APPLICATION OF THE GLOBAL POSITIONING SYSTEM FOR HERMES RENDEZVOUS NAVIGATION

A study of the application of the global positioning system (GPS) for precise real-time relative orbit determination during rendezvous and docking operations in low Earth orbit has been performed. It is a first attempt to analyze this complex problem, in which the relative navigation accuracy during the homing and closing phase of a typical rendezvous mission between the European space plane Hermes and the Columbus Free Flying Laboratory has been investigated. Results are presented of a covariance analysis of a hypothetical on-orbit real-time data processing system, based on Kalman filtering of pseudorange observations acquired by GPS receivers onboard the two spacecraft. The so-called reduced-dynamic technique was applied for the orbit determination of both spacecraft. A method is described to derive the relative position and velocity errors from the absolute state-vector covariances. Two data processing concepts have been investigated. It is shown that using only observations of GPS satellites commonly visible from both rendezvouz spacecraft gives much better results than when all observations are used. Overall, the results indicate that accurate rendezvous navigation using GPS only is quite feasible.