Autonomous Satellite Formation Flying for the PRISMA Technology Demonstration Mission

Abstract

PRISMA, originating from an initiative of the Swedish National Space Board (SNSB) and the Swedish Space Corporation (SSC), is a precursor mission for critical technologies for formation flying and In-Orbit-Servicing. The PRISMA test bed comprises the fully maneuverable MAIN mini-satellite as well as the smaller TARGET subsatellite, both built by SSC. Within PRISMA, a GPS-based onboard navigation system offers precise absolute and relative orbit information in real-time as well as time synchronization. The Phoenix twelve channel single-frequency GPS receiver, selected for PRISMA, provides a code tracking accuracy of better than 0.5 m and a carrier-phase accuracy of better than 1 mm at 45 dB-Hz. The navigation system on MAIN will process in a reduced dynamic Kalman filter local GPS measurements and raw measurements from TARGET transmitted by an inter-satellite radio link. As a result, real-time position accuracies of 2 m for absolute and better than 0.1 m for relative navigation are expected. In addition, PRISMA will conduct the Spaceborne Autonomous Formation Flying Experiment (SAFE) with the objective to demonstrate a fully autonomous, robust and precise formation flying of spacecraft. To this end, a fuel-optimized guidance and control algorithm will be employed providing an accuracy of better than 25 m at typical distances of 100 to 2000 m, which is representative of future bi-static radar satellite formation flying missions. The guidance concept applies the eccentricity/inclination vector separation which avoids collision hazard from along-track position uncertainties through the proper separation of the two spacecraft in radial and cross-track direction.