GPS-Based Spaceborne Autonomous Formation Flying Experiment (SAFE) on PRISMA: Initial Commissioning

The Swedish PRISMA satellites have been successfully launched aboard a Dnepr launcher from Yasny, Russia, on June 15th 2010. A few minutes after launch, the two PRISMA satellites were released, clamped together in launch configuration, into a nominal dusk-dawn orbit at a mean altitude of 757 km. The acquisition of the first S-band signal by the European Space and Sounding Rocket Range (Esrange) ground station in northern Sweden and the subsequent two-days Launch and Early Operations Phase (LEOP) signed the beginning of the first technology demonstration mission for autonomous satellite formation flying and on-orbit servicing in Europe. Among its primary mission objectives, PRISMA embarks the so-called Spaceborne Autonomous Formation flying Experiment (SAFE). SAFE will demonstrate onboard, fully autonomous, safe, and precise formation flying of spacecraft. This is accomplished by spaceborne Guidance, Navigation and Control (GNC) functionalities based on GPS for the maintenance of the relative motion between the two satellites. After a description of the GNC architecture and the experiment in-flight operations plan, this paper presents initial flight results from the commissioning phase of the GPS-based navigation syste