Optimal hypersonic trajectory strategies for supersonic retropropulsion at Mars

Future large-scale Mars surface exploration missions require larger landed masses that are beyond the capability of current entry, descent, and landing technology. High mass missions will likely use supersonic retropropulsion to improve landed mass performance. This work focuses on the characterization of the hypersonic portion of flight for entry, descent, and landing systems using supersonic retropropulsion. Optimal control techniques are used to determine desirable hypersonic bank profiles to achieve favorable supersonic retropropulsion ignition states. Bang-bang bank control is shown to be optimal for objective functions of interest. A clear trade-off between altitude and flight-path angle at supersonic retropropulsion initiation is identified. Minimization of propellant used during powered descent is described and studied parametrically. Results show that ballistic coefficient and lift-to-drag ratio effects largely determine minimum propellant mass fraction; changes to the vehicle state at entry interface have a smaller effect. Reachable supersonic retropropulsion ignition states are presented over a range of vehicle and trajectory parameters of interest. Results indicate ballistic coefficient and lift-to-drag ratio dominate the size and shape of this space and execution of an appropriate hypersonic flight strategy can significantly reduce the amount of propellant required for powered descent and landing.