Mars Lander Engine plume impingement environment of the Mars Science Laboratory

Abstract

The Mars Science Laboratory (MSL) Mission will land a 900-kg rover on the surface of Mars in 2010. Four Mars Lander Engines (MLE's) will be fired during the final propulsive descent to maintain a 0.75 m/s vertical rate of descent, in support of a tethered landing approach referred to as the “Sky-Crane”. At 20 m above the surface the rover will be lowered on a bridle as it continues to descend. At touch-down, a minimum of 6.5 m of vertical separation are provided between the engines nozzle exit plane and the ground-surface below [1]. This maneuver was chosen in part to minimize the ground/soil interaction that occurs when rocket engine plumes are fired into a soil media. In spite of the 6.5 m altitude above the surface, surface impingement pressures are expected to reach in excess of 2000 Pa, a metric previously established by the Viking program to mitigate soil bearing capacity failure. Plume-ground interaction has been a concern of Lunar and Mars propulsive landings for some time, but was not an issue for the Mars Pathfinder and Mars Explorer Rover era due to their use of airbag landing systems [2][3].This was also a concern of the Phoenix lander program, which fired twelve pulsed hydrazine monopropellant thrusters for its final descent and touch-down [4]. Phoenix was concerned with plume impingement soil interaction due to its high surface impingement pressure and potential for diffused gas eruptions. Phoenix was also concerned with landing site alteration due to its lack of mobility as well as instrument and solar array contamination issues. As MSL will operate in a regime that will result in ground-soil erosion a plume-ground interaction program has been undertaken to quantify the amount of soil erosion, namely the trajectory and number flux of particulates and the contamination and erosion this can impart to sensitive instruments and thermal surface coatings.