Posts: 867
From: CA.
Registered: Jan 2011

Posts: 42988
From: Houston, TX
Registered: Nov 1999

posted 07-16-2011 05:26 PM               

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Were the International Space Station's atmosphere pure oxygen, spacewalkers wouldn't need to go through pre-breathe exercises to extract the nitrogen from their bloodstreams.

The ISS Environmental Control and Life Support System (ECLSS) Atmosphere Control and Supply provides and maintains oxygen and nitrogen levels, as well as pressure, in the proportions found at sea level: about 21% oxygen, 78% nitrogen at 14 lbs. per square inch.

Posts: 1309
From: Denver, CO
Registered: Jun 2004

posted 07-16-2011 05:33 PM               

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quote:

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Originally posted by SkyMan1958:
Does anyone know whether the ISS atmosphere is straight oxygen or is it an oxygen/nitrogen mix? Thank you!

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I might be mistaken, but I don't believe that any American space crew has flown with a pure O2 ambient atmosphere since the Apollo 1 tragedy.

Posts: 1522
From: Greensboro, NC USA
Registered: Feb 2006

posted 07-16-2011 06:17 PM               

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Apollo flew with pure oxygen, just not pressurized to 16 PSI. It was only about 5 psi, the partial pressure of O2 in Earth's atmosphere at sea level.

EDIT: I should add that after 10-12 days in space, there was probably a high methane content in there as well!

Posts: 2272
From: Bellevue, NE, USA
Registered: Aug 2007

posted 07-16-2011 10:07 PM               

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Pure oxygen environments were used post Apollo 1 up through ASTP and Skylab. For launch, the crews pre-breathed pure O2 in their suits while the craft was pressurized with O2 and Nitrogen to launch pressure. After liftoff, the nitrogen was replaced as the pressure bled off to a pure O2 environment at about 5 PSI (which was all that was needed since normal atmospheric pressure of about 14 PSI still has about 2/3rds nitrogen to 1/3rd oxygen, or about 5 PSI of the 14 PSI at sea level is oxygen).

In Skylab, the pure O2 environment was okay, but crews reported it was difficult to hear one another across the station due to the thin atmosphere.

The decision was made to go with oxygen nitrogen on shuttle since there were concerns about the long term effects of just O2 use, even though to my knowledge nothing popped up in the medical testing on Skylab.

One of the reasons why sea level oxygen nitrogen was not introduced into Apollo after Apollo 1 was because the craft might rupture like a balloon in a vacuum since it wasn't built to that type of pressure differential (16 PSI on the pad is only about two PSI about sea level, well within the pressure tolerances of what Apollo could take).

This is a primary reason why the airlock system in the docking module had to be developed for Apollo Soyuz, since it was docking with a higher pressure craft featuring a two gas system (although the Soyuz pressure was lowered a little and the N2 O2 mix was altered a little to minimize the need for pre-breathing by the Apollo crew during transfer to the Soyuz).