2009 Continued Testing of the Orion Atmosphere Revitalization Technology
Abstract: An amine-based carbon dioxide (CO2) and water vapor sorbent in pressure-swing regenerable beds has been developed by Hamilton Sundstrand and baselined for the Orion Atmosphere Revitalization System (ARS). In three previous years at this conference, reports were presented on extensive Johnson Space Center (JSC) testing of this technology in a sea-level pressure environment, with simulated and real human metabolic loads, in both open and closed-loop configurations. The test article design was iterated a third time before the latest series of such tests, which was performed in the first half of 2009. The new design incorporates a canister configuration modification for overall unit compactness and reduced pressure drop, as well as a new process flow control valve that incorporates both compressed gas purge and dual-end vacuum desorption capabilities. This newest test article is very similar to the flight article designs. Baseline tests of the new unit were performed to compare its performance to that of the previous test articles. Testing of compressed gas purge operations helped refine launchpad operating condition recommendations developed in earlier testing. Operating conditions used in flight program computer models were tested to validate the model projections. Specific operating conditions that were recommended by the JSC test team based on past test results were also tested for validation. The effects of vacuum regeneration line pressure on resulting cabin conditions was studied for high metabolic load periods, and a maximum pressure is recommended
Summary (4 min read)
2009 Continued Testing of the Orion Atmosphere Revitalization Technology
- Amy B. Button1 Engineering and Science Contract Group/Jacobs Technology, Houston, Texas, 77058 and Jeffrey J. Sweterlitsch2 NASA Johnson Space Center, Houston, Texas, 77058 Baseline tests of the new unit were performed to compare its performance to that of the previous test articles.
- For these and other reasons, this technology has been baselined as the primary CO2 and water vapor removal device for the new Orion spacecraft.
- A third, significantly redesigned, CAMRAS unit with a new, more flight-like, valve style was tested in the ambientpressure portion of a fourth phase of tests during the spring of 2009, and those results are presented in this paper.
A. Test Article
- In each CAMRAS unit, a valve directs airflow from the cabin through the adsorbing bed layers and back to the cabin, while isolating the desorbing bed layers to a direct line to space vacuum.
- The highly porous plastic beads in this next-generation device are coated with a liquid amine, which becomes immobilized in the bead pores.
- Both carbon dioxide and water are adsorbed simultaneously and somewhat independently.
- The CO2 adsorption reaction generates some heat, while the desorption reaction consumes heat; the interleaving of bed layers helps conserve the overall system thermal energy so that no active heating or cooling American Institute of Aeronautics and Astronautics 4.
B. Test Chamber
- The test chamber was a closed and sealed environment directly monitored for temperature and pressure.
- Inside the chamber, a condensing heat exchanger with blower was operated with the coolant loop above condensing temperatures to both control temperature and provide ambient circulation.
- The total free volume of the chamber test volume was approximately 16.14 m3.
- The nominal Orion configuration calls for operation of two CAMRAS units, so for most CAMRAS Phase 4A test cases, which only used one unit, the chamber free volume was further reduced with airtight space-filling boxes to about 8.05 m3, or half the projected vehicle free volume.
- The chamber leak rate at the beginning of the Phase 4A testing was measured at an average 8.9% per day by a CO2 decay test with all external air loop systems (analyzers, metabolic simulator) circulating air out from and back into the chamber and the volume fillers installed.
C. Metabolic Simulation
- A Human Metabolic Simulator (HMS) was used with the chamber for this testing.
- CO2 was separately injected into the air loop from a pressurized and flow-controlled gas source.
- The CAMRAS tests were typically run with simulated loads representing four or six people.* *.
- A six-person crew was eliminated from standard Orion operations plans, but this test series was already in progress when that change was implemented.
- To approximate real-life metabolic loading profiles, the HMS output rates were manually stepped up and down by prescribed amounts every 7.5 minutes for the nearly four hours required for all four exercise and cooldown periods.
D. Test Article Air Flow
- Airflow through the CAMRAS could be controlled within a range of rates, depending on the experimental scenario, and it was designed to overcome the pressure drop caused by the plumbing fixtures and the amine beds themselves.
- Several sensors, including those measuring temperature, moisture, and airflow rate, were tapped into this plumbing stream.
- CO2 analysis was provided both upstream and downstream of the CAMRAS by external analyzers in closed sample loops.
- A cold trap upstream of each CO2 analyzer minimized the adverse effects of water vapor on the accuracy of the readings.
- Both of these were intended to minimize unseen errors in the collected data.
E. Test Article Regeneration
- In the flight environment of the Orion, the CAMRAS would be plumbed through a hole in the spacecraft shell, allowing it direct access to space vacuum for desorption of CO2 and H2O from the sorbent beds.
- The vacuum line pressure near the CAMRAS unit could be varied within a small range to simulate the effects of long and small versus short and wide flow paths to space vacuum.
- When testing a new CAMRAS unit, a few cases are run simulating vendor pre-delivery tests, to ensure that the unit has not been damaged in transit.
- Phase 4A then tested a series of representative flight operations scenarios.
- Baseline cases were run at standard air flow rates and valve cycle time for various metabolic loads to provide direct comparisons to the performance of the other CAMRAS units in previous test series.
A. Pressure Drop Check
- As part of the functional checkouts, the pressure drop across the CAMRAS units at various process flow rates was tested.
- American Institute of Aeronautics and Astronautics 7 B. Vendor Comparison Tests.
- The vendor’s test rig was configured such that CAMRAS inlet conditions were controlled to known setpoints and the outlet conditions were measured.
- There was no mixing volume and the exterior of the CAMRAS unit was exposed to laboratory temperatures.
- Relative to the same test conditions run with earlier CAMRAS test articles, the new CAMRAS unit 3 generally performed comparably to the other two units.
C. Baseline Performance Tests
- To establish the baseline performance of the new test article in the modified test rig, each type of HSIR standard metabolic load was examined with the vendor's original universal operation recommendations of 26 cfm process air flow and 6.5-minute valve cycle times.
- Earlier JSC CAMRAS test series used 25 cfm of process flow for easier development of uniform test matrices, but the Orion Program has been pursuing flow rates of 26 cfm per CAMRAS unit in the vehicle.
- The results of the two insulated CAMRAS test cases were analogous to the baseline test cases.
- The steady-state CO2 levels were effectively the same, and the steady-state dew points were slightly lower than in the baseline tests (within 0.4°C).
- The differences were small, so the tradeoff for the weight of insulating the units on the vehicle would almost certainly not be worthwhile.
E. Recommended Operations
- The cabin CO2 level should be maintained at a partial pressure below 500 Pa (3.8 mmHg) average over the long term.
- The higher the cabin temperature, the higher the minimum dew point value required to maintain the minimum 25% relative humidity.
- In general, controlling the dew point within this relatively narrow band in testing has turned out to be the most significant driver of process flow rate and cycle time.
- High CO2 levels were never an issue in nominal scenario tests so long as the water vapor was sufficiently controlled.
- The test cases (Table 3) all validated the recommended operational settings, as the chamber dew points and CO2 levels were comfortably within the specified ranges, and all except the exercise case used lower flow rates and longer cycle times than both the baseline cases and the projected operations model cases (see next section).
F. Orion Program Model Validation
- Hamilton Sundstrand developed a set of anticipated Orion cabin and ARS operation conditions for the Orion prime contractor, Lockheed Martin, using a computer model that is believed to have been developed based on Hamilton's CAMRAS development laboratory test data.
- The model also assumed different cabin pressures for various scenarios, but the effect of reduced cabin pressure on CAMRAS operations is not yet well understood.
- These scenarios are targeted for JSC testing at reduced pressure in 2010.
- The model validation test results are summarized in Table 5.
- In the two high metabolic load cases, the test article performed notably less effectively than the model had projected, though the model did assume three operating CAMRAS units instead of the tested simulation of two units.
G. Launchpad Operations
- Phase 3 testing, it was demonstrated that the purge gas flow should be equal to or higher than the process air flow rate for acceptable CO2 and H2O scrubbing performance and that the CAMRAS valve cycle time should be short.
- A simulated crew of six on two CAMRAS units was used for the matrix cases to provide worst-case results, and the matrix was based on the process flow rates projected to be available in the vehicle.
- The purge cases then transitioned to an ascent scenario: after the system reached steady-state conditions, the gas flow was shut off, and the length of time between purge shutoff and chamber ppCO2 exceeding 1010 Pa (7.6 mmHg) was determined.
- Further planned tests of CAMRAS units in reduced-pressure environments and with more human test crews will help further refine the results and recommendations developed from these CAMRAS Phase 4A tests.
- The authors would like to acknowledge Tim Nalette, Bill Papale, and Bryan Murach of Hamilton Sundstrand for providing the test article and preliminary test data as well as technical support during the JSC tests and subsequent analysis insights.
- JSC Test Facility Engineers Matt Blackmer, Peter Masi, Adrian Franco, and Jeremiah Nassif designed and directed the facility modifications, and Chamber Operator Technician Mitch Sweeney led the test rig American Institute of Aeronautics and Astronautics 12 buildup effort.
- Amy Button, Melissa Campbell, Su Curley, and Matthew Stubbe conducted the tests, and Jeff Sweterlitsch provided Amy Button assistance with data analysis.
- NASA’s ELS Program, Constellation Program, and Crew and Thermal Systems Division all helped fund the JSC CAMRAS testing program.
- This paper would not have been possible without all their help.
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In three previous years at this conference, reports were presented on extensive Johnson Space Center ( JSC ) testing of this technology in a sea-level pressure environment, with simulated and real human metabolic loads, in both open and closed-loop configurations. The test article design was iterated a third time before the latest series of such tests, which was performed in the first half of 2009. This newest test article is very similar to the flight article designs. Baseline tests of the new unit were performed to compare its performance to that of the previous test articles. Operating conditions used in flight program computer models were tested to validate the model projections. The effects of vacuum regeneration line pressure on resulting cabin conditions was studied for high metabolic load periods, and a maximum pressure is recommended.