There are two US oxygen delivery systems currently used onboard the International Space Station (ISS) - the Respiratory Support Pack (RSP) and the Portable Breathing Apparatus (PBA). The RSP uses the ISS 120 psi oxygen lines and delivers pure oxygen up to 12 L/min. The RSP is for medical O2 usage. The PBA consists of a non-refillable portable oxygen bottle that provides 15 minutes of oxygen and also includes a 30 foot hose to attach to the ISS oxygen lines for long term oxygen supply. The PBAs are distributed throughout the ISS, and a few are available in each module or node. Both the PBAs and the RSP can obtain their oxygen supply from high pressure tanks located on the ISS. The PBAs also attached to the ISS oxygen line for use during the pre-Extravehicular Activity (EVA) pre-breathe protocol (a method of decreasing the body’s nitrogen load and the risk of decompression sickness). The PBAs are also used for emergency oxygen usage. An alternative to the US oxygen mask is the Russian isolating gas mask that can be used during fire or atmospheric contamination events. It provides 70 minutes of oxygen, but has been reported to be bulky, hot, and uncomfortable to wear for long periods of time. The main challenge with the current systems is that when using either the RSP or PBAs, the cabin oxygen concentration is elevated which increases the fire hazard. Modeling results have shown that when a patient is receiving oxygen, the oxygen concentration aboard the ISS rises very slowly secondary to the large volume and good mixing due to ventilation. In a much smaller spacecraft, the oxygen concentration increases much more rapidly and the risk of fire increases accordingly. Even in the ISS well-mixed scenario there is a pocket of elevated oxygen around the astronaut’s head and chest area that creates a high risk situation. If an ignition source is introduced into this area, the resulting fire can rapidly spread through the oxygen-saturated clothing and hair as well as to other astronauts who may be treating the patient. For exploration atmospheres, the ambient atmosphere may be at elevated oxygen and reduced pressure as the norm, increasing the flammability of materials in general.
The chamber is filled from the bottle rack, which contains different O2-N2 blends of 21% O2, 30% O2, and 34% O2. In addition, a combustion products ‘air’ blend is present that contains 1% CO2 and 55 ppm of CO. Additional bottles of 95% O2 and 100% N2 are used to calibrate and purge the oxygen sensor before and after each test, respectively. The oxygen concentrator is placed in the test chamber, draws in the ambient atmosphere from the chamber, and separates the gases to a waste stream that is predominantly nitrogen, and a product stream which is predominantly oxygen. Each of the three flow streams is measured for pressure, flow rate, temperature, humidity, and the oxygen concentration of the product stream is also measured. In addition, the voltage and current draw of the prototype was measured, and CO and CO2 sensors were used in some tests that used a gas mixture with these contaminants present.
At the end of the testing, a report was finished comparing the Ritter PSA Prototype to the Lynntech Electrochemical Prototype investigators received and tested in 2012. Both prototypes were tested in the same lab, and were judged against the current flight oxygen concentrator requirements. Both prototypes met some of the requirements, but not all of them, since these are prototype units and not high technology readiness level (TRL). The PSA prototype successfully met 12 of 23 requirements, and the electrochemical prototype met 8 of 23 requirements. Based on this evaluation, the PSA technology had a clear technical advantage over the electrochemical technology.
In addition, in 2014, two Phase I Small Business Innovation Research (SBIR) were awarded pursuing two different technologies (Vacuum Swing Adsorption - VSA, and a different electrochemical design). The TDA, Inc. SBIR Phase I developed an oxygen generator based on a vacuum swing adsorption (VSA) to produce concentrated medical oxygen. They designed and built and evaluated the performance of the sorbent in a breadboard bench-scale prototype. The unit uses ambient vehicle cabin air as the feed and delivers high purity oxygen. TDA's VSA system uses a modified version of the lithium exchanged low silica X zeolite (Li-LSX), a state-of-the-art air separation sorbent extensively used in commercial Portable Oxygen Concentrators (POCs) to enhance the N2 adsorption capacity. The Reactive Innovations SBIR Phase I developed a modular electrochemical subscale concentrator and performed a preliminary design based on the performance of their arrangement of modular separation units. They demonstrated that modular separation units could be manufactured that separated oxygen from exploration atmospheres to produce pure oxygen. The modular separation units were compact, light-weight, and low cost serving both NASA needs and Reactive Innovation’s commercial pursuits.
Lastly, a technology development plan was updated, and the Oxygen Concentrator Module (OCM) project has had extensive discussions with Johnson Space Center (JSC) and Headquarters (HQ) personnel regarding synergy with EVA high pressure, high purity oxygen requirements for exploration missions. Investigators also identified oxygen needs for pre-breathing prior to EVA and in the event of a toxic spill or fire.
No datasets exist for this study. A final report was archived.
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