Predicting the e ect of surface properties on Enceladus for landing

The prospect of landing on the surface of Enceladus comes with the question of whether the surface 4 conditions permit selection and certi cation of one or more safe landing sites in an area of high science 5 value. On Enceladus, life detection is a high science value objective that correlates with proximity to 6 the south polar terrain where the plume deposition rate is highest; however, such areas may be unsafe 7 if unsintered particles make the landing site unstable. To investigate this, the surface of Enceladus 8 is modeled using the level set discrete element method (LS-DEM). This method models the kinetics 9 and kinematics of large groups of individual ice particles both in contact and sintered together. Using 10 the model, a rigid footpad is initialized at a 1m=s descent just above the ice surface under Enceladus 11 gravity. Parameters studied were the sintering amount, particle size distribution, footpad geometry, 12 and surface slope. The model predicts that some sintering is required for the surface to support a 13 lander, however, too much sintering can cause a lander to bounce. Within the bounds tested, the 14 particle size distribution had little impact on the penetration depth. For tests on sloped surfaces it is 15 shown that landing could be possible on slopes as steep as 20 degrees for certain conditions, but it is 16 safest to land in areas with a slope angle of 15 degrees or less. While slope angle and sintering level 17 were much more important than footpad geometry, the hemisphere footpad had the best performance 18 (lowest sliding) in most cases compared to the cone or disk.