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Method of Separating Oxygen From Spacecraft Cabin Air to Enable Extravehicular Activities

Extravehicular activities (EVAs) require high-pressure, high-purity oxygen. Shuttle EVAs use oxygen that is stored and transported as a cryogenic fluid. EVAs on the International Space Station (ISS) presently use the Shuttle cryo O2, which is transported to the ISS using a transfer hose. The fluid is compressed to elevated pressures and stored as a high-pressure gas. With the retirement of the shuttle, NASA has been searching for ways to deliver oxygen to fill the high-pressure oxygen tanks on the ISS.

A method was developed using lowpressure oxygen generated onboard the ISS and released into ISS cabin air, filtering the oxygen from ISS cabin air using a pressure swing absorber to generate a low-pressure (high-purity) oxygen stream, compressing the oxygen with a mechanical compressor, and transferring the high-pressure, high-purity oxygen to ISS storage tanks. The pressure swing absorber (PSA) can be either a two-stage device, or a single-stage device, depending on the type of sorbent used. The key is to produce a stream with oxygen purity greater than 99.5 percent. The separator can be a PSA device, or a VPSA device (that uses both vacuum and pressure for the gas separation). The compressor is a multi-stage mechanical compressor. If the gas flow rates are on the order of 5 to 10 lb (≈2.3 to 4.6 kg) per day, the compressor can be relatively small [3×16×16 in. (≈8×41×41 cm)].

Any spacecraft system, or other remote location that has a supply of low-pressure oxygen, a method of separating oxygen from cabin air, and a method of compressing the enriched oxygen stream, has the possibility of having a regenerable supply of high-pressure, high-purity oxygen that is compact, simple, and safe. If cabin air is modified so there is very little argon, the separator can be smaller, simpler, and use less power.

This work was done by John C. Graf of Johnson Space Center. MSC-24806-1

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