Modern space suits are direct descendants of the simple “pressure suits” designed as early as 1907 for deep-sea divers. In 1911 an English respiratory physiologist, J. S. Haldane, proposed the use of an oxygen pressurized suit for ascent to high altitudes. The first U.S. patent was granted for a pressure suit in 1918. Through the early 1960s, all such suits were pressure containers. Project Mercury astronauts wore suits adapted from the U.S. Navy MK-IV pressure suit. It consisted of an inner layer of neoprene-coated fabric and a restraint layer of aluminized nylon fabric. The garment design provided a fair degree of mobility, although the suit could not bend with the full hinge motion of the human elbow or knee because it folded in at the joints, reducing overall volume and increasing internal pressure. The Mercury suit would have been pressurized only if spacecraft cabin pressure had been lost. Space suits require a great deal of sophistication. They must meet many vital criteria, including low leakage, thermal control, comfort, stowage, and protection from micrometeoroid strikes. _Gemini 4_ was the first American mission to explore the problems of man functioning outside his spacecraft, with only his space suit for protection. This extravehicular activity required the space suit to be a prime system rather than a precautionary measure. [Illustration: 59. Apollo space suit.] Designed and created primarily for moon-walking, the 28.6-kilogram (63-pound) Apollo space suits, with backpack environmental and communication systems, enabled the lunar astronauts to dispense with the tether used on the Gemini “spacewalks.” The suit’s 21 layers are materials such as teflon fabric, nonwoven dacron, and aluminized mylar. These alternating layers of specialized materials protected the astronauts from the extreme temperatures of space and possibility of micrometeroids striking. Boots and gloves contain a stainless steel cloth to protect against abrasion. Suits had to fit the wearers so precisely that 67 anthropometric measurements were required of each astronaut. [Illustration: 60. Astronaut White takes the first “spacewalk” with only his suit for protection from the space environment.] When the astronauts ventured outside the spacecraft and explored the lunar surface, the following equipment was worn under the suit: a fecal containment system for emergency containment of solid-waste material; a liquid-cooling garment; a bio-belt assembly, urine collection and transfer system. Together with a portable life-support system, this constituted the complete Environmental Mobility Unit (EMU). The liquid-cooling garment consists of an outer layer of nylon spandex material, a network of polyvinyl-chloride tubing, and a nylon-chiffon comfort liner. Even spacing of the plastic tubing permitted the efficient transfer of body heat to the cooling liquid (water) as it circulated through the suit.