Development
The human body can briefly survive exposure to the hard vacuum of space unprotected, despite contrary depictions in some popular science fiction. Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon. Consciousness is retained for up to 15 seconds as the effects of oxygen starvation set in. No snap freeze effect occurs because all heat must be lost through thermal radiation or the evaporation of liquids, and the blood does not boil because it remains pressurized within the body. The greatest danger is in attempting to hold one's breath before exposure, as the subsequent explosive decompression can damage the lungs. These effects have been confirmed through various accidents (including in very high altitude conditions, outer space and training vacuum chambers). Human skin does not need to be protected from vacuum and is gas-tight by itself. Instead it only needs to be mechanically compressed to retain its normal shape. This can be accomplished with a tight-fitting elastic body suit and a helmet to contain breathing gases and protect the ears and eyes.
Original development of such a suit was funded by NASA and conducted by Paul Webb, who published a paper entitled "The Space Activity Suit: An Elastic Leotard for Extravehicular Activity" in the April 1968 issue of Aerospace Medicine. The report was extremely positive, so further work was contracted in order to test various design concepts. Between 1968 and 1971 ten designs of increasing sophistication were built, leading eventually to a series of successful tests in vacuum chambers. The longest test was two hours and forty-five minutes.
The tests were successful: the practicality of a mechanical counter pressure spacesuit was demonstrated conclusively. The energy needed to move about was considerably less than conventional designs, which was a major improvement for long-duration spacewalks. Tests of punctures showed that up to a square millimeter of skin could be directly exposed to vacuum for extended periods with no permanent effect. A similar puncture in a conventional suit would result in a loss of pressure and breathing air. It weighed half as much as the primary pressure suit worn by NASA astronauts for Project Apollo, the A7L.
A number of problems also turned up, primarily related to the problem of keeping the suit in strong mechanical contact at every point on the body. Concavities or small folds in the fabric could lead to fluid pooling in the gaps; the groin area proved extremely difficult to tailor successfully. To correct this, small pads of polyurethane foam were inserted into concavities and were successful in most problem areas. The suits had to be tailored to each individual, although the same was true of the earlier Apollo suits. The largest difficulty was donning and removing the suit. In order to effectively provide the minimum pressure of 29.6 kilopascals (220 mmHg; 4.3 psi) necessary for human physiology, the suit had to be extremely tight-fitting, making donning and doffing a highly strenuous task.
In 1971, Webb, along with James F. Annis, published their findings in NASA CR-1892, "Development of a Space Activity Suit". The report remained positive, and the researchers felt that further improvements were possible. Quoting the Report:
| “ | 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 mechanical 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. | ” |
Read more about this topic: Space Activity Suit
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