Robust Guidance via a Predictor-Corrector Algorithm with Drag Tracking for Aero-Gravity Assist Maneuvers

An atmospheric guidance algorithm to support Aero-Gravity Assist (AGA) maneuvers is developed. The AGA maneuver is divided into four phases: (i) a capture phase, (ii) a cruise phase, (iii) an exit phase and (iv) a terminal phase. In the capture phase, the vehicle tracks a constant drag reference that controls the plunge of the spacecraft into the atmosphere, trying to protect it from excessive heating. During the cruise and exit phases, a reference trajectory planner based on a numerical predictor-corrector algorithm generates the references the spacecraft should fly, from the current to the atmospheric exit conditions. In the terminal phase, the remaining final orbit inclination error is reduced. The robustness of the guidance algorithm is increased by tracking the drag reference obtained from the reference trajectory planner instead of directly commanding the predicted control profile. Monte Carlo simulation results indicate the viability of the approach for on-board closed-loop guidance in the presence of large dispersions and modeling uncertainties.