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A space suit leak is a big deal. In the Shuttle suit, an astronaut can survive 22 minutes with a 1/8" hole in his suit. At that point the pressure will drop to where he is likely to suffer permanent brain damage, if he survives. The Shuttle suit has a secondary oxygen pack pressurized to 5,000 psi. If the primary system cannot maintain pressure in the suit (due, for example, to a 1/8-inch hole), the secondary oxygen pack will open its valve and attempt to maintain the pressure.
If there is a large tear, the astronaut might have a few seconds to live. No matter what he does, severe vascular damage is certain, and the probability of permanent damage to the neural system (including the brain) is extremely high. However, as several notes here have pointed out, the outer layer of the space suit is very tough, and the probability of even a small puncture is low.
A puncture repair scenario would have to include quickly removing the outer layers of the garment to get to the pressurized part of the suit. It could be done, but this would require a complete redesign from existing space suits.
Even after all the hours we've had people working in space suits, there has been only one incident (that I know of) where a suit was punctured in space. That incident was apparently caused by using the glove as a hammer to drive a balky pin. A 1/8" steel bar migrated out of the palm restraint and punctured the glove. In that one case, the steel bar and the astronaut's blood sealed the puncture; he didn't even realize his suit had been damaged until after the flight when the suit techs found blood in the outer fabric of the glove.
The whole suit is pressurized. The pressure layer is a neopreme layer shaped like a wet suit. The helmet bubble attaches with a neck ring that operates sort of like a bayonet fitting on a camera lens. So do the gloves. For a nice close-up look, get the videotape of the Apollo 13 movie and watch the parts where the astronauts are suiting up. That is very technically accurate.
NASA is experimenting with at least three different designs for hard suits, and may come up with something before we have to finalize this part of the Artemis Project. However, the hard suits' gloves aren't working, and that's the part of the suit that really needs improvement. The meteorite shrapnel issue is real; we might wind up with a hard suit that has an outer garment, which gets us right back to where we are without the ability to use laces to adjust to individual body dimensions. So we are not too hopeful about hard suits.
We haven't decided on how to acquire the space suits for the Artemis crew. If we had to do it today, we'd go to Hamilton Standard, the manufacturer of the U.S. space suits. Fortunately, we have some time before we have to make a final decision about suit procurement. At least part of the suit will have to be a new design, perhaps a marriage of the Apollo suit's lower portion with the upper torso of the Shuttle suit to give the crew maximum mobility. (The helmets are the same. They haven't changed since Gemini.)
Don't forget the Russians, though. They have some really nice space suit designs, which in many ways are better than the U.S. space suits.
Space suits are a major procurement item in the budget for the Artemis Project. We're showing $10 million each for them. That might sound extravagent since the custom-made Apollo suits were only hundreds of thousands each, but we're talking about mission-critical equipment. A space suit with its backpack is really an independent spacecraft, providing all the functions of a spacecraft except propulsion.
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