Aerocapture Performance Analysis for a Neptune -Triton Exploration Mission

A systems analysis has been conducted for a Neptune -Triton Exploration Mission in which aerocapture is used to capture a spacecraft at Neptune. Aerocapture uses aerod ynamic drag instead of propulsion to decelerate from the interplanetary a pproach trajectory to a captured orbit during a single pass through the atmosphere. After capture, pr opulsion is used to move the spacecraft from the initial captured orbit to the desired science orbit. A preliminary assessment identified that a spacecraft with a lift to dra g ratio of 0.8 was r equired for aerocapture. Performance analyses of the 0.8 L/D vehicle were performed using a high fidelity flight sim ulation within a Monte Carlo executive to determine mission success statistics. The simulation was the Pr ogram to Optim ize Simulated Trajectories (POST) modified to include Neptune specific atmospheric and planet models, spacecraft aerod ynamic characteristics, and interplanetary trajectory models. To these were added auton omous guidance and pseudo flight controller models. The Monte Carlo analyses incorporated approach trajectory delivery errors, aerodynamic characteristics uncertainties, and atmo spheric density variations. Monte Carlo analyses were performed for a reference set of unce rtainties and sets of uncertainties mo dified to produce increased and reduced atmospheric variability. For the reference uncertainties, the 0.8 L/D flatbottom ellipsled vehicle achieves 100% successful capture and has a 99.87 probability of attaining the sc ience orbit with a 360