Carbon dioxide removal from the Space Station Freedom atmosphere is an essential part of the crew's life support. Freedom must utilize carbon dioxide removal systems in order to prevent crew asphyxiation. This paper describes the design and development of the positive displacement pump selected to operate as an essential part of the carbon dioxide removal assembly (CDRA).
The pump evacuates air from the carbon dioxide adsorbent beds and returns it to the cabin environment saving oxygen and nitrogen. Air is removed from the beds by allowing the pump to pull a rough vacuum while the beds are heated. The oxygen and nitrogen molecules adsorbed by the beds are released prior to the carbon dioxide molecules. This is due to their lower affinity to the selected molecular sieve material.
An oil-less two-stage rotary sliding vane pump was selected as the optimum concept to meet the CDRA application requirements. There were several reasons for selecting this positive displacement pump over other design concepts including its simple design and reliability. Some other positive aspects of this type of design are: 1) Its low weight and small envelope per unit flow, 2) Ability to pump saturated gases and moderate amounts of liquid, 3) No required valves, 4) Small clearance volumes, 5) Low vibration, and 6) It is easily modified to accommodate several stages on a single shaft optimizing space and weight, making the concept ideal for a range of demanding space applications.
Under contract to the Boeing Aerospace and Electronics Company, the Allied-Signal Aerospace, AiResearch Los Angeles Division designed and fabricated a research class two-stage rotary sliding vane pump incorporating several significant improvements over existing designs. Development testing is currently underway with successful preliminary performance results. The research class unit fabricated for development testing was functionally identical to the final flight design. Some components such as the 120 volt DC motor will be modified to meet Space Station Freedom specifications.