GPS Attitude Determination for Spinning Spacecraft with Non-aligned Antenna Arrays

John Carl Adams and Jonathan P. How

Abstract:	Space presents a challenging operating environment for a GPS receiver. These challenges are due, in-part, to the high relative velocities between the spacecraft and the GPS satellites, which results in large Doppler shifts in the received signals and rapid changes in the line-of-sight vectors. Both of these factors strongly effect the signal tracking and acquisition algorithms, as has already been studied by several other researchers. A further complicating factor is that although spacecraft vehicle attitude dynamics are typically at a lower bandwidth than most terrestrial vehicles, space vehicles can undergo very general attitude motions. As a result, for many applications (e.g. inertially fixed or spinning spacecraft) there is no preferred orientation of an array of antennas with aligned bore-sights that will give good GPS constellation visibility at all times. To address this concern, this paper analyzes the use of an array of non-aligned antennas for space applications. Previous analysis has shown that better sky coverage can be achieved with a non-aligned antenna array. However, a non-aligned array introduces several new effects into the differential carrier phase measurements which corrupt the attitude estimation. These effects are typically eliminated through differencing in the more commonly used case of an aligned array. They must be removed in the estimation algorithm in the non-aligned case to provide an accurate attitude solution. A correction is provided in this paper using a new measurement model that includes both near and far GPS transmitters. The result is a set of attitude estimation algorithms that remove the dominant errors. These algorithms are tested in simulation and experimentally in a laboratory GPS environment.
Published in:	Proceedings of the 1998 National Technical Meeting of The Institute of Navigation January 21 - 23, 1998 Westin Long Beach Hotel Long Beach, CA
Pages:	93 - 102
Cite this article:	Adams, John Carl, How, Jonathan P., "GPS Attitude Determination for Spinning Spacecraft with Non-aligned Antenna Arrays," Proceedings of the 1998 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 1998, pp. 93-102.
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