Relative and absolute navigation in earth orbit

Three experiments involving simultaneous collection of GPS data by spacecraft took place between November 1996 and October 1997, with the goal of demonstrating the feasibility of using GPS for relative navigation of spacecraft. The experiments took place within ESA's ATV (Automated Transfer Vehicle) Rendezvous Pre-development (ARP) program. This program aims to validate rendezvous technologies that will be used in ATV for its proximity operations around the international Space Station. The spacecraft involved were the Space Shuttle and the retrievable Astrospas platform for the first flight demonstration ton Shuttle flight STS-80), and the Shuttle and the Russian MIR space station during the STS-84 and 86 flights. CPS receivers were installed in the spacecraft involved and GPS data were collected for several intervals during the rendezvous and separation phases. ESOC Flight Dynamics was entrusted with the challenge of providing the most accurate trajectories that could be computed using the on-board collected GPS data in combination with ground collected data. The paper will present the strategy used to obtain the best estimated trajectories, the problems found during the analysis of the data and the results obtained, including comparisons with trajectories obtained using other tracking systems or algorithms. (C) 1999 COSPAR. Published by Elsevier Science Ltd.