A Real-Time Kinematic GPS Sensor for Spacecraft Relative Navigation

Abstract

The concept and prototype implementation of a spaceborne relative navigation sensor based on a pair of GPS receivers is presented. It employs two individual receivers exchanging raw measurements via a dedicted serial data link. Besides computing their own navigation solution, the receivers process single difference measurements of obtain their mutal relative state. The differential processing prvides a high level of common error cancellation while the resulting noise is minimized by approprate use of carrier phase measurements. A prototype relatve navigation sensor making use of the above concepts has been built up based o the GPS Orion 12 channel L1 receiver and quified in hardware-in-the-loop tests using a GPS signal simulator. It provides a relative navigation solution with representative r.m.s. accuracies of 0.5 m and 0.5cm/s, respectively, for position and velocity. For ease of use the relative state is provided in a co-moving frame aligned with the radial, cross-track and along-track direction. The purely kinematic nature of state estimation and the small latency make the system well suited of maneuvering spacecraft, while the minimalistic hardware requirements facilitate its use on microsatellite formations.