Ice motion in land terminating regions of the Greenland Ice Sheet is controlled in part by meltwater input into moulins. Moulins, large near-vertical shafts that deliver supraglacial water to the bed, modulate local and regional basal water pressure and ice flow by influencing subglacial drainage efficiency on daily to seasonal timescales. Our previous modeling work found that the geometry of a moulin near the water line has substantial effect on subglacial water pressure variations. Here, we develop a new physically based moulin model which can help constrain moulin shape across the ice sheet and its influence on hydraulic head oscillation, and inform the englacial void parameter used in glacier hydrology modeling. The Moulin Shape (MouSh) model (in Matlab and Python) provides new insight into the evolution of subsurface moulin size and shape at hourly to multi-year timescales. The modeled moulin is initialized as a vertical cylinder. The moulin walls melt back above and below the water line due to the dissipation of turbulent energy, open or close due to viscous and elastic deformation, and freeze inward in winter when cold air temperatures and an absence of meltwater allow refreezing. We combine MouSh modeling results with geometric data from two moulins in Pâkitsoq, western Greenland, which we mapped to the water line. The moulins have heterogeneous shapes and volumes in the top 100 m. This suggests that the size and shape of the upper portion is controlled by local and regional pre-existing fractures, which provide preferential paths for water flow and melting, creating stochastic karst-like conduit shapes. Modeling results show that moulin geometry below the water line is influenced by the hydraulic head, which controls the depth-dependent elastic and viscous closure rates, and by the roughness of the walls, which enhances melt-out rates that oppose moulin closure. We show that subglacial water pressure across the ice sheet is likely influenced by moulin geometry, underscoring the need for including moulins in subglacial models.

Over the past three years Stone Aerospace has developed a novel ice penetrating technology known as a Direct Laser Penetration (DLP). DLP uses laser light carried by an optical fiber to a vertically descending ice penetrator and emitted from the nose to melt the ice in front of it at extremely high power levels and melt rates. A penetrator can be made with an onboard fiber spool connected to a surface-based laser, allowing the hole to re-freeze behind, drastically increasing efficiency and providing isolation from the surface. A parallel spool can pay out a communications fiber to carry information from imagers, fiber-based sensors (e.g. temperature, pressure, seismic), and other optical sensors (e.g. fluorescence or Raman). Laser power levels of up to 100 kW (continuous) at 1070 nm wavelength are now available and can be coupled to these probes. Successful laboratory test results at Antarctic ice temperatures show that this approach could lead to the fastest ice penetration rate available to terrestrial targets, with access to any Antarctic sub-glacial lake in under 16 hours. In this way, DLP offers an alternative to traditional, logistically intense ice drilling: a small footprint system that is fast and can deploy sensor strings through the deepest ice in a short period of time. DLP also shows promise in addressing the ‘starting problem’ for extraterrestrial targets such as Europa or Mars where low pressures prevent the formation of water at the surface and thus heat transfer for traditional melt probe architectures. In order to test the effectiveness of this concept, a Europa environment ‘cryovac’ test facility has been built at Stone Aerospace in Austin, Texas. We will discuss quantitative results from initial lab and chamber tests of the DLP concept, including in an ice column at 100 K temperature subjected to vacuum.

Ocean Worlds in our Solar System are attractive candidates in the search for extra-terrestrial life. The best chances for detecting biosignatures and biology on these bodies lie in in situ investigations of sub-ice oceans in contact with rocky interiors. The actual conditions that will confront an ice-penetrating vehicle (“cryobot”) performing such investigations are largely unknown. However, any Ocean World cryobot must be able to, at a minimum, successfully negotiate five different operating regimes to have a chance of reaching a subsurface ocean: starting at the surface in vacuum at cryogenic temperatures; brittle/cold ice transit; ductile/warm ice transit; negotiating or penetrating salt or sediment layers, and other obstacles; and detecting and transiting ice-water transitions such as voids and the final ocean entry. PROMETHEUS (nuclear-Powered RObotic MEchanism Technology for Hot-water Exploration of Under-ice Space) represents a full cryobot concept and set of key technology demonstrations that advance the capability to perform such investigations. The PROMETHEUS concept is targeted for deployment on Europa, and consists of a fully-instrumented science vehicle able to actively control descent through the ice shell and into the subsurface ocean. The concept employs closed-cycle hot water drilling (CCHWD) technology as the primary means of penetrating ice, and making forward and turning progress. A “passive” (purely conductive) heat transfer system enables penetration starting on the surface where liquid water cannot exist until hole closure is achieved and the system proceeds inside a melt water “bubble”. PROMETHEUS is compatible with a small fission reactor (the NASA Kilopower design) and employs a vertical motion control system using a trailing tether frozen into the ice to guard against falling through voids and enabling controlled entry into the sub-ice ocean. The design is capable of achieving a 20 km descent through a Europan ice profile in under a year and under 500 kg vehicle mass, including reactor mass.