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Astronauts “Camp Out” to Prevent DCS
(Filed under: Uncategorized — scubadoc @ 4:37 pm )

Before they embarking on complicated spacewalks, astronauts on the shuttle mission “camp out” in the International Space Station’s airlock for the first time.

The aim is to prevent them from getting decompression sickness, also known as the bends, when they work in their spacesuits, which are at a lower pressure than the station.

Four of the shuttle Atlantis’s six crew members will participate in a total of three spacewalks, with two astronauts performing each spacewalk.

Decompression sickness can occur during spacewalks because the ISS is normally at a pressure of 101.3 kilopascals (14.7 pounds per square inch), but the pressure inside a spacesuit during a spacewalk is just 29.6 kPa (4.3 psi).

Dangerous bubbles
At the higher pressure inside the station, nitrogen in the air can dissolve in the blood and tissues, just as it does for divers in the deep sea. Moving too quickly to lower pressures can cause that dissolved gas to create bubbles and obstruct blood flow, which can sometimes be fatal.

Previously, astronauts prepared for a spacewalk on the ISS by exercising on a stationary bicycle and wearing an oxygen mask. Exercise helps purge nitrogen out of the bloodstream because it increases blood circulation, while oxygen – unlike nitrogen – is used by the body and does not build up in the blood and tissues.

But on this mission, the pairs of astronauts will spend the night before each spacewalk in the equipment lock of the station’s Quest airlock – which will be lowered to a pressure of 70.3 kPa (10.2 psi) – to purge nitrogen from their blood.

Quiet night
“This is a more relaxed approach,” says John McCullough, lead ISS flight director for NASA.

The campout method may actually save the spacewalkers about an hour of time compared to the exercise method, which the crew hopes will make the preparations for their 6.5-hour spacewalks less harried.

“I kind of like it,” says astronaut Dan Burbank, who will make his first spacewalk on the flight. “I like the idea of having a nice quiet night.”

They will do all of their grooming earlier in the night and they will be able to bring cold food into the airlock with them. But while camping out, if nature calls, they will have to use an adult diaper. In the morning, they will be allowed to return briefly to the main part of the ISS to relieve themselves and to grab some breakfast to take back into the airlock before their spacewalk.

The campout is similar to a process used to prepare for spacewalks from the shuttle itself, when it was not docked to the space station – for example, when astronauts serviced the Hubble Space Telescope.

Before those spacewalks, astronauts breathed 100% oxygen for one to two hours at 101.3 kPa (14.7 psi), then reduced the pressure of the entire orbiter to 70.3 kilopascals (10.2 psi) for 10 hours. Finally, they breathed 100% pure oxygen again for the hour just before their spacewalk.
 

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Michael Collins, the Command Module Pilot on Apollo 11 (the third crewman who stayed in lunar orbit) admits having been bent in one of his knees on both Apollo 11 and his previous Gemini flight. But he kept quiet about it as he didn't want the flight surgeons grounding him. Denial is nothing new!

This is despite the Apollo crews breathing pure oxygen for a couple of hours before heading out to board their spacecraft.

That's why, in films you see of Apollo astronauts boarding the van to take them out to the launch pad, they're all sealed up in their suits carrying portable air con/oxygen supplies.
 

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Discussion Starter #3
In theory

Nick Kay said:
Previously, astronauts prepared for a spacewalk on the ISS by exercising on a stationary bicycle and wearing an oxygen mask. Exercise helps purge nitrogen out of the bloodstream because it increases blood circulation, while oxygen – unlike nitrogen – is used by the body and does not build up in the blood and tissues.
Therefore, isn't the most effective deco likely to be finning around like b***ery, waving your arms about - at 4m while breathing 100% O2???

Oh - ignoring the 100% O2 at 4m, thats how most people do seem to do their deco :D
 

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Hypobaric decompression is a bit different to diving decompression. Oxygen bends are a possiblity (whereas they are very unlike in diving) and all sorts of funny things go on.

However, it does fund an awful lot of the research that is subsequently applied to recreational divers.

Janos
 

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Hickdive said:
Michael Collins, the Command Module Pilot on Apollo 11 (the third crewman who stayed in lunar orbit) admits having been bent in one of his knees on both Apollo 11 and his previous Gemini flight. But he kept quiet about it as he didn't want the flight surgeons grounding him. Denial is nothing new!

This is despite the Apollo crews breathing pure oxygen for a couple of hours before heading out to board their spacecraft.

That's why, in films you see of Apollo astronauts boarding the van to take them out to the launch pad, they're all sealed up in their suits carrying portable air con/oxygen supplies.
I thought they binned using 100% O2 after the Apollo 1 fire...

Oh and anyone else seen the remarkable similarity between the Apollo comman module and the new moon/mars craft. It could be that the artist was being very lazy. It could be that the Apollo design was 40 years ahead it its time, but I seriously hope that the budget and time constraints haven't forced NASA into falling back onto old technologies in order to satisfy political whims....
 

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I can't understand why they take air with them. Given that the N2 is just dead weight and the costs of getting anything into orbit, I cannot figure why they don't just take O2 and maintain cabin pressure at 0.21 Bar. I guess they'd have to repressurise by adding N2 before reentry (so that she doesn't squash like an old can) but it would minimise these sort of problems and also be less stress on the structure, which would only need to retain a 02 bar rather than 1.0 bar pressure differential.

Mind you, they ARE rocket scientists, so I guess they have probably thought this through.

Richard M.
 

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I thought they binned using 100% O2 after the Apollo 1 fire...[/QUOTE]

They kept pure O2 but reduced the cabin pressure, to give a ppO2 similar to Earth's surface.

sidthejedi said:
Oh and anyone else seen the remarkable similarity between the Apollo comman module and the new moon/mars craft. It could be that the artist was being very lazy. It could be that the Apollo design was 40 years ahead it its time, but I seriously hope that the budget and time constraints haven't forced NASA into falling back onto old technologies in order to satisfy political whims....
I understand that it's partly because you don't have to worry about bits falling off and hitting the spacecraft. Look at other things like cars, trucks, trains, aircraft - few of those have changed radically in form since 1920.

As I understand it, it's the same shape but because of improvements in all the other technologies, it will be vastly more capable than the Apollo craft.

As an example, the RAAF are the last airforce in the world still flying the F-111, which they've had since the 1970s. The airframe and basic design hasn't changed much but everything else has ben redesigned and rebuilt several times, resulting in big increases in payload, range, safety, speed, manouevrability and general capability. Similar thing really.


Richard M
 

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sidthejedi said:
Oh and anyone else seen the remarkable similarity between the Apollo comman module and the new moon/mars craft. It could be that the artist was being very lazy. It could be that the Apollo design was 40 years ahead it its time, but I seriously hope that the budget and time constraints haven't forced NASA into falling back onto old technologies in order to satisfy political whims....
A staged launch vehicle, and modular crew space/cargo payload system provides the flexibility and efficiency needed to reach beyond earth orbits.

It just goes to show that the Apollo programme approach was valid for reaching a lunar orbit and enabling lunar landings and returns.

Newer life-support and computer technologies (just think your Suunto probably has more processing power than Apollo 11) mean they can exploit this modular system for greater capacity and efficiency.

It will be bigger than the original crew vehicle and landers, and removes the possibility of being affected by chunks of ice falling off the fuel tank as in the Shuttle.

I guess the total size of the new system might be capped by the height of the doors for the Vehicle Assembly Building at Kennedy Space Centre....however, they are quite big!

I took a tour there a couple of years ago, and that is one big building, and the Saturn 5 hangar is the most incredible sight ..... totally awe-inspiring show of engineering achievement!
 
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