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Research Objectives

The objective of this research effort is to demonstrate that Differential Carrier Phase GPS techniques can be employed as the primary means of sensing both the relative position and the relative attitude of two space vehicles for precise, autonomous rendezvous maneuvers in Low Earth Orbit. In pursuit of this goal, an experimental system that can be tested in a well-controlled indoor laboratory environment has been built. Ideally, this system will be transferable to a real space system with little or no modification. Since the experiments take place indoors where GPS satellite signals cannot be received, several GPS pseudolite transmitters have been built and installed around the laboratory to provide the necessary GPS signals. The indoor GPS environment created by the close-range pseudolite transmitters poses some additional constraints on the algorithms used to extract relative position and relative attitude from the carrier phase measurements. Therefore, a secondary objective of this research is to clarify the differences between an indoor GPS system and the orbiting GPS satellite constellation, and to extend Differential Carrier Phase techniques such that they can be applied to near-field (indoor) systems as well as far-field (outdoor and space) systems. This paper presents the theoretical formulation and results of a two-dimensional position control experiment, an intermediate step toward the full rendezvous experiment.

Experimental Apparatus

 Robot Photo

Robot Photo 2

Robot and Target Vehicles Photo

Robot and Target Vehicles (Back) Photo

Pseudolite Photo

Pseudolite Back Photo

Pseudolite Back Open Photo

Space Rendezvous Photo

Contact

Kurt R. Zimmerman