Design and Analysis of an Attitude Command Velocity Hold/ Hover Hold plus Incremental Position Command Blended Control Mode for Piloted Lunar Landing

Abstract

All Apollo landings were performed by the astronauts, manually commanding the Lunar Module (LM) flight path and attitude using Rate-Control Attitude Hold (RCAH) with incremental rate-of-descent (ROD). This control mode was trained extensively and received favorable handling qualities ratings due to, in part, the control power of the LM. Future lunar landing vehicle designs are much larger than Apollo and as a result they may have more sluggish control-response characteristics during flight as compared to the LM. We have investigated alternative control modes to manually control the flight path and attitude of the vehicle while maintaining favorable performance ratings. The ALHAT Guidance, Navigation, and Control (GNC) algorithms for autonomous precision landing were modified to include an Attitude Command Velocity Hold with Hover Hold plus Incremental Position Command (ACVH/HH+IPC) blended control mode, combined with incremental ROD command. The design of the Guidance and Control algorithms are described and pilot interaction is discussed in terms of the control strategy as well as the transition from automatic to manual flight.