Final commissioning of the PRISMA GPS navigation system

Abstract

The real-time GPS-based navigation system carried by the PRISMA satellites is a critical element for the success of the mission. PRISMA, composed of two satellites launched in June 2010 and flying in close formation, aims at demonstrating the maturity of advanced technology and concepts for autonomous formation flying. The onboard navigation system relies on GPS measurements to provide in real-time accurate absolute and relative navigation. This navigation solution is used onboard not only to input numerous autonomous guidance and control experiments but also for the continuous onboard safety monitoring of the formation and its resulting strategy for collision avoidance. The commissioning of the GPS navigation system is therefore a crucial milestone for the mission. It has to be ensured that the on-board navigation solution is always reliable even in the presence of small hardware anomalies and that the navigation performance satisfies the mission requirements. The performance assessment is done using precise orbit products generated by a ground facility for GPS-based precise orbit determination which needs, in turn, to be also commissioned. The paper summarizes the commissioning activities performed to validate both precise orbit products and onboard navigation and presents key flight results to illustrate the overall system performance.