Constrained Beamforming for Space GPS Navigation

NAVSYS Corporation has developed a prototype for a flexible, high-performance Space-based Software GPS Receiver (SSGR) to demonstrate the next generation of tracking and navigation capabilities for space applications. Based on a Software Defined Radio (SDR) approach, the SSGR will provide an integrated precision navigation and attitude determination solution for space applications. In order to support GPS signal tracking in the space environment, a constrained beamforming algorithm tailored to the space environment has been developed that will allow satellites to track weak GPS signals even in very close proximity to other GPS satellites. In this paper we present the theoretical development of this algorithm, details of its deployment on the SSGR, and test results using the NAVSYS Advanced GPS Hybrid Simulator. The ability to track low power GPS satellites in the presence of much stronger GPS signals will extend the use of GPS for precision navigation and timing, particularly for high altitude space missions (above the GPS satellite constellation). With this capability, the SSGR will be suitable for supporting multiple space missions including GPS metric tracking during launch, orbit determination during transfer to geostationary orbits, and high accuracy navigation, attitude control, and timing. The flexibility of the SSGR design will allow it to be reprogrammed for use in launch and orbit entry, station keeping, and autonomous orbit estimation applications.