  A physics-based computer model has been developed to support the development
of volatile extraction from regolith of the Moon and asteroids. The model is
based upon empirical data sets for extraterrestrial soils and simulants,
including thermal conductivity of regolith and mixed composition ice, heat
capacity of soil and mixed composition ice, hydrated mineral volatile release
patterns, and sublimation of ice. A new thermal conductivity relationship is
derived that generalizes cases of regolith with varying temperature, soil
porosity, and pore vapor pressure. Ice composition is based upon measurements
of icy ejecta from the Lunar CRater Observation and Sensing Satellite (LCROSS)
impact and it is shown that thermal conductivity and heat capacity equations
for water ice provide adequate accuracy at the present level of development.
The heat diffusion equations are integrated with gas diffusion equations using
multiple adaptive timesteps. The entire model is placed into a Crank-Nicholson
framework where the finite difference formalism was extended to two dimensions
in axisymmetry. The one-dimensional version of the model successfully predicts
heat transfer that matches lunar and asteroid data sets. The axisymmetric model
has been used to study heat dissipation around lunar drills and water
extraction in asteroid coring devices.
