High Fidelity Numerical Modeling of the Thermal/Hydrodynamics of a Descending Ice Probe

The subsurface oceans of icy moons are thought to be one of the most likely locations of extraterrestrial life within our solar system. Thermal probes, or cryobots, have been proposed to melt through an exterior shell of ice, in order to access the ocean tens of kilometers below. Sufficiently understanding the cryobot system-level architecture presently remains a challenge due to the large uncertainties in the characteristics of these ice shells and previously-unexplained discrepancies between existing models and empirical tests. Here we present the development and performance of a new numerical finite volume model of a descending ice probe. The model utilizes conjugate heat transfer from the probe to the surrounding melt water and ice, in order to predict the descent speed. Unlike existing analytic models, the numerical approach makes no a priori assumptions about the interaction between the probe and the environment. The numerical model was successfully validated with empirical data collected using two subscale ice probes of different designs in testbeds with warm ice (253K) and cryogenic ice (80 K). By adjusting the heat supplied to each probe, the descent speed was modulated to cover a broad range of mission-relevant conditions. Attaining proper thermal and hydrodynamic closure between model and experiment required detailed modeling of the probe interior, including the heater contact with the hull, as well as including the full extent of the ice domain. Just as the early exploration of Mars was enabled by modeling spacecraft descending through an unknown atmosphere, the viability of ocean-access missions will be enabled by models of descent through an unknown ice shell. The validated models inform probe design and constrain the mission architecture. They can also be used to evaluate the range of applicability of lower fidelity, quick-solving analytic models. This is especially enabling of time-to-ocean simulations, which must account for significant uncertainties in the structure of the extraterrestrial ice shells.