Determination of Terminal Landing Footprint for On-Board Terrain Assessment and Intelligent Hazard Avoidance

In this paper we develop a methodology based on ballistics to estimate the landing footprint associated with the powered terminal descent phase of a Mars soft landing. The analysis is based on an idealized two-impulse thrust maneuver and leads to an analytical expression for the elliptical boundary of the landing footprint. Our goal was to develop a method (with low computational overhead) to estimate the landing footprint for use in an on-board fuzzy-logic based inference engine for real-time hazard avoidance. The inference engine is utilized to combine an estimate of the landing footprint with information about the safeness of the Martian terrain to construct an overall landing site quality index. The landing site quality index is a critical parameter that will enable the spacecraft to make intelligent real-time decisions about landing safely on unknown and hazardous terrains. The footprint generated from the ballistic analysis is then compared to the footprint resulting from numerically integrating a representative guidance law. Our study shows that under certain conditions the ballistic footprint provides an excellent estimate of the guidance computed footprint. However, other cases were also observed where the ballistic approach overpredicted the landing footprint associated with the guidance law. It was observed that the guidance footprint was sensitive to the time of guided flight T, the spacecraft initial state relative to the nominal target site, and the structure/order of the guidance law. *Corresponding Author +Graduate Student, University of Idaho, Moscow, Idaho, 83844