NASA Contractor Report 194915

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Characterization of Spacecraft andEnvironmental Disturbances on a5mailSat

Thomas A. Johnson, Dung Phu Chi Nguyen, and Vince Cuda

CTA Incorporated

Hampton, Virginia

Doug Freesland

CTA Defense Systems Incorporated

McLean, Virginia

Contract NAS1-18936

July 1994

National Aeronautics and

Space AdministrationLangley Research CenterHampton, Virginia 23681-0001

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Form ApprovedREPORT DOCUMENTATION PAGE OMB No. 0704-0188

Publ_ repoc_ng I_rden Io¢ this cotleollon ol information III estimated to average I hour per response, M'_cluding the time for reviewing irlstrudlons, sea(chin 0 IXWtlN_ dat411 tourolm,

gathering and maintaining the data needed, and oornp;ming and revmw.mg the ¢o_ecl_on of inton'naUon. Send comments regarding lhl burden estcnata or any other aspect of

¢okclicrl ol informal:on, including suggestions for reducing this burdeh, to Washington Headquarters Sorvtces, D,'ectorate for Informat=on Operations and RepoRs. 1215 Jeflarlon Davis

Highway, Suite 1204, Admgton, VA 22202.4302, and to the Oflaa of Management and Budget, Paperwork Reduct0on P¢olect (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 13. REPORT TYPE AND DATES COVEREDI

July 1994 I Contractor Report4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Characterization of Spacecraft and Environmental Disturbances on a NAS1-18936

SmallSat WU 233-01-01-01

s. AUTHOR(S)

Thomas A. Johnson, Dung Phu Chi Nguyen, Vince Cuda,and Doug Freesland

7. PERFORMINGORGANIZATIONNAME(S)ANDADDRESS(ES)

CTA Incorporated

1 Enterprise Parkway Suite 390

Hampton, Virginia 23666

9. SPONSORING/MONITORINGAGENCYNAME(S)ANDADDRESS(ES)

National Aeronautics and Space Administration

Langley Research CenterHampton, Virginia 23681-0001

8. PERFORMING ORGANIZATIONREPORT NUMBER

10. SPONSORING I MONITORINGAGENCY REPORT NUMBER

NASA CR- 194915

11. SUPPLEMENTARY NOTES

Langley Technical Monitor: William L. Grantham

12a. DISTRIBUTION I AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category 18

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 worde)

The objective of this study is to model the on-orbit vibration environment encountered by a SmallSat. Vibration control issues

are common to the Earth observing, imaging, and microgravity communities. A spacecraft may contain dozens of support

systems and ir_'truments, each a potential source of vibration. The quality of payload data depends on constraining vibration

so that parasitic disturbances do not affect the payloads pointing or microgravity requirement. In practice, payloads are

designed incorporating existing flight hardware in many cases with nonspecific vibration performance. Thus, for the

development of a payload, designers require a thorough knowledge of existing mechanical devices and their associated

disturbance levels. This study evaluates a SmallSat mission and seeks to answer basic questions concerning on-orbit

vibration. Payloads were considered from the Earth observing, microgravity, and imaging communities. Candidate payload

requirements were matched to spacecraft bus resources of present day SmallSats. From the set of candidate payloads, the

representative payload GLAS (Geoscience Laser Altimeter System) was selected. The requirements of GLAS were

considered very stringent for the 150 - 500 kg class of payloads. Once the payload was selected, a generic SmallSat was

designed in order to accommodate the payload requirements (weight, size, power, etc.). This study seeks to characterize

the on-orbit vibration environment of a SmallSat designed for this type of mission and to determine whether a SmallSat can

provide the precision pointing and jitter control required for earth observing payloads.

14. SUBJECTTERMS

Smallsat, Pointing Jitter, Controls Structures Interaction

17. SECURITY CLASSIFICATIONOF REPORT

Unclassified

NSN 7540-01-280-5500

18. SECURITY CLASSIFICATIONOF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATIONOF ABSTRACT

15. NUMBER OFPAGES

106

16. PRICE CODE

A06

20. LIMITATION OF ABSTRACT

Standard Form 298 (Rev. 2-89)Pras_mpedby ANSI Std. Z39-18298-102