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In the April 1968 issue of Aerospace Medicine, a NASA researcher published his work on a Space Activity Suit. This suit was designed to be a skin-tight space suit to permit Apollo astronauts to roam the surface of the Moon with ease. It was much lighter weight than the full pressure suits developed at that time, and permitted much more freedom of movement. The reduced weight and increased dexterity would make working on the Moon much easier, and reduce astronaut fatigue. Unfortunately, it was not ready in time for Apollo 11. All work after Apollo 11 was cancelled. Today's Shuttle space suits are also full pressure suits, and weigh even more than the Apollo suit. This weight might be acceptable in the weightlessness of space, or the 1/6th gravity of the Moon, but the higher gravity of Mars makes a heavy suit impractical. The space suit used on Apollo 15-17 was the A7L-B. It massed 175 pounds, including an 80-pound portable life support system (PLSS) backpack, and a 40-pound backup. The Extravehicular Mobility Unit (EMU) is the suit used on the Space Shuttle. It masses 275 pounds. On the Moon, with its 0.166G gravity, the relative weight of the Apollo suit was only 29 pounds. On Mars with 0.38G gravity, the relative weight would be 66.5 pounds for the Apollo suit, and 104.5 pounds for the Shuttle suit. Obviously, we need a lighter suit. The cooling system for an Apollo suit was plastic tubes sewn into an undergarment. The PLSS included 12 pounds of water, which circulated through the tubes, then was allowed to sublimate into the vacuum. That would permit 8 hours of activity. The SAS simply permits the astronaut to sweat into space to reduce body heat. Insensible perspiration only looses half the metabolic heat of a man at rest, so an astronaut in space would get warm and sweat. Water loss through sweat to eliminate the metabolic heat produced during a normal work load would be 8.2kg, or 18 pounds of water. This would require an 18 pound water bottle for drinking, but the plastic tubes, water circulation and regulation system, and the evaporator would not be needed. The 6 additional pounds of water would be more than offset by eliminating equipment; and no water bottle would be needed for short EVA's. On Mars, the atmosphere is cold. The problem is not staying cool; it is staying warm. The Martian temperature can fluctuate between -8ºC at 2:30pm and -77ºC at 5:30am. Water loss through insensible perspiration would be only 0.8kg for 8 hours. You would need a 800ml drinking bottle to replenish that. Since the atmosphere is thin, conductive heat loss is slower. A good parka would be required. The work by Paul Webb, M.D., in 1967 tested the suit with a volunteer subject. The tests included the volunteer wearing the suit into an altitude chamber with the pressure reduced to 155mm mercury, and an arm inserted into a chamber with the pressure reduce to near vacuum: 5mm mercury. That 5mm mercury is the same atmospheric pressure as Mars. The orginal paper was written in December 1967, published in the Journal of Aerospace Medicine, April 1968 issue. It's available here. NASA funded Paul Webb and James Annis to continue the work for a while. Their contractor report from November, 1971 is available here. A May, 2000, technical paper discussing required pressure and in-situ resource utilisation to provide life support on Mars is available here. Professor Dava J. Newman, a Harvard-MIT Health Sciences and Technology MacVicar Faculty Fellow, is investigating a "skinsuit" based on the same principle. More information on her work is available at Tech Talk. She has been funded by NIAC (NASA Institute for Advanced Concepts) to study a mechanical counter-pressure suit, including “spraying on” or “shrink wrapping” the outer layer. To read more about her "Bio-Suit", see her abstract or slide presentation. |
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