Manufacturing and Characterization of Icy Simulants for Europa

In the exploration of icy ocean worlds, includingEnceladus, Europa, and Titan, the absence of informationrelated to material properties of the surface requires thatsampling subsystems possess a robust capability to interact witha broad variety of potential icy terrain scenarios. To aid in thedevelopment of sampling subsystems that can navigate thechallenges of surface excavation, sample collection, and sampledelivery in a variety of terrain conditions, we aim toreproducibly generate plausible solid icy simulants with a rangeof mechanical properties at a scale relevant to the activities ofsampling tools testbeds. This paper presents a simple methodfor relatively large-scale (kg/hr) manufacturing of granular icebased on a flash-freezing process that enables entrapment ofadditives within the ice particulates at the micron-scale.Employing additives based on magnesium sulfate (MgSO4) as anexemplary system applicable to Europa, we explore the impactof post-manufacturing densification parameters on granular icemechanical properties. Simulants are characterized viaporosity, concentration uniformity, qualitative assessment ofparticle characteristics, Raman spectroscopy, and mechanicalproperties testing (Shore A hardness and 3-point-bend).Our granular ice manufacturing process was found to produceroughly 17 kg of granular ice with MgSO4-based additives in a2 – 3 hour time span. The concentration of MgSO4 was uniformat the gram-scale, and average particle diameters of granularice as-manufactured ranged from 169 µm – 317 µm. Ramanspectroscopy indicated the formation of a glassy phase ofMgSO4 hydrate when freshly frozen, and in consistency withliterature, storage at low temperatures and subsequent(unintentional) thermal cycling resulted in the formation ofepsomite (MgSO4•7H2O) (MS7) and mixed MS7+meridianiite(MgSO4•11H2O) (MS11) phases, respectively.Densification was accomplished using both small(commissioning) and large (scale of sampling activities) pressmolds. A test matrix generated via Design of Experiments (DoE)was used to explore the impact of time (7 days and 21 days),temperature (-10°C, -40°C, -80°C), pressure (1 MPa and 27MPa), and MgSO4 concentration (0.0 wt.%, 2.3 wt.%, and 16.0wt.%); simulants with a range of spatially uniform mechanicalproperties (1 – 72 Shore A hardness, and 39 – 51% porosity)were produced. Images of densified particles revealed thatmelting was likely the primary mechanism of densification, andMgSO4 phase characteristics suggested that formation of MS11during densification was promoted by high MgSO4concentrations and high temperatures. Temperature had thehighest impact on Shore A hardness.Future work aims to broaden the range of accessible simulantmechanical properties by varying granular ice particle diameterand expanding the densification parameter space. Ultimately, arange of densified samples will be tested with sampling tools andsystems to understand the unique ways in which varioussimulant mechanical properties pose unique sample excavation, collection, and delivery challenges.