ADAPT demonstrations of onboard large-divert Guidance with a VTVL rocket

Abstract

The Autonomous Ascent and Descent Powered-Flight Testbed (ADAPT) is a closed-loop, free-flying testbed for demonstrating descent and landing technologies of next-generation planetary landers. The free-flying vehicle is the Masten Space Systems Xombie vertical-takeoff, vertical-landing suborbital rocket. A specific technology ADAPT is demonstrating in the near-term is Guidance for Fuel-Optimal Large Diverts (G-FOLD), a fuel-optimal trajectory planner for diverts during powered descent, which is the final kilometers of descent to landing on rocket engines. Previously, ADAPT used Xombie to fly optimal large-divert trajectories, extending Xombie's divert range to 750 m. However, these trajectories were planned off-line with G-FOLD. This paper reports the successful Xombie flight demonstrations of large diverts using G-FOLD on board to calculate divert trajectories in real time while descending. The culminant test flight of the last year was an 800 m divert that was initiated at an altitude of 290 m while moving away from and crosswise to the landing pad. Hence, G-FOLD had to calculate a constrained divert trajectory that reversed direction, was fully three-dimensional, with horizontal motion nearly three times the initial altitude, and it did so in ~100 ms on board Xombie as it was descending. Xombie then flew the divert trajectory with meter-level precision, demonstrating that G-FOLD had planned a trajectory respecting all the constraints of the rocket-powered vehicle. The steps to reach this flight demonstration of on-board generation of optimal divert trajectories and the system engineering for future ADAPT payloads are also presented.