Validation on flight data of a novel relative navigation approach for spaceborne GPS receivers flying in formation over large baselines

This paper presents and approach for real-time onboard relative positioning of two spacecraft separated of hundreds of kilometers with centimeter-level accuracy. The approach extends techniques developed for long baseline terrestrial relative positioning to spaceborne applications, making use of an on-the-fly ambiguity resolution technique especially developed for the applications of interest. Such technique blends together parametric models of the ionospheric delay, nonlinear models of relative spacecraft dynamics, and partial integer validation techniques, while being capable to comply with typical requirements for real-time on board operations. The approach is validated on flight data from the Gravity Recovery and Climate Experiment (GRACE) mission. Centimeter-level root-mean-square relative positioning is proved to be feasible for spacecraft separations exceeding 260 kilometers. Results show that in a one-day-long dataset 98% of integer ambiguities are fixed almost instantaneously, and less than 2% of these ambiguities are erroneous.