A space suit is clothing worn to keep a human alive in the harsh conditions of space, vacuum and temperature extremes. Space suits are often worn inside the spacecraft as a precaution in the event of pressure loss in the cabin, and they are necessary for working outside the body (EVA), work performed outside the spacecraft. Space suits were worn for such work in Earth orbit, on the surface of the Moon and on the way back to Earth from the Moon. Modern space suits complement basic clothing under pressure with a sophisticated equipment system and environmental protection systems designed to provide user comfort and minimize the effort required to bend limbs, counteracting the natural tendency of soft-pressure clothing to press against the vacuum. Often, to provide complete freedom of movement, regardless of the spacecraft, an autonomous system of oxygen supply and environmental control is often used.

There are three types of spacesuits for different purposes: IVA (intra-exit activity), EVA (extra-stellar activity) and IEVA (intra / extra-stellar activity). IVA suits are designed to be worn inside a spaceship under pressure, so they are lighter and more comfortable. IEVA suits are intended for use inside and outside the spacecraft, such as the Gemini G4C suit. They include more protection against harsh space conditions, such as protection against micrometeorites and extreme temperature changes. EVA suits, such as EMUs, are used outside the spacecraft, either for planet exploration or for spacewalks. They must protect the wearer from any space conditions, as well as provide mobility and functionality.

Some of these requirements also apply to spacesuits designed to perform other specialized tasks, such as high-altitude reconnaissance flight. At heights above Armstrong’s limit, about 19,000 m (62,000 ft), water boils at body temperature and suits are required under pressure.

The first full-pressure suits for use at extreme heights were developed by individual inventors back in the 1930s. The first spacesuit worn by man in space was the Soviet SK-1 suit, which Yuri Gagarin wore in 1961.

The space suit must perform several functions so that its occupant can safely and comfortably work inside or outside the spacecraft. It should provide:

Stable internal pressure. This may be less than in the Earth’s atmosphere, since there is usually no need to transfer nitrogen in the spacesuit (which is about 78% of the Earth’s atmosphere and is not used by the body). Lower pressure provides greater mobility, but requires the occupant to breathe pure oxygen for a while before entering this lower pressure to avoid decompression sickness.

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