Precise Relative Positioning of Formation Flying Spacecraft using GPS

Abstract

Spacecraft formation flying is considered as a key technology for advanced space missions. Compared to large individual spacecraft, the distribution of sensor systems amongst multiple platforms offers improved flexibility, shorter times to mission, and the prospect of being more cost effective. Besides these advantages, satellite formations in low Earth orbit provide advanced science opportunities, such as measuring small scale variations in the Earth's gravity field or higher resolution imagery and interferometry. One of the fundamental aspects of spacecraft formation flying missions is the precise determination of the relative state (position and velocity) between the satellite vehicles within the formation. GPS receivers are often considered as the primary instruments for this task in future spacecraft formation flying missions. As is commonly known, precise relative positioning between GPS receivers in geodetic networks is exercised on a routine basis. Furthermore, GPS receivers are already frequently used onboard satellites to perform all kinds of navigational tasks. Moreover they are suitable for real-time applications and provide measurements with a 3-dimensional nature. This dissertation presents a thorough overview of various GPS based strategies for precise relative spacecraft positioning, which have all been tested using real-world GPS data from the GRACE satellite mission. In addition, a substantial part of this work is also dedicated to quality aspects of the GPS observation data used as well as precise GPS based orbit determination strategies of single spacecraft. This dissertation is therefore recommended to all readers interested in GPS for spacecraft positioning applications.