Abstract: Outgassing of contaminant species from spacecraft materials is a multistep process. A mixture of contaminant molecules diffuses through a porous medium, emerges on the surface, possibly migrates on the surface, interacts with other molecules on the surface, evaporates from the surface, etc. For some outgassing materials, it is reasonable to assume that the rate limiting step is the diffusion process. The diffusion equations and their boundary conditions are assembled and analytic solutions found corresponding to isothermal outgassing measurements, where quartz crystal microbalances set at fixed temperatures are used to collect condensables. The mathematical diffusion solutions and measured data are used in numerical manipulations to determine diffusion coefficients for each of several species outgassing from the source. This analysis provides a means of extrapolating outgassing data over long times using the time dependence of the diffusion equation.!11
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