Astronauts and The Bends

[Bogie]

I was watching a documentary on the space station and one was preparing for a space walk. He exercised breathing pure oxygen to eliminate the bends.

I never heard of astronauts and the bends.

What is the physics behind astronauts and the bends?

 

[bygolly]

I was watching a documentary on the space station and one was preparing for a space walk. He exercised breathing pure oxygen to eliminate the bends.

I never heard of astronauts and the bends.

What is the physics behind astronauts and the bends?

I don't know for sure but it would be fun to guess. I think that the atmosphere inside the suit must be pure O2 and that it is pressurized to a level much less than the pressure inside the station. Entering the suit may be akin to a diver ascending quickly from depth. The suit is probably pressurized to a low level to allow it to flex properly.

 

[knotical]

The physics and physiology are similar to that experienced by pilots, or anyone else going from greater pressure to lesser pressure. See for example:
http://www.faa.gov/pilots/safety/pilotsafetybrochures/media/dcs.pdf
or: http://findarticles.com/p/articles/mi_m1272/is_2689_131/ai_92691054/

 

[lamont]

astronauts go from 1 ata to about 0.3 ata when they EVA.

and given that its about a 3x pressure change its probably similar to going from 60 feet to the surface on after a saturation dive.

 

[spt29970]

From what I read, they go from 1 ata of AIR in the station, to 0.3 ata of O2 in the suit. The reason for the low pressure is to reduce stress on the the pressure suit and allow it to be relatively flexible. Since they will drop pressure once they leave the stations they pre-breath 1ata O2 before closing up the suit to lower their nitrogen load. As far is the physiology is concerned starting a space walk is like a rapid ascent. After being in the suit for a while they are essentially completely purged of N2

 

[DandyDon]

Doctor Deco here on SB is an former NASA expert on such, with extensive experiences with air & space pilots both. We learned ear equalizing from WWII pilots originally, as well as many advancements in applicable blood gases in various pressures.

NASA also has many scuba divers who go in the deep practice pool with the astronauts south of Houston. Before onboard astronauts did the unexpected space walks on the station to replace an AC unit recently, others did it in the pool as surrogate practice and divers were there too.

 

[subcmdr]

Very good, Dandy Don. Lamont & SPT29970 you got it right too. My business actually operates the Neutral Buoyancy Lab that Doctor Deco refers to. Astronauts who are being trained for EVAs spend a lot of time in the NBL in scuba (at first), and then in a space suit, rehearsing the EVA procedures they will execute on orbit. In that environment, they under the same pressure in the space suit that all the safety divers experience around them in the pool. There are very careful measures to ensure that while training in the NBL, DCI is not a concern. (Recall that these rehearsals last as long as the planned missions last, sometimes as long as 8 hours underwater.)

As for operations in space, going from a 1 atm environment with 78% or so N2, to a 0.3 atm environment of pure O2, would cause a lot of N2 offgassing if the N2 weren't first eliminated by pre-breathing pure O2.

 

[DandyDon]

It's a big facility..!

The 6.2 million gallon pool where experiments and training are done to simulate zero gravity

click for lareger
​

more pics at NASA - Neutral Buoyancy Lab

 

[pir8]

Interesting, very interesting.

 

[Gilldiver]

Bends and aircraft/space craft is a very old problem. Go watch some old WWII moves and in the aircraft they always go onto O2 as they climb up pass about 12,000 feet. This was due to oxygen starvation but also so that they had time to breath down and not get bent at bombing altitudes of 20-25,000 feet.

Now go back to the Mercury/Gemini/Apollo films and the astronauts are always seen with helmets on as they go to the space craft for launch. They have been on 100% O2 breathing down as the space craft were only at about 3psi when in orbit. For the shuttle and space station crew, the suits are also at only about 3 psi so that you can flex the arms and legs. Get in a dry suit and blow up till the neck seal burps, now bend your arms, if you can. Your suit is only at 1 psi at most.