Closed-Loop Trajectory Simulation for Thermal Protection System Design for Neptune Aerocapture

A configuration for aerocapture at Neptune is considered with an emphasis on reduction of the overall aeroshell thermal protection system mass. The biconic vehicle is assumed to be capable of bank angle as well as angle-of-attack modulation for guidance and optimal trajectory shaping. A methodology is presented for determining a nominal trajectory that robustly accommodates off-nominal flight conditions with relatively small dispersions in integrated heat load. Such a trajectory, termed nominal robust, is presented for bank-only guidance. A nominal-robust trajectory is also generated for guidance with both angle-of-attack and hank modulation. Simulation of a nominal-robust trajectory with angle-of-attack modulation in the presence of multiple stacked off-nominal conditions is described. The resulting reduction of maximum heat rate and heat load relative to the undershoot and overshoot trajectories is quantified. The thermal protection system response based on closed-loop trajectory simulations for worst-case off-nominal scenarios is calculated and compared with the traditional overshoot/undershoot thermal protection system design method. The results show that the use of the nominal-robust methodology results in a significant decrease in aeroshell mass, and that combined bank and angle-of-attack modulation further reduces trajectory dispersion and stagnation-point-integrated heat load as compared to pure bank-angle modulated trajectories.