1. Estimates of the uncertainties in the various thermophysical properties required are summarized in Table 1. Values of solar absorptance and hemispherical (or directional) emittance of the surfaces of a spacecraft (e.g., coatings and solar cells) are subject to errors in measurement and in application (quality control, adverse environments, detail design of spacecraft). Interface or joint conductance is subject to many factors which are beyond precise control; although some 200 sources of information are given in Ref. 1, the variance of conductance for a specific joint can best be estimated from experimental data. Measured conductances of "identical" joints may vary by as much as -100%; but "normal" variance is estimated, from Refs. 2-7, to be -25%. Values of thermal conductivity, thermal capacitance, and density are most often extracted from handbooks or compilations, but "batch to batch" differences may be expected, e.g., in honeycomb material. The results of Ref. 8 indicate that a variance of - 10% can be conservatively assigned to k}cp, and density data.