Europa Lander Engine Plume Interactions with the Surface and Vehicle

Abstract

NASA's proposed Europa Lander Project would deliver an autonomous robotic lander with a suite of scientific equipment to the icy moon's surface in order to excavate surface samples and search for bio-signatures. This mission concept would land on the Europan surface using JPL's iconic Sky Crane technique, by which a powered descent vehicle is propelled and maneuvered into a hovering position with eight monopropellant hydrazine engines before lowering its lander. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</sup> The gas plumes of these engines would expand rapidly into Europa's near-vacuum surface conditions and impinge upon the moon's surface, the lander, and descent vehicle to potentially detrimental effect. Engine plumes induce torques and heating of spacecraft and can transport gas and liquid propellant byproducts to contaminate sensitive instrument surfaces, impacting science collection. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]–[6]</sup> Major interactions of concern include surface contamination with, and subsurface penetration of, propellant byproducts; the removal and transport of particulates from plume-induced pressure gradients; and the sublimation of surface ices. Therefore it is critical to understand and characterize the proposed Europa Lander's engine plumes. Landings onto Europa and other airless bodies - i.e. those without collisional atmospheres, a class including Enceladus, Earth's moon, and many asteroids - will generate engine plume flow-fields that transition through continuum, rarefied gas-dynamic, and free-molecular regimes. Such complex, non-equilibrium flow-fields require hybrid solution schemes. A one-way-coupled continuum-to-rarefied hybrid scheme has been demonstrated, validated, and deployed for the simulation of single-engine, steady-state lander plumes impinging onto both the Earth's moon and Europa in a multidisciplinary effort at JPL. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[2]</sup> The present work extends that hybrid framework to model the complex interactions of the full set of four Europa Lander descent engine plumes, each canted at 30°, generated during the final Sky Crane bridled descent. We report resultant surface pressure, heating, and contaminant depositions, and we demonstrate a framework that can be applied to model realistically-rough Europa-like surface morphologies. Likewise, we report the pressures, heat fluxes, and contaminant depositions induced by transient descent engine plumes onto both the Europa Lander and descent vehicle envelopes during landing, and we propose and outline several detailed campaigns of future work to the benefit of Europa Lander's engineering and science teams.