Analytical 3D Terminal Guidance Algorithm for Lunar Landing

Abstract

This article presents three-dimensional (3D) terminal guidance scheme for a spacecraft lunar landing maneuver. An analytical solution to a spacecraft terminal guidance problem for achieving the desired spot in the circumlunar space is proposed. The solution is obtained for constant acceleration trajectory when thrust throttling is used to maintain uniform braking deceleration. The pitch program and the yaw program are essentially linear with time. П achieve 6 terminal conditions (position and velocity terminal vectors components) 6 guidance law parameters are used: pitch angle and pitch rate, yaw angle and yaw rate, braking deceleration and time-to-go. The solution is executed in the coordinate frame associated with the desired terminal spot. Current spacecraft position and velocity relative to this frame is supposed to be known at any time during the guidance. The simulation results of spacecraft guidance and control using proposed solution are presented. Analysis of the simulation results validates the basic performance of the proposed terminal guidance scheme. It should be noted that as the proposed scheme presuppose thrust variation on an undisturbed trajectory it makes sense to look for ways of reducing of required throttling range. The next phase of this research will be intended to carrying out terminal errors analysis and comparison of the accuracy of the proposed scheme and some other schemes.