CROSS-VALIDATION OF GPS- AND FFRF-BASED RELATIVE NAVIGATION FOR THE PRISMA MISSION

Scheduled for launch in mid 2009, the Swedish PRISMA mission will enable an in-depth flight demonstration and validation of advanced formation flying technologies. Among its key instruments is the radio frequency formation flying (FFRF) sensor, which has been contributed to the PRISMA mission by the French National Space Agency (CNES) in partnership with the Spanish Centre for the Development of Industrial Technology (CDTI). The FFRF sensor is a fully self-contained navigation system for relative positioning and pose estimation. It does not depend on Global Navigation Satellite System (GNSS) signals and can therefore operate at arbitrary distances from the Earth. The FFRF sensor will thus be vital for astronomical formation flying missions such as PROBA-3 and SIMBOL-X. Missions in low earth orbit (LEO) like PRISMA, in contrast, benefit greatly from the availability of GPS, which enables high precision absolute and differential navigation. To that end the two satellites will be equipped with a dedicated GPS navigation system developed and contributed by the German Aerospace Center (DLR). The GPS navigation system will provide the primary reference for absolute and relative position measurements and thus serve the validation and calibration of other navigation sensors. In preparation of the PRISMA flight, and as key step towards future formation flying missions, extensive ground tests and simulations have been performed by DLR and CNES to assess the achievable relative navigation accuracies of the two sensor types and the potential for in-flight validation of FFRF dat