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Author
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Topic: Apollo spacecraft atmosphere composition
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Jim_Voce
Member Posts: 275
From:
Registered: Jul 2016
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posted 05-03-2018 11:22 PM
   
I believe the Block II Apollo spacecraft used a combination oxygen and nitrogen atmosphere. But the air in the spacecraft was purged at some point and replaced with 100% oxygen at either 3 or 5 psi. Does anyone know at what point the oxygen and nitrogen combination was purged? And also, what was the percentage of nitrogen to oxygen, and was it still 16 psi (instead of 14.7 psi) at sea level before launch? And I believe the Mercury and Gemini spacecraft were at 100% oxygen at all times. But was it at 16 psi at sea level for those spacecraft? |
David C
Member Posts: 1310
From: Lausanne
Registered: Apr 2012
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posted 05-03-2018 11:32 PM
It was purged during launch. I highly recommend reading the Apollo Operations Handbooks. |
oly
Member Posts: 1327
From: Perth, Western Australia
Registered: Apr 2015
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posted 05-04-2018 03:59 AM
NASA introduced a 60:40 mix of nitrogen to oxygen. On the ground, the cabin pressure was around 16 psi, slightly above atmospheric pressure (to allow for cabin pressure seal checks). This was bled during ascent until a cabin pressure of 5 psi was reached (about 1/3 the pressure we breath) by which time all nitrogen was purged, leaving 100% oxygen. Astronauts removed their helmets sometime after reaching orbit, this delay made sure all cabin nitrogen had been purged. The astronauts donned the spacesuits, conducted seal checks, and pre-breathed 100% oxygen prior to leaving the suit up room. This is why Apollo astronauts are seen walking out wearing the full suit and helmets, whereas Mercury astronauts carried their helmets and had their visors up during capsule ingress. (they pre-breath inside the capsule). The suit pressure during lunar surface operations varied between missions, between 3.5 and 5.2 inside the Lunar Module, the higher pressure used during suit leak checks. The suits were reported to be very difficult to bend and move around in at higher pressures (the cabin pressure of the LM was between 3.5 and 4.8 during missions). With lunar surface pressures down to 3.5, this equates to working at altitudes over 10000 feet making strenuous exercises difficult for most people, and explaining why astronauts can be heard heavy breathing during EVA. If the suit pressure were made higher, they could not move in the suit, and suit closure was by zippers. |
MartinAir
Member Posts: 137
From:
Registered: Oct 2020
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posted 12-30-2021 06:20 PM
Vance Brand mentioned that Soyuz spacecraft used oxygen/nitrogen atmosphere all the time and the ASTP docking adapter equalized or compensated for the difference. What are the pros and cons of the Soyuz approach? |
randy
Member Posts: 2529
From: West Jordan, Utah USA
Registered: Dec 1999
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posted 12-30-2021 07:05 PM
If memory serves, one of the cons of the two gas system was that it was more complicated and the hardware was heavier. |
SpaceAholic
Member Posts: 4980
From: Sierra Vista, Arizona
Registered: Nov 1999
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posted 12-30-2021 08:58 PM
quote:
Originally posted by MartinAir:
What are the pros and cons of the Soyuz approach?
Elevated risk of narcosis/bends in the event of cabin decompression. |
oly
Member Posts: 1327
From: Perth, Western Australia
Registered: Apr 2015
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posted 12-31-2021 12:35 AM
Higher cabin pressure which requires a heavier vehicle structural design. With a pure oxygen environment, lower cabin pressure is required to keep the crew alive. The Apollo/Soyuz docking adapter incorporated an airlock that the Apollo crew used to change from the Apollo cabin environment to the Soyuz cabin environment. |
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