Why Don't Space Suits Go Rigid When Astronauts Go On Spacewalks?

Why don’t space suits inflate like a Michelin Man when on the Moon or outside the Space Station?
In this photo, Astronaut David A. Wolf, STS-112 mission specialist, anchored to a foot restraint on the Space Station Remote Manipulator System (SSRMS) or Canadarm2, carries the Starboard One (S1) outboard nadir external camera. Image credit: NASA

In this photo, Astronaut David A. Wolf, STS-112 mission specialist, anchored to a foot restraint on the Space Station Remote Manipulator System (SSRMS) or Canadarm2, carries the Starboard One (S1) outboard nadir external camera. Image credit: NASA

Originally posted on Forbes!

They very easily could! If you had a poorly designed space suit or an overly pressurized suit, an astronaut could very easily find themselves immobilized, unable to contort their suit into a useful position. With the inside of a suit set to normal sea level pressure, and the outside of the suit set to the vacuum of space, a fabric suit with no hinges will very quickly stiffen into an inflated posture, and would be very difficult to bend.

In fact, this very situation posed a serious problem for the first spacewalk, conducted by Alexey Leonov, whose suit inflated, and became an obstacle to re-entering the airlock of his spacecraft. With the airlock too small to accommodate a totally puffed-up spacesuit, Leonov had to manually depressurize his suit so that he could bend his arms and legs enough to creep back into the spacecraft. This is not a recommended path to getting around in space; it gave Leonov a very rapid depressurization experience (like “the bends” that divers can experience if they rise from the crushing depths of the ocean too rapidly): hardly good for you and certainly painful.

NASA invited the public to vote on three cover layer designs for the Z-2 prototype suit, the next step in NASA’s advanced suit development program. By using Luminex wire and light-emitting patches, this design puts a new spin on spacewalking standards such as ways to identify crew members. Image credit: NASA

NASA invited the public to vote on three cover layer designs for the Z-2 prototype suit, the next step in NASA’s advanced suit development program. By using Luminex wire and light-emitting patches, this design puts a new spin on spacewalking standards such as ways to identify crew members. Image credit: NASA

There are two solutions that let you avoid inflation of a suit; one is to reduce the pressure inside the suit, and the other is to build your space suit with hinges, so that you never have to compress the air inside the suit by folding it over on itself. Current space suits usually try to do both, which helps makes the process of leaving the home sanctuary of the space station a little easier on our astronauts.

Instead of being pressurized to one atmosphere at sea level, the current iteration of space suits for spacewalks are typically pressurized to only about a third of that. Having a smaller internal pressure means that the suit is less rigidly inflated when “outside”, in space. However, it does mean that the astronaut has to spend some time getting used to this reduction in pressure, and making sure their blood is still getting a safe amount of oxygen.

Once they’re outside, though, even with a smaller internal suit pressure, the astronauts might still struggle to bend the suit. If you look at the sleeves on a long-sleeved shirt, if you bend your arms, a bunch of fabric folds over onto itself at the inside of the elbows. This is usually not an inconvenience to us, but that’s because the air inside our sleeves is the same pressure as the air outside our sleeves. In space, each crinkle in the suit changes the volume of the suit; any change in volume means that the air pressure changes. If you increase the number of folds when you bend your arms, you decrease the amount of room the air has to fill, and the pressure will increase. The solutions here are to either build a huge number of folds into the suit, so that any bending motion won’t change the internal volume, or to make the suit contain a large number of swivel points.

Developed at NASA Ames Research Center in the 1980s, the AX-5 high pressure, zero prebreathe hard suit was developed. It achieved mobility through a constant volume, using a hard metal / composite rigid exoskeleton design. Image credit: NASA

Developed at NASA Ames Research Center in the 1980s, the AX-5 high pressure, zero prebreathe hard suit was developed. It achieved mobility through a constant volume, using a hard metal / composite rigid exoskeleton design. Image credit: NASA

An extreme version of the swivel point approach is the hard-sided prototype suits that NASA developed in the 1980s. This suit was almost 100% hinge, but the principle was that you would never have to bend the suit - the hard-sided spacesuit would simply be able to reshape itself into the needed configuration. Because there’s no bending, the suit could be pressurized to something closer to sea level air pressure, which means getting into and out of it will take less preparation.

The Z-1 is NASA's next generation spacesuit, a prototype of which is pictured at the Johnson Space Center. Image credit: NASA

The Z-1 is NASA's next generation spacesuit, a prototype of which is pictured at the Johnson Space Center. Image credit: NASA

The current space suits, along with the next generation of suits, are mostly made of flexible fabric, but take the “insert all the folds you’ll think you’ll need” approach, with tactically placed folded segments at elbows, knees, and shoulders. These joints, along with the lower air pressure in the suit, allows the astronauts to move with most of the dexterity they’re used to, and perform the repairs, replacements, and other adjustments that the ISS periodically requires! But if you were to just make an airtight suit, with no particular hinges, and pressurize it to the air pressure at sea level, you would absolutely have an inflation problem.

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Why are NASA's space suits so clunky?

Why are NASA’s space suits so much clunkier than the ones in science fiction or video games?

NASA has a real problem with the space suits that they stick their astronauts in to perform space walks. They’re massive, hard to get into and out of, and phenomenally unwieldy. The fingers on an astronaut’s gloves are so hard to manage that NASA has run competitions trying to get a better design that’s easier to work in. Ideally, we want to be able to stick people in suits that are easy to move around in, while still providing all the protection they would need. This is really, really hard to do.

If your suit is designed for the vacuum of space, you need to have a pressurized suit. Right now, this is done by inflating the suit with air, to compress the body to a point where the astronaut is comfortable, but not so much that it’s so tightly inflated that the astronaut couldn’t bend any of their joints. (This actually was a pretty severe problem for the first Russian spacewalker; his suit was so pressurized he couldn’t get back into his ship without letting some air out. He had to loosen a gasket on his glove to let the air escape, and then he got decompressed so rapidly he got a pretty nasty case of the bends, which is the same problem scuba divers run into if they surface too quickly.) You also need a suit that will provide some radiation protection, protection from tiny pieces of space junk, and on top of all that, you need your astronaut to be comfortable inside it and able to get in and out of it relatively easily.

On top of that, you have additional challenges if you want to land on a planet. Generally speaking, you don’t want to track dirt in from outside, if you’re on the moon or Mars. The dust on the moon (and we suspect on Mars as well) is such a fine powder that it can become embedded in your lungs and do quite a bit of damage. Mars dust might be even worse for you, since a lot of Mars’s surface material is so chemically toxic that it would burn you like bleach - not something you want in your lungs.

Physics is really not on our side for this venture. We’re asking for a pressurized suit that’s still easily bendable, which is also radiation-resistant, and easy to get into and out of, and durable. If you want to go out on the surface, you need to be able to decontaminate it completely. This space suit has to be a pretty impressive piece of technology.

The solution so far for spacewalks has been the kind of inflatable suit we’re used to seeing our astronauts in. Science fiction films and video games tend to prefer suits that are at least partially skin-tight. These aren’t completely impossible, and at least one person at MIT has been working on trying to design a suit that pressurizes the astronaut through mechanical pressure of the suit on the body, rather than the balloon method of air pressure. The mechanical skin-tight suit is really hard to make, because you have to get even pressure over the entire suit, and have it bendy enough to not restrict motion, and be durable enough to not break any wires if you fall on a rock or from bending the suit repeatedly. These skin-tight suits are also a lot harder to decontaminate, so getting all the dust off of them after a trip outside would be really hard to guarantee. NASA has also been testing a suit that you can crawl into through the back. This would be handy, because it means you can leave the suit attached to the outside of the base, and you won’t have to worry so much about getting the dust off. On the other hand, it’s still pretty clunky.

So unlike the science fiction films and video games, which can invent new materials to evenly pressurize an astronaut’s body, and new ways to decontaminate the suit so no one gets chemical burns from the surface dust once they come inside, while still protecting from radiation and puncture damage, NASA is stuck with the materials and methods that we have right now. We’re working on new methods and new technologies, but for the moment we don’t have anything quite as stylish as science-fiction can manage.

Have your own question, or something here unclear? Feel free to ask!