Oxygen is a valuable, but limited, resource on a spacecraft. Much planning is needed to ensure that a crew has enough oxygen during its flight. But what if the unexpected happens and additional oxygen is needed for treatment of an astronaut with a serious injury or major illness? One solution is oxygen concentrators, devices that extract oxygen out of the air using electricity. Current versions, however, are not ideal for space travel due to their large size, mass and power requirements.
Dr. James A. Ritter and colleagues are conducting a research project to determine if it is possible to combine rapid Pressure Swing Adsorption (PSA) technology with new air compressor designs to develop light, compact concentrators that use minimal electricity and can supply oxygen continuously for many days. The researchers will use computer simulations and testing of components to identify approaches to improve the efficiency of the PSA separation and develop oxygen concentrators that are more ideal for use on spacecraft.
James A. Ritter, Ph.D.
University of South Carolina
A source of medical oxygen will be needed at some point to keep an astronaut alive during a space mission. To meet this need, the ideal oxygen source would be a light, compact unit that uses minimal electricity and can supply oxygen continuously for many days. No current technology meets these requirements. Traditional compressed-oxygen cylinders provide a limited amount of oxygen in a heavy, inconvenient package and are not suited for space missions. Oxygen concentrators, which extract oxygen from air using electricity, can eliminate the obvious problems with cylinder storage in space. These kinds of medical oxygen concentrators are already used in residential and military applications.
However, existing systems are too big, use too much power and are too heavy to be carried into space. For example, developing a unit that can produce oxygen continuously at 4 liters per minute (LPM), weigh less than 7 pounds and use less than 100 watts of electric power requires a two-fold reduction in weight and power consumption, compared with the most advanced oxygen concentrators now in production by SeQual Technologies. As proposed in this project, this requirement may be met by combining new air compressor designs with advances in Pressure Swing Adsorption (PSA) technology. SeQual and the team of researchers from the University of South Carolina, Vanderbilt University and the NASA Marshall Space Flight Center (MSFC) are uniquely positioned to achieve this next level of performance.
To determine whether the proposed technology advances are indeed possible, during the second year of this four-year project, the four teams of researchers have been busy carrying out extensive mathematical modeling studies (USC), measuring equilibrium and kinetic parameters for the modeling effort (VU), performing carefully planned experiments with an Eclipse medical oxygen system modified for testing at the bench scale (SeQaul), and gearing up for testing an Eclipse medical oxygen system under different environmental conditions (MSFC). Results from numerous experiments were used successfully to validate USC's Dynamic Adsorption Process Simulator (DAPS). In particular, DAPS was specially modified and calibrated against a SeQual PSA module under controlled conditions with a decoupled compressor, and the process performance was analyzed with respect to cycle speed, temperature and high to low pressure ratio.
Once validated, DAPS simulations focused on varying certain key process parameters to arrive at optimized PSA cycle designs. The learning from the design effort was implemented into a modified PSA module design operating a new PSA cycle, larger feed/exhaust ports, a backfill step, and larger recycle and purge ports. The new PSA module, associated compressor and other components were fabricated and assembled on a breadboard. The breadboard was connected to instrumentation and tested.
The new PSA design successfully delivered 4 lpm of product in about an 8 lb assembly with a compressor shaft power of 130 Watts. This was a significant outcome, especially since the new PSA design was based entirely on predictions from the DAPS. Overall, in the first two years of this four year project, this program is ahead of schedule and definitely on track for improving even further the efficiency of the PSA separation, with the project potentially culminating in a breadboard system that will supply 4 LPM of oxygen, weigh 7.2 lbs, require 106 Watts, and satisfy any new constraints imposed by NASA.
During Year 3, the task outline presented in the original proposal was followed. In this way, carefully planned experiments carried out by the folks at SeQual were used to calibrate and further validate DAPS at USC. This was done in an attempt to further improve the performance of the PSA module and to understand the effects of potential process changes on its performance. These results with DAPS will be obtained in Year 4. SeQual also continued to develop their medical oxygen system based, in part, on the simulation results obtained from DAPS. These developments included breadboard testing, further optimization of bed and PSA cycle design, new prototype subcomponent detailed design and fabrication, new prototype preliminary tests, and improving on their process design and mechanical design capabilities. The team at Vanderbilt is continuing to measure and provide equilibrium and mass transfer properties for adsorbate-adsorbent pairs of interest to NASA adsorption technology. In addition, the entire medical oxygen system is being evaluated based on new constraints imposed by NASA. During Year 3, testing in a vacuum chamber with an Eclipse medical oxygen system has also been underway at the MSFC to determine how it performs under International Space Station (ISS) environmental conditions.
Year 4 will continue to follow the task outline presented in the original proposal. In this way, based on the best predictions from DAPS, a breadboard system will be built at SeQual and tested there, by the folks at the MSFC and by a team at Glen. The intent of the team at Glen is to down-select from the medical oxygen systems under their consideration.
James A. Ritter, Ph.D.
University of South Carolina
A major expectation of the research is the development of smaller medical oxygen concentrators, which will be of benefit not only for spaceflight but also for medical patients on Earth in need of oxygen-enriched air.