Space activity suit

A space activity suit (SAS) or mechanical counterpressure suit is an experimental spacesuit which applies stable pressure against the skin by means of skintight elastic garments. The SAS is not inflated like a conventional spacesuit: it uses mechanical pressure, rather than air pressure, to compress the human body in low-pressure environments. Development was begun by NASA and the Air Force in the late 1950s and then again in the late 1960s, but neither design was used. Research is under way at the Massachusetts Institute of Technology (MIT) on a "Bio-Suit" System which is based on the original SAS concept.

The human body can briefly survive exposure to the hard vacuum of space unprotected, despite contrary depictions in some popular science fiction. Human skin does not need to be protected from vacuum and is gas-tight by itself. Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon. This can be counteracted through mechanical counter-pressure from a suitably designed garment. Consciousness is retained for up to 15 seconds as the effects of oxygen starvation set in. Counteracting this requires a helmet to contain breathing gases and protect the ears and eyes. These effects have been confirmed through various accidents in very high altitude conditions, outer space, and training vacuum chambers.

Cooling of the astronaut with an SAS is generally achieved with evaporation from body perspiration which is emitted from the suit in all directions. Water, salts, and proteins can deposit on optics and other sensitive surfaces causing damage or degradation. This can limit the usefulness of an SAS. For the inflated spacesuits used on the space shuttle, International Space Station, and the Apollo program, cooling was achieved in the Primary Life Support System by sublimation of water in a vacuum.

In 1959 Hans Mauch was working on "breathable" undergarments for the Mercury space suit when he hit upon the idea of a way to build a mechanical counterpressure design. The Mauch team noticed that closed-cell foams, which trap gas within their structure, expand when outside pressure is lowered. By containing the foam within a non-expanding outer layer, it would place increasing pressure on the body as the pressure lowered. This appeared to allow for a design that would offer far better mobility than the almost rigid Mercury design.

...
Wikipedia