Posts: 202
From: Ledignan, Gard (30), France
Registered: Mar 2009

posted 03-16-2024 12:47 AM               

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I would like to know the capacity of the oxygen tank (in liters) used on the portable life support system (PLSS) during the Apollo 11 to 14 flights.

Some written or video sources (MIT on YouTube) give about 640 g of oxygen. At what temperature was it stored (in the PLSS tank) and how do you arrive at the result (formula, equation)?

I can only find a few scraps of information and I don't understand how you can last so long (about 4 hours for Apollo 11) with so little oxygen in reserve? (There's probably something to do with the pressure, but I can't figure it out.)

Posts: 1467
From: Perth, Western Australia
Registered: Apr 2015

posted 03-16-2024 04:14 AM               

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Lunar surface EVA times for the first four missions (Apollo 11 through 14) were limited to 4 hours, with oxygen stored at 1,020 pounds per square inch (7.0 MPa), 3.0 pounds (1.4 kg) of lithium hydroxide, 8.5 pounds (3.9 liters) of cooling water, and a 279 watt-hour battery.

For the extended missions of Apollo 15 through 17, the EVA stay time was doubled to 8 hours by increasing oxygen to 1,430 pounds per square inch (9.9 MPa), lithium hydroxide to 3.12 pounds (1.42 kg), cooling water to 11.5 pounds (5.2 liters), and battery capacity to 390 watt-hours. [Source]

Posts: 202
From: Ledignan, Gard (30), France
Registered: Mar 2009

posted 03-16-2024 06:15 AM               

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Thank you But, I already knew this informations, but what interests me is how "with so little" oxygen grammage the PLSS can provide pressurization for the suit and the astronaut's breathing.

There's something I don't understand.

Posts: 412
From: Derbyshire UK
Registered: Mar 2023

posted 03-16-2024 07:30 AM               

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I don't understand what it is you don't understand.

640g of oxygen is sufficient for 4 hours, as we breathe 850g on Earth per day.

We breathe in and out much more than that but only because we need to extract the carbon dioxide from our lungs and the extra breaths we take flush it out. On Earth at sea level we only absorb about 4% of each breath to fully oxygenate our blood. And we ventilate at approximately 6 litres of air per minute (although, at rest, we only require 15 litres of oxygen per hour).

In terms of litres: A cylinder which contains 640g of liquid oxygen, when brought to standard temperature and pressure would occupy a volume of 448 litres. (This can be calculated thus: all gases at standard temperature and pressure occupy 22.4 litres of volume per unit mole. The molecular weight of oxygen (O²) is 32, the molar quantity therefore being 20. So, the volume occupied = 22.4x20 = 448,) [Explanation edited.]

Posts: 202
From: Ledignan, Gard (30), France
Registered: Mar 2009

Posts: 1467
From: Perth, Western Australia
Registered: Apr 2015

Posts: 202
From: Ledignan, Gard (30), France
Registered: Mar 2009

Posts: 412
From: Derbyshire UK
Registered: Mar 2023

Posts: 202
From: Ledignan, Gard (30), France
Registered: Mar 2009