Guidance and Control system design for Lunar Descent and Landing

This study aims at the preliminary design of a propulsion system concept able to achieve soft precision landing at the Lunar South Pole with an optimal payload mass. The design is constrained by the use of two types of engine sets: main engines with fixed thrust and pulsed assist engines. The requirements are derived from the NEXT Lunar Lander feasibility study performed by the European Space Agency. A guidance strategy has been derived and implemented in software to simulate a complete Descent and Landing profile from circular orbit to touchdown. The trajectory has been optimized taking into account fuel performance and visibility conditions of the landing site. Retargeting opportunities have been determined so that the lander can divert to a hazard-free area once the sensors are close enough to analyse the boulders, shadows and slopes found at the landing site. The effects on the required thrust profile of these divert manoeuvres, as well as the effects of GNC dispersions at key-points, have been assessed and worst case thrust profile has been derived. Finally, the optimal sets of engines have been designed for the 1500 kg on-orbit mass case, achieving a landing at the selected site with the best performance in terms of landed mass, based on a trade-off between higher Isp, lower engine mass and thrust modulation capabilities.