Performance Improvement for GPS-Based Attitude Determination Systems

Luisella Giulicchi, Luigi Boccia, Giuseppe Di Massa and Giandomenico Amendola

Abstract:	In recent years, ESA has been considering the use of GPS as a medium-accuracy attitude sensor for low-earth orbit missions. Theoretical analyses supported by simulation and test results indicate that GPS-based attitude determination can yield an accuracy of 0.5 to 1 deg. The basic measurable in GPS-based attitude determination is a differential measurement across two antennas of the GPS signal carrier phase. The main error source in this measurement is due to reflection and diffraction from surfaces around the antennas (the spacecraft body, solar panels, etc.) that introduce differential phase distortions. This error is normally referred to as multipath error and currently represents the limiting factor in the achievable accuracy of GPS-based attitude determination. To counteract the multipath problem, solutions at both software and hardware level can be applied. The multipath effect on differential phase measurements and attitude estimation can be mitigated with software processing exploiting measurement redundancy or error predictability [Ref. 1]. At the hardware level several countermeasures can be applied: e.g. placement of the antennas far from the reflectors, or improvements in the design of the antennas. This paper describes the results of an ESA project done in collaboration with the University of Calabria to assess the performance of a GPS-based attitude determination system using shorted annular patch antennas. Comparison between different antenna designs analyzed in previous studies [Ref. 2,3] pointed to shorted annular patch antennas as a potential candidate to mitigate the impact of multipath error on differential carrier phase measurements. In the following sections the requirements for a low multipath GPS antenna will be outlined. The design of shorted annular patch antennas and the development of a prototype is then described. The high multipath rejection of the proposed antenna was tested by means of comparative measurements performed using an on-ground GPS test facility. Our results show a reduction of the differential phase error of about 50%.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	2209 - 2215
Cite this article:	Giulicchi, Luisella, Boccia, Luigi, Di Massa, Giuseppe, Amendola, Giandomenico, "Performance Improvement for GPS-Based Attitude Determination Systems," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 2209-2215.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In