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Final Report- Volume 11

Trade Study and Technology

Selection Terhnical Report

D483-10012-2

Spac Station

Systems Technology Stud

(Add-on Task)

(NASA-CE-171416) SPACE STATICN SYSTE14 S N85-25279

TECHNCLOGY STUDY (ALE-CN TISB). YOLU[1E 2.

TRADE STUDY AND IICHNCZCGY SBI.ICTION Filial

in,haical Seport (BCein9 AexcEpace Co., Unclas

Seattle, 6a:^h.) 181 E HC A09/MF AO1 G3/12 21188

®OE/N6

February, 1385 SPECTRA RESEARCH SYSTEMS (SRS)

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D483-10012-2

SPACE STATION SYSTEMS TECHNOLOGY STUDY

' (Add-on Task)

Final Report

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VOLUME Q

TRADE STUDY AND TECHNOLOGY SELECTION,

TECHNICAL REPORT

D483-10012-2

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Conducted for NASA Marshall Space Flight Center

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3* Under Contract Number NAS8-34893

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February 1985

Boeing Aerospace Company

Spectra Research Systems :k

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D483-10012-2

FOREWORD

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

was initiated in ?une 1984 and to be completed in February 1985. The study was con-

`'" ducted for the National Aeronautics and Space Administration, Marshall Space Flight

I;

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

.m

D483-10012-1 Vol. I Executive Summary

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

4k

Report

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

^y

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

R} 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.

11
Technology Category

Autonomous Functional

Control

Attitude Control

Free Flier Controls

and Displays

Test Planning (SRS)

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H. E. Brown D. P Meyer

O. Bakken

P. D. Nacaise M. H. Bantell

F. Roe J. Qualy-White

R. Bradford,

Management

J. Cody

S. Montgomery

iii

D483-10012-2

KEY TEAM MEMBERS

Subject MSFC-Management Team Contractor Team

Study Manager R. F. Nixon R. L. Olson
D483-10012-2 A

TABLE OF CONTENTS

VOLUME 11

Page

1.0 INTRODUCTION 1

2.0 AUTONOMOUS FUNCTIONAL CONTROL 5

2.1 Introduction 5

2.2 Approach 5

2.3 Technical Discussion 12

2.4 Summary of Trade S,!udy Comparisons and Technology Selection 67

2.5 Conclusions 75

2.6 Recommendations 77

2.7 References 77

3.0 ATTITU'DE CONTROL IMPACT FROM STRUCTURAL DYNAMIC MOTIONS 78

3.1 Introduction 78

3.2 Approach 79

3.3 Technical Discussion 86

3.4 Summary of Results 117

3.5 Conclusions 119

3.6 Recommendations 119

3.7 References 119

4.0 CONTROLS AND DISPLAYS FOR OMV, OTV, AND SPACECRAFT SERVICING,

FLIGHT OPERATIONS AND FUNCTIONAL OPERATION 120

4.1 Introduction 120

4.2 Approach 120

4.3 Technical Discussion 127

4.4 Summary of Results 167

4.5 Conclusions 167

4.6 Recommendations 168

4.7 References 169

iv
27

28

29

30

31

32

38

44

54

55

59

80

80

88

91

91

93

v,

D483-10012-2

L IST OF FIGURES

Program Schedule 3

Prioritized rechnology Advancement Candidates 4

Basic NASA Space Station Requirements 8

Typical Guidance, Navigation and Control 13/14

Typical Space Station EPS Configuration 15

Power '?neration 16

Energy Storage 18

Space Station Electrical Power Distribution 20

Space Station Electrical Power Conditioning 24

Page

Typical Communication Subsystem Links

Typical Communication Subsystem Controller

Typical Data Management Subsystem Network Operating System

Typical Network Interface Unit

Typical Pumped Two-Phase Heat Transport System

Architecture for Subsystem Management

The Automated Decision Makers

Flow Chart for Integrating Controller Functions

VM System Configuration (from Reference 1)

Potential IC System Configuration

Reorganized IC Functional Flow

Definition of Symmetric/Anti-Symmetric Bending

Balanced Array Concept Astronaut Deployment for NASTRAN Analysis

Loads and Motions with Collocated Linear Controllers

Disturbance Model for Craw Activity

Crew Motion I rce and Torque Profile

Preferred Berthing Configuration for Orbiter and Disturbance Impulse

Station Acceleration Response with CMG Controller, Crew Motion Profile

Input, Servos Locked

Appendakr 1esponse to Crew Motion Profile

Orbiter Docking Impact at BS A, 1501, No Attitude Control

Orbiter Docking Impact at BS C, CMG Control with/without Gimbal

Rate Limit

v

No.

a.c-1

1.0-2

2.2-1

2.3-1

2.3-2

2.3-3

2.3-4

2.3-5

2.3-6

2.3 -7

2.3-8

2.3-9

2.3-10

2.3-11

2.3-12

2.3-13

2.3-14

2.3-15

2.3-16

2.3-17

3.1-1

3.2-1

3.3-1

3.3-2

3.3-3

3.3-4

3.3-5

3.3-6

3.3-7

3.3-8
3.3-10

3.3-11

3.3-12

3.3-13

3.3-14

3.3-15

3.3-16

3.3-17

3.3-18

3.3-19

3.3-20

3.3-21

3.3-22

4.2-1

4.2-2

4.2-3

4.2-4

4.2-5

4.3-1

4.3-2

4.3-3

4.3-4

D483-10012-2

LIST OF FIGURFS (continued)

rsional Vibration Suppression Performance with CMG and Root or

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

Performance Curves for a Tip Mounted Torsional Damper

Torsional Vibration Suppression Performance with CMG's,

Collocated Suntrack/Tilt Actuators

Comparison of Appendage Response with CMG and Suntrack/Tilt

Actuators

Comparison of Appendage Response with CMG and Suntrack/Tilt

Actuators

Control Response of SERVO Torquers

Appendage Response with CMG and Servo Controilers Crew Motion

Profile Input

Station Response with CMG and Servo Controllers Crew Motion

Profile Input

Application of Eigenstructure Placement to Space Station

Attitude Control, Absolute Positioning

RCS (Resisto Jet) Control of Symmetric Bending Modes Response

to 1000 N-M-sec Torque in Pitch

Waffle Grid Solar Panel Structure

Appendage Response Comparison of SEPS with Waffle Grid Array CMG

Controller, Panel Drive Actuators Locked (arc-sec)

Study Methodology Flow

OMV Simulation Workstation

757/767 Front Instrument Panel

Bl-B Aft Control Station

"Pictorial Format Display" Front Instrument Panel

Mission Scenario Overview

Conceptual Workstation Configurations

Multifunction Display Format Examples

Commercial Aircraft Head-up Display for Landing

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44

Page

99

100

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C 1

116 ^^ )

121 ._.

123

124

125

126 .

131

i 50

152

156

102

103

103

105

106

107

108

109

110

112

116

Y1
WTI 7144777,11,7

D180-27935-21

IC

LIST OF TABLES

p

No. Page

2.2-1 List of Integrating Controller Functions 9

2.2-2 Technology Trade Study Comparison Criteria I I

J

2.3-1 Power Generation Autonomy Factors 17

2.3-2 Energy Storage Autonomy Factors 19

2.3-3 Display do Control Fa^.-tors for EP. S Distribution 21

2.3-4

2.3-5

Power Distribution Autonomy Factors

for

22

Display do Control Factors EPS Conditioning 25

2.3-6 Power Conditioning Autonomy Factors 26

2.3-7 Subsystem Modes 34

2.3-8 Subsystem Reconfigurations 35

2.3-9 Subsystem State Change Factors 36

7 2.3-10 Integrating Controller Software Sizing and Timing 49

2.3-11

2.3-12

Integrating Controller Data Flow 50

Comparison of VM and IC Configurations 53

2.3-13 Analogies Between VM and IC Functions 57

2.3-14 Correspondence Between VM and IC Functions 58

2.4-1 Integrating Controller Benefits Estimate 72

2.4-2 Technology Advancement Cost Estimates 73

2.4-3 Benefits/Cost Ratios 74

2.4-4 Prioritized Technology Candidates 75

3.2-1 Flexible Element Section and Material Properties for Space

* Station 82

3.2-2 Mass Properties of Space Station 83

3.3-1 Linear Controller Identification with Sensor and Actuator

Specification/Location 89

3.3-2 Idealized Impulse Imparted from Orbiter Berthing 89

4.3-1 L'IV Mission Scenario by Mission Phase 128/129

4.3-2 OMV Mission Scenario Functional Analysis 132-147

4.3-3 Display Technology Comparison 158

4.3-4 Qualitative Cost/Benefits of Technology 162

4.3-5 Quantitative Costs/Benefits/Risks of Technology 163/164

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vii
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D483-10012-2

LIST OF ACRONYMS AND ABBREVIATIONS

ACCEL remote body station 1501

ACOR body station 100

ACS attitude control subsystem

AFB Air Force Base

Al artificial intelligence

APSTS Advanced Platform System Technology Study

BAC Boeing Aerospace Company

BIT built In test

BITE built in test equipment

C&D controls and displays

,I

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 l

GN2

a

nitrogren gas r

CO2 carbon dioxide

CP co-pilot

CPU central processor unit

CRT cathode ray tube

DARPA Defense Advanced Research Projects Administration

do/ac direct current/alternating current

DEC Daital Equipment Company

deg/sec degrees per second

DMS data management subsystem

DoD Department of Defense

EASY Engineering Analysis System

I

EC/LSS Environmental Control/Life Support Subsystem

EL Electroluminescent

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D483-10012-2

EPS Electrical Power Subsystem

EVA extra vehicular activity

FO fiber optics

FF Free Flyer

ft feet

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r 1 GL/EF glass/epoxy

GN&C guidance, navigation and control

G R/EP graphite/expoxy

GPS global positioning system

GSTDN Ground Station Tracking Data Network

HR hour

H2O water

HUD head up display

Hz Hertz (a measure of frequency)

IAC integrated analysis capability

IC integrating controller

1. D. inside diameter

IEEE Institute of Electrical and Electronic Engineers

INDA interface from NASTRAN dynamics analyzer

INTF interface

1/0 input/output

IOC initial operational capability

JSC Johnson Space Center

KG kilograms

KW kilowatts

lb pounds

lbm pounds-mass

LCD liquid crystal display

LED light emitting diode

ix
tv

D493-10012-2

LIOH lithium hydroxide

LISP list processor

LR line replacea'ule

MACLISP Macro Lisp

MBPS million bits per second

MCR Martin Company Report

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 Natirr; Al Aeronautics and Space Administration

NASTRAN NASA Structure Analyzer

NIU network interface unit

n-m-sec Newton-meter-seconds

ns nanoseconds (10-9 seconds)

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 payload

PRLCH prelaunch

PSI pounds per square inch

Psia pounds per square inch absolute

X
D483-10012-2

COT,

Psid pounds per square inch differential

Pwr power

QWERTP 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 radiofrequency

RI name of expert system to configure VAX installations

RMS remote manipulator system

R/T receiver-transmitter

SAR synthetic aperture radar

Sec second

SEPS solar electric propulsion spacecraft

SOA state of art

S/C spacecraft

SRI Stanford Research Institute

SRS Spectra Research Systems

TBD to be determined

TDMA time division multiple access

TDRSS tracking and data relay satellite system

TFEL thin-film electro luminescent

TI Texas Instruments

TVC thrust vector control

VAX virtual 96dress extension

VHSIC very nigh speed integrated circuit

VLSI very large scale integration

VM ventilator manager

XCVR transceiver

-i

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xi
D483-10012-2

1.0 INTRODUCTION

This is volume II of the final report on the Space Station Systems Technology Study add

on task conducted for the Marshall Space Flight Center (MSFC) by the Boeing, A'arospace

Company (BAC) and Spectra. Research Systems (SRS). The overall study objcv`slive continues to be to identify, quantify, and justify the advancement of high-leverage technologies for application primarily to the Early space station. The objective has been

addressed through a systematic approach tailored to each of the technology areas

studied. This volume presents the results of the technical effort. Volume III discusses

the research plans developed for each of the selected high-leverage technologies.

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

the Advanced Platform Systems Technology Study (APSTS) that was completed in April

1983 and the subsequent Space Station System Technology Study completed. in April 1984

for MSFC by the Boeing/SRS team. The first APSTS proceeded from the identification

of 106 technology topics to the selection of five for detailed trade studies. During the

advanced platform study, the technical issues and options were evaluated through

u,-called trade processes. Individual consideration was given to costs and benefits for the

technologies identified for advancement, and advancement plans were developed. An

approach similar to that was used in the subsequent study, with emphasis on system

definition in four specific technology areas to facilitate a more in-depth analysis of

technology issues. The results of the initial study are reported in Boeing document

D180-27487 and the subsequent study was reported in 1;:;80-27935.

The current add-on task continued investigation of two of the areas considered in the

previous studies and added a new area for free flier controls and displays. The two areas

that were continued were autonomous functional control which was an outgrowth of the

integration of automated housekeeping considered previously and Space Station attitude

control. The principal extension in the autonomous functional control area was to consider integration of three new subsystems (attitude control, communications, and data

management) and to drive toward a more specific definition of requirements on the

integrating controller. The attitude control area was extended to use the simulation

tools developed in the previous studies to take a look at combined disturbances and to

investigate passive 

he

techniques. The topics of discussion in thi: report volume

include the planned approach, technical discussion, summary of results, conclusions, and

recommendations for each of the three study areas.

1

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D483-10012-2

2

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

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

describe 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 advancement items was made during this latter

tusk. Technology advancement plans were prepared for each of the selected items in

m task 3. The overall study schedule is shown in figure 1.0-1.

I 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. Figure 1.0-2 gives a prioritized listing of the twelve candidates 1de7':cied. The attitude control analysis did not prod-.'.,_'e candidates for technology

I

advancement because the simulation results indicated that available control techniques

were acaquate.

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This volume presents the technical work performed to select these high-leverage items.

The total final report is made up of thh volume, Volume I: Executive Summary, and

Volume III: Technology Advancement Program Plan.
0483-10012-2

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I

Months after ATP

Study tasks 1 2 3 4 5 6 7 8

Major milestones

Orientaticn

review

Midterm review V Final review

Draft final

I re ort

Y 1

Final repori delivery

Task 1-Trade Studies

Autonomous control

Attitude control

Control and displays

I

Task 2-Technology Selection

Trade comparisons rr^

Prioritize and select technologies

Task 3-Technology Definition

Review and establish phasing

Prepare plan

Orientation briefing

Monthly progress reports

Midterm briefing

Final briefing

Final report

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Figure 1.0. 1. Program Schedule

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D483-10012-2

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Candidates Schedule

pressure

General

usefulness

Benefits/cost

Expert systems to conventional S/W 1 2 3

Real time expert systems 4 1 2

Developing effective models 2 5 4

voice recognition and synthesis 9 3 1

Graphics generator 7 4 6

Flat panel 3 7 10

Advanced knowledge engineering 8 0 7

Programmable switch 10 9 5

inputdevices 11 6 8

Head up displays 5 11 11

Space qualified LISP machine 6 12 12

Hand controller 12 10 9

Figure 1.0-2. Prioritized Technology Advancement Candidates
F

,

D483-10012-2

2.0 AUTONOMOUS FUNCTIONAL CONTROL

This section presents the results of an add-on study conducted to further ch?r2'7terize a

system for integrating the automation of the subsystems on an inhabited space station.

It goes beyond the previous Space Station System Technology Study in order to further

identify high leverage technologies.

2.1 INTRODUCTION

In the pr eeviuus technology studies, an integrating controller for automated housekeeping

subsystems was 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.

The following paragraphs report on the approach, results, conclusions, and recommendations resulting from this characterization study and also provide a technical discussion of

the study elements.

2.2 APPROACH

2. 1.1 Task 1 -Trade Study Approach

The following paragraphs describe the nine sub-tasks which make up the trade study task

of this add-on study of autonomous functional control for the Space Station.

5
4

0483-10012-2

2.2.1.1 Describe the Subsystems to be Integrated

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

phase of the study and that consideration was based primarily on generic subsystem

descriptions. In the time since the start of that previous study phase, the Space Station

Concept Development Group (CDG) has defined alternate space station configurations as

well as an additional understanding of space station subsystem functions. The integrating controller functional definitions which were a result of the previous study phase indicated that the process should appropriately 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 is considered: guidance and control, electrical

power, communications, thermal control and data management, were described. The

descriptions were based on Space Station subsystem information available, from results

of previously completed Space Station configuration studies, and from experience held by

subsystem engineers who were interviewed.

2.2.1.2 Define Subsystem Functions

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

where the control parameters are sensed. These functions were based on the descriptions developed in the previous sub-task and on updates of the lists developed in the pre-

, vious study phase for electrical power and thermal control. The listing also included new

functions and sensed quantities for elements to be automated in the guidance and

control, communications and data management subsystems. Emphasis was placed on

identifying subsystem state controlling functions rather than the individual closed loop

r

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 functions requires integration with respect to other

entities on the Space Station. Controller development is concerned with integration of

these entities.

6

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2.2.1.3 Identify Where Integrating Control of Subsystem Functions is Appropriate

Once the subsystem function and sensed quantity lists had been developed, a systems

analysis review was conducted. This review identified where interac is 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.

2.2.1.4 Define Integrating Controller Functions

s

The factors identified in the previous sub-task were reviewed to characterize functions

to be performed by an integrating controller. The result of the review was a description

of the functions needed to integrate each of the subsystems with the rest of the Space

aW Station, and a description of those functions which are common to more than one

subsystem and therefore are candidates for implementation through common processing

by an integrating controller. The Space Station system requirements for autonomy and

for automation served as a guide for defining these functions. Figure 2.2-1 lists those

requirements.

2.2.1.5 Compare Integrating egrating Controller Functional Definitions with those from the

Previous Study Phase

P

;. Six functions were identified for an integrating controller in the previously conducted

study phase (see table 2.2-1 for list). It was desirable to build on those definitions as

much as possible in this add-on study. For that reason, a comparison at some detail was

made between the functions defined in this study and the descriptions developed and

reported for the last study phase.

2.2.1.6 Diagram New or Changed Integrating Controller Functions

y 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.
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D483-10012-2

Table 2.2-1. List of Integrating Controller Functions

• Startup integration

• Electrical power load management

• Inter-subsystem redundant path selection

• Maintenance schedule management

• Materials transfer management

• Inter-subsystem failure isolation

All of the sub-tasks described to this point have been performed to characterize the

integrating controller system. The processes are similar to those used in the previous

study but the subject subsystems are different. These sub-tasks constitute, at most, i/3

of the total trade study effort for autonomous functional control.

2.2.1.7 Determine Implementation of Diagrammed Steps for the Integrating Controller

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.

These implementation descriptions were supported by diagrams where appropriate. As

the implementations were described, they were also categorized so that types of software and devices were identified and isolated for needed technology advancements. This

► sub-task constituted about 1/3 of the trade study effort for autonomous functional

control study. In conducting this sub-task, support from data processing and software

technology personnel was utilized.

a 2.2.1.8 Prepare Preliminary Functional Requirements for an Integrating Controller for

Automated Subsystems of the Space Station

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,

9

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D483-10012-2 )

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

Space Station system.

2.2.1.9 Identification of Technology Needs/Benefits

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

information provided by the functional diagrams, implementation definitions and the

functional requirements. Once these technology needs had been identified, trades were

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

developmental cost expenditures.

2.2.2 Task 2—Trade Study ComFsrison/Technology Selection Approach

The technology candidates identified by the trades for autonomous functional control

were compared and evaluated on the basis of performance, mass, technology advancement, cost, risk, schedule, operations simplification, safety improvements, increased

lifetime, and other appropriate criteria in order to select and rank the technology candidates against those from the other study areas. This comparison produced a crosstechnical area evaluation of the selected technologies.

f"

The following paragraphs describe the sub-tasks of the comparison/technology selection

tasks for this add-on study.

2.2.2.1 Compare Trade Study Results

The technology candidate selections resulting from the task 1 trade studies were compared and evaluated on the basis of appropriate criteria in task 2. Table 2.2-2 gives a

listing of criteria which have been developed in the previous phases of the Advanced

Platform Systems Technology Study and which served as a guide for comparison criteria

for this add-on study phase.

2.2.2.2 Prioritize Technology Advancement Candidates

Using the results of the comparisons, the candidates were ranked according to each of

the 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 which had been

identified by the task 1 trades.

10
11

r

Table 2.2-2. Technology Trade Study Comparison Criteria

The following listing of criteria will be used to evaluate the technology advancement

topics identified in each technology area:

1. Does the identified technology topic require development?

a. What is current level of development?

b. Is technology area already being developed?

c. Has the technology been developed to a point where it is operationally usable

on space stations?

2. Is the identified technology required to support development of current space

station concepts or evolutions from those concepts or is it only enhancing

technology?

3. Does the envisioned advancement of technology produce a benefit to the space

station concept in any of the following areas:

a. Does the technology advancement facilitate a reduction in the cost of

producing, launching, or operating the space station?

b. Does the technology advancement extend the operational lifetime of the space

station?

c. Does the technology advancement facilitate a necessary operational aspect of

the space station or does it simplify operation?

d. Does the technology advancement reduce the mass of the space station or of

the ASE required to deliver the space station components to orbit?

e. Does the technology advancement reduce the volume of the space station

components for transport to orbit, i.e., does it allow for more efficient packing

of the space station., components in the shuttle bay?

f. Does the technology advancement facilitate repair and/or maintenance of

space station elements on nrbit?

g. Does the technology advancement facilitate a necessary performance aspect of

the space station such as poi nting accuracy for science appendages or

antennas; orbit adjust capability, communications or tracking capability,

power generation, or thermal control ?

h. Does the technology advancement improve the safety or comfort of human

habitation of a manned space station?

i. Does the technology advancement facilitate evolutionary expansion of the

space station on orbit?

j. Does the technology advancement facilitate development of future space

station use concepts and configurations?

4. Is the technology advancement possible in the time frame of the envisioned large

space station usage (between now and the mid-1990's)?

006L-022
it

r _

12

D483-10012-2

2.3 TECHNICAL

This section presents in a detailed discussion of the study outputs along with the associated data and conceptual illustrations. The output discussion given by the following

paragraphs is structured according to the sequence of the approach subtasks.

2.3.1 Subsystem Descriptions

The subsystem descriptions for the five subsystems considered for autonomous functional

control wee obtained by interviewing the a ppropriate Space Station and engineering

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

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

control were not for the internal operations of the subsystem but rather were for the

states that the subsystem would assume as they performed their functions.

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Figure 2.3-1 shows a typical Space Station guidance, navigation and control subsystem:

primary functions are shown on the left, simple flow diagrams are shown in the middle,

and typical displays to the crew and controls interactions are shown on the right. This n i

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

significant state control is needed. ^, r

The electrical power subsystem consists of elements for power generation, power transmission, energy storage, power distribution, and power conditioning. Figure 2.3-2 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. Figure 2.3-3

shows a flow diagram and a listing of display and controls factors for the power generation function of the EPS. Table 2.3-1 lists factors which require integrating control in

order to provide autonomous operation of the power generation elements. Figure 2.3-4

gives a flow diagram and a display and control factor listing for EPS energy storage and

Table 2.3-2 lists the associated factors for autonomous control. Figure 2.3-5 shows a

flow diagram for a power distribution system for Space Station and Table 2.3-3 lists the

display and control elements. Table 2.3-4 lists factors needing integration control to
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Table 2.3-2. Energy Storage Autonomy Factors

• Schedule and perform

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Table2.34. Power Distribution Autonomy Factors

• Load switching (scheduled loads management)

• Reconfigure network to match load demand (energy balance)

• Perform periodic system test (BITE) to measure performance

• Redundancy management to detect and isolate faults or failed equipment and

reconfigure alternate interconnection

• Trend analysis of power distribution for load scheduling

• Projection of load trends for power management and growth planning

• Update power availability based upon power distribution planning and circuit

availability

22
23

GD483-10012-2

support automation of the EPS power distribution function. Figure 2.3-6 shows a power

conditioning system flow diagram -and Tables 2.3-5 and 2.3-6 give control and display

factor and autonomy factor listings for the power conditioning element of the E'PS.

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

links. Figure 2.3-7 shows a typical link diagram for Space Station communications.

Automation of the controller for the communications subsystem will need to consider

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

command processing control. Figure 2.3-8 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 r_alled the network operating system which is resident

in the DMS processors. Figure 2.3-9 shows interfaces considered by a network operating

system. The distributed controllers for the DMS are described by the network interface

- units. Figure 2.3-10 shows functional partitioning for a typical network interface unit.

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 easy to 4k P

overlook the need for DMS control to be considered as a subsystem management

! T

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

^^ r integrated just as they are for other subsystems.

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

2.3-11 shows a flow diagram for a typical thermal control subsystem element the space

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

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

integrating controller.

IP

2.3.2 Subsystem Functions to be Automated

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Before an analysis of subsystem functions for automation can be conducted, it is

id necessary to describe the candidate architecture for integrating control. Figure 2.3-12

n

shows a typical controller architecture for the Space Station indicating subsystem

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Table 2.3-6. Power Conditioning Autonomy Factors

• Circuit adjustment to change bias, correct out-of-tolerance or reprogram power

conditioning

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• Redundancy management to detect and isolate faults or failed equipment and

reconfigure to alternate conditioning units

• Trend analysis of conditioned power quality for maintenance scheduling

• Projection of conditioned power quality with time or predictable events

• Update conditioned power availability based upon performance and maintenance

schedule

26

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controllers, module integrating controllers and Space Station level integrating control.

It is desirable for reasons of reliability, commonality, system +olution and conservation

of data flow to adopt a distributed architecture philosophy for Space Station data

management. The use of integrating cunt. ollers at the module and Space Station level

indicate that functionally at least there will be 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 hierarchal character of integrating

control for subsystem management led to a focusing on commonality within subsystem

operational functions. This came about because the principle function of the integrating

controller would be to handle the common aspects of overall Space Station mode and

operations control at the interfaces between subsystems. Tables 2.3-7, 2.3-8 and 2.3-9

list typical subsystem modes, subsystem reconfigurations, and subsystem 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 and

subsystem states.

2.3.3 Identification of Needs for an Integrating Control

Because the Space Station will operate with limited resources over a long period of time

and serve a wide and changing variety of missions, predetermined operations of the subsystems are not possible. If the on-board crew were tasked to manage all of the modes,

reconfigurations and state changes for the subsystems, it is unlikely that they would have

time to support Space Station operations or missions. It is therefore necessary that a

high level of machine autonomy for subsystem management be included in the Space

Station System requirements.

S

In addition to providing automated subsystem management functions, the integrating

controller will be needed to provide the automated decision makers and trend analyzers

necessary to support automation and robotics for other applications on the S pace Station

such as space manufacturing, space construction, satellite servicing, and external space

station maintenance.

r 33

I

r.
D483-10012-2

TABLE 2.3-7 SUBSYSTEM MODES

GUIDANCE, NAVIGATION AND CONTROL

• Attitude hold

• Attitude slew

• Attitude control with orbiter docked

• GMG wheel desaturation

• TVC for orbit trim thrusting

• Acquisition and start up

• Off

• Reconfiguration

ELECTRICAL POWER

• Sunlight normal

• Darkside normal

• Battery reconditioning

• Solar array degradation

• Reconfiguration

• Off

COMMUNICATIONS

• Direct with other spacecraft

• With other spacecraft via TDRSS

• Tracking

• Downlink via TDRSS

• Downlink via GSTDN

• Downlink to user ground station

• Unencrypted (not TOC)

• Reconfiguration

• Off

DATA MANAGEMENT

• Normal (full service)

• Reduced service

o Data dumping to archival memory

• Reconfiguration

• Off

THERMAL MANAGEMENT

• Normal

• Reduced

• Reconfiguration

• Off

34

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TABLE 2.3-8 SUBSYSTEM RECONFIGURATIONS

GUIDANCE, NAVIGATION AND CONTROL

• Thrusters in use

• Allocation of control signal to controllers

• Redundant paths

• Alternate paths

• Sensors in use

ELECTRICAL POWER

• Batteries in use

• Solar array sections in use

• Redundant paths

• Alternate paths

• Power busses in use

COMMUNICATIONS

• Antennas in use

• Redundant paths

• Alternate paths

DATA MANAGEMENT

• Gateway devices engaged

• Redundant paths

• Alternate paths

THERMAL MANAGEMENT

• Radiators in use

• Thermal busses in use

• Pumps in use

• Heat exchanger, in use

• Redundant paths

• Alternate paths

.. .

35
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TABLE 2.3-9 SUBSYSTEM STATE CHANGE FACTORS

GUIDANCE, NAVIGATION AND CONTROL

• Slew rate

• Dead band size

• Identification of principle axes

• System gains

• Wheel desaturations interval

• Wheel denaturation rate

• Wheel desaturation controller gains

• Storage of RCS propellant

• Maintenance schedule

• Failure modes/anomalies

ELECTRICAL POWER

• Load management

• Power source management

• Energy 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/anomalies

DATA MANAGEMENT

• Data rates

• Computer operation rates

• Data stored

• Maintenance schedule

• Failure modes/anomalies

THERMAL MANAGEMENT

• Temperatures

• AT's

• Light/darkside passage

• Maintenance schedule

• Failure mode/anomalies

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D483-10012-2

2.3.4 Definition of Integrating Controller Functions

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Because there is a large volume of data associated with the subsystem management,

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 philosophy of 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. When a subsystem controller

detects a change such as a failure condition, the integrating controller will be advised,

and the overall situation is then examined by the integrating controller so that directions

are given back to the subsystems. Figure 2.3-13 illustrates an example of the, automated

decision making 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 requ•.sted. 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, yaw and roll attitude. The integrating controller checks the status of Space

Station subsystems and mission operations and determines that experiment #16 cannot

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 scheduling an operation on the Space Station which changes

for some unforeseen reason. Again, the integrating controller will be informed and that

function causes directions to be issued to subsystem controllers. The outputs that an

integrating controller would provide to subsystem controllers would be directions to

change control elements within the subsystem controllers. The following is a 1A of

typical status elements that the integrating controller will direct a subsystem controller

to change.

• Prioritization lists

• Scheduling
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• Operating constraints

• 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.

2.3.4.1 Prioritlzation Lists

These are ordered lists of characteristics which will identify which reconfiguration, out

of several possible, the subsystem will execute if a particular anomalous or a deficient

condition is sensed by the subsystem controller.

2.3.4.1.1 Example of Priorities in Use

The EPS subsystem controller senses a rapid decrease in battery charge state. It needs

to reduce load on the system so it opens the switch to the !owest priority load. If the

,- problem still exists the EPS controller opens switch tc next highest priority load, etc.,

3 until the problem is resolved. In addition to opening load switches to low priority loads

the EPS controller conducts internal fault analysis on the battery and finds that the

battery is shorted intermittently. The Controller removes the battery from services and

notifies the IC of the degraded condition.

The IC adjusts the EPS controllers priorities list to indicate that the second priority load

which had been switched off is moved to fifth from bottom in priority. The EPS

controller responds by shutting down the former third in priority load and reinstates the

former second which is now the fifth. If excessive power drains still exist the EPS

controller shuts down the next higher priority load to solve the problem.

The IC alerts astronauts that battery maintenance is required and adjusts the mission and

operations schedules to delay high power use events until after the maintenance. The IC

gives advisories to astronauts on lower power use mode which is then in effect.

t

39
D483-10012-2

2.3.4.1.2 Typical Space Station Items to be Prioritized

The following is a list of typical items to be prioritized within Space Station subsystem

controllers.

• Users of power

• Locations of cold plates

• Locations of cabin air heaters

• Locations of cabin air supply points _.

• Locations of cabin potable water supply points

• Venting locations around Space Station

• Locations of data storage devices

• Storage locations for various substances

2.3.4.2 Schedules }

These are schedules of specific reference point settings, mode shifts, or reconfigurations

anticipated for the subsystems over a particular period of time. The operation of the j

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various subsystems shall be in accordance with schedules applying to each of them which ) 3

is in concert with the overall master schedule of the Space Station. The IC will adjust

schedules in response to anomalies on the Space Station or in response to new schedules

for outside events which may be input by the astronauts.

1 '

2.3.4.2.1 Example of Schedules in Use

Attitude Control (ACS) receives a change in the pointing schedule from the IC to support

needs of earth viewing experiments. ACS controller adjusts the dead band size references in accordance with th(: new schedule, computes a change in the CMG saturation j

rate and schedules a new time for wheel desaturation activities. The ACS controller

then relays this changed schedule to IC which determines that the new schedule for

denaturation is incompatible with the available power since it would be during a darkside

passage. The IC sends an adjustment in wheel desaturation schedule to the ACS —

controller which is the best fit between EPS power availability and ACS needs. The ACS

controller then adjusts the desaturation schedule accordingly.

40 — j!
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D48,1-10012-2

2.3.4.2.2 Typical items to be Scheduled

The following is a list of typical items to be scheduled within Space Station subsystem

controllers.

• Attitude pointing requirements versus time

• ACS wheel desaturation

• Orbit trim times

• TDRSS viewing times

• High/low data rates versus time

• ACS maintenance schedule

• Communication maintenance schedule

• Data storage versus transmission schedule

• DMS maintenance schedule

• Battery reconditioning schedule

• Solar array maintenance schedule

• EPS maintenance schedule

• Power user scheduling

• Thermal control user scheduling

• Thermal control maintenance scheduling

2.3.4.3 Constraints

These are standing orders which restrict or structure the operation of subsystems in

some manner while the constraints are in effect. The operational constraints include

particular ranges of reference points, holds on mode shifts, schedule constraints, or

reconfiguration restrictions.

2.3.4.3.1 Example of Constraints in Use

Life sciences experiments require that the temperature of the air in the life sciences

module be elevated by 150F for the next 6 hours (incubation period for a large number of

plants being tested). This puts a constraint on the configuration of thermal control

system air heaters and on priorities for power use as well as the set point for ai

ature in the life sciences module.

41
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D483-10012-2

Because of the extended period which goes through light and shadow, the constraint will

migrate to affect the power available to other systems and may require shut down of

certain functions. Constraints may also be applied to maintenance operations f,)r other

subsystems. An example would be, advancing maintenance which is connected with

reduced power usage while delaying maintenance which demwids greater power usage.

2.3.4.3.2 Typical Items of Constraint

The following is a list of typical items of constraint through Space Station subsystem

controllers.

• ACS pointing accuracy limitations

• ACS slew rate limitations

• ACS wheel saturation limitations

• Communication data_, rate limitations

• Data storage limitations

• Power availability limitations

• Voltage limitations

• Temperature limitations

• Heat removal limitations

• Mode limitations for any subsystem

• Configuration limitations for any subsystem

• Scheduling limitations for any subsystem

2.3.4.4 Emergency Commands by the Integrating Controller

Emergency commands would override all subsystems controllers in the event of predetermined life or mission threatening emergencies. The astronaut interaction would be

facilitated both as inputs and outputs. The inputs would include a complete manual

override of real time functions when selected by the astronauts. The ground mission

control interface would also include inputs and outputs to the integrating controller but

evolution of Space Station autonomy would have a goal of minimizing this.

42

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T.1483-10012-2

2.3.5 Comparison of Integrating Controller Functional definitions With Those From

PreVaus Study Phase

The functions defined for the integrating controller as a result of this study are different

from those of the last study in several respects. First, the expanded list of subsystems

motivated a more generic look at the functions performed. This resulted in the generalized priority, constraints and schedule functions. Secondly, the desire to consider a more

distributed overall function lead to the concept of embedding the controls for each subsystem in that particular subsystem's controller and having the changes in state control

parameters generated by the Integrating controller. This would give the integrating controller the management by exception role that was mentioned earlier. That role is

intended to keep the data transfer rates between controllers at a minimum. The third

variation is that the need to move toward requirements motivated a ste p-by-step look at

how an integrating controller might perform its generic functions. This has produced the

flow diagram described in the next paragraph.

2.3.6 Diagram New or Changed Integrating Controller Functions

Figure 2.3-14 gives a flow diagram to describe at a top lcvel those steps to perform integrating controller functions.

1. Infurmation 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.

2. A state and mode simulation will be run for ail 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.

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

consequences of letting the current situation continue or to predict 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 the predicted consequences of letting the current

situation continue. Unsatisfactory situatlon^ are identified by the integrating

! l

 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 subsystem 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 predetermired 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.

`i 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.

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

7* 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

45

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D483-10012-2 -

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

subsystem controllers.

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

schedule for retaining those directives will be determined.

2.17 Implementation of Integrating Controller Functions

Based on the flow diagram in Figure 2.3-14, the integrating controller can be partitioned

into seven primary software components. These are:

I/O Handler - This module collects and distributes aR of the data required by the

integrating controller. This includes subsystem data for the subsystem state

models, the Space Station prediction model and to the recording and trending

function. In addition, external changes from the ground controllers and the

astronaut are provided to the Space Station need model and the recording and

trending function. It also distributes change information to the subsystems and

reports status to the ground controllers and astronauts as appropriate. j

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Subsystem Models - These modules, one for each subsystem, are independent,

discrete time , discrete state models. However-, the attitude control, electrical

power and thermal management subsystems may incorporate some continuous state

simulation elements ac part of the models. These modules operate on each update

of subsystem data to construct a complete description of the current subsystem

states.

Space Station Prediction Model - These are also discrete time, fiscrete state

simulation modules. They operate faster than real time on subsystem data plus

data from ground controllers and astronauts, and also use trend analysis results

from the recording and trending functions. The results of these modules are

projections of subsystem and overall Space Station states resulting from hypothetical changes to subsystem priorities and schedules or constraints and also predic46
are -

Can the modules be developed?

Validity and verification of the models

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tions of future states when no changes are made. Expert system implementation

would be used to select the hypothetical chaftes for the predictors to model.

Change Monitor - This module examines the results of the modeling to determine

when an undesirable situation exists or when an undesirable situation is predicted.

The purpose of this examination is to determine when changes in subsystem

operation are required. It also identifies life threatening or mission threatening

situations which need to be handled as emergencies. It's expected that portions of

this module would be implemented as an expert system.

Emergency Handler - This module generates all commands to the subsystems and

necessary communications to the ground controllers and astronauts to respond to

emergency situations.

Change Handler - This module generates the necessary changes to subsystem

schedules, priorities and constraints in response to anomalies reported by the

subsystems or detected by the change monitor. It also processes changes generated

externally or as a result of the trend analysis. To optimize Space Station

operation, and select results of the hypothetical predictions, an expert system may

be used.

Recording and Trending - This module records system and subsystem data to

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maintain a historical record of operation and to perform trend analyses on data for

which changes may not be detected by the change monitor. These are important in

subsystems which are susceptible to longer term degradation. An expert system

may be used to assure efficient storage and retrieval of appropriate data.

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

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

of developing and implementing these items. Some of the factors to be considered
i

D483-10012-2

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 expert

systems. They may require separate processors, but may also be executed on the same

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 2.3.-10. 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

models. The timing column indicates demand for processor throughput (operation per

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

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

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

Another important factor in implementing the integrating controller on the data

management subsystem is the data flow required. Table 2.3-11 indicates, for the major

sources of data flow, the frequency and amount of data flow from the subsystems, from

external sources and to the subsystems. The only data item 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 items

needed for integrating controller operation.

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

models. The timing column indicates demand for processor throughput (operation per

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

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

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

Another important factor in implementing the integrating controller on the data

management subsystem is the data flow required. Table 2.3-11 indicates, for the major

sources of data flow, the frequency and amount of data flow from the subsystems, from

external sources and to the subsystems. The only data item 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 items

needed for integrating controller operation.

2.3.7.10 Feasibility Assessment for Expert Systems r

This section will consider the feasibility of applying expert system technology to the

r integrating controller concept described by Figure 2.3-14. This will be done by

preseni ng two separate high level designs for an expert integrating controller.

2.3.7.10.1 Ventilator Manager - Based Design

This section describes an expert integrating controller based on the design of Ventilator

Manager (VM), an existing e:;pert system described in Reference 1. As described in the

literature, VM helps clinicians at the Pacific Medical Center in San Francisco manage a

mechanical ventilator. The latter device provides total or partial breathing assistance to

patients who have undergone cardiac surgery.

2.3.7.10.1.1 Rationale for VM - Based Design

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VM was chosen as the basis for an Integrating Controller (IC) design for several reasons.

First, both VM and an IC involve interpretation of data over time. This contrasts with

most expert systems which are intended to havidle static rather than dynamic problems.

Static systems base their conclusions or actions on data available at one particular time.

51

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D483-10012-2

2.3.7.10 Feasibility Assessment for Expert Systems

This section will consider the feasibility of applying expert system technology to the

integrating controller concept described by Figure 2.3-14. This will be done by

presenting two separate high level designs for an expert integrating controller.

2.3.7.10.1 Ventilator Manager - Based Design

This section describes an expert integrating controller based on the design of Ventilator

Manager (VM), an existing expert system described in Reference 1. As described in the

literature, VM helps clinicians at the Pacific Medical Center in San Francisco manage a

mechanical ventilator. The latter device provides total or partial breathing assistance to

patients who have undergone cardiac surgery.

2.3.7.10.1.1 Rationale for VM - Based Design

VM was chosen as the basis for an integrating Controller (IC) design for several reasons.

First, both VM and an IC involve interpretation of data over time. This contrasts with

most expert systems which are intended to handle static rather than dynamic problems.

Static systems base their conclusions or actions on data available at one particular time.

Second, both involve the use of models to assist in the decision making progress. VM

incorporates a state transition model of the therapies provided by a mechanical

ventilator. The IC concept, as shown in Figure 2.3-14 involves models that permit

determination of the current as well as required states. In addition, both systems use the

models to generate expectations of future states. These expectations are compared with

the system state at subsequent times to determine if the system is behaving as desired.

Third, both systems involve physical configurations that are similar in their broad

outlines. This point is covered in greater detail in Paragraph 2.3.7.10.1.2.

Fourth, both systems involve similar functions. This point is covered in greater detail in

Paragraph 2.3.7.10.1.3.

52

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Despite the similarities, there are several apparent differences between VM and an IC.

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For example, VM does not perform an integration task. However, because the functions

of VN4 and an IC are similar, it is not clear that this is a crucial difference. In addition,

VM does not actually control the mechanical ventilator but makes suggestions to a

clinician. This does not appear to be due to technical limitations but because clinicianv

are unwilling to surrender control of the mechanical ventilator to VM.

2.3.7.10.1.2 System Configuration

Figure 2.3-15 shows the VM system configuration. This suggests the plausible IC system

configuration shown in Figure 2.3-16. Table 2.3-12 shows the correspondence between

the elements of the two configurations.

Table 2.3-12 Comparison of VM and IC Configurations

VM Element IC Element

Clinician Crew

Patient Space Station

Life Support Sub Systems

Monitoring Information Collection

VM IC

With the exception of data flows, the two configurations are quite similar. The data

flows are different because of the different requirements of the two systems. In the

case of VM, it is necessary that the clinician maintain total control of the system; hence,

VM acts as an assistant who makes suggestions. In the case of an IC, it is desired to

relieve the crew of the need to actively control the on-board subsystem; hence, an IC

acts as an assistant who is expected to perform subsystem control under the direction of

the crew.

The configuration proposed for an IC by Figure 2.3-16 contains one feature not explicitly

present in the IC concept of Figure 2.3-14. In particular, the crew is permitted to state

S,

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D483-10012-2

Life support

Therapy

Observations Interpretations

Patient — — — — — — Clinician Goals

Data

IMonitoring Data --10-1 VM

iigure2.3-15. VMSystem Configuration (from Reference 1)

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D483-10012-2

goals rather than Issue commands if they so desire. For example, the crew could state

that the goal of the day is to prepare for a shuttle rendezvous. The IC would then

translate this goal into specific priorities, schedules, and so forth. The crew would be

given the option of reviewing the latter. By permitting the crew to state what is to be

done (i.e., a goal) rather than how to do it, more time will be available for missionrelated activities. Because Al researchers have extensively studied the design of goaloriented systems, the use of Al techniques is particularly appropriate for the implementation of such systems.

4

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2.3.7.10.1.3 System Functions

VM and an IC have similar functions. Table 2.3-13 lists the VM functions given on Figure

2.3-15. In addition, this table lists the analogous functions for an IC. Table 2.3-14 shows

how the analogous IC functions correspond to the IC functions shown in Figure 2.3-14.

The correspondence shown in Table 2.3..14 is not clairned to be precise, but rather points

out similarities between VM and IC functions. For example, VM function a is clearly

quite similar in intent to IC function 4.

Besides pointing out the similarities between VM and IC functions, Table 2.3-14 suggests

another organization for the IC function flow diagram. Figure 2.3-17 shows this

organization. The following paragraphs describe each function on the new flow diagram

in greater detail.

1. This function corresponds to function 1 shown in Figure 2.3-14. In addition, mission

goals will be collected from the crew.

2. The information collected by the previous function will be validated. For example,

if a data item represents a sensor reading, it will be determined if the reading is

consistent with one likely to be given by a properly functioning sensor.

3. An overall system state estimate will be performed (situation assessment). Because

some of the input data may be invalid, this function must be capable of coping with

erroneous, incomplete, or missing data.

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4. Based on the current system situation as well as trends and mission goals, an

estimate will be made of the future state of the system.

5. The current state of the system will be compa . with previous estimates of what

the current state should be. This will permit detecL.: n of system anomalies as well

as routine adjustments required by subsystems.

6. Corrective actions will be determined for anomalies detected by functions 2, 3, and

5 above.

7. The actions selected by function 6 are performed.

8. Actions will be determined for normally occurring events such as scheduled

reprioritization.

9. The actions selected by function 8 are performed.

2.3.7.10.1.4 Summary of VM—Based Design

The preceding paragraphs have shown how the design of VM might be adapted to the

design of an IC., Since VM is an existing expert system, this provides strong evidence of

V,^e feasibility of applying expert system technology to the IC concept.

2.17.,10.2 Planning-Based Design

This section describes an expert IC based on Al work done in the area of planning. There

are several reasons for describing another design besides the VM-based design. First,

another but dissimilar design shows that it is feasible to apply expert system technology

to the IC concept. Second, the two designs have complimentary strengths and

weaknesses. For example, VM is very good at responding quickly to unexpected changes

in the system ,state whereas a planning-based approach is not. On the other hand, a

planning based approach is good at scheduling tasks, an issue VM largely ignores. Thus,

an actual IC design would probably combine aspects of both VM and planning. Finally, a

60

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0483-10012-2

planning-based approach is more directly applicable to the IC concept give by Figure

2.3-14,

2.3.7.10.2.1 Rationale for Planning-Based Design

In AI, "planning" is defined as finding a sequence of actions that achieves some goal.

Much of the early AT work in planning involved control of mobile robots. For example,

SRI developed a robot call Shakey which had a vision system. It could move about a

room and interact to r; limited extent with objects in the room. Shakey could be given a

goal such as "go to location (X,Y)". Using a planning process, Shakey would determine a

sequence of moves that would get it from its current location to the new location while

avoiding obstacles in the room.

The IC concept strongly suggests the applicability of planning. In particular, function 8

can be viewed as a planning process that determines how to get from the current state as

determined by function 2 to the goal state as projected by function 3.

2.3.7.10.2.2 Planning Issues

In this report, we will not go into as much design detail as we did in the case of the VIMbased design. This is because there are a wide variety of approaches to planning and

there is not sufficient time to do a trade study of the various approaches. A survey of AI

approaches to planning appears in Reference 2. We will, however, describe one of the

more salient issues in planning.

A planning-based system generally involves three components: a planner, a plan

executor, and a plan monitor. The purposes of the planner and the plan executor should

be self-evident. However, when planning is applied to a physical system such as a space

station, there is a distinct possibility that the results of executing the plan deviate from

the results expected by the planner. This may happen for a variety of reasons. For

example, a physical system might be slightly out of calibration. In addition, an

unexpected event may occur that invalidates the plan. The important point is that a plan

monitor is necessary to detect deviations from the plan and initiate corrective action.

61
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The IC concept does not explicitly incorporate a plan monitoring function. It is probably

desirable to do so.

2.3.7.10.2.3 Summary

Planning provides an alternate approach to designing an IC. It provides additional

evidence that it is feasible to apply Al to the IC concept. In addition, an actual IC

design would probably synthesize the VM-and planning-based approaches.

2.3.8 Requirements for an Integrating Controller on the Space Station

This section provides a preliminary listing of function requirements for an integrating

controller for the Space Station.

The integrating controller shall provide data outputs to subsystem controllers to update

priorities, constraints, and schedules based on integrating controller assessments of the

overall Space Station condition with respect to:

• Safety of the crew

• Survival of station subsystems

• Survival of mission

• Crew comfort

• Efficient operation of station

• Consistency of operations with schedules

The controller shall determine the updates to be supplied to subsystem controllers using

state change and performance change data from subsystem controllers as well as from

the operator system interface (OSI) and developed trend data. The determinations shall

be made and ulltlates provided once every TBD seconds and shall be addressed to the

appropriate subsystem controllers by the integrating controller.

The priorities updates shall include changes to the rank order of resource users which

may be considered for shut down in the event of supply shortages. These priorities shall

be organized to be consistent with Space Station resource supply categories.

62

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Constraints which are updated shall include items which are not allowed durin', the

may. : period of the constraint or, which are allowed only in a fashion which is limited to

normal operations. Updates shall include definition of the constraint and the duration of

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the constraint. Mode shifts or reconfigurations, as well as subsystem performance and

schedules, are examples of items which may be constrained.

Schedules which are updated shall include maintenance and mode shift schedules for the

subsystems. The integrating controller shall update those schedules based on the

integrated needs of the Space Station, its crew, its missions, and any anomalies which

exist. Updates shall include the definition of the schedule change the duration of the

change.

In the event that no update of priority, constraint or schedule is generated for a given

r iteration of the integrating controller, an output shall be issued to indicate no change to

the appropriate subsystem controllers.

r

The integrating controller shall assess the overall state of the Space Station for each

iteration and shall issue the above identified change commands to subsystem controllers

on the completion of each iteration.

The integrating controller shall determine if an emergency state exists on the Space

Station and shall issue commands to the subsystem controllers and to an on -board alarm

system.

To determine if an emergency state exists on the Space Station, the integrating

controller shall use subsystem state inputs, astronaut inputs, direct sensor input data,

and trend data as well as outputs from state and predictor simulations.

101 If an emergency condition is detected, the integrating controller shall issue commands to

the subsystem controllers to configure the Space Station as appropriate for survival of

the crew, and to the extent possible for survival of the missions. The integrating

controller shall alert and direct the crew through the on-board alarm system and shall

issue appropriate data to the ground automatically.

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The integrating controller shall provide diagnostic information and advisory data to the

crew on request. The controller shall provide explanation of all change commands on

request, and the controller shall automatically provide emergency information to the

crew at safe haven displays.

The integrating controller shall utilize computing and mass memory equipment which is

part of the Space Station data management subsystem. The equipment used by the

integrating controller shall be capable of performing the Integrating controller functions

after any single fault within that equipment.

2.3.9 9' chnology Needs/Benefits

The objective of this section is to identify the appropriate technologies for implementing

the integrating controlled concepts. In addition, a discussion will be included concerning

quantifiable attributes of these technologies.

2.3.9.1 Simulation Models

The keys to developh.g the integrating controller are: the ability to develop effective

models of the subsystems and the Space Station, and the ability to develop effective

decision making expert systems. For the models, this involves selection of an adequate

model development language, determining how to assess the accuracy of the models, and

how to translate the models into softwares suitable for real-time control. Without

building any models this is a 3 to 6 man-month effort. To develop an experimental model

of a Space Station subsystem and convert for real time use is a 1 to 2 man-year effort.

The number of subsystems multiplied by 2 man-years each gives an indication of the

scope of effort to develop subsystem models. The prediction modeling effort would be at

least as much as the subsystem modeling but would also involve 'the use of expert system

technology.

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f 2.3.9, 2 Background on Expert System Technology

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A software system, including expert systems, can be viewed as comprising the following

conceptual hierarchy:

" 1. Software system

2. System development cools

S r 3. Language

4. Operating system

C5. Hardware

The expert system R1, which configures VAX computers, illustrates this hierarchy. R1

itself corresponds to level 1. According to Reference 3, the original version Gf R1 was

implemented using the expert sya •;c t development tool OPS4, which corresponds to level

2. OPS4 is written in MACLISP., w;;;r_h corresponds to level 3. Reference 3 does not

identify the operating system used. The hardwa-e ubed (level 5) is a PDP-10.

C

Part of the process of designing an expert system is making the appropriate choice at

each level of the hie.-Archy that is not otherwise constrained by system requirements.

3 Software technology experts believe that the choice of development toils at level 2 is

particularly critical. In the case of expert systems, the metrics of most interest are

` generally the followings

o number of rules

• memory used

• computer (which implies MIPS)

2.3.9.3 Discussion of Expert System Metrics

Based on experience, the following 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.

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Reference 4 provides some data on the level of effort required to develop R1.

Essentially, R1 was developed over a four 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 manyears of efforts.

2.3.9.4 Expert Systems Technology Gaps

The objective of this paragraph is to identify the technology gaps that must be closed

before expert system technology can be applied to the problem of IC's for manned space

stations. The following paragraphs describe specific technology gaps.

2.3:9.4.1 Development Tools

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 an expert system. They suffer from thrc-e

general types of deficiencies.

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

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

time.

Second, most ols 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.

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.

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_ 2.3.9.4.2 Hardware

Currently, no All

 hardware is available tha: is suitabie 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.

2.3.9.4.3 Methodology

Existing expert system technology has been generally applied to fairly stable, comparatively well understood technology. If the Space Station involves significant amounts of

novel technology, it will be very difficult to apply existing knowledge engineering

techniques.

2.3.9.4.4 Personnel

Industry's intense recent interest in expert systems has created a shortage of experienced knowledge engineers. This lack of personnel will probably hinder the application

of expert system techniques more than the more technology-oriented gaps discussed in

the preceding paragraphs.

2.4 Summary of Trade Study Comparisons and Technology Selection

The purpose of this section is to discuss the cnm parisons that have been made of the

technologies suggested to support implementation of an integrating controller concept.

The purpose of the comparisons is to provide the basis for prioritization and selection of

technologies that are recommended for advancement.

Section 2.3.9 suggests several technology areas needed for implementation of the

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

technologies.

• Developing effective simulation models

• Adapting expert systems to real time operations

• Developing expert systems that interface well with conventional software
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o Developing knowledge engineering techniques to cope with emerging technologies

o Space-qualified compact LISP computer

2.4.1 Comparison of Technology Candidates

The tr- _hnology candidates suggested above were compared on the basis of three general {I

criteria topics. These three topics are: (1) Schedule pressure or the urgency of initiating

the advancement of the candidate in order to support a mid-1990's Space Station system;

(2) General usefulness of the technology including usefulness on the Space Station as well

as usefulness to other applications; and (3) The benefits to advancement coat ratio for

the candidates.

2.4.1.1 Schedule Pressure

The comparisons of 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.

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For the simulation model advancement, we assume eight subsystems (the five considered }

in this study plus controllers for EC/LSS, mission functions and operations functions of

the Space Station). This subsystem modeling could not reasonably advarce until some

definition of the Space Station has been established. This means that modeling of

subsystems would probably start after the phase B effort is complete. From that point, a

two year simulation effort seems reasonable for the subsystem models. Once the models

have been completed they need to be integrated. After integration the predictor

modeling can be established. The effort following the completion of subsystem modeling

could easily run another two to three ;ears. Validation and verification effort would be

an additional two years. The total duration of the simulation modeling effort for the

integrating controller would easily stretch from the present to 1994. This indicates a

tight schedule for this advancement since the need date has been indicated as the mid- w l

1990's. Because Spa:ec: Station modeling is unique, efforts by other advancement

agencies such as DARPA are not applicable. The schedule pressure is therefore high for T )

this technology.

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For the technologies associated with adapting expert systems to real time operations the

advancement seems to be independent of Space Station unique functions so the 6.25

years identified in paragraph 2.3.9.3 seems appropriate. This indicates a technology

availability by 1992 if the advancement starts In 1985. Because the DARPA strategic

computing initiative is intended to address this technology, it is likely that advancement

-r effort will be started in the near future. For these reasons the schedule pressure for this f

'y I advancement candidate is relatively low.

There is a unique aspect to developing expert systems that interface well with

conventional software; the conventional software needs to be defined first. This means

that Space Station technology cannot advance until the simulation software is well along.

We have concluded that it will be about five years after phase B is complete before the

simulation models are likely to be ready for validation testing. The start point for

f' integration with expert systems could only be a few years prior to that. If we add the

6.25 years of paragraph 2.3.9.3 to that we have 1995 or 1996 for availability of the

technology. It is true that some of the generic background for this technology could

come out of the DARPA stt 'y so perhaps the 6.25 years is pessimistic. Let us say 4

i years so we may be looking at 1994 for this technology which also puts it in the high

schedule pressure category.

The technology of developing advanced knowledge engineering procedures can be pushed

independent from the Space Station design. It Is also true that the DARPA study intends

to consider this area so Space Station may benefit. It appears that the schedule pressure

is lower than any of the other candidates.

Developing a space qualified compact LISP computer is a candidate which has a fairly

long expected duration for advancement. It is reasonable to expect a full 5 to 6 years

for such a program, It could however be started early and might benefit from the

computer development part of the DARPA study. dt appears that a 1990 or 1991

availability is likely if the program were started in 1985 so the schedule pressure is

m oderate.

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Based on schedule pressure, the candidates rank from highest pressure at the top toward

lowest pressure at the bottom as follows:

1. Expert s ystems interface with conventional software.

2. SImulation modeling

3. Space qualified LISP computer.

4. Real time expert systems.

r 5. Knowledge engineering advancement.

2.4.1.2 General Useftdness

General usefulness consists 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 pa; fs of the technical community.

For the simulation model advancement the usefulness to an automated integrating

controller is unquestionable. It is, however, possible for an interim version of the

integrating controller to be deployed which essentially makes decisions based on data

inputs, trends and astronaut inputs. The mid 1990's integrating controller is likely to be

the interim version so the usefulness of the simulation models is somewhat deferred.

The general usefulness of real time and faster than real time modeling for the general

advancement of automation and robotics has been recognized by investigators such as

NASA's Advance Technology Advisory Committee. The general usefulness of this

technology candidate is therefore on the high side of moderate.

Real time expert systems are essential even to the interim integrating controller

mentioned in the previous paragraph. The general usefulness of the technology is

indicated by DARPA's attention to it in their strategic computing study. This candidate

places higher than the simulation modeling on the general usefulness list.

The technology of interfacing expert systems with conventional software has benefits for

other users as well as application to initial versions of the integrating controller. The

application to interfaces with simulation software, however, would not be essential for

the interim integrating controller as was discussed above. This candidate is probably as

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high on the list resulting from general usefulness comparisons as the real time expert

system software.

The effective knowledge engineering advancement has obvious general utility; it is

included in the DARPA strategic computing initiative. The usefulness to the integrating

controller for the Space Station is not unique and may not be significant until several

years after IOC when rapid Space Station changes emerge. This candidate is considered

to be moderate on the general usefulness list.

The space qualified compact LISP computer has little use to the general user community.

The integrating controller could conceivably be implemented using a conventional

computer by converting expert system code to conventional code. Such a practice would

add time to the implementation of an integrating controller and would therefore not be

desirable. However, it would be possible to deploy an interim integrating controller

_ without an on-board LISP machine. This candidate Is at the bottom of the general

r

usefulness comparison list.

Based on the general usefulness comparison then the candidates rank as follows:

1. Real time expert systems

2. Expert systems that interface with conventional software

3. Simulation modeling

4. Knowledge engineering ^dvancement

5. Space Qualified LISP Computer

2.4.1.3 Benefits to Advancement Cost Ratios

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

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

t 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 2.4-1 is included here

to summarize the benefits estimate metrics.

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Table 2.4-1. Integrating Controller Benefits Estimate

o Monitoring effort phased out over five years

• Firs; year full mission control center coverage

• Second through fifth years— mission controllers reduced by 5

• 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

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

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

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Table 2.4-2. Technology Advancement Cost Estimates

10 Developing effective simulation models

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

simulation development costs = MOM

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 tl rt interface well with conventional software

o Estmate DARPA results r squire 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 testin effort in addition to DARPA work

10

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The advancement costs have been estimated and are reported in some detail in volume III

of this report. Table 2.4-2 summarizes the estimates.

The estimates of Table 2.4-1 need to be partitioned according to the contribution of the i

technology candidates to the integrating controller. Using the general usefulness

r ,

considerations for the integrating controller as a guide we can conclude that simulation

modeling would receive slightly more than one fifth of the $54M, because it is somewhat

higher than moderate ($12M).

Real time expert systems is considered essential for the integrating controller so its

share should be significantly greater than one fifth ($18M). The technology for

interfacing is nearly as significant as the real time expert systems ($15M). This leaves

$9M for the remaining two technologies. The LISP computer seems more crucial to

effective implementation of an integrating controller than does the knowledge engineering ($8M) and the remaining ($I M) for knowledge engineering.

Taking €';e advancement cast figures from T . 2.4-2 gives ratios shown by Y'able 2.4-3

in rank order from highest to lowest.

Table 2.4-3 Benefits/Cost Ratios

_ ,C^ ndidates a Benefits /Cost

1. Adapting expert systems to real time operations 37.5

2. Developing expert systems that interface well

with conventional software 12.5

3. Developing effective simulation models 6.0

4. Developing knowledge engineering techniques 4.17

5. Space Qualified Compact LISP Computer 210

2.4.2 Prioritization of Tectmology Candidates

Based on the comparisons discussed in the previous section the five technology

candidates for autonomous functional control can be prioritized as indicated by Yab)e

2.4-4.

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D483-10012-2

It should be recognized, however, that the efforts planned in volume III of this report are

essential if an integrating controller is to be available for a mid 1990's Space Station. If

the DARPA strategic computing initiative is not started or is delayed by a year or more

all five of the technolt candidates should be pursued.

Table 2.4-4 Prioritized Technology Candidates

Candidate Sched Use Benefit/Cost I Combined

Expert systems that interface

well with conventional S/W 1 2 2 5

Adapting Expert Systems to

Real Time Operations 4 1 2 6

Simulation Modeling 2 3 3 8

Knowledge Engineering Tech. 5 4 4 13

Space Qualified LISP Computer 3 5 5 13

2.5 CONCLUSIONS

The conclusions that can be drawn from the study reported here 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 described below

The (defense Advanced Research Projects Agency (DARPA) has plans to establish a

Strategic Computing study (reference S trategic Computing, New Generation Technol ogy

A Strategic Plan for Its Development and Application to Critical Problems in Defenie,

AD-A141992.). In this study the development of basic artifical intelligence technology is

planned, including $-al time expert systems. This will be a large program in which 6 to

10 research centers across the country will be established with a staffing of approximately 100 professionals each. Funding was planned to be $50M for FY84, $95M for

FY85, $150M for FY86, and unspecified amounts for the out years. The total amount for

the first three years was planned to be nearly $300M. Schedules show the development

75
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4. The costs are high but so are the benefits.

This technology advancement is essential if the Space Station autonomy/automation

philosophy is to be implemented.

76

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D483-10012-2

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of a real time capability by 3rd quarter FY90. An initial one third to one half real timcapability was shceduled for completion in 4th quarter FY86.

Because the technologies associated with adapting expert systems to real time opera-

, tions 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 are being 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 as was

dicussed in paragraph 2.4.1.3 above. if the DARPA study proceeds immediately there

may also be a schedule benefit for the candidates identified here. it -mill 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 will be facilitated by r_lose

contact with the development of those results.

The general conclusions listed in paragraph 5.5 of the final report from the previous

study phase are still valid ano are repeated here for completeness.

1. The integrating controller has real and useful functions on a Space Station.

2. The implementation of the controller would profit from expert systems programming.

i

I The implementation will be phased and updated during the early years of the Space

Station operations.

9
0483-10012-2

ro

Is

77

F', 2.6 RECOMMENDATIONS

The recommendations of this add-on study are: proceed with the technology development for the subsystem simulations, proceed with the predictor simulations for the

integrating controller, adapt the results of the DARPA study to the other four

technology candidates, have a significant parallel effort to interface expert systems with

conventional software for the integrating the controller, and have a significant parallel

effort in space qualification of a compact LISP type computer.

Volume III of this report includes a section that defines a plan for development of three

technology candidates for implementation on a Space Station during the mid 1990's which

do not appear to be adequately covered by the DARPA study.

2.7 AtFERENCES

1. L.M. Fagen, J.C. Kunz, E.A. Feigenbaum, and J.•J. Osborn, "Extensions to the RuleBased Formalism for a Monitoring Task," in B.C. Buchanan, E.H. Shorthiffe, RuleBased Expert Systems, Addison -Wesley, 1984, pp. 397-423.

2. A. Barr, E.A. Feigenbaum, and P.R. Cohen, The Handbook of Artifical Intelligence,

3 vols., William Kaufman, Los Altos, CA, 1984.

3. J. McDermott, R1: A Rule-Based Configurer of Computer Systems, Carnegie-Meilon

University Tech. Rep. CMU-CS.-80-119, April, 1980.

4. J. McDermott, "R1 Revisted: Four Years in the Trenches", The Al Magazine, Fall,

1984, pp.21-32.

it

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y

Ic

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9

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D483-10012-2 a

3.0 ATTITUDE CONTROL IMPACT FROM STRUCTURAL DYNAMIC MOTIONS

3.1 INTRODUCTION

3.1.1 Summary of Previous Study Results

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

r

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

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

y the degree to which conventional controller technology is applicable to attitude

regulation of a space station with large flexible solar arrays. 11,

At the outset of the study, it was surmised that attitude stability might be jeopardized

when the control band interacted with the flex modes. However, analysis has shown that

when the modular station cure station can be assumed rigid with respect to the required

control bandpass, then the controlled response is asymptotically stable when the sensors

and actuators are collocated anywhere on the core. A simulation of the flexible station;

and a control system consisting of band limited multiple two axis double gimballed CMGs

and attitude position and rate sensors was implemented. The attitude response of the

system to impulsive disturbance verifies! overall stability and shaved substantial

improvement in the damping of structural vibration in most cases. A modal survey

analysis (reference 1) indicated that controllable normal modes contain motions of all

structure elements with the exception of twist of the solar panels. The time responses

support this claim and would indicate that torsional vibrations of the solar panels are not

controllable with torqu<:rs and angular motion sensors mounted on the rigid core as

expected.

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

This was justified under the assumption that the disturfances 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

3.1-1 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 rnotion of a multiply connected

set of flexible 1ppendages is of both types of bending.
cam,---:^-t---.-

D483-10012-2

i

i

3.1.2 Current Study Objectives

The objective of the current phase of the study will be to extend the effort:, 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. Variations to the existing structural configuration considered

alternate solar array deployment schemes which offer substantially stiffer structures in

torsion.

3.1.3 Overview

In the following sections the results of the analysis and simulation tasks are discussed.

Section 3.2 presents the details of the technical approach. The subtasks are introduced

and the tec'.Acal objectives are stated. The analysis and simulation results are discussed

in Section 3.3. Section 3.4 summarizes the significant results. Conclusions and

recommendations are presented in sections 3.5 and 3.6. References are given in

section 3.7.

3.2 APPROACH

3.2.1 Summary of Current Structural Configt!ration •

i

t

i

y

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.

A pictorial view of the study configuration is shown in Figure 3.2-1. This configuration

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

deployed. Each boom center pivots two panel sections, each section containing four

79

I - ^
I Station \

—J

To

`J station

1 J `/

....- Symmavic banding Amirvmmmic baMhq

y

Figure 3.1-1. Definition of SymmetriclAnti•symmetric Bending

F —'

'I J"

>i

'( sq

k'

^- Y

^s

i'

i^

i^

s

a

i

1 '

I

MIUM

D483-10012-2

ORIGE,`IAL

OF POOR Ql1fAU—iVj

dam

^ t

Mart

1

t

Doom

S."

l;

Fd

Figure 3.2-1. Balanced Array Concept Astromast Deployment for NASTRAN

Analysis

80

rt

n

to Y

no
u.hHMnn ^_^ti, w u

D483-10012-2

separate blankets. The blankets are deployed along cables attached to the stiffer end

plate. Section properties and dimensions for all structural elements are given in

Table 3.2-1.

The solar array booms were modeled as graphite/epoxy tubes, 24 meters long. The solar

array astromasts were modeled as triangular trusses with a design by AFC-ABLE called

{ Continuous-Longeron Able Boom. Sizing, of the boom and astromast was done assuming a

h maximum static load of 0.1g.

The five modules were assumed to be rigid bodies with flexibility at their connection

points with each other and with the orbiter. The stiffness at the ends of the modules was

computed separately for the module and for the docking tunnel, then springs in series

were assumed and the stiffness for the module including the docking tunnel was

computed.

The masses of all the structural members are uniformly distributed along their lengths.

The masses of the solar panels are lumped half at either end of the astromasts and mass

moments of inertia are added to reflect the actual mass distribution. The module masses

are lumped at their c.g: s with moments of inertia to reflect the actual mass distribution.

The Space Station mass properties for the test configuration is given in Table 3.2-2. The

principal axis basis vectors are the columns of matrix M.

1 1 ' 3.2.2 Statement of Tasks

The following four tasks were performed with the structural configuration using SEP5

type solar arrays as described above. The fifth task requires modification of the current

+;I configuration to include arrays with improved structural properties to be described in

discussions to follow. a

3.2.2.1 Loads and Motions Analysis

The current formulation of the model for the crew activity forcing function assl^mes a

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

through the center cf mass. This task incorporates the capability to apply both force-,

and torques at any :'esired point of application on the structure and to monitor the

8i
82

C D483-10012-2

4^1

Table 3.2-1. Flexible Element Section and Material Properties for Space Station

MEiM5ER

NASTRAN

ELEMENT DESCRIPTION MATERIAL A(m2 ) I(m4) 7(m4)

Array Boom Bar Tube GR/EP 2.99E-3 5.43E-5 1.09E-4

d = .381m

t = .0025m

A'tromast Bar triangular 6-GI./EP 1.91E-4 3.82E-6 3.82E-6

truss

d = 9.E-3m

h=.3m

RCS Boom Bar Tube GR/EP 3.99E-4 3.22E-6 6.44E-5

d = .254m

t = .0005m

Cannister Bar Tube GR/EP 7.08E-4 7.57E-6 1.51E-5

d = .302m

t = 7E-4m

Box Bar Tube GR/EP 2.03E-4 4.22E-7 8.44E-7

d = .13m

t = 5E-4m

Stiffener Bar Tube GR/EP 1.56E-4 2.1E-7 4.2E-7

d=.lm

t = 5E-4m

Cables Red Cable CELION 7.85E-7 NA 1.E-11

d =.001m

Material Properties

Jr

' Celion Fiber Cables E = 172E9 N/m2

S Glass/Epoxy E = 52E9 N/m2j

Graphite/Epoxy E = 108E9 N/m2,

,r

a

y

ei

1

G = 6E9 N/m2 P

G = 15E9 N/m2
.iY .aYmr'.rvrrr.®rvns

g

)y ', M1

., f r

1

ss Properties of Space Station

All-Up

Quantity — Configuration I Units

Ix 2.85

f1_

ly 3.32 Kg-m2

x 106

IZ 3.00

Ixy 0

IxZ .36 Kg-m2

x 106

IVZ 0

m(2) 94011 Kg

X(I)cg 1.38, 0, .628 meters

Ip 3.30, 3.32, 2.55 Kg-m2

x 106

.632 0 .774 non M 01 Odim

-.7740.632

i

^I

i

NOTES

(1)cg location with respect to node d, the attach point

of the solar panels, cf fig. 3.3-1.

(2) The total mass of the solar panels is 1652 Kg.

The total area of the solar panels is 1111 m2.

83
s

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resultant state vector (rotational plus translational states) and accelerations at any

selected point of interest. Simulated acceleration data at selected body n'tations are

derived. These data are used to establish control requirements as a function of d u

acceptable levels of acceleration.

The crew activity profile is formulated to accentuate the uncontrollable modes to the

extent that sustained or increasing levels of vibration in various structural elements

especially the solar arrays, is evident.

3.2.2.2 Passive Vibration Suppression

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

passive torsional control elements at either end of the mast . Design concepts for both

tip and root mounted dampers are presented and feasibility for space application is

discussed. It is noted that mechanical vibration dampers act on relative acceleration,

velocity and position in terms of mass, damping factor and spring rate and therefore

qualify as collocated sem;or-actuator pairs. In this regard there is no apparent

distinction between passive and active control when the active control is a collocated

electromechanical measurement-actuator pair. Active control is usually defined in

terms of electromechanical sensing and actuation, the extension being the capability to

spatially separate the two functions.

31.2.3 Active Vibration Suppression

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

incorporate both aspects of performance and vibration suppression. The issue of

performance deals with the pointing of multiply connected flexible bodies where the

terminal bodies have different pointing requirements. The terminal bodies in this case

are the core station and the solar arrays, the core station being rigid at control

frequencies of interest and the solar panels extremely flexible. 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 approach used here will be to apply the technique of

eigenstructure assignment (reference 3.7-2) where both poles (stability augmentation)

and zeros, or more appropriately the eigenvectors, (performance augmentation) are

84
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D483-10012-2

specified in a limited sense and closed loop gains computed accordingly. 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

prelim:nary design of an active vibration suppression is presented where collocation of

sensors and actuators is not a constraint. Sensor and actuator functional requirements

will be highlighted and computational requirements are discussed.

3.2.2.4 Vibration Suppression of Symmetric Modes

The current Space Station is configured such that attitude control with torque actuators

alone cannot control the symmetric modes of vibration. Symmetric bending of the

flexible appendag--s, after referred to as the "butterfly mode", is manifest as motion

where the core translates in a direction opposite the solar panels. A symmetric mode

vibration suppression system was designed using a low thrust reaction jet control system.

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 as shown in Figure

3.2-1. The working fluid is specified to Le carbon dioxide which is assumed plentiful in a

fully operational space station. The control requirements are derived and the feasibility

for application to space station is discussed. The use of reaction jets for flex body

control is documented in the literature. However the application to active vibration

suppression of large space structures is believed to be new. This mode of control is

investigated as an alternative to redesign of the boom and mast servoactuator system. It

is noted that translational control can be realized with torques if the solar panels can be

independently torqued about all three vehicle axes.

3.2.2.5 Modeling of Stiffer Solar Array Structures

Stiffer solar array structures are incorporated into the existing elastic model. The basic

core structure remains unchanged from the reference configuration shown in Figure

3.2-1. The solar array configuration is typical of the design concepts of current interest

at Boeing. The control and dynamic performance of the structure is evaluated assuming

core mounted linear torquing actuators and rotational motion sensors. The objective is

to attempt a reduction in the amplitude of the uncontrolled solar panel modes without

introducing other serious side effects. Such an effect would be increased level of

acceleration at the modular core due to a significant solar panel mass increase. The

85

i

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yu..

I+ v

N

D483-10012-2

implications of stiffer solar array structure are examined and application of the given r

design to Spare Station is discussed.

\\

3.3 TECHNICAL DISCUSSION

3.3.1 Station and Solar Array Regulation Strategies

` A principal purpose of the 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. The basic concept then, is to treat the problem as the design of

five independent rigid body controllers with collocated and coordinated sensors and

^ r

actuators at the hinge points. A variation to this strategy would require decoordination

of sensors and actuators in an attempt to decouple the dynamics of station core and solar

panels.

by

3.3.1.1 Relative Positioning

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

Cazimuth 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 x^

tachometer and position measurements collocated with the actuators as state variables

m

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

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

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

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

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

^i ^ panel and station pointing requirements are compatible.

3.3.1.2 Absolute Positioning

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 latter measurement set represents a

controller decoordination and system stability must be considered. Further refinements

to attempt base motion decoupling results in a decoordinated controller and here again

i

86
D483-10012-2

system stability is a consideration.. The abso lute positioning strategy is reasonable if

allowable base motion is far in excess of solar arra y pointing requirements.

3.3.2 Measurement and Contrniler Definition

A description of the static (panels fixed) configuration indicating the location of all

input disturbances is provided to facilitate the following discussions. In addition, the

control system composition for all passive and active controllers is given here for future

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

3.3-1. Test forces for crew activity were applied at body stations A, B and C. clocking

tunnels exist at the end of the crew and crew extension modules via body stations A and

C. The c.g. of the structure is approximately one meter from the boom centerline, body

station D being the point of attachment of the boom to the raft.

The active controllers are, the CMG cluster, sun track and tilt panel drive actuator.

Measurements indicate absolute (inertial) roll, pitch and yaw angular position and

rate about body axes X, Y, Z. The sensors are collocated with the actuators.

MeasurementsA^,,At,A8bG8brepresent local (relative) angular position and rate as sensed

c by shaft position and tachometer sensors also collocated with the actuators. Points E, b

and F indicate probable locations for sun sensors. Passive controllers were modeled as

linear spring and dashpot elements and are located either at the root position (r) or the

tip position W. The root damper isolates the mast from the solar panel storage box,

sdissipating the energy of point (r) relative to point (b). The tip damper is tuned to the

torsional frequency of the mast and dissipates the energy of point (t) relative to

point (c).

Uv

The controllers evaluated for this study are given in Table 3.3-1. Controllers I - V are

comprised of linear continuous elements, operating principally on the antisymmetric

normal modes. The reaction jet control system operates exclusively on the symmetric K

normal modes. Controllers I - IV constrain all sensors and actuators to be pair wise

collocated and measurements are derived from differenced absolute quantities. Control

" gains are computed to connect pairwise (local) sensor outputs to actuator inputs.

^rController V requires that sensors and actuators be pairwise collocated. However, the

Allk measurements are all absolute quantities and crossfeed gains between spatially separated

sensors and actuators are computed to provide augmentation for pointing performance

and response of the rigid modes. It is noted that absolute positioning of the panels in roll

87
Sun

^m

r.01.1..

Figure 3.3-1, Loads and Motions With Colocated Linear Controllers

D483-10012-2

D

a

I

88
RXF

D493-10012-2

Table 3.3-1 Linear Controller Identification with

Sensor and Actuator Specification/Location

I II III IV V

Control

Element

Actuators

CNIG cluster d d d d d

Suntrack actuator a a

Tilt actuator b b

Root damper r

Tip damper t

Sensors

Rate gyros d d d d a,b,d

Abs. angular position d d d d a,b,d

Tachometer a,b

Rel. angular position a,b

Table 3.3-2 Indealized Impulse Imparted

from Orbiter Berthing

Orbiter Approach Conditions Body Station Dis'[urbance (Impulse)

(N-m-sec)

Linear velocity = .030 m/cec A 4000

Angular Velocity = .35 deg/sec D 5000

89
b

D483-10012-2

vrould most likely receive position updates from sun sensor measurements at inboard tips

at points E, F. The structure of the controllers and accompanying selection rationale t

will b:; discussed in the appropriate sections to follow.

3.3.3 Loads and Motions Analysis 7

The loads and motions study was formulated to investigate the uncontrolled motions of

the flexible appendages when the station is attitude stabilized by core mounted linear

torquers. The implication here is that dedicated vibration suppression systems are

1

absent. A secondary objective was to compute the stress levels at the root stations of

critical flex members during forced notion due to crew activity and orbiter berthing.

The orbiter berthing operation was modeled as a simple impact shock and impulsive

inputs were computed accordingly. #

3.3.3.1 Disturbance Models and Profiles

j' r

Crew Activity Model

The disturbance profile for modeling crew activity is shown in Figure 3.3-•2. The model

represents an astronaut in a soaring maneuver within the Space Station. The r.1otion is

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

..

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

module of about 12 feet in diameter. The resulting impulse disturbance is 40 n-sec forT'^

each element of the doublet. In order to establish a highest upper bound from all

internal sources a value of Fo = 100 N-sec was used for ilmulation and +inalysis.

Crew Motion Profile

The crew motion force and resulting torque profile is .shown in Figure 3.3-3. Crew

motions are assumed to originate at body stations A, B and D as indicated. Only forces )

along Z and Y are introduced since forces along X would imply crew mobility along the

axial dimension of the module. Partitioning of the module prevents knowledge of the f" ")

free flight time along with the realization that forces along Z will induce almost

identical motions in pitch. However, the structural motions in the XY, and YZ planes do r ll

differ markedly although the panels are very stiff Ln the XY plane. The intent of the tom)

profile was to produce a set of crew motions that forced the structure at frequencies

I

I,
a ^

D483-10012-2

q ^

Fo

1

I

Force

Time, sec 1

11

10

Figure 3.3-2. Disturbance Model for Crew Activity

e

r

Form profile

IN)

100

50

0

e 0

LL

•loo

100

b

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•100

100

$ So

a

i

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f

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p

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1 ^0 60 100 TMr 150 200 050

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0 50 100 100 200 250

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C

a 0

H 400

•1000

0 50 100 ISO 200 250

Tim.

N

100

50

0

40

.100

0 50 100 ISO 200 250

TO05

Figure 3.3-3. Crew Motion Force and Torque Profile

91

i

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D493-10012-2

which corresponded with the normal modes, especially those modes which were the

natural frequency of the solar arrays in torsion. It is also noticed that the resulting

torque profile for each axis exhibits a somewhat random pattern in torque magnitude.

Docking Geometry

A schematic drawing of the Space Station with orbiter docked is shown in Figure 3.3-4.

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

station. The impulsive docking loads were estimated based on the approach conditions of

the orbiter shown in Table 3.3-2.

3.3.3.2 Motions Analysis for Controller I

Response to Crew Motion

The acceleration response at remote body station A to the crew motion profile are shown

in Figure 3.3-5. Open loop data represents the free response of the structure. Closed

loop data represents the response with CMG controllers only. It is seen that without the

controllers, the accelerations grow with time markedly, when the "energetic' crew

profile is introduced. The closed loop results also indicate that accelerations along X

and Z are growing at a very slow rate although it is not known whether or not the effect

would be dissipated if the profile were truly random. Steady state accelerations are the

largest along Y at A due to rotational effects induced by antisymmetrl- boom bending.

The tendency for accelerations to grow in X and Z is due to uncontrolled symmetric

boom bending induced by forces along Z and pitch coupling into X.

The appendage response to the crew motion profile is shown in Figure 3.3-6. The

subletter designation indicates the rotation of the first letter with respect to the second

letter, the letters representing points on the structure. Designationspe ,A6 ,A^ indicate

local rotations about X, Y, Z at body stations. For example Mad represents the rotation

of point a (boom tip) relative to d (boom root) about the vehicle X axis. The situation on

the other side of the structure is similar although the signature will depend on the

symmetry or ancisymmetry of the motion. Open loop data shows that appendage motions

grow without bound. Closed loop results would seem to indicate that bending and twist

of the boom are boundable. However the twisting motion of the mastAocb is clearly

growing with time. Residual bending motions of the boom and mast are again due to

+I

c^

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92

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D483-10012-2

Figure 3.3-4• Berthing Configuration for Orbiter and Disturbance Impulse

op'" loop doted bop

e0

Ipsl

so

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RA 0 RA a

i

{

se' ZA

tw __

t ^0 so 100 X11 1ao 100 n

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Figure 3.3-5. Station Acceleration Response with CMG Controller Crew Motion Profile Input,

Servos Locked

1

a

t

t

93
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D483-10012

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Figure 3.3-6. Appendage Response with CMG Controller Crew Motion Profile Input

94

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_ ^ F
i

D483-10012-2

uncontrolled symmetric mode motion due to force inputs. Note that the tv 3 Isting motion

of the boom is poorly damped and the twisting motion of the mast is virtually undamped.

Response to Orbiter Berthing

The response of the .+tructure without control to a berthing impact at body station A is

shown on Figure 3.3-1. The maximum transient acceleration is 10000 V g (.01 g; in X.

The stress units are given in millions of N/m 2. Note that the stresses at the root of the

boom and mast are well within the yield limits of the materials. The appendage motions

are relatively large. However even the largest defection of 3000 arc-sec Wtb), which

represents the slope of the elastic curve at the tip of the mast given as a rotation about

Y is roughly 1 degree. Again, note that even'the most severe loads induce only small

motions of the structure. The loads are small and the motions do not appear to be

detrimental in any perceived sense.

The response of the core attitude in pitch to a berthing impact at body station C is

w shown on Figure 3.3-8. The response of pitch attitude without any controller constraints

shows that the peak torque required to null out the transient is about 4500 N-M. In

s

contrast, the response of the : MG cluster shows that a set of three skylab class CMG's

in a parallel mounted configuration with magnitude and rate limits as indicated is

o unstable in pitch. The control authority of the cluster is easily exceeded as evidenced by

r

the saturation behavior of the three inner gimbals. If the structure is subjected to loads

of the size indicated here, some form of auxiliary control will be required.

95
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D483-10012-2

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0.0 1000

0.0 o

op:i ao^0p

Boom OA •7000

nNr

n 

0 100

Y 2

b 10

0

tl 40i

1 100

o WAR W R w

0.a

70^w 7 0.7 w low

3

:,I

p o

M . ;2^

Man 0.0 4000

linr ]0 IOw

10 ]w

a 10

aw

0 0

so 7100 ` 1000

p0 1 00

lr a Tbr

Figure 3.3-7. Orbiter Docking Impact at Body Station A No Attitude Control

I

i

h

96 lr^

M
97

D483-10012-2

0 1 G9E007

iM1/1] OO

0 EO 100 ISO

V.

10000

Em0

14c^c1

RV 100 ^

7000

0

aaro

6000

X000 ,^

Tonw 7aao

TOH

7000

1000

0

1000

0 60 100 Ilia

T4M

MIND

90000

Py

gi 0000

nv 1a0 t0ao0

0

.10000

0

100 — —

1N N1 300

TOROV •]00

-400

^0

EO TY^I

100 100

740

7]a

lawl

EETAD' ]

190

lE0

10.01

9FTA] I W _

1]0201

0

700

160

411T 00 ^ETA1 1

Etl

0

0 f0 100 1E

Figure 3.3-8. arbiter Docking Impact at Body Station CMG Control with/

Without 6 deq/sec Gimbal Rate Limit
98

D483-10012-2

3.3.4 Passive Vibration Suppression

Passive suppression of solar panel torsional vibrations is incorporated in controllers If and

III (c.f. Table 3.3-1). The mast torsional response performance of these controllers in

terms of an impulse response analysis is summarized in Figure 4,3-9. The following

discussions summarize the findings of the preliminary design for fire solar panel r)ot and

tip mounted damper mechanisms.

3.3.4.1 Motions Analysis for Controller II (Root Mounted Damper)

s^

z

i

i

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

where the solar blanket is attached. The spring constant was selected to be a factor of

100 less than the torsional spring rate of the mast. Also note that the torsional stiffness

of the mast is about a factor of 100 less than the bending stiffness. The results show

that the isolation system has essentially allowed the panel to remain stationary with

respect to an inertial coordinate reference. The low value of the peak displacement and

rate indicate that the damping constant should be realized either by direct interference

friction from some sort of counter rotating coil spring arrangement or from an eddy

current device. Also note that 20% damping was selected arbitrarily and no attempt was

made to optimize the damper design.

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

damper in controller 11 are shown in Figure 3.3-10.

3.3.4.2 Motions Analysis for Controller III (Tip Mounted Damper)

3

ti

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. For an inertia ratio

of .10, the mass required to implement the rotational inertia of the damper is about

36 kg, assuming a uniform rod.. Note that the optimal damping achieved (1536) is

sensitive to the panel parameters, especially the torsional stiffness. However, for worse

case parameter ignorance, the degradation in damping is not severe. The peak

displacement and rate is small and the comments made above for the root mounted i

device relative to mechanical realization apply here. "ihe time histories for the
i

ddnI

I)oIm

Om, Ad

r,6

99

_4 a ^..

C:

^f

k

'^, Im mnl

b Xm^

'^1 Jdt, A0

y Boom C T

Roet moumd dNnpN

t S5\\\ m

/ Ynv

d

D483-10012-2

e

i FO.

e `^ v

f

Constants Puk wriabla for

T.-1000 nm atd

Mtn

Min

Wrap

10c to

KBtt2

Osmpin0

%

K

n.n/r

C

n.d4w

Td

mm

M

dog

dq

dq/m

40,

dti

Tip 1490 1fi8 768 .10 .082 ,077 .05 15

Root 14,90 500 — .30 .044 ,038 1 •0004 20

^t F

y Figure 3.3-9. Torsional Vibration Suppression Performance with CMG and Root or

Tip Mounted Dampers
^ .,^ Yc w l^ 'S

D483-10012-2

^r-C

Np

6 K r c

^ ^ IP

►Mml dynsmia

1.0 -

Iwcrrcl -

ed a 0

-2.00 10 _.-20 30 40 50

Tim

iw -

0

1 ^0 10 20 30 40 5i

e` r

Osmwr dymmia

(wcwe,Nl

]0

Tr 0 ^^^T^_ I

c

-10 ^ 0 ^TT-- r

10 20 Time 30 40 5o

100

eye, ol.

_- —

-150 FAT SI_ I 1

0 10 20 Time 30 40 50

100 --

Dampw mnmmr eOb 

1 —

K - 14.00 N •m/r _2001 ---

C - 500 N•m,we 0 10 20 Time 30 '40 50

Figure 3.3-10. Simulated Response of Root Mounted Torsional Damper for 2015

Damping Tilt Actuator Locked, TX = 1000 N-m

{

100
D483-10012-2 1

appendage and damper impulse response of the tip mounted damper in controller III are

shown M Figure 3.3-11. The damper design curves are shown in Figure 3.3-12.

r

I

Cam'

I

i

A

IIts,

3.3.5 Active Vibration Suppression

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

controllers IV and V. Controller IV utilizes coordinated feedback of relative angular

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

Controller V utilizes crossfeeds of absolute angular motion variables to the panel drive+

actuators in order to decouple base motions from solar panel motions as previously

discussed.

3.3.5.1 Motions Analysis for Controller IV

Boom and mast torsional respons° performance n^ controller IV is summarized in Figure

3.3-13. The following discussions summarize the findings of parametric analysis for

position and rate gains required to achieve the given level of performance.

Panel Roll (Tilt) Axis

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

panel roll attitude and rate relative to station fixed coordinators measured at the

actuator. Design parameters and peak control response to a test torque impulse of 1000

N-m-sec in roll are shown on Figure 3.3-13. The gains Kp and Kv were tuned to give

maximum damping of the panel fundamental torsional mode. The solution 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. Control variations achieved reasonable limits. Physical realization of this

controller seems feasible.

Panel Pitch (Pivot) Axis

The suntrack actuator was used to drive the pivot point of the panel set in response to

perturbations in panel pitch attitude and rate relative to station fixed coordinates

measured at the actuator. The table on Figure 3.3-13 shows design parameters and peak

control response to a test torque impulse of 1000 N-m-sec in pitch. The controller

101
D483-10012-2

c

i

[c

a K c 1

s3a

Iv K

1d

.. 

p

r

1 ^•

I

I

^. I

102

panel dymmic,

(uc•wel

200

4rd 0

-V`

L -200 0

^^

10

I

20 20 d0 50

Time

100

,9d -100^^

—_

0 10 20 30 40 50

Time

r Damper dynemkr

(ercre, N)

10

T1 0^

-.100

10 20 30 40 50

Tim.

rw —^

ISO

^d 1c

0 )0 20 30 40 50

Time

Demwr wnrtems 300 —^-. ••

m-5K0

r•!m 00fo 0

K • 125 N-mlr

C • 169 N•m•rc 2000

10 20 30 40 50

Time

Figure 3.3-11. Response of a Tip Mounted Torsional Damper Tuned for 15%

Damping Tilt Actuator Locked, TX=1000 N-m

l^ )
G%

L-.50.60

Wd/Wp

I

Fs

1

'^ ar

f

! A

i

)

M 1^

y

y

D483-1001?-2

—Cc

1

b K t

1 0 to

1_ - 7676 KO • m=

1460 N•m/r 1000

^.W W ft

r

f

.001 ,01 .10 1,0 ,001 .01 .10

i y Figure 3.3-12. Performance Curves fora Tip Mounted Torsional Damper i

y Man Most 

rK 

TO

• KP 'I'l. ^^. T^ 4 Mm

Km

Mm

Tih Km • { m

4

Tih Im Im

Suntnek KP

i Boom

K

^nwtor t FY

A 

,

l d

W

i p

I

C

i

I

Figure 3.3-13. Torsional Vibration Suppression Performance with CMG's, Colocated Suntrack/Tilt Actuators

103

i

Prk mmrol nri Wlr for hen (Lim FY, F1 -100m A twin

AR 0•mpirq•

10c KP Kr TO, TB CO. CB COm %

n♦n/r mrtl.re (n,m) dq d.4h.a dog

Tit

•aunt, 1490 6764 1.6 .014 .014 .027 43.0

SunnW

utuno. 104 SK104 12 .016 .011 — 70.7
4

c /^

j

D483-10012-2

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

was not required and any level of damping can be achieved. The time histories for the

impulse response and response to the crew motion profile for controller IV is shown in

Figures 3.3-14 to 3.3-18.

3.3.5.2 Motions Analysis for Controller V

The objective here was to apply multivariable control methodology to the given flexible

Space Station. Eigenstructure assignment using,output feedback was selected for the

following reasons. First, note that output feedback results in fixed gain

controllers which do not contain frequency sensitive elements. Fixed gain controllers

are easy to implement. Eigenstructure assignment implies that subsets of the modal

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

subsets depend 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 simulation results are shown in Figure 3.3-19. The eigenvector assignment feature

was used to decouple core motion from solar panel motion. In this simulation the solar

panels remain stationary with respect to the sun and are independent of disturbances

within the core.

_. g

r

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

are achieved when inertial, measurements are implemented as previously mentioned.

Although the sensors and actuators are pairwise collocated, crossfeed between sensors

and actuators at different locations is permitted to satisfy the control objectives.

Spatial separation between sensors and actuators on a flexible structure can lead to

stability problems. However, the bandwidth of the controller was low enough to provide

a stable core and all controllable flex modes were well damped.

1

104
C

105

. ate...

_

_ _ ___. •` alt w r>._r

...

9

1

D483-10012-2

^r

CH

C

e

Roll TO

tagw (MYI

•100°e 10 00 on M w

I C

CMa TM. CMG ♦ lrval

two .644 Ira •teal

e0 — — w

ear . d^Yr a

.^ ao

o

a

.e a.w

d B ta 

441

a,e BaaT dB,d

—

4.08!

100 lao — t

edr 0- — ear e

At V

• IW loo

300000

eBa o — dBa o

Men 4300

':qp\`\ 000

e0a alb

i

ego 10 20 00 40 y w aWa 10 00 00 e0 ea

TW. Tim.

Figure 3.3-14. Comparison of Appendage Response with CMG and Suntrack/fiit Actuators
_, 1

1

i

106

r

D483-10012-2

Qy ^

V

11

t^

talc

Boo

^II•h TB 000

tw+lw tNUI one

Na

We 00 to 70 00 Y M Ch10+tw,M

B two . OW Uwe two •nd

aow " ed,

lu

J

100

AB,n a 

am

ABp

-too

0

.o

fo

at, e

to

u.n

Oda •

o to 20 o• 40 •o

TI,1,

Figure 3.3-15. Comparison of Appendage Response with CMG and Suntrack/Ti/t Actuators

i

100

0

100

e

0

a

fw

ee,.

•100

•0

ae

0 10 00 Oo N f0

To.

r0^

^^_ 1 i
D483-10012-2 b''

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wl

{

h

S: r.t_t b l

r

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1 rf3^

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Boom Into Imports IN, eruct)

ItaB torque dllurbonw

Men wno rwpoom IN, erase)

Ty

ede

As. ea%

^.I

.0

100

0

_— —

---

tm

---

``IIII

Isom V ^-- ^\^— —'^

Core regents (arc•we) Can response (W$w I

ea 

200 _. wo..

460 ,a

e so —^

e

ao a0

Figure 3.3-16. Control Response ofSERVO Torquers

9

t

it

107
D483-10012-2

u

4

108

1

Ji

`v ti

Boom rarpon"

Arad o

t

^^ ^i ^^ HV LU1JJ11 ^^^

am 

^ ^ f r ^. ^^1 11 .

1N

Aped 0

.IN ^ I

I I

Av'd 0

.tN^^.,, r

sumuc r sawtor 0tpon"

to N arc•rccl

To

0

401

—

ta0

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0

• iN •-

Tin actuator

Nam

nrponw

^ Ij

I^

r

1N

.rM

Ap,

Ad

Ty

Soon nrponx

lue.,^el

.rnV

no

0

-300 200 x

Ao at

0 ,

aN

loO

r — — ANSI

At

0 w tN 

i.a. 

1 Ti.

Figure 3.3-17• Appendage Response with CMG +Servo Controllers Crew Motion

Profile ,Input

N oN oe0 w 100 160
PM ..

D433-10012-2

Irl,

VaANG Awtado ruponw

to (x7ia)

.u0 —

mo —

B 0 —

.200,——

a

. — --

7m —

GYM

70o

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0

^

tamua

700

Ty 0

_

I Y --9 6 N T7

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Or11

b

•00

700

4w

tm

ZA 0

100a W im 100 700 250

TIM

- a W 100 !f0 700 760

TIM

Figure 3.3-18. Station Response with CMG +Servo Controllers Crew Motion Profile Input

109

IN +~'s`=.*

.y

Tr
deco

Uses

AOrb

Rail mail

e

Vehicle response

Tx

Od

awe

e_ 1 4., i •

^^ .. a —j?^ t'^ ..,, 

w'^.A, tic•F does IM

a

1

D483-10012-2

e^

tl

i

Talnl

is

►luh axis

eVOWS

Ty

sno

lid

o

i l

Solar array

e

dBad

•mo

u

I

Control response

a

Tb Be

•.oio

b o I

•.o/e

h o

Tor9uo ndables In snynons naynons •.01fo to m ail ae Response variables in arc-sec, arosaelesa

rl.

Figure 3.3-19. Application of Eigenstructure Placement to Space Station Attitude

Control, Absolute Positioning

110

i
r

'3 r

;J 7 1`"+h4 a tsa _

0t 1

9 D483-10012-2 i `,

3.3.6 Vibration Suppression of Symmetric Modes

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, symmetrie

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 3.3-20 illustrates the basic simulation configuration used in the analysis of

candidate control laws. The .13N force ionized gas thrusters were placed as shown at

i

locations A, B, C, and D. There are two positive x-direction thrusters, locations C and

D, and two negative x-direction thrusters, locations A and B. There are four positive and

four negative z-direction thrusters. Angular rate and linear position sensors are located

at the center of the station core and at the ends of the solar array booms, locations S0,

S1 and S2, respectively. Symmetric bending occurs in both the x-y and y-z planes. Peakto-peak amplitudes of the displacements and the rates are small, as mentioned

previously. Peak values of rotational displacements and rates sensed at ends of the solar

array booms in the x-y and z-y planes are about 4.5 aresec and aresec/sec.

3.3.6.1 RCS Control Logic

The RCS thruster control logic w s implemented in the form of a rate damper. The

angular rates sensed at locations S1 and S2 were chosen as rate feedback signals to the

RCS control logic. Since the CMG's are quite effective in damping the other bending

modes, it is desirable to use the RCS thrusters to damp primarily the transverse

symmetric modes. An angular position check comparing the signs of deflection at C locations S1 and S2 was implemented to filter out the symmetric modes.

3.3.6.2 Motions Analysis for RCS Controller

Figure 3.3-20 shows the effect of rate-damping the transverse symmetric modes with

the use of RCS thrusters. The rotational rates about the z-axis shown in Figure 3.3-20

111

^r
D483-1,0012-2

0

^lIIII^ IILL

f

np

f •f` uu ^'I^r-^

Fe(N)

F,iNI

•Af •

112

,/J t

E 1

^r

u,

I

I

I i.ie

n ^'^ f

11 \11 NV

Notes:

Sensors at 81, S2 Any, AO and Ay. A^ relative to SO (arc-sec) is

Sign checit of Ay. Ad at S7, S2 identifies symetric mode ^^ o u

Rate limiuon Ay' - .TSarcaee/wc

Ad - .50 arc-sec/sec

Thmst limit - .13 N 

00 ° i

Figure 3.3-20. RCS (Resisto Jet) Control of Symmetric Bending Modes Response

to 1000 N-m-sec Torque in Pitch
a

0483-10012-2

3.3.6 Vibration Suppression of Symmetric Modes

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.

r

Accordingly, the purpose of the task was to take a quick look '.t the feasibility of using a

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

f' 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 3.3-20 illustrates the basic simulation configuration used in the analysis of

r candidate control laws. The .13N force ionized gas thrusters were placed as shown at

locations A, B, C, and D. There are two positive x-direction thrusters, locations C and

l?, and two negative x-direction thrusters, locations A and B. There are four positive and

r

four negative z-direction thrusters. Angular rate and linear position sensors are located

at the center of the station core and at the ends of the solar array booms, locations 50,

t 51 and S2, respectively. Symmetric bending occurs in both the x-y and y-z planes. Peakfli

to-peak amplitudes of the displacements and the rates are small, as mentioned

x; previously. Peak values of rotational displacements and rates sensed at ends of the solar

array booms in the x-y and z-y planes are about 4.5 aresec and aresec/sec.

r

3.3.6.1 RCS Control Logic

s^

The RCS thruster control logic was implemented in the form of a rate damper. The

angular rates sensed at locations S1 and S2 were chosen as rate feedback signals to the

i RCS control logic. Since the CMG's are quite effective in damping the other bending

modes, it is desirable to use the RCS thrusters to damp primarily the transverse

symmetric modes. An angular position check comparing the signs of deflection at

locations S1 and S2 was implemented to filter out the symmetric modes.

3.3.6.2 Motions Analysis for RCS Controller

Figure 3.3-20 shows the effect of rate-damping the transverse symmetric modes wi

the use of RCS thrusters. The rotational rates about the z-axis shown in Figure 3.3-:

113
v

t

D483-10012-2

m

were reduced from the undamped 4.5 aresec/:; to less than .4 aresec/s peak-to-peak in 25

sec. less desirable performance was observed in the y-z ;lane. The z-axis thruster

firing and the rotational rates about the x-axis indicate a new disturbance and RCS

thruster chattering. As the solar arrays were modelled as lying in the x-y plane, minimal

excitation of the solar array bending modes occurred. However, in the y-z plane, the

RCS thruster firings result in the excitation of the solar array symmetric bending modes.

Although the rotational rates are reduced from the undamped rates of 4.5 aresec/s to

less than 1 aresec/s peak-to-peak, the continuous RCS thruster firing may not be

desirable.

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.

3.3.7 Modeling of Stiffer Solar Array Structures

G

.. J

. i

., 

a

The preceding discussions clearly 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 controllability of solar panels with

improved stiffness must still be determined. The problem is to compare the structural

motions of the SEPS type array with the stiffer arrays for controller 1, viz., assuming the

panel drive actuators are locked.

3.3.7.1 Waffle Grid Solar Panels

A solar panel design of current interest at Boeing is shown in Figure 3.3-21. 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 SEPS array mass.

i114
D483-10012-2

3.3.7.2 Motions Analysis for Controller 1

The Space Station flexible model with the wafflerid solar g pPanels included 21 flexible ,

modes up to the first panel bending mode of 1.05 Hz. At control bandwidths of interest

all significant bending and torsion is seen to occur in the supporting structure, the panels

remaining essentially rigid.

r

The comparative response of the solar arrays and supporting structure is shown in Figure

3.3-22. Th^ simulation results indicate that the most severe motion is in pitch. It is

manifested primarily as symmetric boom twist and bending. Symmetric torsion in the

boom is mild;; augmented by CMG control, because some damping in pitch is required.

Yr Panel roll axis torsion and accompanying vibrations in the supporting structure were j

found to be negligible. Y

I ^ l

i v

i y

t

j r

I

M,.

115

i
D483-10012-2

• Substrate backed by lightweight waffle grid structure•

• Foldable panels with tapered thickness

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

• Packaging less efficient than SEPS type solar array

• Mass increase over SEPS type by 2.5

Figure 3.3-21. Waffle Grid Solar Panels

Ae 4

m^ mA 0

0

M

eeN o e0NE.a

•1N0 10 A A N •IJ

T1..

eye,

me,

eme,

- Ta -. Tm

Figure 3.3-22. Appendage Response Comparison of SIPS with Waffle Grid Array

CMG Controllor, Panel Drive Actuators Locked (arc-sec)

116

I,

4

-I^

r .^

II

•_ is

i

i r--

I

ji,

FI

YoY

1N

FFJ

Ee 10 T^e A N

!En we"llow

N ^ eyN E

.1^ N

o.o mp e

•IN

ae ^ N®

ey

mr

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tN E

eEb a ms a

l^ Is

eti a eM eJ

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rw

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;

nml

FFJIW^ ^^ 10 TMr A N

eye

m,

4,

ml

en
:. e. .. •_ °%'APL—icy

1

I

1

D483-10012-2

3.4 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.

3.4.1 SEPS Arrays

3.4.1.1 Loads and Motions with Locked Panel Drives

• Dedicated vibration suppression required for solar array torsional modes.

• Results based on worse case ad hoc disturbance model.

• Stability guaranteed at control bandwidths of `merest.

3.4.1.2 Control Laws

• 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.

o Simple RCS symmetric bending mode damper with antisymmetric discriminator is

effective and feasible.

3.4.1.3 Active Control

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

• Current SOA relative motion sensors are adequate.

3.4.1.4 Passive Control

• Root mounted damper best choice for mr^t isolation, least sensitive to parameter

variations.

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

117
D483-10012-2

3.4.2 Stiff Solar Arrays

3.4.2.1 Motions with Locked Panel Drives

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

suppression controllers.

• Mass increase by 2.5.

118
D483-10012-2

3.5 CONCLUSIONS

The conclusions of the study can be summarized as follows. 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 to the bandwidth of the sensors and actuators, all modes in the proximity and

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

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

one of augmenting uncontrollable modes when such augmentation is necessary. The

study has shown that coordinated control using' collocated sensors and actuators will

provide effective vibration suppression. In this particular application it was shown that

CMG control of the central modular core, in conjunction with the panel positioning

actuators, 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, attitude control development

for a 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 where SEPS 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, insuring the

stiffness of the supporting structure is adequate.

3.6 RECOMMENDATIONS

Continuing effort in attitude control for space station 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.

3.7 REFERENCES

1. "Space Station Systems Technology," Volume 11, Final Report, D180-27935-2.

119

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D483-10012-2

a 4.0 CONTROLS AND DISPLAYS FOR OMV, OTV do SPACECRAFT

N SERVICING, FLIGHT OPERATIONS & FUNCTIONAL OPERATION

(y This section presents the results of a study conducted to characterize a ;multifunction

workstation on-board Space Station for the servicing and operation of spacecraft. This 1

EAR characterization could potentially fulfill all the workstation needs for Space Station

which would incorporate a high degree of design commonality.

k \ S

4.1 Introduction

^

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'r 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

Tinterfaces and vital function to the safe operation of Space Station. It is an area that is

r

rapidly advancing. Efforts to develop this technology could benefit the Space Station if i

they were conducted for Its specific needs. This study will identify 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.

The following paragraphs report on the approach, results, conclusions and recommendations _,,esulting from this characterization study and also provide a technical discussion of j

7 the study elements,

4.2 Approach

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

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

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. The methodology flow is illustrated in Figure 4.2-1.

120
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D483-10012-2

4.2.1 Definition of Functional Requirements

i

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

ar

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. The scenario is presented in

Figure 4.3-1 and Table 4.3-1.

The 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.

In developing the scenario, we drew on our recent OMV simulation experience. A realtime simulation was developed to study operator performance during a remote rendezvous and docking operation. A simple workstation was built for this purr.ose and is shown

in Figure 4.2-2.

4.2.2 Review of Flight Deck Control and Display Technology

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

its 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. The review included the research done for the

Boeing 757/767 flight deck, Bl-B aft control stations and Air Force Flight Dynamics

Laboratories' Pictorial Format Displays contract (figures 4.2-3, 4. 2-4, and 4.2-5).

4.2.3 Design of Conceptual Configurations

Based on the results of Tasks 4.2.1 and 4 . 2.2, two workstation configurations were

developed that satisfied all the scenario functional requirements and operat

efficiently. Hardware specification at this point was limited to equipment characte

zation, i.e., visual displays, full color, high resolution, 10-inch and 15-inch diagou

sizes. The configurations are illustrated in Figure 4.3-2. Software specification %

also limited to characterization at this point.

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' 4.2.4 Identification of Technologies Required f

Due to the unique conditions of Space Station, the hardware and software required tc

Implement the workstations led to the examination of Innovative technologies. These

technologies included flat panel displays, programmable switches, hand controllers, voice s'

recognition, voice synthesis and touch input devices. Various options within each

technology were evaluated for compliance with Space Station restrictions.

k

4.2.5 Technology Trade Studies

_

!^

Those technologies found to be most promising during Task 4. 2.4 were evaluated further

i

on a cost/benefit basis. The new technologies were compared to their existing

I

respective counterparts in terms of power, weight, volume, crew time, recurring and

nonrecurring costs.

' 4.3 Technical Discussion t

The foilewing sections include a detailed discussion of the study outputs with illustrations. The order follows the sequence of the Approach subtasks.

4.3.1 Definition of Functional Requirements

The next two subsections preaant the discussion of the mission scenario development and

functional analysis upon which the conceptual workstation configurations were based.

4.3.1.1 Mission Seenatio

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

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

experience.

I'

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

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

I

scenario was broken into phases as shown in Table 4.3-1. Below each major mission

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

127
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D483-10012-2

Table 4.3-1. OMV Mission Scenario by Mission ,°hase

1.0 Prelaunch checkout requires C&0 and EVA operators

• Powzrup 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)

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

('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

- Select manual control

• Complete power-up sequence (C&D)

(Radar, Star scanner, etc.)

3.0 Launch OMV (requires C&D operator) -

• Fire GNz thrusters to move away from Space Station TED ft

- When at TBD ft switch to AUTONOMOUS CONTROL

Set up subsystem monitoring configuration

('may require two C&D operatorsto monitor functions*)

4.0 Rendezvous/dock/repair/retrieve (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 GNz 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
D483-10012-2

P' ,

•

'able 4.3-1. 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 GN2 to back up from target

With target 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 TB ft from Space Station

• Turn onloff pertinent subsystems

• Switch to GN 2 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 Free-Flyer from target spacecraft (C&D)

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

• Grapple Free-Flyer with RMS and move into Containment Area (C&D)

• Place in position and connect Umbilical (EVA)

• Download computers (C&D)

129

D006_ro3 I Ipg 2 '"^ ,j
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step in the scenario development served as the basis for further refinement in the

C

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ol functional analysis.

Even at this gross level, some of the important features of the workstation were already

evident. For examnle, a means of communication ) the EVA operator was necessary;'

some means of controlling the OMV and RMS was required; status information must be

presented and so on. The scenario basically served as an ideal pool for further

development during the functional analysis. However, certain items listed in the

scenario were not developed further: the EVA workstation was out of the scope of this

study; and insufficient data was available to further detail the repair task.

4.3.1.2 Functional Analysis

During this subtask several aspects of the mission description were completed. The

storyline of the scenario was filled out, including how each task could be accomplished.

The division of labor between the crew and the system was determined. An idea of the

crew workload level was obtained. Lastly, we were able to start defining the generic

equipment required to successfully complete the tasks.

ii

A summary flow diagram of the completed scenario is shown in Figure 4.3-1. It is keyed

to the detailed listing of the functional analysis presented in Table 4.3-2. 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.

Based on our recent experience with OMV and OTV we estimated that a ground crew of

10-20 was required to control such a vehicle remotely through an entire mission. Such

manloading is not feasible for Space Station. In looking for alternatives, we decided that

an expert system could greatly reduce the manpower requirements by handling the

subsystem monitoring tasks. However, the remaining tasks still appeared to create too

high a workload level for one operator. The division of labor became: one operator

primarily responsible for the operation of the OMV, and the other operator primarily

responsible for the operation of the RMS. Each operator would also serve as backup for

one another during critical tasks, i.e. docking to a target spacecraft. The expert system

would track subsystem status and monitor the ONIV in transit.

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From the functional analysis, several other facts became apparent. In order to control

the vehicle, an operator requires visual data on vehicle attitude and location In addition

to numeric data. However, some of the operations could only be handled by indirect

vision such as video or sensor data. For other operations, direct vision might be

desirable but it may also be difficult to accommodate and restrict Station operations.

Advanced avionics and information presentation are also required in addition to the

expert system, to handle the vast amounts of data generated during such a scenario.

4.3.2 Flight Controls and Displays Technology Literature Review

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

We were looking for new concepts and to discover problems with them or with the old

concepts. The results of the searches are listed below.

One of the most promising ideas for information presentation is the use of pictorial

formats. This concept relies on th,4 use of 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. In this way, the operator can make better use of his decision-making

capabilities rather using his time and energy in the data-gathering mode. This concept

has been researched extensively at the Air Force Flight Dynamics Laboratories at

Wright-Patterson AFB.

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. By using voice however, the visual channel

of the op=_rator is offloaded as well as one or both hands. Similarly, with voice output or F^

voice synthesis, the operator can listen to a message rather than have to read it. The

use of voice is being studied at several military research bases as well as at Boeing for

y

use in commercial cockpits.

The use of expert systems has already been mentioned: This also is a relatively new area

that appears to be quite promising for use on Space Station. Since a previous section in

this report addresses this topic, not much will be said here other than its use would seem

to reduce crew manloading requirements and crew workload.

148
D483-10012-2

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The use of multifunction displays and controls is not new but they still offer many

advantages. A multifunction display or control is one that is not dedicated to one

particular function. The display may present navigation data at one point, then when

requested by the operator, change to a • logistics display or any other desired display. The

same concept is true for multifunction controls. The underlying idea is that only the

information necessary or desired at any one time is what is displayed and no more. For

example: if an operator is controlling an OMV, information on the supply module is

unnecessary so it should not be cluttering up the panel.

The last concept to be discussed is eye-gaze control. With this method, an operator's

eyes are monitored to determine where they are gazing. The operator's gaze activates

or deactivates the control as the case may be. As such, this technology was not pursued

any further.

4.3.3 Conceptual Workstation Configurations

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 4 .3-2. The primary difference between the two configurations is that 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. The following discussion presents the general

features of the workstations.

As mentioned earlier, one configuration uses a window while the other does not. Direct

vision is usually the preferred means of viewing an operation. De pth perception, relative

rates, resolution and color detection are usually better with direct vision. The window

size was conceived to fill a visual angle of 60-degrees. This is the size of the normal

binocular vision cone without eye or head movement.

However, an operator's field of view and line of sight are limited by the size and location

of the window. Requiring a window at the workstation further restricts the operator

since the operator can no longer move to another window or workstation to perform the

task.

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While remote vision is not as desirable due to loss in resolution, color and lack of depth,

r' it does offer other advantages. If the sensor is mounted on a pan/tilt platform and has

zoom capability, the field of view can be changed dramatically while the line of sight

can be virtually limitless. Operationally, remote vision is used for critical OMV

operations such as docking to a target spacecraft or payload and repairing another

( spacecraft by using a robotic arm. Grappling a spacecraft with the RMS also requires

remote vision.

The geometry of the workstation is based on zero-g posture, line of sight and reach

envelopes for the 95-percentile male to the 5-percentile female. It was assumed that

adjustable foot restraints were either not available or not functional so that all

crewmembers' feet would be basically at the same height above the floor.

The following paragraphs discuss the specific features of the workstations. The number

preceeding each feature is keyed to Figure 4.3-2.

(1) The displays must all be high-resolution, full color graphic displays with a short risefall. time for dynamic scene presentation. The center display is a 15-inch diagonal

screen, primarily used for the presentation of sensor and graphic data directly related to

the control of OMV or RMS. The three other displays are 10-inch diagonal screens, also

high-resolution, full-color graphic type. These displays are primarily used for subsystem

data presentation, one subsystem per display. An alternative method is to use larger

screens, reduce the total number of displays and partition the screens for the simultaneous display of various system and subsystem information on the same screen. This

screen partitioning method has been used successfully in many ground control situations.

Any display should be capable of presenting any type of information on any system or

subsystem that is requested by the operator. Hence, they are called multifunction

displays. The information can be presented in several different types of formats,

w sP

including pictorial, graphie-, analog or video, in color or monochrome. Examples of some

format concepts are shown in Figure 4.3-3.

1

(2)&(3)Programmable switches offer many advantages over dedicated switches for a

number of applications. Most switches at a workstation are used a very small percentage d

of the time during a mission. As a result, much of the panel real estate is occupied by

many switches that may only be used once during an entire mission. A few dedicated

a programmable switches can replace many switches. Alphanumeric as well as graphic

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g D483-10012-2

data can be displayed to match the programmable switches and changed as desired.

These switches can be used to lead an operator through a checklist or present status

Information. They can include caution and warning messages in addition to simple on/off

indications. Most important, only the data, controls or checklists required need be

displayed at any one time. Programmable switches can reduce operator error rate,

workload level and training requirements.

(4) Certain functions, however, do require a dedicated switch. Specifically, any function

that is life-sustaining (Environmental Control/Life Support System) or perhaps critical to y'

the safe operation of Space Station (Coinmunications) should have a dedicated switch

that is hardwired rather than tied to the data bus. Many types of dedicated switches

exist and can be suited to the needs of this workstation. v

(5) Some means of rotational and translational input is necessary for the control of OMV 7

and RMS. Traditionally, two three-axes hand controllers have been used, one for

translation and one for rotation. When an operator is responsible for additional tasks i

other than vehicle control and has both hands occupied, real problems can result. Cne

s?x-axes controller offers the advantage of freeing one hand while putting all the motion

V

axes in the other, potentially increasing the accuracy of control. Some preliminary J

studies using the six-axes controller thus far have not indicated any training problems

nor any cross-control problems.

(6) Touch input d=vices allow display screens to make control inputs. Highlighted areas

or objects can be touched on the screen for convenient control. Touch input devices are

relatively new devices but have had high user-acceptance thus far. They could be used to

make display selections, move a cursor or possibly draw graphics. Touch screens are the

most common but are not very well suited for Space Station use. While the resolution of

touch screens has improved from the early versions, accidental activation can still occur. 4

In a free-floating zero-g environment, the likelihood of accidental activation may be )

higher, which would be hazardous. Touch pens are an alternative that use a stylus to

activate a statically charged screen. The screen is only activated when touched by the

stylus thereby reducing the accidental activation problem. While using a stylus is very

natural, it may pose some reactionary problems in the zero-g environment.

(7) Research has indicated that 90% of the information we process is received through

the visual channel. As such, that channel usually tends to be overloaded. Voice J

recognition and synthesis offer alternative means of operator input and system output.

E 1

153
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A^W^ D483-10012-2

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By using voice recognition, an operator does not have to divert his attention from the

F task at hand to locate the keyboard and type in the data. Addressing the computer and

saying the data would be a convenient alternative. Similarly, using voice synthesis

allows an operator to continue working at the task with t having to again divert the

operator' s attention to look at a screen for the computer output. A synthesized voice

could just tell the operator the results. This is also an excellent means of getting the

operator's attention for a caution or warning message.

A voice recognition system has been characterized for this purpose. The characteristics

include: ( 1) capable of recognizing connected speech at least but would prefer

continuous speech recognition; (2) at least 500 words and phrases in the stored vocabulary with 100 to 150 words and phrases available at any one time; (3) capacity for a

minimum of 70 vocabulary subdivisions; ( 4) require 2 or less training passes per word or

phrase; ( 5) recognition accuracy of at least 99% and a ;ombined substitution and- false

acceptance error rate of less than 0.05%; response time :)f 0.1 sec; and (8) capable of

speaker identification and adaptability.

A voice synthesis system also has been characterized for the workstation. Its features

include: (1) speech generated by using phonemes rather than a prerecorded digitized

voice; (2) a minimum vocabulary of 20,000 words; (3) generate speech that is distinctive,

intelligible and coarticulated; and (4) generated speech that is capable of intonation,

inflection and is speed-variable.

(8) A keyboard is also provided for data entry, so an operator may have the choice of

data entry method - keyboard, voice recognition or touch input device. The keyboard at

this workstation was c pneeived to use programmable switches. This implementation

allows the keyboard to be configured in standard QWERTY fashion or in special

configurations specifically suited to the task at hand.

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(9) A clipboard is provided at the workstations for the operator to use as desired.

(10) A Head-Up Display (HUD) was incorporated into the windowed workstation a.,

unique feature. A HUD is an instrument where relevant computer-generated dynar

symbology is projected onto a clear combining surface mounted in the operator's field

view, thereby overlaying the symbology on the viewed scene. The operator then has

necessary information in his immediate field of view, lessening eye accommodation i

attention-diversion problems. An example of a HUD developed for commercial alrer

154
M, 777 ..

D483-10012-2 7

is shown In Figure 4.3-4. The symbology includes an airplane, flight path angle, horizon

and pitch ladder representation. The symbology is csrlaid on a runway scene.

The HUD for Space Station application would be used to present control and status

information graphically while directly viewing an OMV or RMS operation. When the

operation was not in the line of sight, the HUD would display sensor information overlaid

F

with control and status information graphics. The HUD should be fairly large so that the

operator's head does not have to maintain a fixed position which could be quite difficult

In zero gravity. If the display was not large enough, the operator could lose the 4

symbology with head movement. Here, the HUD was conceived to fill the same visual

angle as the window.

Two other technologies were identified as part of the workstation but are not

represented in the figure. These include computer-generated imagery and artificial

intelligence/expert systems; both are software -based technologies. The y are discussed in

the following paragraphs.

Computer-generated imagery (CGI) can include various forms of data representation

fa.

from simple graphics through detailed dynamic scenery. The entire range of CGI types

would be used at this workstation. The workstation computer hardware and software

must be capable of generating the full line of CGI, boti; in real-time and in nonreal-time. °< I

Nonreal-time generation requires additional storage and retrieval capabilities. In

addition to the stored or canned graphics, the software should allow the operator to

eo.)rnpose unique displays easily.

As mentioned earlier, an expert s1stem is required to monitor the OMV subsystems and

in transit progress. This expert system N necessary to maintain an appropriate level of I

operator workload. The expert system would also interact with the caution and warning

systeci ind the voice synthesis/recognition system. Since expert systems were studied in

a parallel effort with the controls and displays and were discussed earlier in this report, ^•

no further discussion will be found in this section. t

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4.3.4 Technology Identification

The following subsections present the pros and cons on the various options for the

technology items presented in the previous section. ` .g

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4.3.4.1 Displays

The standard for display comparison is the cathode ra; tube (CRT). CRT's are readily

available in many sizes, with low-, medium-, or high-resolution, and with full color or

monochrome screens. The rise-fall time of CRT's is very short (approximately 0.1

millisecond) making it ideal for the presentation of dynamic imagery. However, CRT's

are also very heavy, bulky, consume much power and as a result dissipate much heat

requiring forced-air cooling. These c ,atA,_'scks could have a serious effect on Space

Station consumables. Potential source: Hitachi, Mitsubishi, Tektronix.

Flat panel technology is the current replacement for CRT's. Typically, these displays

are quite shallow in depth, 1-2 inches versus 12-14 inches. They are usually lighter in

weight and have low power consumption. Due to the low power requirements, they have

a longer lif and higher reliability. Three flat panel technologies seemed to warrant

further investigation for use a a multifunction display: liquid crystal displays (LCD),

plasma displays and thin-film electroluminescent (TFEL) displays. These technologies

are discussed below.

For comparison purposes only, the display information in Table 4.3-3 is provided. This

information was compiled from a report done at VPI&SU (ref. 1). Note that the display

technology field has advanced significantly since the report was published.

Liquid crystal display technology is probably the most promising of all the flat panel

technologies. LCD's are among the lowest power consumers, do not require forced-air

cc.oling and have few inherent limitations. They are much lighter in weight than CRT's

and are much smaller in volume, typically only one to two inches in depth. LCD's have

some drawbacks however. Currently, the majority of displays are monochrome with

tricolor and full color displays just being developed. The resolution is no greater than

medium for the best monochrome and low for color displays. Only small sizes are

available. The rise-fall times have been shortened from what is reported in the table.

Potential source: PaneiVision, Seiko.

Plasma displays are also thinner and lighter than CRT's but their power consumption is

not tYubstantially lower. They do not require forced-air cooling. . The resolution of

plasma monochrome displays tends to fall in the medium to high category. They are

available in many sizes, from small to very large. Color displays do exist but are

157
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small, have low resolution and luminance. Their availability is limited. Potential source:

Hitachi, NHK Labs.

TFEL displays have similar power, weight and volume characteristics as plasma displays

and are typically available in the smaller sizes. Neither tricolor nor full color displays

have been demonstrated and some color shift problems have been reported with the

monochrome displays as they age. Potential source: Texas Instruments.

4.3.4.2 Programmable Switches

Flat panel technology is also being used in programmable switches. 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 both military and commercial

aircraft application.

LED's are available in tricolor units. They produce red and green colors separately.

Combined, the two produce amber as the perceived color. The resolution of these

switches is sufficient to present good-quality graphics as well as legible a.lphanumerics.

They are heavy power consumers, however, and require either forced-air cooling or a

cold plate to remove excess heat. The LED's can be packaged into a switch size (1.0 x

.75 inches) or into a larger display area (2 x 3 inches) with one-inch units edge-abutted.

Potential source: Microswitch, Littzin Systems.

TFEL light bars have also been incorporated into switch housings using a touch screen for

activation. Currently, they are only available in monochrome units in green and amber.

Other colors are certainly feasible using different dyes. Tricolor units are not

commercially available. Again, these are heavy power consumers and require a cold

plate for cooling. The resolution is comparable to the best LED switch. Potential

source: Microswitch, and FarWest Manufacturing.

The incorporation of LCD's into a switch housing is a very recent development and is

quite immature as a technology. It will certainly benefit from the research going on in

the display area. Tricolor switches are feasible but are not yet commercially available.

As with the larger LCD displays, the switches are lower power consumers and do not

require cooling. Potential source: Litton Systems.

.. i

159
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D483-10012-2

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4.3.4.3 Dedicated Switches

As stated in the previous section, many types of dedicated switches are currently

available. Some of the types include toggles, pushbuttons, discrete and continuous

rotaries, lever locks, etc., all of which can be guarded or unguarder. Potential source:

Korry, Microswitch.

4.3.4.4 Hand Controller

These are two methods of implementation for hand controllers. The first is the

displacement type where the grip alone or the grip and shaft can move an appreciable

distance, usually up to 0.25 to 0.50 inch. The second method is a force-feel type where

the grip and shaft move a very small distance but the force input is actually detected by

pressure transducers. A displacement type controller is in the prototype stage and the

results from preliminary testing have been good. A force-feel type is in the design

stages. Potential source: CAE Electronics, Lear Siegler.

4.3.4.5 Touch Input Device

' The most common }.ouch input device presently is the touch screen. There are two basic

methods of implementation: beam-interrupt and pressure -sensitive overlay which is

implemented in different ways. Pressure-sensitive screens usually have better resolution

than the beam-interrupt and are less p prone to accidental activation. With either

implementation, the screen surface tends to smudge from fingerprints. Potential source:

Hewlett-Packard, MicroSwitch.

The touch pen is an alternative to the touch screen. It uses a stylus to activate a

statically-charged mesh overlay which also serves as a contrast enhancement filter.

Since the stylus is needed to activate the screen, the chance of accidental activation is

less. The resolution of this device is also fairly high. Potential source: Sun-Flex Co.

f

4.3.4.6 Voice Recognition and Synthesis

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

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

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

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160
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D483-10012-2

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

source: Texas Instruments, ITT.

Voice synthesis is much further advanced than voce recognition. Stored vocabui.aries

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

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

choice of voice types. Potential source: Digital Equipment Corp., SpeechPlus.

4.3.4.7 Head-Up Display

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 his eyes in a fixed position In space in order

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

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windscreen. This technique may be applicable to the Space Station needs. Potential

source: Svena.

4.3.4.8 Computer-Generated Imagery

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, 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. Potential source: Lexidata, ADAGE.

4.3.5 Technology Trade Studies

The previous section I;resented various technology alternatives or described what stateof-the-art systems could do. This section will describe the technology option that

appears most promising and evaluate it further on a cost/benefit basis. The qualitative

and quantitative results are shown in Tables 4.3-4 and 4.3-5.

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4.3.5.1 Liquid Crystal Display

Of the flat panel display technologies, LCD appears to be the most promising. In

addition to the technical market, LCD technology is receiving much support from the

consumer market. Some problems still have to be resolved however. The major problem

is a full-color display. Such displays have been demonstrated but they have their

shortcomings2 . One method is to use some type of backlighting, either TFEL or a lamp

source and produce the color by field -sequential techniques. Using either of these

techniques requires a high power illumination source thereby reducing the low-power

advantage. The other method involves using various dye deposits in the crystal matrix.

The colors thus far have not been as saturated as CRT colors and the luminance level is

quite low whe y, compared to CRTs. Resolution is quite low also. However, this

technique dots allow a color display while maintaining a low power profile and seems to

offer the greater advantage for Space Station. This technique is actively being

developed in Japan.

When LCD's are compared to CRT's over the life of Space Station, the benefits could be

significant. Eve. though the development costs will be high ( $3 million, not 3 million

percent), the savings in power, weight and volume in addition to the increased reliability

and reduced production costs could prove to be quite advantageous.

4.3.5.2 Programmable Switches

At present, the LED technology is the most promising for use on Space Station. It is

already developed, tested and used in various applications. The switchas can be heavy

power consumers when all of them are lighted. However, the duty cycle of the individual

LED's per switch and the duty cycle of the switch bank as a whole mt.st be evaluated

before a determination of real power consumption can be made.

As LCD color technology progresses, the application of this technology to programmable

switches would again prove beneficial to Space Station. As shown in the table, the

production costs and power savings are significant when compared to the LED's. Therc

will not be any savings in weight or volume since the major factors in those two

parameters are the switch housing and mechanism. They will be basically the same

regardless of the flat panel technology used.

165

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D483-10012-2 j

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Currently the TFEL technology does not appear promising for a tricolor display.

Manufacturers have quoted a development time of approximately 10 years. There does

not seem to be much of a push on this technology.

4.3.5.3 Dedicated Switches

,J•. No required new development indicated. Present equipment is satisfactory.

4.3.5.4 Hand Controller

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The displacement six-axes controller seems to be the most promising new technology for

this application. The table may be misleading in reporting no development costs

however. Since this item is not yet in production, some of the nonrecurring costs are

rolled into the production costs for the units. Since there is only one controller per

'

station, there is a reduction in weight and volume as compared to using two three-axes

controllers. The power consumption will probably be the same since the total number of

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axes is the same and the number of input/output signals is the same.

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The touch pen appears to meet the needs of this workstation the best. Since it is an item

already developed, the only risk is the space qualification of the item. The production

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r z, mentioned in the previous section may outweigh the slightly higher costs.

E4.3.5.6 Voice Recognition and Synthesis 3

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The costs for a system that will meet the requirements described earlier is rather high j

when compared to the current systems. However, such a system does not exist and the

s current systems could do the job but not as efficiently. A significant cost factor that is

not reflected in the table is the cost per hour of the operator's time. The reduction in

crew time required for an operation could be significant and may be great enough to

offset the initial high costs of procuring the system.

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D483-101!12-2

4.3.5.7 Head-Up Display

At this time it is rather difficult to assess the costs of developing a HUD that would

meet our requirements. First, the need for a HUD needs to be established. If there is a

need, the field of view requirements need to be evaluated. At present, no such

technology exists for such a wide field of view display and it is not clear how it could be

!mplemented. w ^'

4.3.5.8 Computer-Generated Imagery

At this time, it is difficult to assess a need for further development of CGI hardware or K

software. Until such time as the formats are defined, no trade studies can be made on

this topic since no requirements as yet exist. t

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ll4.4 SUMMARY OF RESULTS

ll An OMV rendezvous and docking scenario was developed. The premise for the scenario

y^ was controlling the OMV from the Space Station with no ground control intervention. A

functional analysis was performed on the scenario to determine division of labor between

the operator and the computer system, the number of operators required and to

t

characterize the workstation. Two workstation configurations were designed, one with a=

k• window for direct viewing and one without a window using remote viewing. The

technology required to complete the workstations was evaluated based on the goals of

low power consumption, low weight and volume, high reliability and favorable human

interface characteristics such as sufficient luminance, good color saturation, safe and

easy operation. The promising technologies were then evaluated for recurring and

nonrecurring costs and compared to existing technology costs.

4.5 CONCLUSIONS

B

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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:

167 ^.
j D483-10012-2

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i yV o Liquid .Irystal display technology for use In both multifunction displays and

programmable switches. Beside the Space Station benefits already discussed, this

technology would also benefit the consumer market and high-technology areas.

'e

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:

o Touch pen or screen

o Dedicated switches

o LED programmable switches

{

4.6 RECOMMENDATIONS

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

^. include:

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

g

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

the workstation as well as in the module.

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

size, location at the workstation, presentation of sensor data, illumination and

trans m iss ivity.

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

' ments.

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0.7 REFERENCES

1. Snyder, Harry L. Human Visual Performance and Flat Panel Display image Ouality.

Office of Naval Research, Code 455, Department of the Navy, .Arlington, VA. 1-.y

1980. ONR-80-1.

2. Society for Information Display Digest of Technical Papers, SID International

Symposium 1984, San Francisco. Paper 13.4. Palisades Institute for Research

Services, Inc., New York. June, 1984.

169