On wikipedia, I believe that it will be the same as at sea level (101 kPa), or reduced (55 - 70 kPa). But what pressure will be normal in the cabin? What will the pressure be there during the flight?
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2$\begingroup$ I think the 101 kPa will be used before and a short time after launch. The reduced pressure will be used in flight when the ambient pressure outside the capsule is lower. The nitrogen - oxygen mixture will be different for both pressures. $\endgroup$– UweCommented Dec 19, 2022 at 19:43
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2$\begingroup$ At least according to a preliminary document, the Lunar Gateway will be pressurized to 62 kPa. At the time of docking, the Orion capsule should be pressurized at the same level as the Gateway. That document however is over two decades old. I do not know if this is the current thinking. $\endgroup$– David HammenCommented Dec 20, 2022 at 7:25
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1 Answer
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Answer: Orion’s Atmosphere Revitalization System performs to specification over a wide pressure range, from 8.3 to 14.7 psi. This range is available to mission planners and allows docking with other spacecraft which have cabin pressures within this range.
Orion was pressure tested to 20 psi. which is
1.25 times greater than what it is expected to encounter during crewed operations. https://www.spaceflightinsider.com/missions/human-spaceflight/orion-spacecraft-undergoes-pressure-testing-em-1-flight .
This implies a maximum operational pressure of 16 psi. This is in line with the 14.7 psi cabin pressure used in Space Shuttles and ISS.
The Gateway will be pressurized to 9.0 psi
primarily to reduce nitrogen and oxygen repressurization requirements, reduce atmosphere leak to space, and to minimize EVA pre-breathing time required. Additional structural benefits may be derived. This pressure is equivalent to the atmosphere pressure in Denver, therefore should be acceptable for human spaceflight. The oxygen-enriched cabin atmosphere of 70% nitrogen and 30% oxygen also maintains material flammability limits within the range currently tested and approved for spaceflight.” https://history.nasa.gov/DPT/Architectures/Libration%20Points%20&%20In-Space%20Ops%20Libration%20Point%20Gateway%20Final%20Report%20DPT%20Oct_01.pdf
For Orion to dock with Gateway, it will need to equalize pressure at 9.0 psi, then maintain that pressure for the duration of the mating.
This 2013 paper https://ntrs.nasa.gov/api/citations/20130011191/downloads/20130011191.pdf tests Orion's cabin air system’s combined CO2 and humidity scrubbing system CAMRAS under normal (14.7 psi) and reduced pressure conditions of 10.2 and 8.3 psi..
Orion has 3 CAMRAS units, with only 2 being needed for normal operation. In an emergency, a single unit could maintain safe CO2 levels for 6 crewmembers. The test included the added CO2 load on the CAMRAS system of exercising crew.
The tests showed acceptable CO2 partial pressures and humidity under all conditions tested, with slightly higher CO2 levels at lower pressure.
