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Space Activity Suit
American space suit, tested 1971. Prototype for a Mechanical Counter Pressure suit made up of six layers of elastic material accompanied by a full bubble helmet.

Status: tested 1971. Gross mass: 24 kg (52 lb).

The goal was to improve the range of activity and decrease the energy cost of work associated with wearing conventional gas filled pressure suits. The suit would also be half the weight, simpler, and not endanger the astronaut's life if punctured.

The human skin was almost an ideal pressure suit. It had a high tensile strength, almost no gas permeability, and very good water retention characteristics. The skin required only an applied pressure equal to the pressure of the breathing gas to function normally. A second skin was conceived, capable of augmenting the biological skin using Mechanical Counter Pressure (MCP) to mimic a pressurized environment. An MCP suit would not only require less energy by the astronaut for motion, but would be safer and more reliable than full pressure suits since suit rupture would not mean loss of life supporting gas pressure. If designed properly, a small tear in an MCP suit would only expose a local body region to reduced pressures. This exposure would cause the wearer discomfort, and possibly pain, but would allow them to return to safety without major injury. Tests of the Space Activity Suit directly exposed areas of skin as large as 1 square millimeter to vacuum without problems.

The life support system was greatly simplified since body cooling was accomplished by the simple and natural method of sweating. The suit was porous, and the sweat simply evaporated through the second skin. Tests of the suit in vacuum chambers showed no signs of excessive fluid loss, or freezing of the skin. They also demonstrated that, at such a scale, the skin withstood the tensile loads. Without the need for thermal control, the life support system became a tank of oxygen with pressure regulators and a carbon dioxide scrubber.

In the 1971 program ten successively refined prototypes of the suit were built, including 13 hours of wear by test subjects in vacuum chambers of up to 2 hours 45 minutes duration. The tests showed no significant problems in comparison to conventional suits. But whereas the energy cost of simple tasks in the Gemini or Apollo suits was typically 2.26 times that for a nude subject, in the SAS it was 1.64 times. And the mass of the suit, was half that of the Apollo suit.

But the tests also showed the major detailed technical challenges of completing development of such a suit. Most important was swelling/edema in parts of the body. To prevent blood pooling, the pressure across these regions needed to remain smooth. The most difficult areas to accomplish this in the crotch. There was also swelling of the hands, but this was reduced by using palm pads. This problem was seen as primarily mechanical in nature, and could be solved by further development, improved design, and use of new stretch materials.

Another issue major issue was the need to tailor each suit precisely to the form of each subject. In the prototype suit this required extended suit donning and doffing times. A production suit would have to use different techniques to ensure easier donning and fitting. The prototype suit had to be tailored to individual subjects and consisted of no fewer then eight garments that had to each be fitted and adjusted precisely and donned in the correct order:

  • Slip layer: required individual tailoring. (the torso pressurizing breathing bladder assembly was donned immediately over the slip layer).
  • Helmet-bladder restraint garment to limit bladder expansion and assist in preventing helmet rise. The torso section was custom fitted to subjects and constructed of Nomex, a suitable non-stretch fabric. The top was securely anchored to a split ring baseplate. Four zippers at front, back, and the midlines were needed to allow donning. Circumferential size adjustments were made at two mid-lateral anterior lace take-ups .
  • Second helmet-bladder restraint garment to assist the primary helmet-bladder restraint garment. This layer was a full-body garment with a torso section of non-stretch (Nomex) material and limb segments of bobbinet. The limb segments supplied a minimum of 25 mm Hg over the thigh (the largest circumference). A strap of non-stretch material passed through the crotch for joining the elastic leg segments. The vertical length of the torso fabric was determined initially from subject measurements and finally during fitting trials. The neck opening was sized to fit snugly (when closed) into the angle formed by the junction of the baseplate and breastplate assembly--hence covering the shoulder portion at the breastplate. A full length torso zipper was inserted along the front midline of the torso section.
  • Arm balance layer: This layer was used to balance the pressurization of the arms with that on the legs
  • Full body bobbinet layers: Two each full body bobbinet garments based on individual tailoring. These garments should supply 15 mm Hg each on the torso and a minimum of 30 mm Hg and 25 mm Hg on the largest circumference of the arms and legs respectively.
  • Girdles: Two girdles, each of the heavy powernet fabric, fabricated to augment pressurization of the upper thigh-lower torso (below bladder) and to improve the pressure transition across the area of the body.
  • Gloves, pads: Gloves and molded rounding pads selected for each individual subject
  • Foot covers: Foot covers (booties) selected for each individual subject

Family: Space Suits. Country: USA. Agency: NASA. Bibliography: 4471, 6913.

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