Nonlinear tracking control for satellite formations

A sliding-mode tracking control law places member satellites into a desired formation for distributed aperture sensing after their initial deployment and maintains the formation in the presence of orbital perturbations. To minimize fuel usage required to maintain the formation, each satellite must reside near a natural orbit, Control forces are applied only to maintain the desired relative motion by correcting for initial offsets and perturbation effects that tend to disperse the formation. These perturbations include effects due to Earth asphericity, atmospheric drag, and third body effects from the sun and moon. Parametric equations describing the member satellites' relative motion with respect to the leader satellite are essential in this design. Furthermore, the discontinuous control forces model the physical limitations of propulsive thrusters. Numerical simulations, using a high-fidelity, nonlinear model, demonstrate the control law performance for the full nonlinear dynamics with high order perturbations.