How (not) to lose communication with your submersible on Europa: An experimental study for characterizing the shear performance of tethers under confinement in ice
Abstract
Future exploration of Ocean World interiors, believed to harbor conditions conducive to life, will require penetrating an ice shell up to 10s of km thick while maintaining robust communication with a surface lander. Micro-tethers offer unparalleled data transfer rates (for minimal size, mass & power) and sufficient length (20+ km), but are not rated for survivability under the thermo-mechanical conditions expected at Europa.
The Europa Signals Through the Ice (STI) project aims to characterize the viability of employing various tethers by measuring their strength/performance & deployment mechanism in a laboratory setting that simulates shearing and fault conditions at Europa. For this work (fig. 1), double-jointed blocks of polycrystalline ice with controlled grain size, porosity, and impurity content are fabricated in a three-compartment mold. Tethers currently employed for polar submersible exploration are embedded in the ice and retained in tension. A custom Tether Tensile Tester (T3) apparatus is used to calibrate optical working strength & ultimate tensile strength. A servo-hydraulic biaxial cryogenic deformation apparatus is used to shear the tethers across two sliding ice "faults", at an applied shear stress, velocity, temperature & ice composition. Normal stress of 100 kPa is maintained, with a vertical piston driven at a constant shear rate until optical and/or mechanical failure. We consider end-member scenarios for shear rates on strike-slip faults, between creeping (10-7 m/s) and icequakes (10-3 m/s), and characterize communication performance with an Optical Backscatter Reflectometer for fiber optics (optical power loss & strain), and a milliohm meter for copper tether (resistance for conductors). Failure mode is identified by microscopic characterization. Preliminary results of T3 calibration & double shearing tests for tethers in Europa-like ice and environmental conditions will be discussed. Results will be used to map out viable stress regimes for communication using tethers, along with identifying effects of pre-tension on tensile strength & communication performance. Europa STI will enable development of tethered communication techniques to operate in harsh conditions, with implications for subsurface exploration of ocean worlds and the search for extraterrestrial life.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P51B..06S
- Keywords:
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- 0728 Ice shelves;
- CRYOSPHERE;
- 6221 Europa;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6282 Enceladus;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6297 Instruments and techniques;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS