Integrated INS/GPS Attitude Determination for Manned Space Flight

Alfred .Anderman

Abstract:	Design trade options for precisely determining the attitude, and aligning the inertial measurement unit, applicable to the proposed NASA Advanced Manned Launch System/Personnel Launch System (AMLSI PLS) are presented in this paper. The NAVSTAR Global Positioning System (GPS), using intcrfcrometric differential carrier doppler phase measurements, not only provides high accuracy position data, but can also provide an attitude reference of accuracy compatible with the flight control system. Star trackers capable of providing attitude precision measured in arc-seconds may be required for optical telescope pointing. However arcinute attitude accuracies are adequate for most manned space vchiclcs and their payloads, for flight control and uplink/downlink antenna-pointing at least up to S-Band frequencies. Starting from the Space Shuttle Orbiter (SSO) GN&C subsystems as a baseline, it is shown how enhanced GPS can eliminate the need for rcdundant star trackers, with all the complications imposed by optical windows and the associated accessories. Space Shuttle accessories include 1)Light shade assemblies defining the field-of-view (FOV) of the tracker, 2)Shutter mechanisms, automatically opened/closed by 3)Bright object sensor,to prevent damage by an object such as the sun or moon, and 4)Redundant electric motors for door-opener mechanisms. GPS interferometric attitude measurement accuracies, using three or four antennas, are dominated by the noise of the carrier tracking phase lock loop (PLL) of the GPS rcceivcr. Some error sources, contributed by l)GPS rcceivcr, 2)GPS satellite, 3)GPS satellite ephemeris, 4)Common mode multipath and 5)Selective availability (SA) effects, can be removed through diffcrencing techniques. New approaches to remove phase ambiguity and cycle slip errors, as recently verified by C.S.Draper Labs and elsewhere, could enable considerable commonality to be achieved between navigation and flight control sensors, and are also discussed.
Published in:	Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991) September 11 - 13, 1991 Albuquerque, NM
Pages:	161 - 170
Cite this article:	.Anderman, Alfred, "Integrated INS/GPS Attitude Determination for Manned Space Flight," Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991), Albuquerque, NM, September 1991, pp. 161-170.
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