Sediment Sequestration for Hot Water Drilling Cryobots

This Phase II proposal focuses on an innovation to resolve the sediment problem in deep ice drilling. Accumulated insoluble debris could hinder descent of a cryobot (ice-penetrating robot) on a mission to explore icy ocean worlds or ice strata on Mars. Section S13:01 of the 2022 SBIR solicitation stated: preference will be given to those proposals that would benefit in situ studies of icy ocean worlds, especially techniques that would be beneficial to systems that will descend through kilometers of cryogenic ice. The MJOLNIR innovation aims to address this call by mitigating the risk of debris accumulation for cryobots by periodically creating side pockets in the ice where debris can be sequestered. Phase I work used computational fluid dynamic particle tracking code to model a wide range of parameters that affect the ability to move collected insoluble material into sequestration pockets. We identified a feasible CONOPS: 1) downward closed-cycle hot water drill (CCHWD) jetting proceeds until the vehicle descent is slowed due to debris collection; 2) it switches to passive melting until the nose reaches the debris accumulation; 3) lateral jets near the nose cut deep side pockets; 4) jet flow turbulence moves the particles into the pockets; 5) the vehicle resumes passive melting to slowly move past the side pockets as particles settle out in the pockets; and 6) the vehicle resumes CCHWD jetting descent. Phase II focuses on three laboratory investigations: 1) measuring ground truth geometry of the sequestration pockets created under a wide range of jet parameters; 2) testing the ability to sequester a wide range of insoluble particles; and 3) examining the effect ofice temperature onthe side pocketapproach. The CCWD approach enables cryobots to breach debris-laden ice and the MJOLNIR innovation will provide debris mitigation enabling long descent distances. NASA mission applications include exploration of Mars polar ices and all ice-covered ocean worlds. This work addresses the challenge of sediment mitigation for ice penetration via hot water drill (HWD) sondes and cryobots. HWD technologies are the workhorse of deep ice access in terrestrial polar regions and closed-cycle hot water drilling has been explored as a way to penetrate ice on other worlds in support of exploration and science. As ice refreezes behind a descending cryobot, the refreezing process will exclude foreign materials such as sediment trapped in the ice column. Over the course of many kilometers this sediment accumulation could damage pumps, insulate ice from HWD jets, or otherwise impede the function of the cryobot. Existing techniques such as debris traps are insufficient for long duration or heavy sediment loads. The technique of side-pockets for lateral diversion was demonstrated in the field (TRL5) but has never been used for sediment. Using side-pocket and circulation control for sediment sequestration will enable greatly enhanced robotic mobility and will open new subsurface and terrestrial frontiers by enabling cryobots to pass through dirty and briny ice. Objective 1: SSP Geometry: Test sediment sequestration pocket (SSP) geometry vs jet focus; fluid temperature; fluid velocity; duration of operation; ice composition (pure water; homogeneously-distributed non-soluble particles and layers; and soluble contaminants including NaCL and MgSO4. Conduct these tests in -30°C ice blocks then create 3D models of pockets as ground truth reference for future work. Milestone 1: Create a digital database of SSP geometries for the above-defined parameters.  Objective 2:  SSP Effectiveness in Debris: Determine effectiveness of moving insoluble debris into SSPs and identify factors to maximize cryobot descent progress. Test debris parameters: particle fraction; composition/density; size/shape distribution; and layer thickness/fraction. Create library of SSP ground truth information applicable to a wide range of cryobot designs. Milestone 2: Create a database of SSP effectiveness for distributed and discrete-layered non-soluble debris in ice.  Objective 3: SSP Ice Temperature Dependency: Test the highest performing approaches observed in Q1-6 in cryogenic ice (77° K, no vacuum).  We will use the same SSP post-test casting, scanning, and archiving procedures as Q1-6. Milestone 3: Create database of SSP effectiveness over a select set of test variables involving both homogeneously distributed and discrete-layered non-soluble debris in cryogenic ice  

MJOLNIR allows ice-penetrating cryobots such as THOR to breach debris-laden ice (ice fraction >50%), providing steady state debris mitigation over long descent distances. Potential NASA mission application include: Mars polar cap (2-3 km) subsurface access and sampling; Europa’s 10-40 km ice crust with ocean access; Ganymede’s rocky ice crust for strata and sampling studies; Enceladus’s estimated 10-40 km thick ice crust with ocean or cryovolcanic access; and other icy ocean worlds The MJOLNIR system may be implemented on terrestrial hot water drill rigs to manage sediment for glacial and astrobiological investigations: Basal access to bedrock layer through heavily debris-laden ice at base of ice sheets in Antarctica and Greenland; heavy debris alpine glacier penetration for strata-based sampling, and access to subsurface water conduits; volcanic caldera glaciers

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