Optimization of Outgassing Bake-Out Temperatures and Duration of Space Systems

Spacecraft systems are baked under vacuum to remove occluded and absorbed gases, solvents, plasticizers, and other materials acquired during their manufacture and exposure to the environment. The procedure is intended to reduce outgassing during subsequent vacuum exposure, decrease the quantity of potential contaminants which may deposit on critical surfaces, and limit the gaseous environment induced by the outgassing around a spacecraft. The determination of the temperature and of the duration of the bake which accomplishes a major portion of the outgassing and is not unduly high and long is of considerable importance for the integrity of the system and cost effectiveness. In this paper, the percentage of the outgassing mass removed as a function of bake-out temperatures in the range of 45 to 85°C and bake durations of up to 200 hours have been provided in terms of the percentage removed after 24 hours of bake at 125°C. It has been shown, among others, that extending the bake-out from 60 hours to 100 hours or even to 200 hours will release only a few percent more of the outgassing at those bake temperatures. For example, in extending the bake from 60 hours to 200 hours at a temperature of 65° one removes only an additional 6 percent outgassing if the outgassing decays lineraly with time which is often found experimentally. On the other hand, the additional release is about 15 percent for the same conditions if the outgassing decays with the square root of time which represents a diffusive outgassing process. It is obvious that considerable savings in time and money can be made using as a guideline the data reported here to decide on the duration of the bake after having selected a maximum acceptable bake temperature which does not degrade the system. The data can also be used for the outgassing tests of materials in optimizing the test duration.