The six flights of the Mercury series were followed by ten flights in the Gemini program. Suit designers were faced with new problems. Not only would a Gemini suit have to serve as a pressure backup to the spacecraft cabin, but also as an escape suit if ejection seats had to be fired for an aborted launch and as an EMU for extravehicular activity. To increase mobility and comfort of the suit for long-term wear, designers departed from the Mercury suit concept. Instead of fabric joints, they chose a construction that employed a bladder restrained by a net. The bladder was an anthropomorphically shaped layer of neoprene-coated nylon. That was covered in turn with a layer of Teflon®-coated nylon netting. The netting, slightly smaller than the pressure bladder, limited inflation of the bladder and retained the pressure load in much the same way automobile tires retained the load in inner tubes in the days before tubeless tires. The new spacesuit featured improved mobility in the shoulders and arms and was more comfortable when worn unpressurized during space flights lasting as long as 14 days.
The first Gemini astronaut to leave his vehicle ("go EVA") was Edward White, II. White exited from the Gemini 4 space capsule on June 3, 1965-just a few months after Leonov made the first Soviet spacewalk. For a half-hour, White tumbled and rolled in space, connected to the capsule only by an oxygen-feed hose that served secondary functions as a tether line and a communication link with the capsule. Although the term "spacewalk" was coined for the Gemini program, no actual walking was involved. On his spacewalk, White used a small hand-held propulsion gun for maneuvering in space. When he pulled a trigger, the gun released jets of nitrogen that propelled him in the opposite direction. It was the first personal maneuvering unit used in space.
Upon completion of the Gemini program, NASA astronauts had logged nearly 12 additional hours of EVA experience. Approximately one-half of that time was spent merely standing up through the open hatch.
One of the most important lessons learned during the Gemini program was that EVAs were not as simple as they looked. Moving around in space required a great deal of work. The work could be lessened, however, by extensive training on Earth. The mosteffective training took place underwater. Wearing specially-weighted spacesuits while in a deep tank of water gave later Gemini crew members adequate practice in maneuvers they would soon perform in space. It was also learned that a better method of cooling the astronaut was required. The gas cooling system could not remove heat and moisture as rapidly as the astronaut produced them, and the inside of the helmet visor quickly fogged over making it difficult to see.
Following Gemini, the Apollo program added a new dimension in spacesuit design because actual spacewalks (on the surface of the Moon) were now to occur for the first time. As with Mercury and Gemini space garments, Apollo suits had to serve as a backup pressure system to the space capsule. Besides allowing flexibility in the shoulder and arm areas, they also had to permit movements of the legs and waist. Astronauts needed to be able to bend and stoop to pick up samples on the Moon. Suits had to function both in microgravity and in the one-sixth gravity of the Moon's surface. Furthermore, when walking on the Moon, Apollo astronauts needed the flexibility to roam freely without dragging a cumbersome combination oxygen line and tether. A self-contained portable life-support system was needed.
The Apollo spacesuit began with a garment that used water as a coolant.
The garment, similar to long johns but laced with a network of thin-walled
plastic tubing, circulated cooling water around the astronaut to prevent
overheating. A multi-layered pressure garment was worn on top of the cooling
suit. The innermost layer of this garment was a comfort layer of lightweight
nylon with fabric ventilation ducts. On top of this was a layer of neoprene-coated
nylon surrounded by a nylon restraint layer. This layer contained the
pressure inside the suit. Improved mobility was achieved by bellow-like
joints of formed rubber with built-in restraint cables at the waist, elbows,
shoulders, wrist, knees, and ankles. On top of the pressure layer were
five layers of aluminized Mylar® for heat protection, mixed with four
spacing layers of non-woven Dacron®. Above these were two layers of
Kapton and beta marquisette for additional thermal protection and a nonflammable
and abrasion-protective layer of Teflon®-coated filament beta cloth.
The outermost layer of the suit was white Teflon® cloth. The last
two layers were flame resistant. In total, the suit layers provided pressure,
served as a protection against heat and cold, and protected the wearer
against micrometeoroid impacts and the wear and tear of walking on the
The life-support system, a backpack unit, provided oxygen for breathing and pressurization, water for cooling, and radio communications for lunar surface excursions lasting up to eight hours. Furthermore, back inside the lunar lander the life-support system could be recharged with more oxygen and battery power for additional Moonwalks.
During the Apollo program, 12 astronauts spent a total of 161 hours of EVA on the Moon's surface. Additional EVAs were spent in microgravity while the astronauts were in transit from the Moon to Earth. During a total of four hours, one astronaut, the command module pilot, left the capsule to retrieve photographic film. There was no need for the portable life-support system away from the Moon, as those astronauts were connected to the spacecraft by umbilical tether lines supplying them with oxygen.
NASA's next experience with EVAs came during the Skylab program and convincingly demonstrated the need for astronauts on a spacecraft. Spacesuited Skylab astronauts literally saved the Skylab program.
Skylab was NASA's first space station. It was launched in 1973, six months after the last Apollo Moon landing. Trouble developed during the launch when a micrometeoroid shield ripped away from the station's outer surface. This mishap triggered the premature deployment of two of the six solar panels, resulting in one being ripped away by atmospheric friction. The second was jammed in a partially opened position by a piece of bent metal. In orbit, Skylab received insufficient electrical power from the remaining solar panels: the station was overheating because of the missing shield. Instead of scrapping the mission, NASA assigned the first three-astronaut crew the task of repairing the crippled station. While still on board the Apollo command module, Paul Weitz unsuccessfully attempted to free the jammed solar panel as he extended himself through the open side hatch. On board Skylab, the crew poked an umbrella-like portable heat shield through the scientific airlock to cover the area where the original shield was torn away. Later, on an EVA, the metal holding the jammed solar arrays was cut, and the panel was freed to open. During an EVA by the second Skylab crew, an additional portable heat shield was erected over the first.
The Skylab EMU was a simplified version of the Apollo Moon suits. There was no need for the portable life-support system because the crew member was attached to the station by an umbilical tether that supplied oxygen and cooling water. An astronaut life-support assembly, consisting of a pressure-control unit and an attachment for the tether, was worn on the chest, and an emergency oxygen package containing two supply bottles was attached to the right upper leg. A simplified visor assembly was worn over the pressure helmet. Lunar protective boots were not needed. Skylab astronauts logged 17.5 hours of planned EVA for film and experiment retrieval and 65 hours of unplanned EVA for station repairs.