Safety Control of Gas Displacement in the Environmental System of Space Station Experiment Rack

A number of experiment and maintenance of equipment on the space station requires a confined space. Some of the experiment and maintenance may require a environment with high concentration of nitrogen, which need the replacement of waste gas with nitrogen. In some other cases, the waste gas generated in the experiment should be exhausted out of the cabin, then the space is recharged to the atmospheric pressure with nitrogen or fresh air. Therefore a special experimental rack (ER) is designed with a confined space for these operation. In this paper, the confined environment system is designed in the ER, which is connected to an external high-pressure nitrogen supply equipment. Furthermore, it has interfaces to vent waste gas to extravehicular environment and has another interface to the cabin environment. Safety control strategies for charging and exhausting is applied in this environment system. The pressure of ER is controlled within a tolerable range to prevent structural damage. The performance of gas displacement systems is analyzed. As the displacement rate using nitrogen is much higher than that of air displacement, the nitrogen is used as the main supply gas in the gas displacement.