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A space activity suit is a kind of spacesuit which provides mechanical pressure by means of elastic garments, as opposed to pressurizing the suit with the breathing gas, as is standard practice in regular suits. The suit consists of a pressurized bubble helmet, a positive-pressure breathing system, and an elastic leotard which provides mechanical counterpressure to the body. Because skin is itself quite airtight, the elastic fabric can press directly on the body, and cooling is accomplished by the evaporation of sweat through the fabric instead of by water cooling systems.
Original research was done by Paul Webb, who in 1968 published a paper titled "The Space Activity Suit: An Elastic Leotard for Extravehicular Activity" in the April 1968 issue of Aerospace Medicine. Research was funded by NASA.
In 1971, Webb, along with James F. Annis, published NASA CR-1892, "Development of a Space Activity Suit", including experimentation with a human volunteer put into a low-pressure chamber to exercise and perform tasks requiring manual dexterity. The results were positive, and the researchers felt that further improvements were possible.
NASA discontinued research into the space activity suit, and pressurized suits are still used as of 2005. However, research is under way at the Massachusetts Institute of Technology (MIT) on a Bio-Suit System as a preparation to president Bush's new space vision.
A space activity suit consists of a pressurized bubble helmet (much like those in fully pressurized spacesuits), a positive-pressure breathing system, and an elastic leotard, which provides mechanical counterpressure to the body. The main difference from a pressure suit is that the counterpressure to the surface of the body is provided by an elastic non-airtight fabric instead of gas pressure (amazingly our skin is actually quite airtight).
This has certain advantages: Cooling is accomplished by the evaporation of sweat through the fabric (instead of water cooling systems). The unpressurized and elastic suit allows finer and less laborous movements (which leads to less fatigue and more manual accuracy), has less mass and is much simpler. It is also thought to be safer, since isolated damages to the suit may lead to localized skin swellings or injuries, but not to general (deadly) decompression.
Quoting the NASA Contractor Report from 1971:
In conclusion, the SAS at its present stage of development will protect man from the effects of the vacuum environment, in a garment, which permits improved mobility and natural body movements. Physiologically the approach is sound, and although there remain many problems to be solved, they are principally mechanically in nature. It has been suggested that solution of the mechanical problems, combined with careful tailoring based upon biomechanical analysis, plus the development of specific elastic fabrics, could eventually lead to a space qualified version of the SAS.
| The above article is licensed under the GNU Free Documentation License. From Wikipedia, the free encyclopedia ( https://en.wikipedia.org/wiki/space_activity_suit ). Apparel Industry definition modified by Apparel Search 8/3/06 |
The central problem of a gas-pressurized suit is that pressure fights movement: every bend of an elbow or knee changes the suit's volume and takes work, and the astronaut must keep spending that effort to hold the joint bent. Mechanical counterpressure removes most of that fight. An elastic garment presses on the body the way a tight athletic garment does, so joints move almost as freely as they do unclothed, fatigue drops, and delicate hand work becomes more accurate. The suit also has less mass and far fewer parts than a full pressure suit.
Safety arguments run in its favour as well. A puncture in a gas-pressurized suit can cause general, dangerous decompression. In an elastic suit, isolated damage is expected to cause only localized skin swelling or injury at the damaged spot, because the rest of the garment keeps pressing as before. Cooling is simpler too: sweat evaporates through the fabric, the body's own system, instead of requiring the water cooling loops of a conventional suit.
The 1971 NASA report concluded that the approach was physiologically sound and that the remaining problems were principally mechanical: making an elastic garment that presses evenly everywhere, including over concave areas of the body where fabric naturally bridges rather than presses, and tailoring it closely enough, using biomechanical analysis, that pressure stays correct as the body moves. Specific elastic fabrics had to be developed for the purpose. Those tailoring and materials problems, rather than any flaw in the concept, are why the space activity suit remained a research garment while pressurized suits flew.
A regular spacesuit is pressurized with breathing gas, which makes it stiff like an inflated balloon. A space activity suit instead uses an elastic leotard to press mechanically on the body, so only the helmet and breathing system are pressurized. The result is lighter, simpler and far easier to move in.
Paul Webb published the design in 1968 in Aerospace Medicine, in a paper titled The Space Activity Suit: An Elastic Leotard for Extravehicular Activity, with research funded by NASA. In 1971 Webb and James F. Annis published NASA report CR-1892 on the suit's development, including tests with a human volunteer in a low-pressure chamber.
NASA discontinued its space activity suit research and pressurized suits remained standard. Research continued elsewhere, notably at the Massachusetts Institute of Technology, where work on a Bio-Suit System carried the mechanical counterpressure idea forward.