New Control Strategies for Underactuated Tethered Formation Flight Spacecraft

We introduce a decentralized attitude control strategy that can dramatically reduce the usage of propellant, by taking full advantage of the physical coupling of the tether. Motivated by a controllability analysis, indicating that both spin-up and relative attitudes are fully controllable by the reaction wheels, we report the first propellant-free underactuated linear and nonlinear control results for tethered formation flying spacecraft. We take a nonlinear control approach to underactuated tethered formation flying spacecraft, whose lack of full state feedback linearizability, along with their complex nonholonomic behavior, characterizes the difficult nonlinear control problem. We introduce several nonlinear control laws that are more efficient in tracking time-varying trajectories than linear control. We also extend our decentralized control approach to underactuated tethered systems, thereby eliminating the need for any inter-satellite communication.