Simultaneous Control of Relative Position and Absolute Attitude for Electromagnetic Spacecraft Swarm

摘要

Electromagnetic Formation Flight uses electromagnetic force to control the relative positions of multiple satellites without using conventional fuel-consuming propulsion. In order to cope with the electromagnetic torque generated with the desired electromagnetic force, most of the previous studies assume all satellites to have reaction wheels (RWs) in addition to the electromagnetic coils. However, the values of angular momentum loaded in RWs (RVV angular momentum) become non-uniform distributed among the satellites because the value of electromagnetic torques usually has different values for each satellite. Without a proper control scheme, the deviation becomes larger with time. Then RWs saturate relatively quickly; as a result, the attitudes of each satellite cannot be controlled. To solve this problem, this paper proposes a new control law for simultaneously controlling electromagnetic force and torque. The kinematics of EMFF derived from the conservation of angular momentum is used for controller design. This control law theoretically realizes a uniform distribution of RW angular momentum among each satellite. Combining with a simple unloading control only by the chief satellite, the proposed control law theoretically eliminates the accumulation of angular momentum of the entire system. Moreover, this control law enables the control of n satellites' relative position, absolute attitude, and RW angular momentum only by using one set of RWs in addition to the electromagnetic coil. This paper demonstrates the effectiveness of the proposed control law through the simulation of formation maintenance by five satellites as an example. Finally, a decentralized control strategy is discussed to achieve a larger-scale electromagnetic formation flight and spacecraft swarm using the EMFF system.