Spacewalk

Concept and terminology

An EVA is activity an astronaut performs outside a spacecraft in vacuum. It covers fully external spacewalks, stand-up EVAs in an open hatch, and lunar or planetary surface exploration. In English, extravehicular activity (EVA) is the general term for all of these; Soviet, Russian and European usage says внекорабельная деятельность (ВКД) for the wider category. The Soviets called leaving their own craft выход в открытый космос, and Russian retains that phrase for outside work. A spacewalk is one form of EVA, not the whole of it.

EVAs may be tethered, with the crew member secured to the vehicle by a safety line and oxygen hose, or untethered. The first untethered spacewalks, made in 1984 with a Manned Maneuvering Unit, showed that outside work need not depend on a tether.

Different definitions of the start and end

because Soviet craft had a separate, depressurisable airlock from the outset, the Soviet count began when the cosmonaut depressurised the airlock and reached vacuum, and ended when the hatch was closed. The early American capsules had no airlock; the whole cabin had to be depressurised, so the American count began when the astronaut's head passed the hull. The modern American standard starts the EVA when the suit switches to battery power and ends it when repressurisation begins. The same flight can therefore be timed differently depending on which rule is applied.

The first spacewalk in the US-Soviet race

Voskhod 1 and 2 were Vostok capsules converted in haste to compete with the American Gemini and Apollo programs. Voskhod 2, fitted with an inflatable airlock, launched with Alexei Leonov and Pavel Belyayev aboard. Leonov pushed out to the end of his tether and looked down at the Earth, but his suit ballooned in vacuum, and after returning he had entered the airlock head-first and got stuck sideways; he only freed himself by bleeding his suit down below safety limits. His body temperature rose 1.8 degrees in twenty minutes. He did not report these difficulties over the radio, and Soviet state radio and television stopped broadcasting from the craft once the mission ran into trouble. TASS told the public he felt well, and the details emerged only after the mission ended. Nearly four years passed before the Soviets attempted another EVA.

The United States followed on June 3, 1965, when Edward White spent 21 minutes outside on Gemini 4. The first EVA crew transfer, between Soyuz 4 and Soyuz 5, came on January 16, 1969; almost nine years passed before a third Soviet EVA. Apollo 11's moonwalk on July 20, 1969 was the first surface EVA, and Al Worden made the first deep-space EVA on August 5, 1971, retrieving film canisters on the way home from the Moon.

Expansion of the technique

In 1973 the Skylab 2 crew used EVAs to free a jammed solar panel and deploy a sunshade, repairing a spacecraft in orbit for the first time. The Soviets resumed EVAs from Salyut 6 and Salyut 7 between 1977 and 1982, and on July 25, 1984, Svetlana Savitskaya and Vladimir Dzhanibekov welded and brazed metal outside Salyut 7, the first metalwork in open space; Savitskaya became the first woman to walk in space.

From the shuttle era, with life support carried in an Extravehicular Mobility Unit independent of the spacecraft, EVAs were increasingly used for construction and repair. Hubble servicing and the assembly of the International Space Station were performed this way, and China conducted its first independently carried out EVA from Shenzhou 7 in September 2008.

Hazards

EVAs are dangerous, both because orbital debris strikes at relative speeds that make even a fleck of paint lethal and because the space environment is hard to model in advance. Drifting away from the spacecraft, a damaged suit, or a punctured glove can be fatal. No death has yet been attributed to an EVA, but the risk remains real, and designers have long tried to reduce the need for outside work through remote-controlled robots. Korean usage often distinguishes 선외활동 (the general category) from 우주유영 (drifting clear of the hull).