ESA GNC Conference Papers Repository

A secondary GPS receiver experiment, called the SGR-GEO, was carried into orbit on Europe's first Galileo demonstrator satellite GIOVE-A. After 6 years of successful transmissions of prototype Galileo signals, GIOVE-A was retired to make way for the IOV satellites, and this enabled the activation of the GPS experiment. The SGR-GEO’s primary goal was to demonstrate the application of GPS receivers in altitudes above that of the GPS constellation (20,000km) and potentially the mapping out of GPS signal patterns outside the main antenna beam. Designed and built by SSTL’s GNSS Receivers team with the support of the European Space Agency and the BNSC (now UKSA), the SGR-GEO is a 12 channel L1 C/A code GPS receiver with several adaptations enabling its application in high altitude orbit. Experimentation began in September 2012, and has continued into 2014. The SGR-GEO was able to track many signals and achieve position fixes and track signals for a large part of the orbit. The tracking of GPS signals by the SGR-GEO allows the investigation of the antenna pattern of the transmitting satellites, including the sidelobes not normally visible to ground-based users. The performance of GNSS receivers at high altitudes is very sensitive to sidelobe strength, and so the SGR-GEO helps future GPS at GEO operators understand the behaviour that might be expected. This paper will present recent results from the SGR-GEO, including positioning and mapping of the GPS constellation transmit antennas using weak signals. Pattern variations between different GPS Blocks will be identified, and compared with published information from the operators.