Network-Based Tracking Control of Spacecraft Formation Flying with Communication Delays

The formation tracking problem for multiple spacecraft in the framework of networked control systems (NCSs) is investigated. A reference trajectory is generated by the force-free linearized equations of the relative motion (known as Hill's equations). A sampled-data representation of the NCS is considered for the tracking control of relative motion between the leader and follower spacecraft in the presence of variable communication delays and bounded external disturbances. By adding a buffer which is longer than the worst case delay and augmenting the system model to include past values of system input as additional states, a new discrete time-invariant model is formulated, and a digital controller is developed to guarantee the exponentially uniformly ultimate boundedness (UUB) of the tracking errors and to ensure desired formation objectives. Numerical simulations are presented to demonstrate the effectiveness of the controller. The proposed controller is successful in establishing projected circular formation with the maximum magnitude of the steady-state tracking error 0.056 and the control forces remain bounded within 50 mN.