Time dependent finite difference modeling of outgassing of asteroids via bulk heating

We have developed an integrated mathematical model of the outgassing processes associated with thermal mining of carbonaceous asteroids based on thermodynamics, geophysics, and gas-dynamic considerations to account for variability in material properties. This is a time dependent quasi-one-dimensional model of the heating and diffusion of volatiles as they are outgassed from a spherical target. The model accounts for radiative heat transfer into the surface, conductive heat transfer through the interior, and endothermic phase change processes of water and selected other volatiles bound within constituent minerals. The model is based on theoretical considerations with empirical factors for unknown quantities. This model was implemented as a numerical simulation via finite differences and programmed in Python. We used the program to simulate several scenarios mirroring those tested in the experimental effort as well as direct bulk heating of large-scale systems with an eye toward eventual mission application. In the related experimental program 200 to 700 gram samples of granular serpentine mineral, agglomerated and granular Carbonaceous Ivuna (CI) type meteorite simulants, and a Carbonaceous Mighei (CM) type meteorite (Jbilet-Winselwan) where heated in an instrumented vacuum system with outgassed volatiles collected in a cryotrap. The model gave good agreement with experimental results for the serpentine and the CI simulants, predicting a total water yield within 10% of that found from the experiments. Carbon dioxide yield predictions were also in close agreement with experiment; however, predictions for other carbonaceous gas species were less successful due to uncertainties in the stoichiometry of released volatiles. The model of a typical CM meteorite composition over-predicted the total water yield of the CM meteorite relative to experiment probably due to differences between the modeled composition and the actual meteorite composition, which was not available at the time of publication. We also used the model to simulate heating of full-scale CI-composition asteroids in space. We found that water extraction by simple heating is too slow a process to have direct industrial value. There is an upper size limit for practical volatiles production from individual bodies, controlled by the production rate required. Work on a related process called Optical Mining™ is examining approaches to improve production rates.