Multi-Constellation GNSS for Absolute and Relative Navigation in Highly Elliptical Orbits
The goal of this research project was to determine to what order of magnitude relative positions of formation flying spacecraft in highly elliptical orbits (HEO) can be measured using Global Navigation Satellite Systems. The orbit of the European Space Agency’s upcoming PROBA-3 mission, with a roughly 600 km perigee and 60500 km apogee, was chosen as the test case throughout the research project. The key result was that, provided there were sufficient measurements, relative positioning could be accomplished throughout the HEO orbit to the sub-metre level in the absence of maneuvers, and to the sub-10 m level when a tight formation flying phase bracketed by maneuvers was simulated during the apogee arc. In the case of maneuvers or of too few measurements, the additional uncertainty prevents sufficiently rigorous blunder detection from being carried out, and the filter becomes extremely susceptible to outliers. In addition to answering the original research question, it was concluded that the regional navigation systems offer a significant advantage for above the constellation users, because the slower relative motion translates into longer arcs of uninterrupted measurement data. Using live signals collected from a low Earth orbiting CubeSat, Satellite Based Augmentation System (SBAS) tracking over the Earth’s limb was demonstrated, and it was proven for the first time that SBAS ranging is a viable source of positioning information for users in highly elliptical or other above the constellation Earth orbits. Finally, it was determined in the preliminary visibility studies that the entire positioning problem is extremely sensitive to the receiver’s ability to acquire and track weak GNSS signals. Hardware-in-the-loop simulation and receiver design work on a software research receiver confirmed that the power in the GNSS side lobes hovers slightly below the acquisition and tracking threshold of a standard receiver, but that these signals can be acquired and tracked making use existing weak signal algorithms, dramatically improving both absolute and relative positioning accuracies.
Kahr, E. J. (2017). Multi-Constellation GNSS for Absolute and Relative Navigation in Highly Elliptical Orbits (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/27024