Variable angle-of-attack profile entry guidance for a crewed lifting body

The feasibility of flying a crewed lifting body, such as the HL-20, during entry fromlow-Earth orbit without steady-state body flap deflections was evaluated. This entry strategy mitigates the severity of the aerothermal environment on the vehicle's body flaps and reserves control power for transient maneuvers. A numeric predictor-corrector entry guidance algorithm was developed to accommodate the range of vehicle trim angle-of-attack profiles possible when steady-state body flap deflections are prohibited. Results show that the guidance algorithm is capable of steering the vehicle to a desired target from low-Earth orbit while satisfying a reasonable suite of trajectory constraints, including limits on peak heat rate, peak sensed deceleration, and integrated heat load. Uncertainty analyses confirm this result and show that the vehicle maintains significant performance robustness to expected day-of-flight uncertainties. Additionally, parametric scans over mission design parameters of interest indicate a high level of flexibility is available for the low-Earth orbit return mission. Together, these results indicated that the proposed entry strategy is feasible: crewed lifting bodies may be effectively flown without steady-state body flap deflections.