analysis System

EC/LSS Environmental Control /Life Support Subsystem

EL Electroluminescent

EPS Electrical Power Subsystem

ES expert syst-m

EVA extra vehicular activity

FAB fabrication

FO fiber optics

FF Free Flyer

ft feet

FY fiscal year

GL/EP glass/epoxy

GN& C guidance, navigation and control

GR/EP graphite/expoxy

GPS global positioning system

GSFC Goodard Space Flight Center

GSTDN Ground Station Tracking Data Network

HOL higher order language

HR hour

H2O water 

HUD head up display

Hz Hertz (a measure of frequency)

IAC integrated analysis capability

IC integrating controller

I.D. inside diameter

IEEE Institute of Electrical and Electronic Engineers

INDA interface from NASTRAN dynamics analyzer

INTF interface

I/O input/output

IOC initial operational capability 

ix
D483-10012-i

JPL Jet Propulsion Laboratories

JSC Johnson Space Center

KG kilograms

KW kilowatts

LAN local area network

lb pounds

lbm pounds-mass

LCD liquid crystal display

LCLV liquid crystal light valve

LED light emitting diode

LeRC Lewis Reseat,ch Center

LIOH lithium hydroxide

LISP list processor

LR line replaceab:e

MACLISP Macro Lisp

MBPS million bits per second

MHz megahertz

MIL-STD military standard

MIPS million iterations per second

MMH Monomethyl Hydrazine

MPA multi-beam phased array

MSFC Marshall Space Flight Center

NASA National Aeronautics and Space Administration

NASTRAN NASA Structure Analyzer

NIU network interface unit

n-m-sec Newton-meter-seconds

NOS network operating system

NRZ nonreturn to zero

ns nanoseconds

X
D483-10012-1

Obi C operations and checkout

O.D. outside diameter

OMV orbital maneuvering vehicle

OPS4 an expert system development tool

ORACLS optimum regulator and control of linear systems

ORU orbital replaceable unit

C/O check out

OSI operator system interface

OTV orbital transfer vehicle

P pilot

PDP model designator for line of DEC computers

P/L pay load

?RLCH pre launch

PSI pounds per square inch

Psia pounds per square inch absolute

Psid pounds per square inch differential

Pwr power

QWERTY Top left hand row of keys on a typewriter

R&D research and development

RCA-PRICE Radio Corporation of America Price Modeling Program

RCS reaction control system

RF radiolrequency

RI name of expert system to configure VAX installations

RMS remote manipulator system

ROM read only memory

R/T receiver-transmitter

RTOP research technology objectives and plans

SAR synthetic aperture radar

Sec second

XI

x7 rt=;
xii

C

C?

G

C

D483-10012-1

SEPS solar electric propulsion spacecraft

SOA state of art

S/C spacecraft

SRI Stanford Research Listitute

SRS Spectra Research Systems

SS Space Station

STS space transportation system

TBD to be determined

TCS thermal control system

TDMA time division multiple access

TCRSS tracking and data relay satellite system

TFEL thin-film electro luminescent

TI Texas Instruments

TMS teleoperator maneuvering system

TVC thrust vector control t

t

1

VAX virtual address extension

VHSIC very high speed integrated circuit

VLSI very large scale integration

VM ventilator manager

XCVR transceiver
D483-10012-1

1.0 INTRODUCTION

This is the Executive Summary, volume I, of the final report for the Space Station

Systems Technology Study add-on task. The study has been conducted for the Marshall

,. Space Flight Center (MSFC) by the Boeing Aerospace Company (BAC) and Spectra

Research Systems (SRS). The overall study objective is to identify, quantify, and justify

..' the advancement of high-leverage technologies for application to the early space station.

Research plans were developed for each of the selected high-leverage technologies. The

objective was fulfilled through a systematic approach tailored to each of the technology

areas studied.

1 The current Space Station Systems Technology Study add-on task was an outgrowth of

the previous segments of the Advanced Platform Systems Technology Study (APSTS).

The previous segments were completed in April 1983 and February 1984 for the MSFC by

the Boeing/SRS team. The initial study segment proceeded from the identificatior. of

106 technology topics. Of those topics, five were selected for detail trade studies. The

technical issues and options of those five were evaluated through detailed trade

processes during the initial study. Individual consideration was given to costs and

benefits. Advancement plans were subsequently developed for the five topics. A similar

approach was used in the second study segment with emphasis on system definition in

four specific technology area3 out of the initial five. In the current add-on task two of

the initial five areas have been examined further to expand the definition of the

concepts and one new area has been added to cover a function emphasized by emerging

Space Station operational definitions.

C-1 

The three study areas addressed in the add-on task are: (1) autonomous functional

control of Space Station subsystems, (2) the impact from structural dynamic motions on

Space Station attitude control, and (3) controls and displays for OMV, OTV, and

spacecraft servicing, flight operations, and functional operation. The first two areas are

extensions of areas identified during the previous study segments. They were conducted

to facilitate a more in-depth understanding of the technology issues. Different study

approaches were used for each of the three study areas. System concepts were studied

in the autonomous functional control task. In addition to conducting investigations of an

1

Ct
D483-10012-1

autonomous functional controller at a greater level of detail, this add-on task considered

additional subsystems: guidance, navigation and control; local data management, and

communications. For the attitude control study add-on task the principal methodology

was to simulate the Space Station dynamics with various models of disturbances and to

use that simulation to evaluate various control system concepts. The controls and

displays study was a new task and therefore contained more basic definition information

as part of the technology need assessment. Each of the approaches produced useful

advancements in the understanding of technology issues and development needs. The

summary discussions are presented in the following sections.

The overall study was divided into three tasks. During task 1, the design concepts in

each of the three study areas were refined. The concepts were used to annunciate

specific technology options upon which comparative studies were conducted. Candidate

high-leverage advancement technologies were then selected from the options. The cost,

benefits, schedules, and life cycle costs for each of the options were evaluated in task 2.

Selection of the technology i.dvancement items was made during this latter task. Technology advancement plans were prepared for each of the selected items in task 3. The

overall study task flow is shown in figure 1.0-1.

This volume presents a summary of the work performed to select the high leverage

items. The total final report is made up of this volume, Volume II: Trade Study and

Technical Selection Technical Report, and Volume III: Technology Advancement

Program Plan. More detailed discussion of the trades conducted and the technology

advancement plans are given in volumes II and III respectively.

1.1 TECHNOLOGY SELECTIONS AND RATIONALE

Twelve potential technology advancement items were identified during this study. These

items were analyzed and evaluated in task 2, considering technical as well as cost benefits and schedule criteria. Study plans were prepared for six of the selected high

leverage items. The items selected for planning are:

a. Development of effective models to support an automated integrating controller.

b. Development of technology to interface expert systems with conventional

software.

2
D483-10012-1

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n483-10012-1

C. Space qualified inferencing processor development for an integrating controller.

d. Very wide field of view head-up display development for control stations.

e. High performance color flat panel LCD display development.

f. Development of high performance color programmable multifunction switches.

The following sections summarize the rationale associated with selections made in each

of the three study areas.

1.1.1 Autonomats Functional Control Rationale

An automation and robotics philosophy has been established as a goal for the space

station. This philosophy calls for the initial space station to evolve to a nearly

autonomous facility within a number of years after orbital operations begin. This

philosophy is in agreement with the needs of a Space Station to provide a facility for a

wide range of missions without encumbering the crew (or mission controllers) with 

excessive hours for station upkeep. This philosophy is also in agreement with the needs

for efficient and balanced operation of the Space Station's complex systems over

extended lifetimes with limited consumable and power resources. Autonomous functional control is justified because it provides subsystem management for a lung life,

allows =pace station functions to evolve, and enables the crew to do productive

PYperimental and/or operational work. The rationale for this kind of control is that it

provides the decision, malting functions that would otherwise be left to mission ground

controllers and astronauts. The processes involved in developing the integrating 

controller to implement autonomous functional control drive out needs for advancements

in artificial intelligence software, space qualified data processing equipment, sensors, 

actuators, and devices for interacting p ith the crew. Because the development lead

times are long for many of these advancements, there is an urgency for starting

advancement programs for the integrating controller technologies as soon as possible.

The cost benefits assessment of this study modify the conclusions of the previous study

because of the expectation of supporting advancements from the DARPA Strategic

Computing Study. These expectations have reduced the advancement costs for technologies that have generic characteristics. The benefits were not modified from those

4 
0483-10012-1

developed during the previous study because no new information on benefits was

uncovered. The result was that the benefits versus cost ratio improved and was also

partitioned over the several technology advancement candidates. Table 1.1-1 gives the

benefits versus cost ratios estimated for five technology advancement candidates

identified for autonomous functional control. These candidates include the three that

were planned for development as discussed in volume III. Table 1.1-2 gives the

prioritization of the five candidates based on three unweighted criteria elements. Note

that the real time expert system development and knowledge engineering development

were considered to be sufficiently generic so that DARPA results would provide

sufficient advancement support.

1.1.2 Attitude Control Rationale

The objective of the add-on task study in attitude control was to extend the efforts of

the previous studies to include; symmetric mode analysis, elemental structure damping,

active controller evaluation, and incorporation of stiffer structure in the solar array

design. Accordingly, a detailed evaluation of space station control and dynamic

performance in the presence of structural interaction excited by orbiter berthing

operations and crew activity was performed. Control requirements for the symmetric

._ modes were derived and motion of the flexible appendages was studied in detail. The

uncontrollable modes identified in the previous study phase were controlled by selected

techniques including passive and active stabilization. Passive stabilization of solar array

torsional vibration focused on the design of discrete viscous damping mechanisms in the

astromast structure. Active torsional vibration suppression considered the use of the

-' beta tilt arid sun tracking actuators. Variations to the existing structural configuration

considered alternate solar array deployment schemes which offer substantially stiffer

structures in torsion.

The conclusions of the study can be summarized as follows. Generally it is recognized

that attitude performance requirements for a habitable Space Station in low earth orbit

are lax. This study has clearly demonstrated that when the control bandwidth is small

compared with the bandwidth of the sensors and actuators, all modes in the proximity

and above the controller pass band are effectively gain stabilized. Thus robustness

U

s
Candidate

Expert systems that interface

well with conventional S/W

Adapting Expert Systems to

Real Time Operations

Simulation Modeling

Knowledge Engineering Tech.

Space Qualified LISP Computer

Sched

1

4

2

5

3

D483-10012-1

Table 1.1-1 Autonomous Functional Control Candidates

Benefits/Cost Ratios

Candidate

1. Adapting expert systems to real time operations

2. Developing expert systems that interface well

with conventional software

3. Developing effective simulation models

4. Developing knowledge engineering techniques

5. Space Qualified Compact LISP Computer

Benefits/Cost Ratio

37.5

Table 1.1-2 Prioritized Autonomous Functional Control

Technology Candidates
D483-10012-1

(stability with a margin) is guaranteed under these conditions and the fundamental issue

• . becomes one of augmenting uncontrollable modes when such augmentation is deemed

necessary. The study has shown that coordinated control using collocated sensors and

r actuators will provide effective vibration suppression In this particular application it

was shown that CMG control of the central modular care in conjunction with the panel

positioning i ctuators gives vibration suppression for all modes, with the exception of the

symmetric bending modes. Worse case amplitudes of appendage motion due to

symmetric bending was found to be negligible. Based on these observations it is

concluded that attitude control development for Space Station is not significantly

influenced by flexibility. The need for a dedicated vibration suppression system is

eliminated by collocated and coordinated regulation of modular core and solar array

motion. However, preference toward a locked panel tilt actuator may require some

passive damping to dissipate solar array torsional vibrations especially in the case whereSEPS type arrays and deployment are utilized. If a type of stiff substrate backed panel

or equivalent is employed, then the severity of the vibration problem is mitigated, if not

totally eliminated. In this case, one need only insure that stiffness of the supporting

structure is adequate.

1.1.3 Controls and Displays for OMV, OTV and Spacecraft Rationale

The area of controls and displays is a new one to the Space Station Systems Technology

Study. It was selected as an area of concern due to its inherent complexity, numerous

interfaces and vital function to the safe operation of Space Station. Since it is rapidly

advancing, the Station could benefit from the technology by directing that advancement

for its own needs.

Based on the developed mission scenario and functional analysis, a minimum of two

operators is required to successfully complete the mission. To assist the operators, an

expert system is also required to monitor subsystem status of the OMV and RMS, monitor

enroute progress of the OMV on its mission, and control the caution and warning system.

The following technologies were found to best satisfy Space Station workstation

requirements but require further advancement:

C

C

7
D483-10012-1

o Liquid crystal display technology for use in both multifunction displays and

programmable switches. Beside the numerous Space Station benefits, this technology would also benefit the consumer market and high-technology areas.

o Six-axes hand controller. This technology requires further testing, especially in a

zero-gravity environment.

o Voice recognition and synthesis technology. There is a potential benefits interaction with military and commercial development. It may become the favored

means of computer interface.

o Wide field of view head-up display. A need must be established yet.

The following technologies were found to satisfy Space Station workstation requirements

and do not require further advancement but do require zero-gravity testing:

• Touch pen or screen

• Dedicated switches

• LED programmable switches
I C^

^ f

D483-10012-1

2.0 TECHNICAL SUMMARIES

This section summarizes the results of the trade study and technology advancement

planning efforts conducted for the Space Station System Technology Study add-on task.

2.1 INTRODUCTION

The trade study Pffort characterized system concepts in order to define cost versus

benefits for autonomous functional control and for controls and displays for OMV, OTV,

and spacecraft servicing and operation. The attitude control topic focused on characterizing the Space Station attitude control problem through simulation of control system

responses to structural disturbances. The first two topics, mentioned above, focused on

specific technology items that require advancement in order to support an early 1990s

initial launch of a Space Station. while the attitude control study was an exploration of

the capability of conventional controller techniques.

The characterization studies for the autonomous functional control and attitude control

were structured to start with the issues identified in the previous segments of the

Advanced Platform System Technology Study. Those studies led to a detailed

characterization of the topics. The controls and display area was developed for this addon task based on a mission need model and this led to definitions of various concepts

needed to implement those missions. A definition of concepts based on Space Station

needs and constraints was developed for each of these areas as an initial step in the

current study. These concepts were based on requirements that were derived from Space

Station related documentation or from requirements known to exist for similar missions.

The next step was to develop the characterizations to identify options within the trade

topics. Based on life cycle costs and benefits, or in the case of attitude control

performance results, the options were evaluated and technologies necessary to support

the more promising options were identified.

Cost and schedule factors related to advancing the technologies recommended in the

autonomous functional control and controls and displays areas are also summarized in

this section.

i

The three study topics are presented in this final report in the order that was established

by the RFP. That order is autonomous functional control first, then attitude control, and

lastly, controls and displays for OMV, OTV and spacecraft servicing and operations. A

9
D483-10012-1

summary of the study approaches and results of the three topics is presented in this

volume. Detail trade study technical information is in volume II, and detailed

advancement planning information is provided in volume III.

2.2 AUTONOMOUS FUNCTIONAL CONTROL

In the previous technology studies, an integrating controller for automated housekeeping

subsystems has been identified and characterized as a prime area for technology

advancement to support the Space Station. This study extends the systems analyses to

characterize the functions of an integrating controller at a level of detail which will

allow initial functional requirements to be defined. In addition to extending the systems

analysis to greater detail, the study has been expanded to cover more of the subsystems

which will be automated on the Space Station. In particular, the guidance, navigation

and control, communications, and data management subsystems will be added to the

electrical power and thermal control subsystems considered in the previous study phases.

The life support subsystem automation has been considered significantly in the previous

studies and will not be analyzed further in this add-on study.

2.2.1 Approach

Three housekeeping subsystems of the Space Station were considered in the previous

phase of the study which were primarily based on generic subsystem descriptions. The

integrating controller functional definitions which were a result of the previous study

phase indicated that the process should cover subsystems other than the three which had

been considered. For these reasons, a review of subsystem descriptions for the Space

Station was conducted as a first step in this expanded study. In performing this first

step, each of the five subsystems considered; guidance and control, electrical power,

communications, thermal control and data management, were described. The descriptions were based on Space Station subsystem information from results of previously

completed Space Station configuration studies, and from experience held by subsystem

engineers who were interviewed.

A listing of subsystem functions to be automated was then developed to a level of detail

where the control parameters are sensed. Emphasis was placed on identifying subsystem

state controlling functions rather than the individual closed loop functions such as those

for feedback attitude control. An example of such state controlling functions is the

state of control moment gyro wheel inertia loading for attitude control. Control of such

10
functions requires integration with respect to other entities on the Space Station. The

development of an integrating controller concerns these functions.

Once the subsystem function had been developed, a systems analysis review was

conducted. This review identified where interactions between subsystems could occur,

where common outside factors could influence subsystem states, or where common and

recurring events could occur in more than one subsystem. These factors pointed to

functions which the integrating controller would need to perform if Space Station

autonomy is to be implemented.

For those integrating controller functions which are new or changed from those

described in the previous study phase, logic/functional diagrams were prepared to

describe the functions.

t

A step-by-step analysis has been conducted to describe the processes needed to implement each controller element. The implementation description covers software as well

as hardware for controller processing. The emphasis in this sub-task was on implementations for use on an early Space Station with some recognition of the need for

evolutionary growth planning.

A functional specifications listing was prepared to define preliminary requirements,

based on the logic and functional diagrams and the implementation descriptions developed in the previous sub-tasks. These requirements covered functions, inputs, outputs,

software features, and hardware characteristics of an overall controller for an early

Space Station system.

An assessment was made of specific needs for technology based oo all of the descriptive

information provided by the functional diagrams, implementation definitions and the

functional requirements. Once technology candidates had been identified, trades were

conducted to compare benefits in system performance and life cycle cost savings with

developmental cost expenditures.

Using the results of the trades, the candidates were ranked according to each of the C, following categories: (1) schedule pressure, (2) general usefulness of the technology and

(3) benefits/cost ratio. These rankings were combined to give an overall prioritization of

the candidates which provided a focusing in order to clarify the technology advancement

needs, but was not intended to eliminate any candidate.

11
D483-10012-1

The results of this prioritization were used to determine those technology areas requiring

advancement planning.

2.2.2 Technical Discussion

The subsystern descriptions for the five subsystems cons ! -`ered for autonomous functional

control were obtained by interviewing the appropriate Space Station and engineering

technology subsystem engineers to obtain diagrams and definitions for each of the

subsystems. The descriptions needed to support an analysis of autonomous functional

control were not for the internal operations of the sub:v3tem but rather were for the

states that subsystem would assume as they performed their functions.

Figure 2.2-1 illustrates a typical space station guidance, navigation and control

subsystem. In this figure the primary functions are on the left, simple flow diagrams are

in the middle and typical displays to the crew and controls interactions are on the right.

This figure shows that there are many modes of guidance and control operation and that

significant state control is needed.

The electrical power subsystem consists of elements for power generation, power transmission, energy storage, power distribution, and power conditioning. Figure 2.2-2 shows

a typical electrical power subsystem (EPS) configuration for the Space Station. On the 

left the figure shows an overall Space Station distribution of EPS elements and on the

right EPS elements within a single module of the Space Station are shown. Table 2.2-1

lists factors which require integrating control in order to provide autonomous operation

of the power generation elements.

The communication subsystem for the Space Station will function through many different

links. Automation of the controller for the communications subsystem must consider

elements of network control, subsystem element reconfiguration and mode control and

command processing control. Figure 2.2-3 shows elements of a typical communications

subsystem controller.

The control of a typical local area network data management subsystem (DMS) is

accomplished by control software called the network operating system which is resident

in the DMS processors. f= igure 2.2 -4 shows interfaces considered by a network operating

system. Because the integrating controllers at the module and Space Station level as

well as the subsystem controllers are likely to be embedded in the DMS processors, it is

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easy to overlook the need for DMS cor,trol to be considered as a subsystem management

function. The modes, reconfiguration, and scheduling for the DMS will need to be

integrated just as they are for other subsystems.

The last subsystem considered in this study is the thermal control subsystem. Figure

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1 2.2-5 shows a flow diagram for a typical thermal control subsystem element in the Space

Station. The management of the configuration of the elements of a thermal control

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subsystem distributed on the Space Station would be part of the function of any

` • integrating controller.

IBefore an analysis of subsystem functions for automation can be conducted, the

candidate architecture for integrating control must be described. Figure 2.2-6 shows a

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typical controller architecture for the Space Station indicating subsystem controllers,

module integrating controllers and Space Station level integrating control. For reasons

of reliability, commonality, system evolution and conservation of data flow a distributed

architecture philosophy for Space Station data management should be adopted. The use

of integrating controllers at the module and Space Station level indicate that there will

Cbe some centralization of control functions within data management. It is, of course,

possible to distribute those controller functions physically over different processors or

with redundant processors while a centralized functional aspect is retained. The

principle function of the integrating controller is to handle the common operations which

i occur at the interfaces between the subsystems of the space station. Because the

integration of control for subsystem management is hierarchal, the operational functions

^— of each subsystem which were common to one another were considered. Tables 2.2-2,

2.2-3, and 2.2-4 list typical subsystem modes, subsystem reconfigurations, and subsystern

state change factors respectively for the five subsystems considered. To integrate the

operation of these subsystems with the overall operations and missions of the Space

Station, the integrating controller will need to orchestrate these modes, reconfigurations 0 and subsystem states.

Because there is a large volume of data associated with the subsystem managerent and

automation and robotics support functions of an integrating controller, the overall

system must be designed to minimize the flow of information between the elements. For

that reason the concept discussed here operates on a management by exception. This

means that each subsystem controller will manage its own affairs so long as everything is

normal and going according to plan. Wren a subsystem controller detects a change such

as a failure condition, the integrating controller will be advised. The overall situation is

• 19
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TABLE 2.2-2 SUBSYSTEM MODES

GUIDANCE, NAVIGATION AND CONTROL

• Attitude hold

• Attitude slew

• Attitude control with orbiter docked

• GMG wheel denaturation

• TVC for orbit trim thrusting

• Acquisition and start up

• Off

• Reconfiguration

ELECTRICAL POWER

• Sunlight normal

• 0arkside normal

• Battery reconditioning

• Solar array degradation

• Reconfiguration

• Off

C041MUNICATIONS

o T)irect with other spacecraft

I') With other spacecraft via TDRSS

• Tracking

• Downlink via TDRSS

• Downlink via GSTDN

• Downlink to user ground station

• Unencrypted (not IOC)

• Reconfiguration

• Off

DATA MANAGEMENT

• Normal (full service)

• Reduced service

• Data dumping to archieval memory

• Reconfiguration

• Off

THERMAL MANAGEMENT

• Normal

• Reduced

• Reconfiguration

• Off

22
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TABLE 2.2-3 SUBSYSTEM RECONFIGURATIONS

GUIDANCE, NAVIGATION AND CONTROL

• Thrusters in use

• Allocation of control signal to controllers

• Redundant paths

• Alternate paths

• Sensors ir. use

ELECTRICAL POWER

• Batteries in use

• Solar array sections in use

• Redundant paths

• Alternate paths

• Power busses in use

COMMUNICATIONS

o Antennas in use

u Redundant paths

o Alternate paths

DATA MANAGEMENT

• Gateway devices engaged

• Redundant paths

• Alternate oaths

THERMAL MANAGEMENT

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• Thermal busses in use

• Pumps in use

• Heat exchanger in use

• Redundant paths

• Alternate paths

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n483-10012-1

TABLE 2.2-4 SUBSYSTEM STATE CHANGE FACTORS

GUIDANCE, NAVIGATION AND CONTROL

o Slew rate

o Dead band size

o Identification of principle axes

o System gains

o Wheel desaturations interval

o Wheel desaturation rate

o Wheel desaturation controller gains

o Storage of RCS propellant

o Maintenance schedule

o Failure modes/anomalies

F_LECTRICAL POWER

• Load management

• Power source management

• Fnergy balance

• Management of excessive power

• Light/darkside passage

• Maintenance schedule

• Failure mode anomalies

COMMUNICATIONS

• Frequencies (S-band or Ku-band)

• Data rates

• TDRS in use when more than one available

• Maintenance schedule

• Failure modes/anornalies

DATAMANAGEMENT

• Data rates

• Computer op rates

• rata stored

• Maintenance schedule

• Failure modes/anomalies

THERMAL MANAC rMENT

o Temperatures

o OT's

o Light'darkside passage

o 'Maintenance schedule

o Failure mode/anomalies
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d483-10012-1

then examined by the integrating controller so that directions are given back to the

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subsystems. Figure 2.2-7 illustrates an example of the automated decision rrdking

process using attitude control as an example subsystem. The subsystem controller in this

example checks its status every few milliseconds. As long as the status is okay no

' integrating controller action is requested. When the status is not okay, the subsystem

^— controller performs its internal diagnostics and informs the integrating controller. In

this example the attitude control subsystem controller detects a failure in LR-22 and

assesses the consequences of a switch to the redundant element as a transient in pitch,

C^ I yaw and roll attitude. The integrating controller checks the status of Space Station

subsystems and mission operations. Then, it determines that experiment 116 cannot

f tolerate the predicted attitude transient. The integrating controller therefore directs

` the attitude control subsystem controller not to switch to the redundant element.

This example indicates one type of decision making to be performed by an integrating

controller. Another type is rescheduling decisions for operations on the Space Station

resulting from unforeseen events. A;ain the integrating controller will be informed

(usually by astronau ,,: inputs) and the information results in a need to change directions

issued to subsystem controllers. The following is a list of typical status elements that

the integrating controller will direct a subsystem controller to change.

o Prioritization lists

o Scheduling

o Operat;ng constraints

o Override commands for emergency conditions.

These directions for change would affect mode and state control of the individual

subsystems in response to anomalies or unscheduled events.

Figure 2.2-8 gives a flow diagram to describe at a top level those steps to perform integrating controller functions.

1. Information is collected by the integrating controller from the astronauts via

control and display units, from the subsystem controllers via the data management

system, and from the ground via the telecommunications system (IOC especially

but less of this as Space Station autonomy is developed). This information will

indicate state changes, reconfigurations, schedule changes, environment changes,

and anomolies which effect the operation of the Space Station.

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2. A state and mode simulation will be run for all Space Station subsystems. This will

produce a description of the mode, configuration: and output performance parameters of all of the subsystems resulting from the passage of time as the simulation

is periodically updated based on the collected information.

3. Separate state simulations will be run faster than real time to predict the

consequences of letting the current situation continue, or to simulate the results of

hypothetical inputs to subsystem controllers in response to anomalous conditions.

4. Trend data and other historical data are updated to reflect the latest collected

information.

5. An assessment is made for each subsystem interface based on current state outputs

from the mode simulation and from the the predicted consequences which would

occur by letting the current situation continue. Unsatisfactory situations are

identified by the integ. ating controller and assessed (probably an E.S. application) to

be either life or mission threatening indicating an emergency condition or non-

) threatening indicating an anomalous condition.

6. When an emergency condition exists, the integrating controller will generate emergency commands to be issued to the subs y stem controllers. These commands will be 

designed to place the station in a condition which will support the life of the crew

and sustain the mission in accordance with predetermined priorities. Another part

of the emergency command process will be the activation of alarms and emergency

(explain type) information displays to the crew and transmissions of data to earth.

7. The integrating controller will issue; the emergency commands to the appropriate

subsystems and alarms and will determine the schedule and sequence for removing

those commands either with a continuation of the emergency state or after

collected information shows a return to normal.

8. For those conditions which are judged to be anomalous, but not life or mission

threatening subsystem change directives are needed. For these, the integrating

controller will determine (again E.S. technology may be needed) a workable

compromise using the various predictions from the hypothetical simulations as well

as trend data and direct input data. Once a workable compromise has been

28
0

D483-10012-1

selected, the integrating controller will generate change directives to be issued to

C_i, i subsystem controllers.

dr)

9. This is similar to step 7 in that appropriate subsystems will be directed and the

schedule for retaining those directives will be determined.

CThe key components of the integrating controller are the simulation modules and the

expert systems. Most of the feasibility assessment depends on the feasibility of

^3J developing and implementing these items. Some of the factors to be considered are:

Can the modules be developed?

Validity and verification of the models

Speed of the models

Cost to develop the models

The state change rate is expected to be low relative to the processing speed so several

software modules can be executed in series in a single processor, but more than one

processor will probably be needed for all of them. The same is also true of the e.-pert

systems. They may require separate processors, but may also be ex-cuted on the Name

processor if the time is available.

The impact of the integrating controller on the data management subsystem depends on

the program size and processing throughput required for the various program modules.

Quantitative estimates cannot be made without further specification of the data

_ management subsystem computers and additional characterization of the integrating

controller functions. Some qualitative estimates however can be made and are

summarized in Table 2.2-5. Size refers to the amount of memory required for the

program modules and their data. Those indicated as large are the simulations models and

the expert systems. These are expected to require on the order of half of the memory of

(

a DMS processor. The subsystem models may require much more since they are multiple

,.^ rr.odels. The timing column indicates demand for processor throughput (operation per

second). This is given in two parts, frequency and loading. The frequency indicates how

C.) often the module needs to be executed. As shown, all are required continually except

the Emergency Handler and Change Handler which are required in response to changes in

CI

conditions. The loading refers to how much of the processor's throughput is required.

(12

Another important factor in implementing the ntegrating controller on the data

management subsystem is the data flow required. Table 2.2-6 indicates, for the major

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sources of data flow, the freq-rency and amount of data flew from the subsystems, from

external sources and to the subsystems. The only data itern likely to place demands on

the data management subsystem data buses is operational data. Care must be taken in

the development of the integrating controller in selection of the operational data iterns

needed for integrating controller operation.

The key to developing the integrating controller is the ability to develop effective

models of the subsystems of the Space Station and effective decision making expert

systems. For the models, this involves selection of i , ,i adequate model development

language, proper assessment of the accuracy of the mu,lels and methods to translate the

models into software suitable for real-time ccntro'. Without building any models this is

about a 3 to 6 man-month effort. To develop an expe- i nental model of a Space Station

subsystem and convert for real time rise is a 1. t • 2 man-year effort. The number of

subsystems multiplied by 2 man-years each giv:-!, an indication of the scope of effort to

develop subsystem models. The prediction mc• ailing effort would be at least as much as

the subsystem modelling but would also invo!ve the use of expert system technology.

Based on experience, the following expert system metrics for an IC are "guestimated."

Approximately 1000 to 5000 rules will be required. The computer used should run at

about 2 MIPS and have from 1 to 4 megabytes of memory. 

Essentially, RI was developed over a lour year period at a rate of about 850 rules per

year. There was an expenditure of about 4 man-years of effort per year. Based on these

figures and the estimates of the preceding paragraph, an IC will require from 1.25 to

6.25 years to develop and from 5 to 25 man-years of efforts.

The use of expert system development tools is essential if an acceptable level of

productivity is to be achieved during the development process. Unfortunately, most

existing tools are not suitable for developing expert system for the integrating

controllers. They suffer from three general types of deficiencies.

First, existing tools are designed to handle static rather than dynamic situations. An IC,

of course, requires the ability to monitor and respond to situations that develop over

time.

Second, most tools interface very poorly with existing software or software based on

conventional rather than Al principles. A successful IC will require a blend of

conventional and Al techniques.

32
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D483-10012-1

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1 ^ Third, and related to the second deficiency, most existing tools are designed to interface

with a human user rather than other systems. Clearly, the latter capability will be

required in an IC.

Currently, no Al hardware is available that is suitable for "field" use such as on a space

station. This problem may correct itself in the future since TI has announced the

development of a compact Lisp machine for the Navy.

The discussion above suggests several technology areas needed for implementation of the

integrating controller concept. The following is an unranked listing of those suggested

technologies.

o Developing effective simulation models

o Adapting expert systems to real time operations

o Developing expert systems that interface well with conventional software

o Developing knowledge engineering techniques to cope with emerging technologies

o Space-qualified compact LISP computer

2.2.3 Technology Candidate Comparisons

The comparisons of the technology areas based on schedule pressure have considered the

following: (1) The anticipated duration of the advancement program, (2) contributions

from other advancement activities such as the DARPA strategic computing initiative

program, and (3) the anticipated need date of the technology.

General usefulness comparisons of the technology areas consist of two parts: (1) usefulness of the technology to the integrating controller and (2) usefulness of the technology

to other parts of the Space Station and other parts of the technical community.

The benefits resulting from an on-board integrating controller over the first ten years of

Space Station operation were estimated in the previous study chase and no new

information has been developed in this phase. The estimate is described in some detail

by paragraph 5.3.8 of Boeing document D180-279354-2 but Table 2.2-7 is included here

to summarize the benefits estimate metrics.

The advancement costs have been estimated for each technology candidate and are

reported in some detail in volumes II and III of this report as well as on Table 2.2-8.

33
D483-10012-1

Table 2.2-7. Integrating Controller Benefits Estimate

o Monitoring effort phased out over five years

o First year full mission control center coverage

o Second through fifth years—mission controllers reduced by 5

o After fifth year—mission controller and onboard monitoring reduced to 1/10

time for each

o Labor rate for mission controllers is $1500 per day and astronaut is $77,000 per day

o Efficiency and maintenance cost savings is $2.5M per year

o The integrating controller provides half of total benefits = $54M for ten years.

34 
D483-10012-1

l

Table 2.2-8. Technology Advancement Cost Estimates

o Developing effective simulation models

0 2 man year effort per model X 8 models = 16 man years plus real time

simulation development costs = $2.OM

o Adapting expert systems to real time operations

o Estimate 4 man years to adapt DARPA results to I.C. usage = $480K

o Developing expert systems that interface well with conventional software

o Estmate DARPA results require a ten man-year effort to adapt software

concepts to I.C. use = $1.2M (note: $2.04M effort under technology definition

includes effort to integrate software with Space Station processors)

o Developing knowledge engineering techniques to cope with emerging technologies

o Estimate DARPA results plus 2 man-year effort to adapt to Space Station usage

_ $240K

o Space qualified compact LISP computer

o Estimate $4M development and testing effort in addition to DARPA work

35
D483-10012-1

The estimates of Table 2.2-7 were partitioned according to the contribution of each of

the technology candidates to the overall bendfits provided by the integrating controller.

Using these partitioned benefits, the benefits to cost ratios were computed. Volume 11 of

this report gives the partitioning rationale used. The resulting benefits to cost ratios of

the five candidates are given as Table 1.1-1 of this volume.

Based on the schedule pressure, general usefulness, and benefits to cost comparisons

discussed above, the five technology candidates for autonomous functional control were

prioritized as indicated by Table 1.1-2 in the Introduction section of this volume.

2.2.4 Conclusions

The conclusions that can be drawn from this study are that several technology

advancements are necessary if an automated integrating controller is to be part of the

Space Station system. The urgency of NASA initiatives in each of these areas is

tempered somewhat by the DARPA plans for a strategic computing study. 

Because the technologies associated with adapting expert systems to real time operations and the advancement of techniques for knowledge engineering are significant parts

of the DARPA study, and because those two candidates have limited connection with the

unique characteristics of the Space Station, this add-on study has not developed

advancement plans for them. 

The three advancement candidates that have been considered in the advancement

planning for this add-on task will also benefit from the DARPA study. The effect of that 

benefit will be an improvement in the benefits to cost ratios for the candidates. if the

DARPA study proceeds immediately there may also be a schedule benefit for the

candidates identified here. It will be necessary for NASA to be in close contact with the

DARPA study to insure that the advancements produced are applied to the Space Station

in a timely manner. It will also be necessary to adapt the DARPA results for Space

Station use and that adaptation will be facilitated by close contact with the development

of those results.

2.2.5 Technology Advancement Plans 1 

Advancement plans for the integrating controller technologies will be developed to cover

two phases. Phase I is intended for the IOC Space Station. It will consist of the 

36
D483-10012-1

- development of subsystem models designed to evaluate state and mode conditions of

seven prime subsystems and an overall Space Station needs model. These subsystem

models will continuously assess the current operating conditions and synthesize the

status information needed by the IC. The overall station model will be operating

concurrently to define the needs of the Space Station as a whole. The actual functional

conditions will be compared with the generated requirements and displayed to the

\ astronauts and ground controllers. Initially, corrective action will be determined and

+ subsystem adjustments made by humans with the IC acting in an advisory capacity.

Phase 11 will incorporate the overall integration of autonomous functional control. An

expert system will be developed to perform the situation comparison task and determine

corrective action necessary through the use of encoded knowledge derived from experts

/ in the subsystem fields and the experience of the ground controllers and astronauts

involved in Phase I.

' Figures 2.2-9 through 2.2-11 and Tables 2.2-9 through 2.2-11 describe plans for the

_ three technology candidates which are not considered to be adequately covered by the

( DARPA Strategic Computing Study: (1) effective Space Station software simulation

models, (2) expert system/conventional m;,:roprocessor interfaces, and (3) inference t

processors for spacecraft applications. The plans are presented as staid alone programs.

However, in the case of the software interface development, the inference p- ocessor is

I the heart of the expert s; stem which is one side of the inter :acc, znd therefore must be

— available in order to design and build the software. In the case of the Space Station and

(— y subsystem simulation development, the models produced by the technology program will

`_ ! be much more useful if produced using hardware and software techniques resulting from

_ the real-time expert system and the inference processor programs. Initial model

development using conventional techniques should be acceptable, though.

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2.3 ATTITUDE CONTROL IMPACT FROM STRUCTURAL DYNAMIC MOTIONS

The objective of the previous study phase was to initiate the identification of

technologies required for the solution of the control-structure interaction problem in

Space Station design. The approach was to determine through analysis and simulation

the degree to which conventional controller technology is applicable to attitude

regulation of a Space Station with large flexible solar arrays.

The objective of the current phase of the study will be to extend the efforts of the

previous study to include symmetric mode analysis, elemental structure damping, active

controller evaluation and incorporation of stiffer structure in the solar array design.

Accordingly, a detailed evaluation of Space Station control and dynamic performance in

the presence of structural interaction excited by orbiter berthing operations and crew

activity was performed. Control requirements for the symmetric modes were derived

and motion of the flexible appendages was studied in detail. The uncontrollable modes

identified in the previous study phase were controlled by selected techniques including 

passive and active stabilization. Passive stabilization of solar array torsional vibration

focused on the design of discrete viscous damping mechanisms in the astromast

structure. Active torsional vibration suppression considered the use of the beta tilt and

sun tracking actuators. Vibrations to the existing structural configuration considered

alternate solar array deployment schemes which offer substantially stiff-r structures in 

torsion.

The previous phase of the study considered only the anti-symmetric modes of vibration.

This was justified under the assumption that the disturbances were manifest as pure

couples. This assumption is not valid since the most frequent source of disturbance is

derived from crew activity which imparts both force and torque to the vehicle. Figure

2.3-1 defines symmetric and antisymmetric bending modes. The sketch depicts typical

normal mode shapes for a simple structure where the mass of the solar arrays are

concentrated at the tip of the boom. Symmetric and antisymmetric bending is excited

by forces and torques respectively as shown. The actual motion of a multiply connected

set of flexible appendages is of both types of bending.

2.3.1 Approach

The structural model developed in the previous phase of study will be reviewed here.

This brief discussion will help to establish a reference for subsequent discussions. 

44

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D483-10012-1

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Symmetric banding Amirymmetric banding

Figure 2.3-1. Definition of Symmetric/Anti-symmetric Bending

45
D483-10012-1

A pictorial view of the study configuration is shown in Figure 2.3-2. This configuration

represents the all-up fully evolved configuration with SEPS type solar panels partially

deployed. Four simulation tasks in this study were performed with the structural

configuration using SEPS type solar arrays indicated above. The fifth task requires

modification of the current configuration to include arrays with improved structural

properties.

The previous study formulation of the model for the crew activity forcing function

assumed a pure torque couple about the center of mass with no resultant translational

forces through the center of mass. This study can apply both forces and torques at any

desired point of application on the structure and use the resultant state vector

(rotational plus translational states) and accelerations to establish control requirements

as a function of acceptable levels of acceleration.

The uncontrolled vibration in the solar array structure is damped by introducing discrete

passive torsional control elements at either ends of the mast. Designs for both tip and

root mounted dampers are presente r' and feasibility for space application is discussed.

.Active stability augmentation when applied to a large structure like the Space Station 

should incorporate both aspects of performance and vibration suppression. The control

objective for performance would be to shape the closed loop response such that motions

of core and solar arrays are decoupled. This would imply for example, that disturbances

due to crew activity would impart motion to the core but would tend to keep the solar 

panels fixed with respect to the sun. The actuator package includes a three axis linear

core mounted torquer, solar array sun tracking and beta tilt actuators. The sensors

include a core mounted rotational sensor package, and rotational motion measurements

at critical locations on the flexible elements. The preliminary design of an active

vibration suppression is presented where collocation of sensors and actuators is not a

constraint.

A symmetric mode vibration suppression system using a low thrust reaction jet control

system has been simulated a part of this study. The control objective was to null

translational rates of the boom and mast relative to the core using resisto jet controllers

mounted on the solar panel booms. This mode of control was investigated as an

alternative to redesign of the boom and mast servoactuator system.

46
47

D483-10012-1

Figure 2.3-2. Balanced Array Concept Astromast Deployment for NASTRAN

Analysis

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D483-10012-1

Stiffer solar array structures have been incorporated into the existing elastic simulation

model. The objective was to attempt a reduction in the amplitude of the uncontrolled

solar panel modes without introducing other serious side effects due to a significant solar

panel mass increase.

2.3.2 Technical Discussion

A principal purpose of vibration suppression study is to examine the amount of damping

induced in the flexible elements as a matter of course in the positioning of the station

and solar panels.

A relative positioning strategy implies that the panels track the sun in elevation and

azimuth by commanding a position profile perhaps through a rate command with periodic

position updates to account for rate sensor errors. This strategy would use shaft

tachometer and position measurements collocated with the actuators as state variables

to be regulated. Since the tilt angle for sun elevation has yearly variation, the tilt

actuation could be locked and activated only at discrete intervals. If the tilt actuator is

locked, some passive augmentation of the panel torsional modes is required. Locking the

roll actuator then serves to justify the investigation of passive means of control the

uncontrollable panel torsional modes. The relative positioning strategy is reasonable if

panel and station pointing requirements are compatible.

An absolute position strategy implies that the panels track the sun in elevation and

azimuth by regulating panel attitude through the use of sun sensors. The rate loop could

be implemented either by direct rate measurement or a derivation resulting from base

(core) rate and shaft tachometer signals. The absolute positioning strategy is reasonable

if allowable base motion is far in excess of solar array pointing requirements.

To facilitate the following discussions, a description of the static (panels fixed)

configuration indicating the location of all inputs disturbances is provided. In addition,

the control system cornposition for all passive and active controllers is given here for

future reference. Accordingly, the location of the control system elements is shown in

Figure 2.3-3.

The disturbances profile for modeling crew activity is shown in Figure 2.3-4. The model

respresents an astronaut in a soaring maneuver within the Space Station. The motion is

envisioned as being a pushoff from one wall and a deceleration on the far wall. The

48

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D483-10012-1

F

0

Force

`

Sun

Full iw

Figure 2.3-3. Loads and Motions With Colocated Linear Controllers

Figure 2.34. Disturbance Model for Crew Activity

49
D483-10012-1

parameters of the motion are presented for a large astronaut in the flight within a

module of about 12 feet in diameter.

A schematic drawing of the Space Station with orbiter docked is shown in Figure 2.3-5.

The longitudinal axis of the orbiter is assumed colinear with the yaw axis of the Space

Station.

The solar array mast torsional response performance of CMG controllers with root or tip

mounted dampers in terms of an impulse response analysis is summarized in Figure 2.3-6.

The root mounted damper was designed to isolate the deployment mast from the base

where the solar blanket is attached.

The time histories for the appendage and damper impulse response of the root mounted

damper in the controllers for CMGs and actuators for suntrack and tilt are shown in

Figure 2.3-7.

The tip mounted damper was designed to provide damping to the panel torsional mode for

a reasonable penalty in mass. For a given damper to panel inertia ratio the spring and

damping constants were tuned to the natural frequency of the mast. The time histories

for the appendage and damper impulse response of the tip mounted damper in the

controller collocated with the CMGs are shown in Figure 2.3-8.

Active vibration suppression of both boom and most torsional modes is incorporated in

controllers which utilize as a first option a coordinated feedback of relative angular

motion variables to the pairwise collocated set of sensors and panel drive actuators. A

second option utilizes crossfeeds of absolute angular motion variable to the panel drive

actuators in order to decouple base motions from solar panel motions.

Boom and mast torsional response performance of controllers which utilize the first

feedback option defined above is summarized in Figure 2.3-9. For this option the tilt

actuator was used to drive the base of panel in response to perturbations in panel roll

attitude and rate relative to station fixed coordinators measured at the actuator. The

control law is sensitive to knowledge of the panel parameters. However, a sensitivity

analysis indicated that the degradation in damping due to reasonable ignorance of the

panel torsional properties was not severe. The option also uses the suntrack actuator to

drive the pivot point of the panel set in response to perturbations in panel pitch attitude

50
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D483-10012-1

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Figure 2.3-5. Berthing Configuration for Orbiter and Disturbance Impulse

51

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Root 14.90 500 — .30 .044 .036 .0004 20

Figure 2.3-6. Torsional Vibration Suppression Performance with CMG and Root or

Tip Mounted Dampers

52 
CJ D483-10012-1

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Figure 2.3- 7

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Figure 2.3-8. Response of a Tip Mounted Torsional Damper Tuned for 15%

Damping T-*': --: tuator Locked, TX = 1000 N-m

S4
D483-10012-1

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C

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55

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D483-10012-1

and rate relative to station fixed coordinates measured at the actuator. The controller

was designed to provide isolation between the boom and the mast. Tuning of parameters

was not required and any level of damping can be achieved.

For the second option identified above, the objective was to apply multivariable control

methodology to the given flexible Space Station. Eigenstructure assignment u.;ing output

feedback was selected for the following reasons. First, output feedback results in fixed

gain controllers which do not contain frequency sensitive elements. Fixed gain controllers are easy to implement. Eigenstructurc assignment implies that subsets of the modal

frequencies and the closed loop eigenvectors can be arbitrarily specified. The size of the

subsets depends upon the number of sensors and actuators comprising the controller.

Eigenvalue assignment provides modal stability augmentation. Eigenvector assignment

allows the closed loop specification of relative motions between various elements of the

structure. Finally, eigenstructure assignment theory- is a multivariable tool allowing the

control system to be synthesized in a single run. However, the theory does not guarantee

stability of the closed loop system.

The results of the experiments with eigenstructure indicate that the control objectives

are achieved when inertial measurements are implemented. Spatial separation between

sensors and actuators on a flexible structure can lead to stability problerns. However,

the bandwidth of the controller was low enough to provide a stable core and all

control l able flex modes were well damped.

The simulation data clearly indicates that appendage translational amplitudes due to

symmetric mode excitation from impulse doublet forcing are negligible. However,

docking and module berthing shocks could induce significant solar panel motions and

attendant central core translation especially for stations with large power requirements.

Accordingly, the purpose of the task was to take a quick look at the feasibility of using a

propulsion system comprised of resisto jet type thrusters driven by appropriate control

logic to damp the translational (butterfly) modes. As mentioned previously, symmetric

bending modes are not controllable using torquers unless the panel drives are such that

each array can be independently controlled over the two degrees of freedom.

Figure 2.3-10 illustrates the basic simulation configuration used in the analysis of

candidate control laws. 

56
D483100121

11

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Sign check of Ly. 60 at S1, V identifies symetric modes

^41 Rate limits on 6t • .25 arc-sec/sec

60 - .50 arc4adsoc

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Figure 2.3-10. RCS (Resisto Jet) Control of Symmetric Bending Modes Response

to 1000 N-m-sec Torque in Pitch

am

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(J 57
As the Space Station solar arrays rotate 360 0 about y-axis to track the sun, it would be

difficult to fire the RCS thrusters and not excite the solar array bending modes.

However, if some RCS thruster chattering is permissible, then the thrusters can be used

to effectively damp the transverse symmetric modes of the solar array boom.

The preceding discussions clear ly indicated that vibrations induced in very flexible solar

array structures can be easily managed by employing simple techniques with component

hardware currently in existence. However, the question remains to determine the

controllability of solar panels with improved stiffness. The problem is to compare ;he

structural motions of the SEPS type array with the stiffer arrays assuming panel drive

actuators locked.

A solar panel design of current interest at Boei.ig is shown in Figure 2.3-11. The design

features a substrate backed by a lightweight waffle grid structure. The waffle grid adds

the required stiffness. The panel sections are foldable in accordion fashion with tapered

thickness. The dynamic characteristics are improved due to the extent that the first

bending mode is 1.05 Hz. Packaging is less efficient than the SEPs type array and the

increase in mass required to obtain the given improvement in first mode frequency is

about twice the SEFS array mass.

The simulation results using models of these stiffer arrays indicate that the most severe

motion is in pitch, manifested primarily as symmetric boom twist and bending.

Symmetric torsion in the boom is mildly augmented by CMG control, which is required

for some damping in pitch. Panel roll axis torsion and accompanying vibrations in the

supporting structure were found to be negligible.

2.3.3 Summary of Results

The issues relating to attitude control impact from structural dynamic motions for a

planar space station configuration have been addressed. The following statements

summarize the findings of the study.

For SEPS arrays with locked panel drivers:

• Dedicated vibration suppression is required for solar array torsional modes.

• Results based on worse case ad hoc disturbance model.

o Stability guaranteed at control bandwidths of interest.

58
r

r r ^.

• Substrate backed by lightweight waffle grid structure

• Foldable panels with tapered thickness

C

* Improved dynamic characteristics (first mode frequency = 1.05 Hz) 

• Packaging less efficient than SEPS type solar array

o Mass increase over SE'S type by 2.5

Figure 2.3-11. Waffle Grid Solar Panels

t-^

59
ki

Control law considerations with SEPS arrays are:

• Collocated (coordinated) control of station and solar panels provides both rigid body

attitude regulation and vibration suppression.

• Decoordinated control provides the added benefit of panel/station motion decoupling, introducing potential for instability.

• Dedicated (RCS) control of symmetric bending modes not required for the planar

balanced configuration.

• Simple RCS symmetric bending mode damper with antisymmetric discriminator is

effective and feasible.

Active control considerations with SEPS arrays are:

• Use of panel drive servo actuators is effective and feasible.

• Current SOA relative motion sensors are adequate.

Passive control considerations with SEPS arrays are:

• Root mounted damper best choice for mast isolation, least sensitive to parameter 

variations.

• Mechanical design may be difficult to implement due to small motions.

Stiff solar array motions with locked panel drives:

• Use of waffle design (or equivalent) could eliminate need for dedicated vibration

suppression controllers.

• Mass increase by 2.5.

2.3.4 Conclusions and Recommendations

The conclusions for this study area are summarized under paragraph 1.1.2 of this report

volume. Continuing effort is recommended in attitude control for space station and that

effort should concentrate on defining functional requirements for rigid body control of a

dynamically evolving Space Station. The findings of this study, or equivalent, should be

used to estimate the effects of flexibility and to assess the need for dedicated vibration

suppression systems.

60
" 2.4 CONTROLS AND DISPLAYS FOR OMV, OTV & SPACECRAFT SERVICING, FLIGHT

OPERATIONS do FUNCTIONAL OPERATION

C-^

The area of controls and displays is a new one to the Space Station Systems Technology

Study. It was selected as an area of concern due to its inherent complexity, numerous

interfaces and vital function to the safe operation of Space Station. The rapid

r advancement of control system technology could benefit the Station by directing some of

the technology advancement to suit its own needs. This effort identifies three areas of

_ technology: (1) those items that will be available for an early Space Station of their own

accord; (2) those items that would be available for an early Space Station if pushed; and

(3) those items that would be available at a later time. A cost/benefit analysis of the

various technologies was also part of the study.

2.4.1 Approach

i The objective of this study was to define OMV workstation technology requirements in

c -_

order to (1) determine any open technology issues unique to Space Station, (2) identify

potential benefits and risks associated with the development and use of advanced

technology, and (3) develop an implementation plan for advancing those technologies.

The following paragraphs present the methodology used to define the workstation

C

r - configuration and required technology. Summarily, an operational scenario was developed and a functional analysis of the individual tasks was performed. From this analysis,

_ optimal solutions for task implementation in terms of workstation configuration were

determined. Technology identification and cost/benefit trades were then performed.

Prior to designing the workstation, we had to understand the functions that had to be

/ accomplished through the controls and displays (C& D) suite. An operational scenario was

developed for an OMV controlled from the Space Station and included checkout, launch,

rendezvous, docking, return and retrieval mission phases.

CThe scenario was then used as the basis for a functional analysis of the required tasks.

Through the functional analysis, we gained a solid understanding of what tasks needed to

be accomplished simultaneously and what information was required to accomplish the

tasks. Also, priorities were assigned to the data display requirements.

(J

61

0
D483-10012-1

.,

A literature review of past and current research on control and display technology and

implementation was conducted. The purpose of this review was to determine any

potential benefits or problems with the various technologies and their implementation

based on fellow researchers' experiences.

Two workstation configurations were then developed to satisfy the scenario functional

requirements and to provide for efficient operationsThe unique conditions of Space Station and the scope of hardware and software required

to implement the workstations led to some innovative technologies. These technologies

included flat panel displays, programmable switches, hand controllers, speech recognition, voice synthesis, and touch input devices. Various options within each technology

were evaluated and traded against compliance with Space Station needs.

2.4.2 Technical Discussion

The mission scenario defined the limit of operational tasks that would be considered and

the order of those tasks. The development of the scenario drove out potential

sequencing problems, manloading requirements and offered a preliminary look at the

i operational timeline. The development of the scenario was based on previous OMV

experience.

The scenario was limited to the control of one OMV on a rendezvous and docking mission,

including checkout, launch and retrieval upon return to Space Station. The mission

scenario was broken into phases as shown in Table 2.4-1. Below each major mission

phase heading are listed some of the tasks at the gross level for that phase. This initial

step in the scenario development served as the basis for further refinement in the

functional analysis.

A summary flow diagram of the completed scenario is shown in Figure 2.4-1. It is keyed

to the detailed listing of the functional analysis presented in Table 2.4-2. The numbers

in the bottom of the boxes correspond to the numbering system in the functional

analysis. The flow diagram provides an overview of the sequence of events while the

analysis provides the details of how the tasks are accomplished.

V DoD, NASA, and Boeing documentation was searched to locate related research topics.

62 
c

_ Table ?A-1. OMV Mission Scenario by Mission Phase

1.0 Prelaunch checkout (requires C&D and EVA operators)

(-

• Power-up OMV (C&D)

Check OMV subsystems using BIT through umbilical (C&D, EVA)

- Power, fuel, thrusters, video docking, apparatus, radar, communications,

computers, GN&C, etc.

( • Complete OMV visual inspection (EVA)

2.0 Move to launch position (requires C&D and EVA operators)

• Disconnect umbilical (EVA)

• Grapple with RMS (C&D)

t • Using RMS, move OMV to launch position (C&D)

l (*may want windows to check position*)

• Check thrusters if not done previously (C&D)

• Check any subsystem necessary (C&D)

- Nav program loaded into computer

I - Select manual control

• Complete power-up sequence (C&D)

(Radar, Star scanner, etc.)

3.0 Launch OMV (requires C&D operator)

• Fire GN Z thrusters to move away from Space Station TBD ft

- When at TBD ft switch to AUTONOMOUS CONTROL

- Set up subsystem monitoring configuration

(*may require two C&D operators to monitor functions*)

4.0 Rendezvous/dock/repairiretrieve (requires C&D operator)

For docking, repair and retrieving:

• Automatically stop at TBD ft from target spacecraft

• Select manual control, GNz RCS, cameras, lamps, range sensor, etc.

( - Locate target with cameras and focus, adjust aperture, etc.

• Close on target using GN Z RCS

— • Extend grapple fixture

• Dock with target and soft latch

• Complete hard latch

For repairing only:

/ • Extend Robotic arm, remove ORU from target and store on Free-Flyer

• Remove ORU replacement and position on target

• Stow arm

63

049L-007, ve 
D48310012 

1

Table 2.4-1. OMV Mission Scenario by Mission Phase (Concluded)

5.0 Return to Space Station (requires C&D operator)

Without target spacecraft attached:

• Unlatch from target spacecraft

• Use GN Z to back up from target

With tartlet spacecraft attached:

• Turn off cameras, lamps, range sensor, and associated equipment

• Turn on AV and MMH RCS

• Set in return course

• Reset to AUTOMONOUS CONTROL

• Stop at TBD ft from Space Station

• Turn on/off pertinent subsystems

• Switch to GNz RCS and manual control

• Maneuver to RMS pick-up point and stop

6.0 Berth Free-Flyer (requires C&D and EVA operators)

Without target spacecraft attached:

• Grapple using RMS (C&D)

• Power down, turn off propulsion (C&D)

• Using RMS, move into Containment Area (C&D)

• Place in position and connect umbilical (EVA)

• Download computers (C&D)

With target spacecraft attached:

• Unlatch OMV from target spacecraft (C&D)

• Grapple target spacecraft wtih RMS and move into Containment Area (C&D)

• Grapple OMV with RMS and move into Containment Area (C&D)

• Place in position and connect Umbilical (EVA)

• Download computers (C&D)

64

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...... 

-

Table 2.4-2. .JMV Mission Scenaflo Functional Analysis 

Mission Phase: 2.0 Move to launch Position 

Copilot Computer OMV 

Using hand 

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• 'RMS STOWED' 

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One of the most promising ideas in the literature for information presentation is the use

of pictorial formats. This concept relies on the use c: graphics and object representation

rather than columns and rows of numbers and characters to communicate information.

Various pieces of related data are integrated into a single format that is readily

comprehended by an operator. !n .nis way, the operator can make better use of

decision-making capabilities.

The use of voice both as a means of data input and output is another new promising area.

Voice input or voice recognition can be used for many of the same types of tasks that are

presently accomplished through a keyboard.

Based on the results of the functional analysis plus the research review and mission

scenario, two workstation configurations were designed. The configurations are shown in

Figure 2.4-2. The primary difference between the two configurations is the first has a

window for direct viewing of proximity operations and the second has no window using

indirect or remote vision only. The configurations served to define the number and type

of displays and controls, i.e., high resolution, full color graphics displays, 10-inch and

15-inch on the diagonal, are required.

For comparison purposes only, the somewhat outdated display information in Table 2.4-3

is provided. 'Vote that the display technology field has advanced significantly since this 

information was published.

Flat panel technology is being used in programmable switches in addition to being used

for displays. Light-emitting diode (LED), thin-film electroluminescent (TFEL) and liquid

crystal display (LCD) technologies are being incorporated into various switch housings

for this purpose. The most mature of these is the LED switch which is being developed

for bot'i military and commercial aircraft application.

Much research is being done in the area of speech recognition, spurred on by military and

commercial applications. The current systems are speaker-dependent and recognize

isolated or connected speech. The stored vocabulary size is less than 500 words with

approximately 50-75 words available at one time. Training the systems requires three to

four passes on each word. Speaker adaptation and identification is limited.

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Voice synthesis is much further advanced than speech recognition. Stored vocabularies

can be 10,000 words with some degree of inflection and intonation. Some systems use

digitized voice whereas others use phoneme-based speech. Some systems also allow a

choice of voice types.

The current technology of head-up displays has achieved a maximum horizontal field-ofview (FOV) of 30 0. The combining surface for such a FOV is usually 4-8 inches from the

operator's eyes. The operator must maintain their eyes in a fixed position in space in

order to view the entire display. These features are unacceptable for this workstation.

Real-time graphics and high-resolution dynamic imagery is feasible with current

technology and it is continually advancing. Potential areas of concern with current

technology include the size of the machine necessary to generate the displays and its

power, volume and weight specifications. However, until the display formats are at least

superficially defined, any estimate on machine capacity requirements would be unrealistic.

2.4.3 Technology Candidate Comparisons

Tables 2.4-4 and 2.4-5 describe the technology options that appear most premising and

evaluate them further based on a cost/benefit basis.

2.4.4 Conclusions and Recommendations

The conclusions for this study topic are summarized under paragraph 1.1.3 of the report

volume. Some issues discussed in this study area are recommended for further research.

,...

These issues include:

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o Establish the need for a window at the OMV workstation. If a need is established,

the requirements for the window need to be determined such as size and location 3t

the workstation as well as in the module.

0 o if a window is found to be required, a Head-Up Display for that window should be

developed. Again, the requirements for the HUD need to be determined such as 0 size, location at the workstation, presentation of sensor data, illumination and

transmissivity.

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o Development of display formats for vehicle control, system and subsystem information, caution and warning messages and other pertinent data presentation requirements.

C

o Refine the mission scenario and workstation design as required. The design

developed for this study was primarily a strawhorse to drive out technology

requiremen Ls.

o Determine the benefits of using a stereoscopic display of video or computergenerated imagery for the OMV and RMS control tasks. Select a suitable technology

for implementation. r

2.4.5 Technology Advancement Plans

Advancement plans have been prepared for three technologies related to controls and

displays for OMV, OTV and spacecraft servicing, flight operations and functional

operations from Space Station work stations. The first, is the development of a head-up

rdisplay device with a very wide field-of-view (600 ) to accommodate all operaror at an

OMV teleoperator control station. While there is a significant amount of effort be;ng

expended in the development of new display techniques, no effort to widen the field-ofview to this extent has been identified in industry or within government agencies. The

possible reason is a lack of specific requirement for a very wide FOV version. Typically

aerospace needs are satisfied by the side field of view configuration (30 0) such as the one

that has already flown in the Space Shuttle.

(^ f^ The next two plans cover the emerging technologies in liquid crystal displays. The first

is the development of large flat panel displays (8 inch diagonal) using LCD technology to

I 1 replace CRT screens. The second is the application of flat panel technology to a switch.

` A single switch would be used for many p urposes by p, -seramming its function and the

I label on the switch.

The requirements for and benefits of these technologies in an OMV teleoperations

workstations are discussed in detail in volume II of this report. The programs described

in Figures 2.4-3 thru 2.4-5 and Tables 2.4-6 thru 2.4-8 summarize the basic technology

planning information needed to capture those technologies needed for early evolutionary

versions of the Space Station. The detailed advancement planning discussion supporting

these summaries is provided in volume III of this final report.

89

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