Penetration mechanics modeling & validation of blade implements into porous, brittle comet simulant

This paper presents an experimental and theoretical investigation of the interaction between a thin blade penetrator and materials representative of what is expected for the outermost 20cm of a comet's nucleus. The blade dimensions investigated are thicknesses of 1, 1.5mm and 2mm, width of 120 to 184 mm, surface contact speeds of 0 to 15m/s, and penetration depth of up to 140mm. Earth snow is used as a conceptual comet analogue. Comet surface analogues used for experimentation are variations of foam glass and a simulant developed at the Jet Propulsion Laboratory. An apparatus developed for this study inserts blades into simulants via spring potential energy and blade kinetic energy. During insertion, recordings at >60kHz are made for forces acting on the blade and for the blade position. Parameters varied to explore effects on penetration dynamics include penetrated material, blade material and dimensions, blade speed at surface contact, and spring potential energy at blade surface contact. The physics-based penetration model presented is shown to be useful for predicting the interaction between the blade shaped penetrators and comet-line materials. Behaviors predicted include penetration time, maximum penetration resistance, penetration velocity profile, and penetration resistance vs. depth profile. The model input variables are blade dimensions, comet microstructure strength, blade-comet friction (friction coefficient and cavity pressure), comet grain friction (as a damping coefficient), and system energy at contact. The penetration model has applications beyond studying penetration behavior. An optimization routine is shown to be useful for estimating comet/simulant mechanical properties from experiments. The prediction of penetration performance for a large design space enables identification of advantageous designs with less experiments than would otherwise be practical.