A cabin is a pressure, an oxygen fraction, a volume, and a temperature. The mass of a nitrogen-oxygen mix follows the ideal gas law. Dry-gas oxygen partial pressure is the total pressure times the oxygen fraction. Inspired oxygen, the number NASA-STD-3001 writes as PIO2, subtracts 47 mmHg of water vapor at body temperature before that multiplication. [1]

Two presets are on the form. One is the ISS-like sea-level case, 14.7 psia class at 21 percent oxygen. The other is the exploration example quoted with that standard, 8.2 psia at 34 percent oxygen, whose inspired oxygen is about 128 mmHg. The standard's normoxia target for indefinite exposure is about 145 to 155 mmHg. Landing in the target band is not a clearance to fly the mixture. Fire, decompression sickness, and the diluent-gas minimum are separate requirements in the same standard. [1]

Screen

The 22 C temperature is a blank you can change. It is not a NASA setpoint. A leak in kilograms per day is also yours. The time to a floor pressure assumes that mass leaves at a constant rate. A real orifice does not. Leave the leak at zero if you only want the inventory. The oxygen mass is the oxygen part of the mix, not a second atmosphere.

Class A instrument

Screening sheet. Not for flight, medicine, or operations. Ideal gas, nitrogen-oxygen mix, constant mass leak if you type one.

Mass is P V M / (R T). Inspired oxygen is (PB - 47 mmHg) times the oxygen fraction, the form in NASA-STD-3001. A constant kg/day leak is not how a real hole behaves. The 22 C temperature is your assumption until you change it.

What this is not

It does not size a compressor, a meteoroid shield, or a suit. It does not say a person is safe. Crew budget turns crew size and days into oxygen and water mass using the life-support baseline, which is a different document from the atmosphere standard. Ambient Mars pressure, for comparison, is Pressure and the areoid.

See also

References

  1. NASA OCHMO. Habitable atmosphere technical brief, quoting NASA-STD-3001 Volume 2 on inspired oxygen, 14.7 psia at 21 percent, and 8.2 psia at 34 percent. https://www.nasa.gov/wp-content/uploads/2023/12/ochmo-tb-003-habitable-atmosphere.pdf

Categories

Engineering