Predicting spacecraft self-contamination in space and in a test chamber

The self-contamination of a spacecraft, defined as the return and deposition of outgassed molecules on its critical surfaces, was investigaed. Theoretical relations for the flux, density, and pressure of the emitted gas as a function of altitude, radius, and distance from the spacecraft surface were developed. The flux of these outgassed molecules which return to the emitting surface was also obtained and shown to be dependent on altitude, dimensions, and on the magnitude of outgassing. The rate of condensation and the time for the formation of a monolayer of the returning molecules can be calculated. The self-contamination of a spacecraft undergoing vacuum chamber test was also analyzed and compared to the equivalent parameters for the orbital conditions.