GPS-Based Spaceborne Autonomous Formation Flying Experiment (SAFE) on PRISMA: Initial Commissioning S. D’Amico 1 , J.-S. Ardaens 2 , S. De Florio 3 , O. Montenbruck 4 German Space Operations Center (DLR/GSOC), Oberpfaffenhofen, 82234 Wessling, Germany and S. Persson 5 , R. Noteborn 6 Swedish Space Corporation, P.O. Box 4207, SE-171 04 Solna, Sweden The Swedish PRISMA satellites have been successfully launched aboard a Dnepr launcher from Yasny, Russia, on June 15 th 2010. A few minutes after launch, the two PRISMA satellites were released, clamped together in launch configuration, into a nominal dusk-dawn orbit at a mean altitude of 757 km. The acquisition of the first S-band signal by the European Space and Sounding Rocket Range (Esrange) ground station in northern Sweden and the subsequent two-days Launch and Early Operations Phase (LEOP) signed the beginning of the first technology demonstration mission for autonomous satellite formation flying and on-orbit servicing in Europe. Among its primary mission objectives, PRISMA embarks the so-called Spaceborne Autonomous Formation flying Experiment (SAFE). SAFE will demonstrate onboard, fully autonomous, safe, and precise formation flying of spacecraft. This is accomplished by spaceborne Guidance, Navigation and Control (GNC) functionalities based on GPS for the maintenance of the relative motion between the two satellites. After a description of the GNC architecture and the experiment in-flight operations plan, this paper presents initial flight results from the commissioning phase of the GPS-based navigation system. I. Introduction A. M RISMA is a precursor mission for critical technologies for formation flying and on-orbit-servicing originating from an initiative of the Swedish National Space Board (SNSB) and the Swedish Space Corporation (SSC) 1,2 . The PRISMA test bed comprises the fully maneuverable Mango (or Main) small satellite as well as the TANGO (or Target) sub-satellite both built by SSC. Total program cost excluding the onboard equipment supplied by international partners, but including spacecraft development, launch and operations is about 50 million USD. The mission objectives of PRISMA may be divided into the validation of sensor and actuator technology related to formation flying as well as the demonstration of experiments for formation flying and rendezvous. Key sensor and actuator components comprise a ission Description • Phoenix-S GPS receiver system of the German Aerospace Center (DLR/GSOC) 3 , • Vision-Based Sensor (VBS) of Technical University of Denmark (DTU) 4 , • Formation Flying Radio-Frequency (FFRF) sensor of the French Space Agency (CNES) in partnership with the Spanish Centre for the Development of Industrial Technology (CDTI) 5 , • High-Performance Green Propellant (HPGP) system of SSC/ECAPS 6 , P • Cold-gas Micro-thrusters system of SSC/NANOSPACE 7 . American Institute of Aeronautics and Astronautics 1 1 Scientist, Space Flight Technology, Muenchener Str. 20, 82234 Wessling, Germany. 2 Scientist, Space Flight Technology, Muenchener Str. 20, 82234 Wessling, Germany. 3 Scientist, Space Flight Technology, Muenchener Str. 20, 82234 Wessling, Germany. 4 Deputy Head, Space Flight Technology, Muenchener Str. 20, 82234 Wessling, Germany. 5 PRISMA Phase C/D Manager, Space Systems, Swedish Space Corporation, P.O. Box 4207, SE-171 04 Solna, Sweden. 6 PRISMA GNC Responsible, Space Systems, Swedish Space Corporation, P.O. Box 4207, SE-171 04 Solna, Sweden. AIAA Guidance, Navigation, and Control Conference 2 - 5 August 2010, Toronto, Ontario Canada AIAA 2010-8130 Copyright © 2010 by S. D'Amico. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.