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Meeting	ACGS Committee Meeting 93 - Colorado Springs - March 2004
Agenda Location	6 SUBCOMMITTEE B – MISSILES AND SPACE VEHICLES 6.4 Mars Pinpoint Landing Study
Title	Mars Pinpoint Landing Study
Presenter	Tim Brand, Linda Fuhrman, David Geller, Phil Hattis, Steve Paschall, and Y.C. Tao
Affiliation	Draper Laboratory
Available Downloads*	presentation
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Abstract	Draper Laboratory is supporting the Jet Propulsion Laboratory in an on-going assessment of technology requirements to enable autonomous pinpoint landing on Mars. The goal is to realize a 3-sigma expected miss distance of less than 100 m as compared to about 100 km of expected landing uncertainty experienced on Mars landings to date. Pinpoint landing capability is sought within a decade for missions that can deliver 2000 kg of useful payload to landing sites up to 2.5 km above the planetary mean surface altitude. The landing process for the candidate missions involves alternative planetary approaches (e.g., direct descent from various interplanetary trajectory types vs. descent from Mars orbit), followed by a hypersonic deceleration phase using an aeroshell, then a supersonic and subsonic phase using an aerodynamic decelerator (e.g., a parachute), and finally a terminal propulsive descent to a soft landing. The realizable landing accuracy is a function of navigation accuracy upon approach to Mars and during descent, dispersion effects experienced during descent, uncertainty in the true target position, as well as available control authority to remove detected trajectory errors. Key dispersions include navigation errors, atmospheric density uncertainty, unpredicted wind components experienced during descent, and map tie errors at the landing site. The contributions of the dispersions to expected landing errors and the available control authority to remove the dispersion effects were separately addressed for each phase of planetary approach and descent. Atmospheric density dispersions were found to have a dominant effect during the hypersonic aeroshell phase, while wind dispersions were found to have dominant effect during the supersonic and subsonic aerodynamic decelerator phase. The season being experience by the Mars landing site target was also found to affect the expected landing error because of the changes in the magnitude of the atmospheric, altitude-dependent dispersion effects that are correlated to seasonal changes in the density profile of the atmosphere. The altitude of the landing site with respect to the planetary mean was found to affect landing accuracy by limiting the envelope of feasible entry paths that achieved sufficient deceleration before initiation of terminal propulsive descent. Realization of the desired accuracy goal was found to require a combination of technical improvements that included: More precise planet approach navigation methods; means for landing target-relative position determination; improved or added means for control authority; near-Mars infrastructure to provide data to limit navigation and environment uncertainties. An incremental technology development plan is being formulated and pursued to realize the pinpoint landing accuracy goal.