Technologies for Spacecraft Formation Flying

John Adams, Andrew Robertson, Kurt Zimmerman and Jonathan How

Abstract:	Differential carrier phase GPS for orbit and attitude determination is emerging as a very promising low cost alternative to more conventional methods, such as horizon sensors, sun sensors, magnetometers, and star trackers. Relative spacecraft position and attitude determination are important for missions involving formation flying, such as those proposed for stellar interferometry under NASA’s New Millennium Program, and LEO missions for atmosphere and gravity modeling and for coordinated Earth observing. Our research involves developing a GPS based relative position and attitude sensing system in a laboratory environment for future application on spacecraft formations Previous research by Zimmerman[ 1,2] created a fully functional demonstration of spacecraft rendezvous and capture in 2D, in an indoor GPS environment using simulated spacecraft on an air-bearing table. Current work includes extending the previous GPS based sensing to a formation of three prototype spacecraft, and developing the algorithms for formation control. Control of a three-vehicle formation is studied with overhead vision sensing as a surrogate for GPS sensing. Two control architectures, using absolute and relative commands are investigated experimentally. A layered formation sensing strategy is being investigated, using GPS code phase measurements, code phase with differential corrections, differential carrier phase, and other higher precision measurements in a hierarchy. An analysis of the applicability of a proposed wide area differential GPS correction system to LEO spacecraft navigation, in terms of availability and performance, is presented. An estimation technique for autonomous integer bias resolution using a motion based technique has been demonstrated in simulation and validated using experimental carrier phase data from a two vehicle formation in the laboratory.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	1321 - 1330
Cite this article:	Adams, John, Robertson, Andrew, Zimmerman, Kurt, How, Jonathan, "Technologies for Spacecraft Formation Flying," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 1321-1330.
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