GPS-Based Real-Time Navigation for the PRISMA Formation Flying Mission

Abstract

The paper addresses the design, implementation and validation of the on-board navigation system for the PRISMA technology demonstration mission. The objective of the navigation system is to provide in real-time absolute and relative orbit information for the PRISMA space segment which consists of two satellites flying in formation in Low Earth Orbit. The key drivers for the design of the navigation system are the accuracy requirements on the absolute and relative orbit determination which amount to 2 m and 0.1 m respectively (3D, r.m.s.). Furthermore, a high level of robustness and flexibility imposed by the numerous formation flying scenarios is required during the mission lifetime of about eight months. The paper focuses on the description of the navigation software architecture and algorithms. In contrast to earlier approaches that typically separate the GPS-based navigation task into the independent reconstruction of absolute and relative states, here a single reduced-dynamic Kalman filter has been developed which processes pseudorange and carrier-phase data from both spacecraft in order to exploit the full GPS measurements information at all times. Emphasis is given to the validation of the software via real-world simulations. The flight application is executed on a LEON2 processor in order to evaluate the orbit determination performance in real-time using a representative PRISMA flight hardware.