NEAR-OPTIMAL EXPLICIT GUIDANCE AND REDUCED-ATTITUDE CONTROL FOR LUNAR DESCENT AND PINPOINT LANDING

This study proposes and tests a new guidance and control architecture for pow-ered descent and pinpoint landing at the lunar South Pole. Guidance employs three subsequent explicit schemes: (1) Lambert-based finite-thrust guidance, (2) locally-flat near-optimal guidance, and (3) predictive bang-bang vertical guid-ance. These are based on either the Lambert theorem, optimal control applied to simplified dynamics, or prediction along the final vertical path. The attitude control system has the final goal of aligning the actual thrust direction with the desired one, provided by the guidance algorithm. The resulting reduced-attitude control problem is addressed through a recently introduced quaternion-based nonlinear control algorithm, which is proven to enjoy asymptotic stability prop-erties. The attitude actuation system is composed of 12 monopropellant thrust-ers, ignited using pulse width modulation, in conjunction with an array of single-gimbal control momentum gyroscopes. The spacecraft dynamics is propagated in a high-fidelity dynamical framework, with inclusion of several relevant orbit perturbations. A Monte Carlo campaign with nonnominal flight conditions testi-fies to the effectiveness of the guidance and control architecture at hand, in terms of propellant consumption and precision at landing