Drift Recovery and Station Keeping Results for the Historic CanX-4/CanX-5 Formation Flying Mission

Specialized drift recovery and station keeping algorithms were developed for the Canadian Advanced Nanospace eXperiments 4 and 5 (CanX-4 & CanX-5) formation flying mission (launched 30 June 2014), and successfully verified on orbit. These algorithms performed almost exactly according to predictions. The highly successful CanX-4 and CanX-5 formation flying demonstration mission was completed in November 2014, ahead of schedule. CanX-4 & CanX-5 are a pair of identical formation flying nanosatellites that demonstrated autonomous sub-metre formation control, with relative position knowledge of better than 10 cm and control accuracy of less than one metre at ranges of 1000 to 50 metres. This level of performance has never before been seen on nanosatellite class spacecraft to the author’s knowledge. This capability is crucial to the future use of coordinated small satellites in applications such as sparse aperture sensing, interferometry, ground moving target indication, on-orbit servicing or inspection of other spacecraft, and gravitational and magnetic field science. Groups of small, relatively simple spacecraft can also replace a single large and complex one, reducing risk through distribution of smaller instruments, and saving money by leveraging non-recurring engineering costs. To facilitate the autonomous formation flight mission, it was a necessary precondition that the two spacecraft be initially brought within a few kilometres of one another, with a low relative velocity. Complicating this was the fact that the CanX-4 and CanX-5 spacecraft were released separately from their shared launch vehicle, drifting thousands of kilometres apart in the short time it took to fully commission one spacecraft. Therefore, a system to calculate fuel-efficient recovery trajectories and produce the corresponding spacecraft commands was required, another first on the nanosatellite scale. This system was also extended to provide station keeping capabilities in the time between individual formation experiments, to keep the spacecraft safely separated without allowing their distance to grow large again