ESA GNC Conference Papers Repository
Formation Flying Testbed at DLR's German Space Operations Center (GSOC)
This paper describes the Formation Flying Testbed (FFTB) developed by the German Space Operations Center (DLR/GSOC) and presents key results from its usage in the frame of formation flying missions currently operated at GSOC. The FFTB constitutes a mission-independent framework for the design, implementation, rapid prototyping, testing and validation of advanced guidance navigation and control (GNC) systems for multi-satellite missions. It is intended to support all phases during the lifetime of a GNC system, from the preliminary design to the system functional and performance verification to the post-facto analysis during mission operations. The realization of the FFTB takes advantage from the achievements and the experience gained during the development activities of some pioneers autonomous formation flying missions like PRISMA and TanDEM-X. In particular the DLRs GNC contributions to these missions have been validated making use of the FFTB described in this paper. The complete project is implemented in a Matlab/Simulink environment, which offers model-based capabilities, a user-friendly interface, high modularity, and is well-known among the aerospace community. The applications of interest 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 flight data and real-time hardware-in-the-loop tests comprising real GPS receivers and a 2x12 channels Spirent GSS7700 GPS signal simulator. Furthermore the complete GNC application can be ported to a Real Time Executive for Multiprocessor Systems (RTEMS) environment in a LEON-3 FPGA board, representative of spaceborne onboard processors. As a demonstration of its versatility, the FFTB has been recently integrated with the DLRs European Proximity Operations simulator (EPOS 2.0) to enable the verification of algorithms for real-time rendezvous and docking. As shown during the PRISMA and TanDEM-X missions, the FFTB can be used to reliably verify the behavior of on-board software in-orbit. In this case orbit and attitude propagation functionalities as well as sensors and actuators emulators are simply substituted by Simulink functions able to read real flight data from the telemetry stream. Since the flight software is fed with the same inputs received in orbit, the FFTB can be used to support the tuning of the on-board algorithms. Finally flight data retrieved from the ongoing missions give the possibility to cross-validate the environment emulator of the FFTB. To this end real observations are compared with the simulated environment produced by the models employed in the FFTB.