Thermal-fluid analysis of an RTG-powered ice penetrator for europa subsurface access: CFD modeling with phase-regime analysis

Europa, Jupiter’s ice-covered moon, harbors a subsurface ocean representing a prime target for astrobiological investigation. This study presents computational fluid dynamics (CFD) analysis of a radioisotope-powered thermal ice penetrator (cryobot) designed for Europa subsurface access, with explicit treatment of the melting-sublimation phase regime transition. A dual-regime thermal model is developed: a sublimation-dominated surface regime (depth <0.5 m, pressure <611 Pa) and a pressure-assisted melting regime (depth >0.5 m) where the penetrator’s weight and meltwater column raise local interface pressure above the triple point. Two-dimensional axisymmetric CFD simulations using the enthalpy-porosity method predict steady-state descent rates of 0.19 mm/s in the sublimation regime and 0.92 mm/s in the melting regime under baseline conditions (4.4 kW thermal power, temperature-dependent ice conductivity k(T) = 651/T W/(mK)). A multi-angle parametric study (cone half-angles 30°, 45°, 60°, 75°, 90°) independently establishes geometry-dependent flux concentration factors ranging from 1.0 to 14.8, revealing that the 120° apex (60° half-angle) achieves η geom,eff = 12.4 through combined geometric focusing and thermal conduction concentration. Richardson extrapolation on three systematically refined meshes confirms spatial convergence with Grid Convergence Index GCI fine = 0.32%. Sensitivity analyses demonstrate descent rate varies linearly with power (±10% power yields ±9.1% rate change) and inversely with ambient ice temperature (4.7% improvement per 10 K). Critical refreezing analysis confirms safe operation (L cr < 4 cm) throughout the 125–180 K range. Including the sublimation-limited surface transient and temperature-dependent properties, a 10 km penetration depth is achievable about 120 days (97–148 days). This work establishes validated thermal-fluid design parameters for kilometer-scale ice penetration missions to Europa and other ocean worlds.