Robust Skip Entry Guidance and Control for a Capsule Returning from Lunar Orbit

Next generation space exploration missions will require extremely versatile vehicles that should be able to safely carry both cargo and crew to LEO and beyond LEO destinations and back to Earth. The re-entry phase is very important for the success of such missions and becomes critical in the case of high speed (high energy) entries, which arise in Lunar and Mars missions. Moreover, modern requirements call for flexibility for long ranges, and in case of a low L/D vehicle a controlled skip would be necessary to obtain such requirements. This article presents the development of a fully integrated guidance and control (G&C) system as part of a complete robust GNC system for high-speed entry. An Apollo derived guidance method and a QFT designed attitude control system have been implemented to guide a conical capsule in the context of a long range skip entry from a Lunar return mission. The system has been extensively tested, with 6 degrees-of-freedom simulations performed on re-entry scenarios developed using a high-fidelity functional engineering simulator. The vehicle is steered to the desired landing site and successfully controlled during the most critical phases of the trajectory, being pull out, exit of the atmosphere to perform the commanded skip, and the final entry with reduced velocity. The G&C scheme has proved robust against realistic modeling of dispersions and uncertainties throughout the re-entry.