Challenges and prospects of Coulomb spacecraft formations

Spacecraft formation flying using Coulomb forces is a relatively new technology for spacecraft control, and may have application for a wide variety of mission objectives including attitude control, collision avoidance, and orbit perturbation correction. Coulomb-controlled formations appear ideally suited for close formation flying in high Earth orbits to perform wide field of view imaging missions using separated spacecraft interferometry. Preliminary research has shown that it is possible to induce Coulomb forces and torques comparable with those of candidate high-efficiency electric thrusters with less than I Watt of on-board power. This paper discusses the challenges and prospects of developing spacecraft formations utilizing Coulomb forces. Formation flying on the order of tens of meters is very difficult using conventional ion propulsion methods, because the exhaust plumes will quickly interfere with the delicate on-board sensors. The Coulomb forces would allow the relative motion of satellites to be controlled without such contaminations. The fuel efficiency of the control makes. very long duration missions possible. Static equilibrium solutions of Coulomb formations are discussed. Further, the behavior of a two-satellite Coulomb formation is discussed at GEO. A non-linear, orbit elements based control law is introduced to stabilize the relative motion and drive the orbit element differences toward desired values.