Feasibility assessment of formation flight control by differential drag in eccentric orbit for the FACTORS mission

FACTORS is an M-class mission proposal led by JAXA/ISAS. It aims to elucidate energy coupling mechanisms and mass transport between Earth and space, at around 350-3500 km altitude in high latitude regions. Measurements of the electromagnetic field, particle sampling, and auroral imaging are planned. Simultaneous data at several kilometres to tens of kilometres apart will be obtained, using two satellites in formation flight in an eccentric polar orbit. Differential aerodynamic drag offers a promising resource for propellant-free formation control, since the perigee is located in the atmosphere. A control method for an in-track linear formation is developed and tested using a high-fidelity numerical orbit simulator. Disturbances are added to represent attitude control error, aerodynamic lift, and open-loop command uplink with space weather prediction error. Good performance is obtained even for close-proximity operations with km-scale separation. Based on the results, fully aerodynamic control is possible, though a thruster is desirable for perigee altitude adjustment and out-of-plane manoeuvring. To the authors’ knowledge, this is the first detailed study on formation flight control via differential drag in an eccentric orbit.