Differential Drag Control Scheme for Large Constellation of Planet Satellites and On-Orbit Results

A methodology is presented for the differential drag control of a large fleet of propulsion-less satellites deployed in the same orbit. The controller places satellites into a constellation with specified angular offsets and zero-relative speed. Time optimal phasing is achieved by first determining an appropriate relative placement, i.e. the order of the satellites. A second optimization problem is then solved as a large coupled system to find the drag command profile required for each satellite. The control authority is the available ratio of low-drag to high-drag ballistic coefficients of the satellites when operating in their background mode. The controller is able to successfully phase constellations with up to 100 satellites in simulations. On-orbit performance of the controller is demonstrated by phasing the Planet Flock 2p constellation of twelve cubesats launched in June 2016 into a 510 km sun-synchronous orbit.