Skylab, the first U.S. manned orbiting laboratory, was launched on May 14, 1973; over the next 9 months it served as living
and working quarters for three successive crews of
astronauts. Skylab's basic structure was a converted S-IVB rocket, the third stage of the Saturn 5 booster designed to send Apollo spacecraft to the Moon. It
provided a cylindrical shell enclosing a cabin about 14.6 m (48 ft) long and 6.4 m (21 ft) in diameter, with about 283 m7 (10,000 ft7) of usable living space. It housed its crews for 28, 59, and 84 days respectively. The third crew set a record for continuous residency in space that lasted until 1978, when it was surpassed by cosmonauts Yuri Romanenko and Georgi Grechko aboard the Soviet station Salyut 6. Skylab's basic module was called the orbital workshop (OWS). Attached to it were three other major sections. An astronomy section, the Apollo telescope mount (ATM), carried instruments for observing the Sun in the visible, ultraviolet, and X-ray portions of the spectrum. A second section, the multiple docking adapter (MDA), held the controls for the telescope array and provided the docking port for the Apollo spacecraft that carried the crews to and from the Earth. Separating the docking adapter from the workshop was an air-lock module (AM) that housed various life-support, electrical, and communications systems and through which the astronauts passed to change film in the solar telescope. The workshop, air-lock module, and docking adapter together provided about 360 m7 (12,700 ft7) of space, equivalent to a two- or three-bedroom house. The first crew, consisting of astronauts Charles Conrad, Paul Weitz, and Joseph P. Kerwin, was launched on May 25, 1973, 11 days after the unmanned Skylab achieved its 432-km (268-mi) orbit. Their primary and perhaps most important task was to repair Skylab itself, one of whose two solar panels had been completely ripped off and the other damaged during Skylab's ascent. Not until 2 weeks into the mission were Conrad and Kerwin, after much planning, consultation with officials on the ground, and false starts, able to free the damaged panel so that it could open and provide the station with solar electrical power. Meanwhile, the mission's research schedule was already under way. In addition to astronomy, the plans included an elaborate program of photography of the Earth to monitor volcanoes, earthquake faults, pollution, atmospheric conditions, and natural resources. Besides exercising to keep in shape during the long period of weightlessness, the crew carried out a variety of biomedical studies, using such equipment as Skylab's built-in exercycle. By the time the crew returned to Earth on June 22, 1973, they had amassed 30,242 photographs of the Sun and more than 14,000 photos of the Earth, including 31 American states and 9 foreign countries. Four weeks in space produced slight weight loss in all three astronauts, who found that the more exercise they performed in space, the easier was the readaptation to Earth's gravity afterward. Astronauts Alan Bean, Jack Lousma, and Owen Garriott constituted the second crew, launched on July 28, 1973. Shortly after their arrival, Garriott and Lousma shared a 4-hour, record-setting spacewalk to deploy an external sunshade to help keep Skylab's internal temperatures down. Astronomical and Earth photography were continued, along with various biological experiments to evaluate the effects of weightlessness on life forms such as minnows, plant seedlings, and spiders (observed to see if any changes occurred in their web-spinning patterns). Eating and drinking were accomplished by sucking food out of special containers; going to bed involved being laced into a sort of snug sleeping bag mounted against a bulkhead; excretory and urinary functions were aided by suction devices. Although moving around in the weightless environment was possible by simply "swimming" across the cabin, the astronauts occasionally jetted around using hanpistollike maneuvering units or backpacks. The crew photographed several large solar flares as well as the optical source in the vicinity of the X-ray star Scorpio X-1. The crew also conducted several materials-processing experiments, such as welding and brazing, to study how the lack of gravity affected these techniques. They returned to Earth on Sept. 25, 1973. The final crewÑGerald Carr, Edward Gibson, and William PogueÑwas launched Nov. 16, 1973; they continued the types of experiments begun by the previous Skylab teams and also conducted extensive studies of the comet Kohoutek. Touted in advance as "the comet of the century," it turned out to be less than spectacular for Earthbound observers, but the Skylab crew had an ideal view and documented it with a variety of instruments, some provided especially for Kohoutek's coming. The astronauts returned to Earth on Feb. 8, 1974. A command to the space station to turn off its telemetry transmitter was sent from Earth a day later. Skylab was intended to remain in orbit until 1981-82, when it could be refueled by the Space Shuttle and regain altitude. NASA, however, underestimated the level of solar activity, which exerted a cumulative drag and caused the station's orbit to decay too rapidly. The reentry of Skylab, the largest space vessel to fall back to Earth, was a matter of public concern for months because of uncertainty as to where it would fall. Skylab came to a fiery end on July 11, 1979, when it entered the Earth's atmosphere and disintegrated, showering debris over the Indian Ocean and uninhabited regions of Australia.