Aeroassisted orbital maneuvering with variable structure control

Abstract

Aerocapture consists in a low altitude pass through the atmosphere to slow down a vehicle and put it in orbit about the planet. One of the most difficult problems in aerocapture is the presence of strong air density variations in the upper atmosphere. In atmospheric maneuvers a spacecraft must have closed loop controls to deal with unpredictable density condition. Design of such a method is the primary purpose of this work. The basic approach is based on tracking a reference trajectory in the state space. By first changing the independent variable from time to mechanical energy a control method was developed based on variable structure control (VSC). This control approach gives very good results in state errors in the presence of large variations in atmospheric density. The closed loop controller uses only kinetic variables measurements and there is no need for density estimation. Extensive Monte Carlo simulations have been performed to test the robustness of the algorithm. Results of a representative case are presented.