Energy Depletion Guidance for Aerobraking Atmospheric Passes

An energy depletion guidance algorithm for shallow, high-altitude atmospheric flight, consistent with aerobraking atmospheric passes, is proposed. The guidance algorithm is based on optimal control solutions to the energy minimization problem and uses variable drag area for trajectory control achieved through articulated solar panels. The algorithm includes three control modes to limit heat rate, heat load, or both while attempting to maximize energy depletion. A closed-form approximate solution of the equations of motion for aerobraking atmospheric passes is used to generate steering commands in real time. Numerical simulation of aerobraking at Mars illustrates the performance of the algorithm modes for a range of initial conditions. Results indicate that the guidance algorithm increases nominal energy depletion by approximately 1600% relative to the uncontrolled case over a single aerobraking pass, equivalent to an increase in ΔV of approximately 1600%. Monte Carlo simulation analyses show that dispersed flight performance is consistent with nominal performance; the standard deviation of the depleted energy is at maximum 13.8% of the mean, and the maximum difference between the mean and the maximal energy depletion solution is lower than 1.4%.