Rules of similarity analysis are applied to develop criteria for deducing from model experiments steady-state and transient temperature distributions for a typical space vehicle element exposed to space conditions. The specific purpose is to determine if useful information can be obtained on models in space environment chambers. Thermal similarity criteria are deduced from expressions for transient conduction with radiation boundary conditions. Based on these criteria, a prototype and nominally one-half -scale model were designed and tested in a space chamber. To attain thermal similarity, some geometric distortion was necessary in the model. Both prototype and model were thermally cycled. Temperature data for prototype and model are compared at equivalent locations and times. Results show that temperatures agree within an average of approximately 1 percent with a maximum deviation of approximately 5 percent. The model was subsequently altered, thus destroying its thermal similarity. After alteration, the temperature data differed significantly from that of the thermally similar model and prototype. These experimental results demonstrate the correctness of the derived criteria and show that close adherence to similarity rules is required.