Resolving Integer Ambiguity of GPS Carrier Phase Difference

A new approach to resolve integer ambiguity and achieve instantaneous spacecraft attitude from phase information of Global Positioning System (GPS) signals, without requiring independent attitude information from traditional attitude sensors is presented. A newly approached algorithm based on Gram-Schmidt orthonormalisation (GSO) is proposed for medium length baseline observations. By using a newly developed attitude algorithm from vector observations, an instantaneous estimated attitude is obtained from only four phase measurements collected from only two baseline observations. The implemented algorithms are tested with flight data collected onboard a mini-satellite orbiting in low Earth orbit. The results show that a coarse attitude solution is achieved from phase information of stand-alone GPS signals.