Autonomous Navigation and Control of Formation Fliyng Spacecraft on the PRISMA Mission

PRISMA is a small-satellite formation flying mission created by the Swedish National Space Board (SNSB) with the Swedish Space Corporation (SSC) as prime contractor and additional contributions from the German Aerospace Center (DLR), the French Space Agency (CNES), and the Technical University of Denmark (DTU). This mission will serve as a test platform for autonomous formation flying and rendezvous of spacecraft. PRISMA comprises a fully maneuverable small-satellite (MANGO) as well as a smaller sub-satellite (TANGO) which have been launched together in a clamped configuration on June 15th 2010 and separated in orbit after completion of all checkout operations. The mission schedule foresees a targeted lifetime of at least eight months. Through PRISMA, novel approaches in the areas of formation flying guidance, GPS based relative navigation, impulsive relative orbit control and space mission operations will have an in-flight validation. DLR’s key contributions comprise the on-board GPSbased absolute and relative navigation system, the Spaceborne Autonomous Formation Flying Experiment (SAFE), the Autonomous Orbit Keeping (AOK) experiment as well as the on-ground Precise Orbit Determination (POD) layer. In this paper in-flight results of the PRISMA on-board GPS based navigation system are presented. The onboard navigation performance is estimated through a comparison with the on-ground POD results and is evaluated in terms of accuracy requirements fulfilment and robustness in critical situations (e.g., attitude and orbit control maneuvers, large GPS data gaps). An overview is also given of the innovative and flexible PRISMA operations concept and the DLR’s PRISMA Experiment Control Center (ECC).