Cryotwin: Physically Consistent Performance Modeling for Cryobot Dynamics

Space exploration for the existence of extraterrestrial life has been a topic of paramount interest. The icy moons of our solar system are among the promising candidates. Characterized by a thick outer ice shell that covers a subsurface ocean layer, the definitive establishment of life on these moons would require examining the water physically. A comparatively convenient way to access the water is to melt through the ice shell, i.e., thermal drilling using cryobots. Before a cryobot can be used on an icy moon, the Antarctic ice sheets serve as a suitable terrestrial analog testing site. Among several constraining factors, total energy and transit time are of substantial significance for these missions. A digital twin that provides a virtual framework integrating physics and data can help assess these constrained scenarios and inform decision-making. In this work, we present two innovations. Firstly, we introduce Cryotwin, a digital twin for assessing cryobot performance. We describe its concept, use cases, and applicability across different mission phases. Secondly, we introduce a new physically consistent, state-of-the-art semi-analytical model that serves as the primary component of Cryotwin and enables performance assessment. This model, for the first time, considers both global thermal and force equilibrium while representing the complex multiphysics phase-change process observed during thermal drilling, to calculate cryobot velocity and the melt channel radius. Specifically, cryobot velocity, which controls transit time, and total efficiency, which controls total energy, are considered quantities of interest for the performance. Finally, we present a case study demonstrating the potential of Cryotwin, together with the new model, to facilitate cryobot design and development and to aid in crucial decisions regarding the optimization of total energy and transit time, subject to operating conditions.