Robust predictor-corrector guidance for aeroassisted orbital transfer

Abstract

The safety zone guidance, relative to the exit phase of the atmospheric pass of an aeroassisted orbital transfer (AOT) vehicle is extended, so as to incorporate both the entry and exit phases of the atmospheric pass and to include the automatic determination of the switch time from entry to exit guidance. The guidance goals are 1) to contain the peak heating rate during the atmospheric pass, 2) to ensure that the AOT vehicle exits the atmosphere in the correct orbital plane, ascending afterward to the specified apogee, and 3) to achieve robustness vis-a-vis severe parameter dispersion effects resulting from navigation errors, atmospheric density errors, aerodynamic coefficient errors, and system errors. Numerical tests show that this guidance scheme exhibits high performance and relatively high robustness vis-a-vis dispersion effects resulting from these errors. The guidance robustness is due to two factors: 1) the switch time from entry phase to exit phase is the result of a proper engineering compromise and 2) for the exit phase, the control is not determined by aiming only at the desired apogee; instead, for each altitude-velocity pair, a special value of the path inclination is determined by maximizing the control margin while aiming at the desired apogee during the atmospheric pass.