Experimental Demonstration of GPS for Rendezvous Between Two Prototype Space Vehicles

Abstract

The objective of this research is to demonstrate that Differential Carrier Phase GPS techniques can be em- ployed as the primary means of sensing both the rel- ative position and the relative attitude of two space vehicles in order to perform complex maneuvers such as multi-vehicle rendezvous and station-keeping in Low Earth Orbit. An experimental hardware sys- tem, consisting of a prototype space robot, target ve- hicle, and GPS system, has been devised to closely emulate real spacecraft. Since the experiments take place indoors where GPS satellite signals cannot be received, several GPS psetidolite transmitters have been built and installed around the perimeter of the laboratory to provide the GPS signals. The indoor GPS environment created by the close-range pseudo- lite transmitters poses additional constraints on the algorithms used to extract relative position and rel- ative attitude from the carrier phase measurements. Therefore, a secondary objective of this research is to develop GPS for indoor sensing, where it has the potential to be applied to indoor mobile robots and to automated manufacturing systems. This paper presents the theoretical formulation and results of a rendezvous experiment between a prototype space robot vehicle and a passive target vehicle. An mpeg movie of this experiment can be viewed at http://sun- valley.stanford.edu/movies/movies.html.