Adaptive control for Mars atmospheric flight

Abstract

The new vision for space exploration will focus on sending humans to the moon and eventually to Mars. This endeavor presents new challenges that are critically different from the past experience with robotic missions to Mars. For example, the strict landing accuracy requirements for a manned space vehicle make it necessary to fly a controlled entry trajectory rather than a more robust ballistic entry trajectory used for some robotic missions. The large variations in Mars atmospheric properties make a controlled entry and a safe precision landing for manned missions a difficult engineering problem. Model reference adaptive control is a candidate solution for the Mars entry control problem. This type of controller has an adaptation mechanism that reduces tracking errors in the presence of uncertain parameters such as atmospheric density or vehicle properties. This thesis develops two different adaptive control systems for the Mars ellipsled, a vehicle which is much larger than those that carried robotic payloads to Mars in the past. A sample mission will have multiple ellipsleds arriving at Mars carrying an assortment of payloads. It is of critical importance that the vehicles land in close proximity to each other to best assure that the crew has manageable access to their payloads. The scope of this research encompasses the atmospheric flight of the ellipsled, starting at the entry interface point through the final parachute deployment. Tracking performance of an adaptive controller for prescribed entry trajectories in the pres¬ence of atmospheric and vehicle model uncertainties is shown here. Both adaptive controllers studied in this thesis demonstrate successful adaptation to uncertainties in the Martian atmosphere as well as errors in the vehicle properties. Based on these results, adaptive control is a potential option for controlling Mars entry vehicles.