Non-Linear Transformation Guidance for Aero-Assisted Lunar Return Trajectories. Department of Aerospace Engineering Report No. 9419

The use of non-linear transformations is investigated in the context of an aero-assisted orbital transfer from lunar return to a space station. Analytic prediction of the minimum altitude for a skip entry into the atmosphere is used to provide the reference for the constant altitude guidance. Feedback linearisation is used to maintain this altitude while a matched asymptotic solution to the exit trajectory problem is used to target the required apogee and so determine the "pull-up" point. During the exit phase the predictions made in targeting the apogee are used to generate an analytic reference trajectory in flight. Feedback linearisation is then used to guide the vehicle along the predicted trajectory, artificially improving the accuracy of the predictions and closely matching the actual apogee to the desired apogee. Autonomous return to the station has advantages over a return to ground in terms of both time and manpower