Spacewalk

Development history
NASA planners invented the term extra-vehicular activity in the early 1960s for the Apollo program to land men 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-man Earth orbiting spacecraft. However, the Soviet Union was fiercely competitive in holding the early lead it had gained in manned spaceflight, so the Soviet Communist Party, led by Nikita Khrushchev, ordered the hasty 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 the first manned Gemini was launched.
The Soviets' avionics technology was not as advanced as that of the United States, so the Voskhod cabin could not have been left depressurized by an open hatch; otherwise the air-cooled electronics would have overheated. Therefore a spacewalking cosmonaut would have to enter and exit the spacecraft through an airlock. By contrast, the Gemini capsule's avionics were designed so the cabin could be exposed to the vacuum of space when one of two large hatches was opened, so no airlock was required, and both the spacewalking astronaut and his companion command pilot were in vacuum during the EVA. Due to the different designs of the spacecraft, the American and Soviet space programs define the duration of an EVA differently. The Soviet (now Russian) definition is the time when the outer airlock hatch is open and the cosmonaut is in a vacuum. An American EVA begans when the spacewalking astronaut has at least his head outside of the spacecraft.