Analysis and design of propulsive guidance for atmospheric skip entry trajectories

Abstract

A study of the ability to use propulsive guidance for atmospheric skip entry trajectories was completed. The analysis centered itself around the proposed design of NASA's Crew Exploration Vehicle. The primary aerodynamic guidance system must execute an atmospheric skip maneuver when attempting to reach distant landing sites. These maneuvers result in the loss of aerodynamic control authority during the skip phase. The physics of the problem were studied through an analysis of the minimum impulsive AV. This analysis was completed for a number of different trajectories with varying energies. The framework of the propulsive guidance algorithm, derived from the Powered Explicit Guidance law of the Space Shuttle, was presented and the augmented design was explained. The sensitivity of the propulsive guidance solution to a given trajectory was explored as well as its response to altitude constrained maneuverability. The robustness of the algorithm is measured using Monte Carlo techniques. The results showed that the current design of the Crew Exploration Vehicle and the current implementation of the primary aerodynamic guidance system are inadequate for a precise, long range, crewed return from the Moon. It was also shown that the lower energy trajectories are more favorable given the altitude reorientation constraint. It was recommended that the skip phase be redefined such that it does not begin until the altitude reorientation constraint is met. It was shown that a combination of increasing the total amount of thrust available, AV allowance, and the entry guidance precision are necessary to bring the success rate to acceptable levels for a precise, long range, crewed return from the Moon.