Design and Evaluation of an Acceleration Guidance Algorithm for Entry

This paper presents the design and performance evaluation of Evolved Acceleration Guidance Logic for Entry (EAGLE), an algorithm intended for future space transportation vehicles. The most distinguishing feature of EAGLE is its ability to plan a threedimensional trajectory and thereby handle large crossrange entries. EAGLE consists of two integrated components: a trajectory planner and a trajectory tracking law. The planner generates reference drag acceleration and lateral acceleration profiles, along with reference state and bank angle profiles. The tracking law, based on feedback linearization, commands the angles of bank and attack required to follow the reference drag and heading profiles. The planner and tracking law are described along with additional higher level logic included in EAGLE. Extensive simulations for a range of return-from-orbit and suborbital entries demonstrate that EAGLE consistently achieves the desired target conditions within allowable tolerances and satisfies all other entry constraints.