Extravehicular activity (EVA) is any activity performed by an astronaut in outer space outside of a spacecraft. This includes spacewalks, lunar or planetary surface exploration (commonly known as moonwalks), and stand-up EVAs (SEVAs) where astronauts stand through an open hatch without fully leaving the spacecraft. EVAs have been conducted by the Soviet Union/Russia, the United States, and China, with astronauts from Canada, Japan, the United Arab Emirates, and the European Space Agency also participating in EVAs conducted by those nations. Since there is no atmosphere in space, the astronaut is completely dependent on the space suit for environmental support. On March 18, 1965, Alexei Leonov conducted the first spacewalk, lasting 12 minutes and 9 seconds during the Voskhod 2 mission. Neil Armstrong performed the first moonwalk on July 20, 1969, during the Apollo 11 mission, lasting 2 hours and 31 minutes. Svetlana Savitskaya became the first woman to conduct a spacewalk in 1984, spending 3 hours and 35 minutes outside the Salyut 7 space station. Astronauts on the last three crewed lunar landing missions, Apollo 15, 16, and 17, also performed deep space EVAs to retrieve film canisters. In 1973, American astronauts Pete Conrad, Joseph Kerwin, and Paul Weitz conducted an EVA to repair launch damage to Skylab, the United States' first space station. EVAs can be tethered, where the astronaut is connected to the spacecraft with an umbilical cable for oxygen and power, or untethered. Untethered spacewalks were conducted on three missions in 1984 using the Manned Maneuvering Unit (MMU) and in a 1994 flight test of the Simplified Aid For EVA Rescue (SAFER) safety device worn on tethered U.S. EVAs.
Development history NASA planners invented the term extravehicular activity (abbreviated with the acronym EVA) in the early 1960s for the Apollo program to land humans on the Moon, because the astronauts would leave the spacecraft to collect lunar material samples and deploy scientific experiments. To support this, and other Apollo objectives, the Gemini program was spun off to develop the capability for astronauts to work outside a two-person Earth orbiting spacecraft. However, the Soviet Union was fiercely competitive in holding the early lead it had gained in crewed spaceflight, so the Soviet Communist Party, led by Nikita Khrushchev, ordered the conversion of its single-pilot Vostok capsule into a two- or three-person craft named Voskhod, in order to compete with Gemini and Apollo. The Soviets were able to launch two Voskhod capsules before U.S. was able to launch its first crewed Gemini. The Voskhod's avionics required cooling by cabin air to prevent any kind of overheating, therefore an airlock was required for the spacewalking cosmonaut to exit and re-enter the cabin while it remained pressurized. Unusually, and by contrast, the Gemini avionics did not require air cooling, allowing the spacewalking astronaut to exit and re-enter the depressurized cabin through an open hatch. Because of this, the American and Soviet space programs developed different definitions for the duration of an EVA. The Soviet (now Russian) definition begins when the outer airlock hatch is open and the cosmonaut is in vacuum. An American EVA began when the astronaut had at least their head outside the spacecraft. The U.S. has changed its EVA definition since.
First instance The first EVA was performed on March 18, 1965, by Soviet cosmonaut Alexei Leonov, who spent 12 minutes and 9 seconds outside the Voskhod 2 spacecraft. Carrying a white metal backpack containing 45 minutes' worth of breathing and pressurization oxygen, Leonov had no means to control his motion other than pulling on his 15.35 m (50.4 ft) tether. After the flight, he claimed this was easy, but his space suit ballooned from its internal pressure against the vacuum of space, stiffening so much that he could not activate the shutter on his chest-mounted camera. At the end of his space walk, the suit stiffening caused a more serious problem: Leonov had to re-enter the capsule through the inflatable cloth airlock, 1.2 m (3 ft 11 in) in diameter and 2.5 m (8 ft 2 in) long. He improperly entered the airlock head-first and got stuck sideways. He could not get back in without reducing the pressure in his suit, risking "the bends". This added another 12 minutes to his time in vacuum, and he was overheated by 1.8 °C (3.2 °F) from the exertion. It would be almost four years before the Soviets tried another EVA. They misrepresented to the press how difficult Leonov found it to work in weightlessness and concealed the problems encountered until after the end of the Cold War.
Project Gemini
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