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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