The Air Force goal is to develop vibration control techniques for large flexible spacecraft by addressing sensor, actuator, and control hardware and dynamic testing. The Active Control Evaluation for Spacecraft (ACES) program will address the Air Force goal by looking at two leading control techniques and implementing them on a structural model of a flexible spacecraft under laboratory testing. The first phase in the ACES program is to review and to assess the High Authority Control/Low Authority Control (HAC/LAC) and Filter accomodated Model Error Sensitivity Suppression (FAMESS) control techniques for testing on the modified VCOSS structure. Appropriate sensors and actuators will be available for use with both techniques; locations will be the same for both techniques. The control actuators will be positioned at the midpoint and free end of the structure. The laser source for the optical sensor is mounted on the feed mast. The beam will be reflected from a mirror on the offset antenna onto the detectors mounted above the shaker table bay. The next phase is to develop an analysis simulation with the control algorithms implemented for dynamics verification. The third phase is to convert the control laws into high level computer language and test them in the NASA-MSFC facility. The final phase is to compile all analytical and test results for performance comparisons

Pearson, J.

Yuen, W.

English

NASA Technical Reports Server

N87-16019
#,CTIVE CONTROL EVALUATION FOR SPACECRAFT (ACES)
J. Pearson and W. Yuen
Air Force Wright Aeronautical Laboratories
Wright-Patterson AFB, OH
First NASA/DOD CSI Technology Conference
November 18-21, 1986
F_.CEDI_IG pAGE BLANK NOT F|t.MF.D
67
https://ntrs.nasa.gov/search.jsp?R=19870006586 2020-03-20T12:06:46+00:00Z
THE LARGE SPACE STRUCTURE CONTROL PROBLEM 
Historically, spacecraft have been relat ively small a n d  s t i f f s  w i t h  
a1 i gnment and poi n t i  ng performed by ri g i  d-body techniques . 
requirements f o r  large space structures (high-resolution radars and 
antennas, 1 arge opti c5 and 1 asers) requiring accurate pointing and 
tracking, flexible-body control methods m u s t  be used. Figure 1 i s  a n  
a r t i s t ' s  i l l u s t r a t ion  of a representative spacecraft w i t h  a v  offset-feed 
antenna t h a t  will require active ccntrol o f  the al ignment  of the feed 
niast. The Air Force goal i s  t o  develop vibration control techniques for 
1 arge f l  exi b l  e spacecraft by addressi ny  sensor, actuator,  and control 
hardware and dynamic testing. The Pctive Coritrol Evaluation f o r  Spacecraft 
(ACES) program will address the Air Force goal by looking a t  two leading 
control techniques and implementing them on a structural  model of a f lexible  
spacecraft under 1 aboratory testing. 
Because of new 
Figure 1 
68 
ACTIVE CONTROL OF SPACE STRUCTURES (ACOSS) SIUDIES
The control techniques that will be studied in this program were initially
investigated in the Active Contro_ Of Space Structures (ACOSS) program
sponsored by Defense Advanced Research Projects Agency (DARPA). The ACOSS
program started in 1978; in six years it involved eighteen contracts and
seven major contractors to develop and demonstrate the technology to
suppress vibration in large space structures. The control goal was to
meet the stringent line-of-sight and jitter control requirements of
representative spacecraft. Various experiments with beams, plates,
trusses, and frame structures were conducted using damping augmentation
and elastic mode control. Disturbance models were developed, sensors and
actuators were surveyed, and system identification studies were performed
(Figure 2). The ACOSS studies were chiefly analytical, with limited
laboratory testing. The leading techniques resulting from this program
were High Authority Control/Low Authority Control (HAC/LAC), Positivity,
and Filter Accomodated Model Error Sensitivity Suppression (FAMESS).
ENVIRONMENTAL
_VIBF, ATION
CONTROLI
SENSORS
ACTUATORS
t
SLEWING
V VvV' ,'vv
INTERNAL
VIBRATION
• ANALYTICAL DEVELOP ACTIVE
CONTROL CONCEPTS
-LOW FREQUENCIES
-SPACECRAFT MODELS
-CONTROL ALGORITHM
• SLEWING AND ENVIRONMENTAL
DISTURBANCES
• QUANTIFYING POINTING
PERFORMANCE
Figure 2
69
VIBRATION CONTROL OF SPACE STRUCTURE (VCOSS) FARDWARE 
The VCOSS I program extended the ACOSS program by applying modern cont ro l  
techniques and s t a t e -o f  - t h e - a r t  hardware concepts  t o  the Draper Model two 
s t r u c t u r e  developed under ACOSS. The VCOSS I1  program was a coope ra t ive  
e f f o r t  between the NASA Marshall Space F l i g h t  Center (NASA-t4SFC) and the 
Air Force Wright Aeronautical  Labora tor ies  (AFWAL) t o  b u i l d  
s t a t e - o f - t h e - a r t  cont ro l  hardware ( o p t i c a l  s enso r s  and 1 i n e a r  proof niass 
a c t u a t o r s )  and apply i t  t o  a l abora to ry  test  structure c o n s i s t i n g  o f  a 
modified Astromast (F igure  3) .  The  hardware k a s  tested a t  the NASA-MSFC 
Ground Test  V e r i f i c a t i o n  F a c i l i t y .  TRW developed the cont ro l  hardware and 
Control Dynamics Company developed the tes t  structure f o r  t he  VCOSS I1 
program (Refs.  1-3). 
- . . . . . . . .- 
Figure 3 
70 
ACES PROGRAMDEVELOPMENT
With the analytical work and control hardware development completed urlder
ACOSS and VCOSS, the next step was to utilize the available structure and
hardware for comparing the control techniques. The Strategic Defense
Initiative Organization (SDIO) was interested in evaluating the relative
control performance of the techniques on the same structure and
sensor/actuator hardware. The Active Control Evaluation for Spacecraft
(ACES) program is designed to carry out this evaluation in a cooperative
DOD/NASA effort (Figure 4). A portion of the ACES work will be
contracted to Control Dynamics Company, who will prepare the structural
hardware and control algorithms for testing in the Marshall facility.
I-_XT
_- 80 i 81 i 82 i 83 i 84 i 85 i 86 i 87
ACOSS
(DARPA)
]__ vcoss i i_ vcoss i_(DARPA, AFWAL) (AFWAL, MSFC)
ACES
(SDIO, AFWL,
MSFC, AFWALI
Figure 4
PROGRAM OBJECTIVES
The objective of ACES is to assess leading control techniques for large
space structure vibration control (Figure 5) using a common structure and
fixed configuration of sensors and actuators. These control techniques
will be implemented in hardware and tested on the modifiea VCOSS structure
with optical position sensors and proof mass actuators. The control
objective is to minimize a line-of-sight pointing error between the
structure's offset antenna and the end of the feed mast structure.
• IMPLEMENT AND ASSESS LARGE SPACE STRUCTURE CONTROL DESIGN TECHNIQUES
• TEST THE CONTROLLERS IN THE NASA-MSFC LSS GROUND TEST VERIFICATION
(GTV) FACILITY
• MINIMIZE LINE-OF-SIGHT POINTING ERROR BETWEEN STRUCTURE'S ANTENNA AND
FEED MAST
Figure 5
72
ORBGlNAL PAG-7 
OF POOR QlJALW 
ACES STRUCTURE 
For the ACES program, the VCOSS structure i s  configured w i t h  an 
of fse t  antenna and counterbalance arm weights (Figure 6).  
truss structure i s  cantilevered vertically from a hydraulic shaker table  
and gimbal motors. 
connected such tha t  a helical triangular cross section truss i s  created; 
the truss supports only tension loads. There are  two bays, located a t  the 
m i d p o i n t  and f ree  end of the structure, f o r  placement of control 
actuators, 
aimed a t  a mirror on the of fse t  antenna; the reflected beam will be used 
as feedback by the controller t o  reduce the j i t t e r  t o  l e s s  t h a n  a 
specified line-of-sight e r ror  between the antenna and the end of the feed 
mast. 
The 13-met r 
Truss members are made from fiberglass and are  
A l aser  source i s  mounted a t  the top o f  the s t ructure  and 
Figure 6 
73 
PROGRAM APPROACH
The first phase in the ACES program is to review and to assess the HAC/LAC
and FAMESS control techniques for testing on the modified VCOSS structure
(Figure 7). Appropriate sensors and actuators will be available for use
with both techniques; locations will be the same for both techniques. The
control actuators will be positioned at the midpoint and free end of the
structure. The laser source for the optical sensor is mounted on the feed
mast. The beam will be reflected from a mirror on the offset antenna onto
the detectors mounted above the shaker table bay. The next phase is to
develop an analysis simulation with the control algorithms implemented for
dynamics verification. The third phase is to convert the control laws
into high level computer language and test them in the NASA-MSFC facility.
The final phase is to compile all analytical and test results for
performance comparisons,
• REVIEW AND ASSESS PROPOSED TECHNIQUES FOR TESTING ON VCOSS II STRUCTURE
• SUPPORT DESIGN, FABRICATION, AND INSTALLATION OF NECESSARY HARDWARE
• APPLY TECHNIQUES TO STRUCTURAL MODEL USING VCOSS II SENSORS AND ACTUATORS
• DEVELOP A GENERIC SIMULATION TO EVALUATE PERFORMANCE OF CONTROL LAWS
• COMPILE ALL ANALYTICAL AND TEST RESULTS FOR PERFORMANCE COMPARISON
Figure 7
74
ACESCONTROLHARDWARE
Major components of the control hardware will be provided by NASA-MSFC.
Existing hardware set up at the NASA facility for the testing includes a
shaker table from which the structure is suspended, three-axis base
accelerometers and gyros, and three-axis tip accelerometer and rate gyros
(Figure I0). The base shaker table will be used to apply the two
disturbance spectra to the ACES configured structure. A disturbance
signal generator, gimbal torque amplifiers, and a system health monitor
will be tied into a Hewlett Packard 9020 computer that is dedicated to
control. The HP 9020 is also linked with NASA's mainframe COMSEC computer.
Additional equipment to be added are bidirectional cold gas thrusters, an
optical detector system, and two gimbal systems.
SYSTEM CONSOLE
POWER SUPPLY
DISTURBANCE SIGNAL GENERATOR
GIMBAL TORQUE AMPLIFIERS
SYSTEM HEALTH MONITOR
MODIFIED ASTROMAST
HEWLETT PACKARD 9020
COSMEC 1
Figure 10
PRECEDING PAGE BLANK NOT FILMED
7@ --]%
77
HIGH-AUTHORITY/LOW-AUTHORITYCONTROLTECHNIQUE
TheHAC/LACcontrol technique, developed by Lockheed, addresses the
particular problem of instabilities in the system created by spillover(Figure 11). Spillover is the interaction of the controller with unmodeled
modes. The control design must not destabilize, poorly knownhigh
frequency modeswhile controlling the low frequency modes. HAC/LAC
approachesthis problem on two levels. The HACdesign incorporates high
dampingover a low bandwidth to meet performance goals; this is a
frequency-shaped extension of LQGmethods. The second level, the LAC
design, incorporates low damping over a high bandwidth to eliminate
spillover-induced instabilities (Ref. 4).
IMPROVED
DAMPING
RATIOR
PERFORMANCE
UNSTABLE
HACEFFECTS
HAC
BANDWIDTH
F ,ACj ' ZEG'ON
LACEFFECTS
LACBANDWIDTH
AUGMENTEDI __ ,I
DAMPING LAC_FREOUENCY --'-
IMPROVED INTEGRATEDHAC/LAC
DAMPING =
RATIOR [_PERFORMANCE REGION
UNSTABLE--'
HIGHAUTHORITY
• LARGEDAMPINGRATIOCHANGES
• EIGENVECTORCHANGES
• LQGSYNTttESISWITHFREOUENCYSHAPING
• ENHANCEDCONVENTIONALLQGROBUSTNESS
LOWAUTHORITY
• BROADBAND AMPINGAUGMENTATION
• ROBUSTAGAINSTMODELINGERROR
• SIMPLIFIEDSYNTHESIS(LEASTSOUARES,
JACOBI'SPERTURBATION)
Figure 11
78
, .
. .. , :
CONTROL CRITERIA
The goal of this test is to have the controller minimize line-of-sight
error between the antenna and the feed mast (Figure 14). In minimizing
this error, several criteria will be considered in evaluating each
technique's performance. These will include total reduction of
line-of-sight error, computational efficiency (meeting the speed and
memory requirements of the available digital system), arm robustness
(controller performance for off-optimum structural parameters). These
criteria will be applied to both disturbance spectra.
• MINIMIZE _NTENNA/FEED MAST LINE-OF-SIGHT POINTING ERROR
• DETERMINE PERFORMANCE OF CONTROL TECHNIQUES"
-ROBUSTNESS
-COMPUTATIONAL EFFICIENCY
Figure 14
PRECEDING PAGE BLANK NOT FilMED
81
PROGRAM RESULTS
The results of this evaluatior, will give a better understanding of the
trade-offs involved with each control technique (Figure 15). With the
number dnd location of sensors and actuators fixed and the control goal
specified, a good evaluation of the techniques can be performed.
By eliminating particular sensors or actuators and observing how
well the control techniques respond to this change in the system,
robustness will be determined. The control design must meet the
requirements of the digital system in terms of computational speed and
memory capacity. The effects of sampling and computational lags should
also be accounted for by the control technique. The degree of
line-of-sight error correction will determine the limits of control
technique capability with the available hardware.
• BETTER UNDERSTANDING OF CONTROL TECHNIQUE TRADE-OFFS
• ROBUSTNESS, COMPUTATIONAL EFFICIENCY, AND PERFORMANCE OF
TECHNIQUES DETERMINED
• A COMPARISON OF THE TECHNIQUES PERFORMED
Figure 15
82
PROGRAMAPPLICATIONS
The payoff from this program will be twofold. Capabilities of these
control techniques will be better understood, and these techniques may
then be applied to specific control problems in other programs (Figure
16). The Air Force Weapons Laboratory plans to use the results of this
program in determining a control technique for their Joint
Optics/Structures Experiment (JOSE) program. AFWAL plans to incorporate
one of the ACES techniques into the Large Space Structure Active Vibration
Control program and into their in-house Large Space Structure Technology
Program. The results from the ACES evaluation will also increase the
confidence in each technique.
FY 86 I 87 I 88 j 89 I 90
I JOSE(AFWL)
ACES L
LSS ACTIVE VIBRATION CONTROL(AFWAL)
I LSSTP(AFWAL)
Figure 16
83
REFERENCES
I. Lockheed Missiles & Space Company, Inc: Vibration Control of Space
Structures VCOSS A: High and Low-Authority Hardware Implementation.
AFWAL-TR-83-3074, July 1983.
2. TRW Space and Technology Group: Vibration Control of Space Structures
VCOSS B: Momentum Exchange and Truss Damping. AFWAL-TR-83-3075, July 1983.
3. TRW : Vibration Control of Space Structures (VCOSS II). AFWAL-TR-86-3073,
1986.
4. Control Dynamics Company: ACOSS Seventeewl (Active Control of Space
Structures). RADC-TR-84-186, Sept. 1984.
84


Active Control Evaluation for Spacecraft (ACES)

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server