Attitude Determination with Three-Axis Accelerometer for Emergency Atmospheric Entry

Eduardo      Garcia-Llama

Abstract

This research paper presents two algorithms that will be able to determine the aerodynamic angles, that is, the angles of attack and sideslip, of a symmetric capsule-type spacecraft during atmospheric entry with the use of a 3-axis accelerometer. The algorithms are conceived only for emergency entry situations in which no attitude from the primary and backup navigation systems is available. The aerodynamic angles are provided in both methods with different degrees of accuracy and with different processing requirements. Both methods will increase the probabilities of flying a successful emergency ballistic entry that will, in turn, increase the probabilities of crew survival. Navigation reliability and tolerance to failures is traditionally achieved through the implementation of redundant elements. The algorithms presented in this paper increase reliability of the overall system through the utilization of a navigation instrument, the 3-axis accelerometer, for a use other than that for which it is designed. The algorithms presented in this research paper are documented in the NASA Disclosure of Invention and New Technology Number 5022510. They have been submitted to the U.S. Patent and Trademark Office with U.S. Provisional Application Number 61/212996.

Keywords: Atmospheric entry, emergency entry, attitude determination, Attitude Determinat, Accelerometer, dynamic pressure, Orion spacecraft, Aerodynamic attitude, incoming airflow, Aerodynamic angles, axial aerodynamic force