Advanced smart structures flight experiments for precision spacecraft

Acra Asrmnaufica Vol. 47, Nos. 2-9, pp. 389-397, 2000 Published by Elsevier Science Ltd Printed in Great Britain 0094-5765/00 $ - see front matter

Pergamon

PII: SOO94-5765(00)00080-l

www.elsevier.com/locate/actaastro

ADVANCED SMART STRUCTURES FLIGHT EXPERIMENTS FOR PRECISION SPACECRAFT Keith K. Denoyer, R. Scott Erwin, and R.Rory Ninneman Air Force Research Laboratory AFRLiVSDV 3550 Aberdeen Ave. SE Kirtland AFB, NM 87117-5776. U.S.A. Phone:+1 (505) 846-9335 Fax:+ I (505) 846-8265 email: [email protected]

ABSTRACT This paper presents an overview as well as data from four smart structures flight experiments directed by the U.S. Air Force Research Laboratory’s Space Vehicles Directorate in Albuquerque, New Mexico. The Middeck Active Control Experiment - Flight II (MACE II) is a space shuttle flight experiment designed to investigate modeling and control issues for achieving high precision pointing and vibration control of future spacecraft. The Advanced Controls Technology Experiment (ACTEX-I) is an experiment that has demonstrated active vibration suppression using smart composite structures with embedded piezoelectric sensors and actuators. The Satellite Ultraquiet Isolation Technology Experiment (SUITE) is an isolation platform that uses active piezoelectric actuators as well as damped mechanical flexures to achieve hybrid passive/active isolation. The Vibration Isolation, Suppression. and Steering Experiment (VISS) is another isolation platform that uses viscous dampers in conjunction with electromagnetic voice coil actuators to achieve isolation as well as a steering capability for an infra-red telescope. Published by Elsevier Science Ltd.

These experiments are focused on demonstrating technological advances and examining integration issues related to large sparse optical array systems [I]-[3]. A concept for a deployed space-based optical system is shown in Figure I.

Figure 1. Concept for Deployed Optical System

To the meet the technical challenges of these and other high precision space systems, AFRL has been investigating and developing a variety of advanced passive and active technologies for isolating against disturbances, suppressing vibrations within a lightweight space structure, and the precision pointing of spacecraft and associated sensor payloads.

INTRODUCTION

During the past decade, significant advances have been made in the area of adaptive or “smart” structures. Adaptive structures are defined as a structural system whose geometric and inherent structural characteristics can be changed beneficially to meet mission requirements either through remote commands or automattcally in response to external stimuli [4]. These advances have included advanced control algorithms, new sensor and actuator technologies that allow integration into a structure, and lightweight efficient power electronics. The missing element for many years has been the successful integration and flight demonstration of these technologies to develop the necessary heritage for implementation into real

The primary goal of Air Force sponsored research and development efforts is the investigation and discovery of new technologies that provide new or enhanced defense capabilities, and the transition of these technologies into planned defense systems. A secondary objective is the commercialization of technologies for the development of consumer related products. The United States Air Force Research Laboratory (AFRL) is currently engaged in advancing technologies related to high precision deployed optical systems and other space systems requiring unprecedented structural stability and pointing accuracy. 389

\\orld space \I \tenii 1tils paper provides an wer\ le\r (11 four such c\pcrlment\-that are hr~ng conducted b! the Air Force Kcwarch l.ahcrrdtor\ 111coniunctlon ~.~th II\ acddein~c. Indu~trlal. and ~o~crnment partnw

MIDDECK

ACTIVE

CONTROL

EXPERIMENT

1 he M~ddecl\ Act~\c‘ Control F.\pertment (MAC’F ) [i 1 I\ d bpace shuttle tltsht zxperlment 11hlch tie\+ OH S I S-67 111 March 1995 MAC‘I. was funded h\ NASA L.an:leh Resrarch Center (NASA I.aKC) and ~omtl> debelopcd b\ the Ma\sachusrttA lnstnutc oflechnolog> (M1T) and Payload System<. Inc The experiment I\ deslgned to investigate modelmg and control ISSUC‘S needed to achwc high precision pomttn, u and L lhration control ot tuture spacecraft systems Ihe hlACL ekperlment IS sho\+n durmg operatwn on STS-6’ m Figure 2.

Figure

2. MACE

in Operation

During

STS-67

I he prtmar) objectwe ofthe or&al MACE csperlment \+as to demonstrate the effectiveness of structural control m impravmg spacecraft stabtIlt and to assess the predictabillt! of controller perforniance based on analysis and I-g testing 70 accomplish these ob,jectlves. a varwt! of techniques were developed to obtam accurate O-y models. along with assoctated parameter uncertaint! models. usrng finite element modeling and l-g ground testing. These models were then used to destgn a vartet\ of filed-gain control laws which were demonstrated on orbit and later modified during fltght to improve performance and robustness using on-orbit data. The euperlment was hlghl! successful and demonstrated that structural control could be effectively accomplished us~ng the developed technique5

Iksp~te thcsc slgmticant achie\etnents. the MAC.f: pro<‘ram also revealed several limitations of the modelbased ti\-ed-gain linear control approach These limltiltlons Include: slgniticant expense and time ,!ssocrated \\ith de\eloptnz high tidelit? finite element models needed for control design. loss of robustness due tn unhnown or unmodeled O-g dynamics. difiiculite~ m handims nonlinearnles. and the potential for loss of

pertormancc or ln\tahlllt) due 10 time-bar! mg d\narnlc\ or- wdden t’:tllure> of wnsors and actuators

I o ,Iddrrs\ thex dtf.ticultre\. thcrc hrl been a s~gniticant intc‘rest In using adaptive methods for controlling structurns III high precision aerospace appltcattons. I his IS heoffer the potential to c;,,,>c adapt]\ c methods ~utonomousl> adjust to system characteristics different trom those modeled or seen m qualllication testing. This I\ especlall\ true of spacecraft.which are generally testrd In a I-g en\tronment Despltc extensive research, “clACf t and other experiments habe shown that it remaIn\ e\tremel> difficult to predict on-orbit O-g beha\Ior In addltton. \>stem dynamics often tend to be t~rne hark III~. This can take the form of SIOM.changes due to dr:radation of matertak and agino of the spacecraft or sudden failures such as the loss of a sensor or actuator I hew eient5 become increasingI> likeI> as spacecraft hecome more complex and are expected to be in service for longer periods of time. B!’ decreasing modeling and trstmg requtrements. lowering operations and maintenance activities, and Increasing reliability. adaptive methods have the potential to significantly reduce cost and increase performance of these systems. Because ofthese potential benefits, AFRL has conducted a series of programs to further develop adaptive control methods. particularly those that utilize artificial neural net\vorks. The use of neural networks has become increasingly mature m a number of areas such as Image processin! and speech recognition. However. despite a number ot publications on the subject. very few instanct‘i exist where neural networks have actually been used In control (particularly structural control) applications. One such application has been the demonstration of neur&network-based feedforward cancellation algorithm ttir rejecting multl-tone disturbances on the Air Force’s ASTREX test article [6].[7]. Other efforts are also currentI> underway to demonstrate adaptive neural structural control and other control approaches on the UltraLITE Phase I ground experiment. [8]-[ I I]. Specific issues addrewd include- developmg more reliable methods for predicting convergence and performance of the algorlthmh. reducing the prohibitive computational burden needed to implement adaptike control. and familiarizing the community ofpotential users \\ ith adaptive methods.

\\ u e\tenslon of these efforts. Af’KL 15 no\+ conduct“1~ 2,1.4CE II. which fill be the tirst experiment to Investl:atc and demonstrate adaptive structural control in a rnrcwgravit!, space environment. MACE II will ansirer Le! questtons about the abilit) ot.adapttve control algorithms to maintain performance of a complex space sybtrm as Its d> namics change from 1-gqualification testing to 0-g. It utll also demonstrate the capability to autonomousl> recover from subsystem failures such as the loss

50th IAF Congress of an actuator or sensor. MACE II is being conducted by a diverse team that includes representation from govemment, industry, and academia. In addition to AFRL. other team members include: MIT; Planning Systems, Inc.; the University of Michigan; Payload Systems, Inc.; Virginia Polytechnic University (VPI); Sheet Dynamics, Ltd.; Lockheed Martin Missiles and Space: and NASA LaRC.

392

eration. Some specific objectives

I.

Demonstrate that ground-achievable can be achieved on-orbit

without

performance

the need for con-

trol redesign. 2.

Demonstrate autonomous such as sensor/actuator

Description

include:

failure recovery to events

failure.

of the Test Article

The MACE II experiment will utilize the same hardware used in the original MACE experiment. The experiment consists of an approximately I.5 meter flexible structure which can be reconfigured into various orientations. A schematic of MACE test article is shown in Figure 3.

3.

Demonstrate the savings that can be achieved by reducing modeling and testing currently achieve a high level of performance non-adaptive

4.

required to

with fixed-gain

controllers.

Demonstrate that adaptive algorithms mented successfully

can be imple-

using limited computational

power consistent with space applications. 5.

Collect data for further evaluation

of the ability

nonlinear modeling and identification

of

tools to accu-

rately predict O-g on-orbit behavior.

Figure 3. Schematic of MACE II Test Article

Rigid body motion is controlled by three reaction wheels located at the center of the bus and precision pointing is achieved using the two-axis gimbals located at the ends of the bus. A suite of various sensors and actuators exists for implementing a variety of control approaches.

The first bending mode ofthe MACE around 2 Hz. There are approximately in the O-60 Hz control bandwidth.

structure occurs at 15 modes present

The control processor for MACE II is the TMS320C30 DSP. The signal processing package will be capable of acquiring I6 I2-bit A/D inputs as well as 4 digital encoder inputs. The system is also capable of supplying up to 12 l2-bit D/A outputs. The MACE software is being upgraded for MACE II to able to incorporate generic C code blocks for implementation of adaptive rather than fixed-gain controllers.

MACE

II Objectives

The primary purpose of MACE II is to validate the ability of adaptive neural network-based and other adaptive algorithms to control, with little or no prior system knowledge. a representative small satellite system which alters its dynamics between l-g qualification and O-g op-

The MACE II Experiment is currently undergoing flight qualification testing and performance testing. While a firm manifest date has not been set at the time of this writing, MACE II is expected to fly midyear of 2000.

ADVANCED CONTROLS TECHNOLOGY EXPERIMENT The ACTEX-I flight experiment was funded by the Ballistic Missile Defense Organization (BMDO), managed by the Air Force Research Laboratory, and designed and manufactured by TRW, Inc. The primary objectives of the ACTEX-I program were the demonstration of on-orbit active structural control, adaptive structures, and adaptive controls using PZT sensors and actuators. Secondary objectives were the validation of pre-flight design and performance prediction tools and the collection of data on the long-term effects of the space environment on active control components.

A photograph of the flight hardware is shown in Figure 4. It consists ofthree active members, constructed of I in. by I in. by 17.7 in. T300 graphite-epoxy composite box beams embedded with piezoceramic material coupons to provide sensing and actuation. Each face of each beam is embedded with one actuator coupon (0.048 in. wide by 7.5 in. long by 0.010 in. thick). one collocated sensor coupon (0.048 in. wide by 0.5 in. long by 0.010 in. thick). and a noncollocated sensor coupon (0.048 in. wide by I .O in. long by 0.010 in. thick). The top plate of the ACTEXI hardware contains seven accelerometers that are used to determine vibration-induced motion and gauge active

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393

50th IAF Congress

A PIC microcontroller controls interaction between the SUITE experiment and the host satellite on-board computer via a Controller Area Network (CAN) bus. The SUITE software is a combination of fixed macro functions (firmware) and reprogrammable routines that can be uplinked from a ground station. The reprogrammable nature of the DSP processor will allow SUITE to demonstrate any algorithm that can be executed within the timing constraints imposed by the computational power of the hardware, including multivariable and adaptive control strategies.

Figure 6. SUITE Flight Hardware

A photograph of the SUITE flight hardware is shown in Figure 6. The SUITE hexapod assembly (HXA) consists of six hybrid active/passive struts that allow vibration isolation and control of the top platform in six degreesof-freedom. Each struut contains a damped mechanical flexure to provide passive isolation of the top platform at frequencies above approximately 28 Hz or greater. A piezoelectric stack actuator in series with this flexure provides control actuation along the axis of the strut. An electromagnetic velocity sensor integrated within each strut provides vibration measurements. The hexapod arrangement is designed to minimize cross coupling between the struts, although some cross coupling is unavoidable. Six additional velocity sensors measure the response in the X, Y, and Z directions on both sides of the hexapod.

Figure

7. SUITE

Flight Electronics

SUITE includes a custom Data Control System (DCS). designed and manufactured by Trisys. Inc. of Phoenix, AZ. as is shown m Figure 7. The DCS manages all command and control functions for SUITE, including implementation of control algorithms, data collection, and interaction with the host satellite computer. The heart of the SUITE DCS is a Texas Instruments TI C3 I Digital Signal Processor (DSP) with a clock speed of 40 MHz.

SUITE has been integrated with PICOSat, a 70 kg. Satellite designed and manufactured by Surrey Satellite Technology, Ltd. (SSTL), Guildford, UK.

A complete duplicate of the SUITE flight hardware resides at AFRL’s Space Vehicles Directorate in K&and AFB. NM. This duplicate unit serves as both a source of spare parts for the flight unit in the event of a failure during testing and as a platform for will be made available for testing algorithms and software prior to uplink to the experiment. More complete details of the SUITE flight experiment hardware can be found within the references [ l8]- [21].

VIBRATION

ISOLATION, STEERING

SUPPRESSION,

AND

CVISS)

The Vibration Isolation and Suppression System (VISS), shown in Figure 8, was designed to isolate a precision payload from spacecraft borne disturbances using passive isolation in combination with voice coil actuators. [22]-[25]. VISS utilizes six hybrid isolation struts in a hexapod configuration. The passive isolation is provided by Honeywell’s flight proven D-Strut design and is very compliant with the six hexapod suspension frequencies in the 2 to 5 Hz frequency range. The D-strut contains viscous fluid which is exchanged between metallic bellows through narrow orifices. The passive design is further supplemented at lower frequencies by a voice coil based active system mounted in parallel to the D-strut. This active system can effectively lower the hexapod suspension frequencies by an order of magnitude so that isolation is achieved over a broader frequency range. Another benefit of the active system is that it can be used for vibration suppression and steering functions. Vibration suppression is needed to counteract disturbances from noisy devices, such as cryocoolers, that are directly attached to the optical payload. The steering function enables the VISS device to be used as a precision tracking gimbal for the optical payload. Accelerometers are mounted to the payload side of each struut and are used as feedback sensors for all ofthe control functions. The entire system is robust because, in the event of a power failure on orbit. the voice coil actuators will have zero

stiffness and the system will gracefully revert to Its passive isolation performance. Because the passive suspension frequencies are quite low. a launch lock system based on a shape memory alloy design is used to protect the system during launch.

rectorate for system integration. performance testing. and flight qualification, and the Jet Propulsion LaboratoQ (JPL) for the control system design and implementation. Performance tests and flight qualification tests were completed at the AFRL Space Vehicles Directorate. The performance tests showed that all three control functions perform well when run simultaneously or independently. A plot showing representative isolation performance from ground tests is shown in Figure 9. VISS successfulI! completed random vibration and thermal-vacuum flight qualification testing in the Aerospace Engineering Facility at the AFRL PhIllips Research Site. The VISS experiment was integrated with the STRV-2 experiment and has completed further flight qualification testing, including acoustic, random, thermal as part ofthe integrated STRV-2 payload at JPL. STRV-2 will be mounted to a satellite designed by Orbital Science Corporation and is scheduled to fly on board a Pegasus launch vehicle in 1999.

Figure 8. VISS Flight Hardware

VISS is scheduled to flj as part of the Ballistic Missile Defense Organization’s (BMDO) Space Technology Research Vehicle-2 (STRV-7) in 1999. STRV-2 is an ongoing collaborative effort between the BMDO and the United Kingdom Ministy of Defense to provide key space data to enhance design and risk reduction efforts for space-based surveillance platform designs. VISS will be used to isolate, suppress cryocooler vibrations. and steer. in six degrees of freedom. an experlmental midwavelength infrared (MWIR) sensor which is also a part of the STRV-2 payload module.

The principal performance goal for VISS is to isolate the MWIR telescope by a minimum of 20 dB at frequencies of 5 Hz and above. VISS will also be used to demonstrate steering of the telescope bj -l- 0 3 deg with an accurac! of 0.02 deg. The steering profile required by the telescope for the space mission is composed of?. 4. and 6 Hz Fourier components of a triangle wave. The hybrid actuators have a linear stroke of +i- JO mils which is sufficient for the steering requirement. Finally, VISS will also be used to mitigate the effects of the cryocooler vibrations on the MWIR performance. Specifically. VISS will demonstrate cryocooler vibration suppression by 20 dB for the first three cryocooler harmonics (55. I IO. and 165 Hz) at the VISS:MWIR interface plate.

VISS was developed under contract with the Air Force Research Laboratoc (AFRL) Space Vehicles Directorate at Kn-tland AFB with sponsorship and funding from BMDO. The entire experiment was developed using a team-based approach, ieveraging the capabilities of Honeywell and its electronics subcontractor Trlsys Inc. for design and manufacture, the AFRL Space Vehicles Di-

The hey components of the Hybrid D-Strut used in the VISS system are shown in Figure IO. The strut is a single-axrs device acting along the stinger or z-axIs. The payload is connected to a strut by an interface mount. The mount holds a payload accelerometer and connects to a biaxial flexure at the end of the stinger. The biaxial flexure provides rotational compliance about the x and y axes. Compliance in the bellows at the base, acting over the length of the stinger. allows for translation along the x and y axes at the payload mount. The strut is designed to tolerate limited motion in these four degrees-of-freedom without performance degradation. The voice coil bobbin is attached to the stinger. which is connected to the base through the primary bellows stiffness. A base supports the voice coil stator, a pair of primary bellows, and a pair of secondary, thermal compensation bellows. with preload springs, position sensor, and base accelerometer.

For VISS, six hybrid

actuators were arranged to sym-

Figure 9. VISS Isolation Performance

Results

395

50th IAF Congress

large acceleration signals due to the disturbance of the cryocooler and steering motion of the MWIR. For the target problem, the expected peak acceleration of 200 micro-g due to the base disturbance force is 200 times (46 dB) smaller than the peak acceleration due to the cooler and steering vibration of 40 milli-g. To circumvent this problem, the accelerometer signal for the isolation loop is first subtracted by the acceleration steering profile thereby removing the steering component and then filtered by a 5 Hz, first order low-pass filter which reduces the cryocooler signal component by a factor of ten. The resulting small amplitude acceleration signal is subsequently amplified and digitized before it is used as an input to the isolation compensator.

Figure IO. VlSS Actuator

Assembly

metrically support an optical payload. This Stewart Platform, or hexapod arrangement of the hybrid struts, provided six degree-of-freedom isolation and steering of the payload. Since the VISS system cannot support the payload weight during launch, a releasable launch retention system is necessary to provide payload support during launch. Protecting a soft system such as VISS during launch is much simpler than it is for a rigid system. First, restraint systems must be more rigid than the system they are protecting to avoid transmitting launch loads. Secondly, the attachment process must be very precise to avoid the imposition of excessive strain during the lock down process. VISS uses a launch retention system that pulls the optics platform down approximately 0.060 inches against hard stops. It releases on-orbit and the Dstrut with passive control restores the system to its neutral and operational position.

Vartous types of devices are available for the launch lock function. The actuator used is known as a Frangibolt and is manufactured by the TiNi Alloy Company. It has been qualified and flown successfully on the Clementine spacecraft.

The acceleration signals for the suppression and steering loops are passed through I50 Hz anti-aliasing filters. Using this overall strategy, the large signal and small signal ratio can be reduced by at least 20 to 26 dB. Also, to alleviate the mixed large-small signal problem at the digital to analog converter (DAC) output, the three command signals for isolation, suppression and steering are combined in analog form. The output from the isolation DAC is filtered through another 5 Hz lowpass filter before the analog summation. This is necessary to smooth out the digital to analog converted isolation output signal from the low bit count. A reconstruction filter of 250 Hz is used to smooth the suppression and steering control outputs.

The system sampling rate for all three control functions is I KHz. All of the acceleration signal paths go into a l6-bit analog to digital converter (ADC) with a multiplexer. The output signals are generated by a l6-bit DAC. A Texas Instruments TMS320C3 I Digital Signal Processor (DSP) calculates the control inputs. The base acceleration signals are sent through the 150 Hz antialiasing filter and are then sampled by the l6-bit ADC. The remaining sensor signals (temperature, gaps, and cryocooler feedthrough signal) are sampled by a l2-bit ADC.

CONCLUSIONS The system to be controlled consists of the six hybrid struts supporting the payload, including the voice coil actuators and payload accelerometers. The payload accelerometer for each strut is used as the feedback sensor for the voice coil on the same strut. Thus. each strut has collocated single input / single output (SISO) control. Flexible dynamics in the base, the struts, and the payload are captured in the measured plant transfer functions. The six payload acceleration signals are measured and then passed to two different signal paths. The filtering along the two different signal paths was chosen to separate the small acceleration signal due to base motion from the

This paper provides an overview of four space experiments being conducted by the U.S. Air Force Research Laboratory and its partners. These flight demonstrations are both validating and developing the necessary flight heritage of smart structures technologies that have been under development over the past decade. Successful completion of experiments such as MACE II, ACTEX-I. SUITE. and VISS are viewed as critical in allowing this technology to go from state-of-the-art to state-of-thepractice. The benefit of this transition will be the availability of space systems with unprecedented performance due to their inherent ability to provide extreme

stabiltr? on a lIghtweIght

zubmmrd

space platform

to ItEt,Aerospacr

Conference.

Snot\-

mass. CO. March 3 I-28. 1998

ACKNOWLEDGEMENTS

19) Denoyer. I‘racking

This work has been partially funded by the Ballistic Missile Defense Organization (BMDO). The authors wish to also thank the numerous other academic, industrial. and government partners involved in these challenging efforts.

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The ACTEX

[‘I

Aerospace

California.

formance

Davis. I. I). and Hyland,

Structure

Paper No. 93-l I

MIT Space En-

Research Center Report. SERC #7-96.

June 1996. I61

Laborat

1996.

R. A.. Wyse. R. E., and Schubert. S. R..

“An Advanced Campbell.

IO- I?. 1998.

USAF Phillips

Report, Februac

“Development

[ 141Manning.

Paper fi 92-2339-CP D. W.. Crawley.

submit-

and Control

I Design and Develop-

Report”.

.AIAA/AHS/ASEE Structures for 141 Wada. B.K. and litku. S.. “Adaptive DeploymentConstruction of Structures in Space.“

Miller.

Kalman

Speed and Noise Sensitivity”

ment”. AIAA

CO. Feb. 1997

I51

txtended

to Rapid System Identification,

ted to the AIAA

Technical

AIAA

San Diego. CA.

July 19-24. 1998.

ment Technical

.lero.ypuce

of to

Control Architecture,”

1997.

System.” IEEE

submitted

on Optical Sciences.

[I 11Hyland. D.C.. Denoyer, K.K.“An

J.. Bell. K.. Boucher. R.. Rob-

and Active Opto-Mechanical

Symposium

and Instrumentation,

Filter Approach Powers. M.. Leltner.

19-24. 1998

Con-

ference. Snowmass. CO. Feb. 1996.

ertson. L.. Schrader. K.. and Hackney.

Sympoand

( IO] ShelIe). S.. Sharp. T.. and Denoyer. K. “An Adap-

%PlE International

111Bell. K.. Boucher. R.. Vaceh. R., and Hopkms. M..

InversIon

using Neural Net-

Neural

I Test Article.”

on Smart

for Space”. Proc. Smart Structures and Conference,

ego. CA, February

Paper No. 2448-2

1995.

I. San Di-

391

50th IAF Congress [IS] Anderson.

E., Leo, D.. and Holcomb.

et Platform for Act&e

Vibration

M., “Ultraqui-

Isolation”

[24] Davis. L. P.. Cunningham,

SPIE Vol. 27 17. p. 436-45 I; also in Smart Struc-

35th AIAA

tures and Materials

Conference,

1996: Smart Structures and Inte-

grated Systems, lnderjit

D.. Harrell.

Structures, Dynamics, Hilton

Head, SC, April

[25] Davis. T. and Davis, L. P. “High Isolation,

Steering, and Suppression for

Space-based Sensors,” 3 I st Aerospace Mechanisms Symposium, May,

NASA

Marshall

(Hybrid)

Isolation”

terials Conference,

for Science and Technology

The USAF PICOSat Mission

Mic-

Conference

on

Small Satellites. Paper SSC97-V-4. E. H., et. al., “Satellite

tion Technology

Experiment

chanical Subsystems”, Materials,

Control

Conference.

Isolator.”

AIAA

G. “A Soft American

Seattle, June 1995.

[27] Davis. L. P.. Carter. D. R., Sullivan.

Ultraquiet

Isola-

J. M.. Hoffman,

T. J.. Das. A, and Hyde, T. T.. “Vibration Suppression,

(SUITE):

Vibration

Isolation,

and Steering for Precision Spacecraft

Payloads.”

67th Shock and Vibration

Monterey,

CA. November.

Conference.

1996.

Electrome-

SPIE 6th Annual

Symposium

Newport

1996.

Missions:

Using the SSTL Mod-

I Ith AIAiUSU

ular Microsatellite,”

Pas-

SPIE Smart Structures and MaSan Diego, CA, February

[26] Spanos, J., Rahman, Z.. and Blackwood,

[20] Tobin, David M., Haag, et. al., “Off-the-Shelf

International

Performance

sive Viscous Isolator Element for Active/Passive

6-axis Active

[2 1] Anderson,

1994.

Space Flight Center,

1997.

rosatellites

System,”

and Materials

Chopra; Ed.

[ 191 Bennett, S.. Davis, T., Cobb, R.. and Sullivan, J.. “Vibration

J.. “Ad-

vanced I .5 Hz Passive Viscous Isolation

Proc.

of Smart Structures and

Beach, CA, l-5 March

1999.

BIOGRAPHY

Paper No. 3674-36 [22] Tupper Hyde, T. and Anderson, with Built-in Structurtal

Viscous Damping Control.”

AIAA

E. H.. “Actuator for Isolation

Journal, 33(l),

and January

1996. [23] Davis, L. P., Carter D. R.. and Hyde, T.T., “Second Generation

Hybrid

D-Strut,

and Materials Conference, 1995.

SPIE Smart Structures San Diego, CA. February

Keith Denoyer received a B.S. in Mechanical Engineering from the University of Michigan in 1990, a MS. in Mechanical Engineering from Stanford University in 1992, and a Ph.D. in Aerospace Engineering Sciences from the University of Colorado in 1996. He is the Technical Advisor to the Space Vehicle Technologies Branch at Air Force Research Laboratory’s Space Vehicles Directorate located at Kirtland AFB, NM. He currently directs research activites in the areas of precision control, spacecraft protection, integrated structural systems, and advanced power systems.