A space walk, also known as extravehicular activity (EVA), is an activity or maneuver performed by an astronaut outside a spacecraft. Astronauts perform EVAs for a variety of reasons, including exploration, research, and construction of structures in space. The first space walks of the Soviet Union and the United States in 1965 proved that humans could venture from their spacecraft into space. To judge by the reactions of some astronauts, walking in space was an exhilarating experience. Edward White, the first American space walker, overextended his EVA, and returned to his Gemini spacecraft with great reluctance.
Nevertheless, space is a hostile environment to unprotected astronauts. It lacks oxygen and water. Without Earth's atmosphere to filter the sunlight, temperatures can reach 170°C (338°F), while in shadows the temperature can drop to -120°C (-184°F). Hazardous micrometeoroids and radiation also threaten spacewalkers, and with no atmosphere and therefore no atmospheric pressure, fluids in the human body would boil. To explore and work in space, human beings must take their environment with them. Inside the spacecraft, the atmosphere can be controlled so that special clothing is not needed, but when outside, humans need the protection of a space suit.
In March 1965, Soviet cosmonaut Alexei Leonov became the first person to don a space suit and walk in space. His exploit was followed in June of that year by White's twenty-two-minute space walk. White was protected by a multilayer space suit that included a pressure bladder and a link-net restraint layer to make the whole suit flexible. In his hand White held a small maneuvering unit, but he remained tethered to the spacecraft. The first space walk to test whether humans could perform useful activities in space occurred during the flight of Gemini 9 in May 1966. A complicated series of tasks were to be performed by astronaut Eugene Cernan as a prelude to testing a sophisticated maneuvering unit. Soon after beginning his EVA, however, Cernan became overheated and his helmet visor fogged over. Finally, after two hours, Cernan was ordered back inside. Similar problems occurred during a space walk on Gemini 11.
The experience of early spacewalkers underscored the need for detailed planning and training for an EVA. By the time of Gemini 12 in November 1966, preparations for EVA included extensive practice sessions in water tanks that simulated the effect of weightlessness. During that mission, Edwin "Buzz" Aldrin performed numerous tasks with few of the problems that struck Cernan and others. Aldrin set an EVA record of five and a half hours for a single space walk, unscrewing bolts and tightening them and checking electrical connections. He had proved that astronauts could perform useful work during a space walk.
Walking on the Moon
Walking on the Moon's surface a quarter million miles away from Earth posed new problems for spacewalkers. Not only did astronauts have to be protected from jagged rocks and the searing heat of the lunar day, but the suits also had to be flexible enough to allow the astronauts to bend over and gather samples. When Apollo 11 crew members Neil Armstrong and Buzz Aldrin set foot on the Sea of Tranquility in July 1969, their EVA suits contained a number of innovations.
Numerous layers provided protection against micrometeoroids and thermal extremes. Mobility was enhanced by bellows-like molded rubber joints at the shoulders, elbows, hips, and knees. Underneath it all was a liquid-cooling garment with a network of water-filled tubes to keep the astronaut cool. A portable life support system provided oxygen for breathing, suit pressurization, and ventilation for Moon walks lasting up to seven hours. Clad in this gear, Aldrin concluded that he was able to move about rapidly and with confidence.
Tasks for Apollo moonwalkers grew more complex as the program progressed, and modifications were made to the space suit for the Apollo 15 through Apollo 17 missions to provide greater flexibility. In July 1971, Apollo 15 astronauts David Scott and James Irwin stepped into the dazzling light of the lunar day and boarded a dune-buggy-like lunar rover at the foot of the Moon's Apennine Mountains. When they returned from their first tour, the rover's odometer had accumulated 10 kilometers (6.2 miles). The next day, the two astronauts made a 12.5-kilometer (7.8-mile) trip up the slope of the Apennines. At the end of the third EVA, Scott and Irwin had spent a highly productive eighteen and a half hours on the lunar surface and had packed away 77 kilograms (170 pounds) of rocks.
Apollo 17 launched in December 1972, marked the first time a geologist walked on the Moon. Harrison "Jack" Schmitt used his geologist's eye to spot "orange soil" initially believed to be evidence of volcanic venting of water from the Moon's interior. On the third day on the Moon, the final EVA produced a satisfyingly varied collection of samples. In all, Schmitt and mission commander Eugene Cernan conducted three Moon walks for a total of twenty-two hours and two minutes.
Construction Workers and Repairers
Apollo 17 was the last lunar flight, but spacewalking astronauts continued to perform important tasks in space. In 1973 astronaut Charles "Pete" Conrad literally saved America's first space station , Skylab, by donning his space suit and fixing a damaged solar panel. After making repairs and deploying a parasol-type sun shield, the workshop became fully operable. The second Skylab crew erected another sun shield during an EVA. These successes were testament to the growing space walk experience of the National Aeronautics and Space Administration (NASA) and advances in EVA training. NASA has increasingly relied upon simulations in water tanks as an essential tool for EVA training of astronauts and the design, testing, and development of tools and equipment. For astronauts, these facilities provide important preflight familiarization with planned crew activities and with the dynamics of body motion under weightless conditions. Major advances have also been made in space suit design to further facilitate space walk activities.
To work in the cargo bay of the space shuttle or in space, astronauts now wear the shuttle Extravehicular Mobility Unit (EMU) space suit, which was designed to be more durable and more flexible than previous space suits. The upper torso, lower torso, arms, and gloves come in different sizes and can be assembled in combination to fit men and women astronauts. In all, the EMU comprises the space suit assembly, the primary life-support system, a display and control module, and several other crew items designed for space walks and emergency life support.
The shuttle era also witnessed the first untethered space walks by U.S. astronauts in orbit. The Manned Maneuvering Unit (MMU), a one-person, nitrogen-propelled backpack, allowed astronauts to fly in or around the orbiter cargo bay or to nearby free-flying payloads or structures. Astronauts wearing MMUs have deployed, serviced, repaired, and retrieved satellites. Other spacewalkers attached to the end of the shuttle's remote manipulator arm have repaired and refurbished the Hubble Space Telescope.
Spacewalkers faced an unprecedented challenge in constructing the International Space Station. To prepare for the challenge, engineers and astronauts have been methodically practicing procedures, preparing tools, testing equipment, and gaining experience during more than a decade of shuttle space walks. Since 1991, over a dozen "practice" space walks have been conducted from the space shuttle as part of NASA's preparations. Other space walks have evaluated new tethers, tools, foot restraints, a jet-pack "life jacket," and space suit enhancements. Astronauts have also gained experience handling large masses. In addition, three servicing missions to the Hubble Space Telescope have helped prepare for the intricate work needed to build the space station.
In August 1996, NASA announced the first International Space Station EVA assembly crew of Jerry Ross and James Newman for space shuttle flight STS-88. In June 1997, five more crews of spacewalkers were named to the first six shuttle assembly missions, some of them more than two years ahead of their scheduled mission. The early naming of crew members allowed the astronauts time to train for their complex and crucial missions. Overall, about 160 space walks, totaling 960 clock hours, or 1,920 person-hours, are planned to assemble and maintain the International Space Station.
In addition to new spacewalking tools for assembly of the International Space Station, spacewalkers have an enhanced space suit that features replaceable internal parts; metal sizing rings that allow in-flight suit adjustments; new gloves with enhanced dexterity and heaters; a new radio with multiple channels; new helmet-mounted flood-and spotlights; and a jet-pack "life jacket" to allow an accidentally untethered astronaut to fly back to the space station in an emergency. In 2001, a Joint Airlock Module was attached to the space station, allowing astronauts wearing Russian or U.S. space suits to conduct space walks directly from the station.
Since Edward White stepped out of an orbiting Gemini spacecraft in 1965 to become the first American to walk in space, NASA has conducted about 400 hours of space walks. In the years to come, however, the record of space walks will grow enormously, as new generations of astronauts explore, conduct research, and build structures in orbit, on the Moon, and beyond.
see also Life Support (volume 3); Space Suits (volume 3).
John F. Kross
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