Offline and Hardware-in-the-loop Validation of the GPS-based Real-Time Navigation System for the PRISMA Formation Flying Mission

Abstract

The German Aerospace Center (DLR) provides various key contributions to the Swedish led PRISMA formation flying mission. These comprise a redundant GPS hardware architecture for the two spacecraft, a real-time navigation software to support formation flying during all phases, and dedicated experiments for absolute and relative orbit control. This paper addresses the testing and validation of the GPS-based flight software as a standalone unit prior to its full integration into the spacecraft onboard computer. Thank to the model based PRISMA onboard software design, the navigation software can be executed on different platforms in a fully consistent manner. As illustrated in the paper, this allows a seamless transition between offline simulations using GPS flight data from the Gravity Recovery and Climate Experiment (GRACE) and real-time hardware-in-loop tests comprising real Phoenix GPS receivers and a 2x12 channels Spirent GSS7700 GPS signal simulator. Furthermore the complete application is ported to a Real Time Executive for Multiprocessor Systems (RTEMS) environment in a LEON-3 board, representative of the PRISMA onboard computer. Overall the test campaign shows the compliance of the navigation software to the challenging requirements of the PRISMA mission and paves the way for the PRISMA system level tests with hardware-in-the-loop.