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In the early 90's I remember seeing a program where they were discussion new designs in space suits that would be more flexible and allow for less restrictive movements of the occupant. These suits were not pressurized at the body like the suit commonly used today but rather formed to the body much like a wet suit but had a pressurized helmet that was actually smaller than the helmets used today.

What advances have there been? Have any of the advanced designs been tested in space yet?

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The "trick" that @john3103 mentions in his answer, that the suits have to be engineered to provide sufficient support, is actually pretty important, and belies some additional difficulties which are the primary reasons this type of suit hasn't yet been adopted.

Pretty much any spacesuit, whether mechanical-counter-pressure (MCP) or gas-pressurized, is required to provide uniform pressure across all surfaces of the body. While human skin is gas-tight and so will not dehydrate or shrivel in a vacuum (as many sci-fi authors incorrectly illustrate), it will swell due to the lack of external pressure, and this is painful, restricts movement and can be permanently damaging over a large enough area. To prevent this, the suit must provide counter pressure on every square inch of skin. Gas-pressure suits are basically a bag that holds a low-pressure atmosphere around the wearer (current US suit designs simulate an atmosphere at about 8000 feet, which when filled with pure oxygen provides a similar partial pressure of oxygen as you'd find at sea level), and gas, being a gas, will then expand uniformly to put equal pressure over all surfaces of its container, including the wearer's skin. As such, as long as the suit is airtight, the wearer is fine.

However, an MCP suit must simulate this pressurized-gas environment by applying elastic tension over every surface of the body. While that alleviates the need to maintain a perfectly airtight membrane (which is easily damaged by anything from a tool to a toenail, rendering the entire suit inoperable until it's patched), thus dramatically increasing safety and reliability, it creates several additional engineering problems for an MCP suit, which a current gas-pressurized suit more or less avoids:

  • Each suit must be custom-fit to the wearer, and can only be worn by them. That wasn't as big a deal with the two versions of the SAS, because at the time all spacesuits had to be custom-made to fit their wearer. Nowadays, NASA's EMU suits come in small, medium and large, and cover the 95th percentile of both male and female body types; Russia's ORLAN and Chinese knockoffs are one-size-fits-all with various adjustments possible. However, these suits are also \$12 million a pop; one of the BioSuit's big advantages is that the actual bodysuit can be constructed for a few thousand dollars, and the helmet-and-backpack system would be interchangeable between any two suits, so even though you're making more suits you still come out ahead.

  • The suit, by design, must be skin-tight everywhere. First, this makes getting into the suit more difficult; the wearer of the original SASes pretty much had to grease up from the neck down in order to squeeze into it, and both SAS designs required assistance from at least one other person, which would make suiting up quickly in an emergency a practical impossibility. EMUs have similar problems due to their bulk, and also require an assistant; an ORLAN can theoretically be donned by one person but still takes the better part of an hour. The BioSuit was designed to be donned by the wearer in less than ten minutes without assistance, and in situations where it's likely to be needed, the bodysuit is thin and breathable enough to be worn long-term, as if it were a pair of long johns. The helmet, backpack, gloves and boots are relatively quick to put on once the bodysuit is in place.

  • Not every square inch of the body can have the necessary mechanical counter pressure applied uniformly. Such pressure is practically impossible to give to the surfaces on and in the head, and is notoriously difficult to provide where small joints are involved, namely hands and feet, and on the insides of "tight corners" like the armpits and groin. While the BioSuit solves the armpit/groin problem through its design, the current functional version still uses a pressurized "fishbowl" helmet and gas-pressurized gloves and boots, though alternate options like neoprene-foam gloves and boots are being considered.

  • Mechanical counter pressure must be carefully applied to maximize freedom of movement and minimize energy cost of movement. These issues were the main problems with the first incarnation of the SAS; the thick neoprene construction meant that range of motion and energy cost were only slightly improved over the contemporary Mercury-era pressure suit, and the SAS was just as bulky. The second-generation SAS was better, but its multi-layer construction was still cumbersome, and the uniform flexibility of the material over large areas provided an increased cost of movement. The BioSuit was specifically designed to be superior in both these respects; the spandex is reinforced by elastic bands that traverse "lines of non-extension" on the body, so you aren't working against the primary source of mechanical tension when you move, and the bands in turn allow the thinner spandex to provide the needed pressure in a relatively thin layer.

  • Climate control can be a problem. The original SAS, as mentioned, was not breathable (though not completely gas-tight), and so the suit had to be fitted with a liquid cooling system. The second-generation SAS and the BioSuit, both more or less breathable (the BioSuit more than the SAS), expose sweat to the vacuum, so it will evaporate more or less normally and with the same function as in air. However, that's the limit of climate control in such a suit; there's no air convection to either warm or cool the body, so you're relying on the body's natural temperature control mechanisms to perform in a vacuum the same way they do in an atmosphere. There is evidence from tests of the second-generation SAS that this won't be a major problem; the BioSuit hasn't gotten that far yet.

  • Thin and form fitting is better for mobility, but poses modesty concerns. As wearers of a wetsuit or leotard can attest, they are among the least flattering things that clothing designers have ever produced. They also do not leave much to the imagination, either male or female (the SAS cheated a bit by using strategically-placed polyurethane foam to transfer pressure from the suit to the groin, which also reduced the... definition in that area). While such concerns are ultimately rather petty in an environment like space, in the interests of crew morale, they're not to be ignored. The BioSuit is thin enough to wear under a standard-issue NASA jumpsuit, retaining a modest outward appearance, at least while in the spacecraft. The only full suit in existence is for the program's director, Professor Dava Newman, so we don't yet know what a male BioSuit will look like.

So in summary, MCP suits have interested NASA since the dawn of the U.S. manned space program; the safety issues of a gas-pressure suit and subsequent costs and procedures inherent in avoiding them have long been known. However, until recently, the best options available had their own significant drawbacks which made the gas suits the better option. I personally have high hopes for the Bio-Suit; it's a dramatic leap forward in wearability, and even with the need to custom-fit them it should be far cheaper overall to have a BioSuit (or two) for each individual astronaut than to buy and maintain the current generation of EMU suits.

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I believe you're referring to the Space Activity Suit.

There's been a number of versions and approaches to the problem over the years, but they all are based on mechanical pressure (i.e. compression through elastic fabrics) to help support the skin against vacuum. The trick is to engineer them to give sufficient support while not constricting movement.

The most recent iteration is the BioSuit, being developed by Dava Newman at MIT. Her design incorporates a deeper study of biomechanics - knowing how the human body actually moves, and accurately building tension into the suit at the appropriate points.

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