A space suit is a garment that is used to keep a human alive in the harsh environment of outer space, emptiness and extreme temperatures. Space suits are often used within the spacecraft as a safety precaution in case of loss of cabin pressure, and are necessary for extra-vehicular activity, work performed outside the spacecraft.
Space suits have been used for such work in the orbit of the Earth, on the surface of the Moon and on the way back to Earth from the Moon. Modern space suits increase the basic pressure garment with a complex system of environmental equipment and systems designed to keep the user comfortable, and to minimize the effort required to bend the limbs, resisting the natural tendency of the soft pressure garment to harden against the vacuum.
Frequently an autonomous system of oxygen supply and environmental control is used to allow complete freedom of movement, independently of the spacecraft.
There are three types of space suits for different purposes: VAT, EVA and IEVA. VAT suits are meant to be used inside a pressurized spaceship, and therefore are lighter and more comfortable.
The IEVA suits are designed to be worn inside and outside the spaceship, such as the Gemini G4C suit. They include more protection against the harsh conditions of the space, like protection against micrometeorites and extreme changes of temperature.
EVA suits, such as the EMU, are worn outside the spacecraft, either for planetary exploration or spacewalks. They must protect the user against all space conditions, as well as provide mobility and functionality.
Some of these requirements also apply to pressure suits used for other specialized tasks, such as high altitude reconnaissance flight. At altitudes above Armstrong’s limit, around 19,000 m, water boils at body temperature and pressurized suits are needed.
The first high-pressure suits for use at extreme altitudes were designed by individual inventors as early as the 1930s. The first space suit used by a human in space was the Soviet SK-1 suit worn by Yuri Gagarin in 1961.
A space suit should allow the user a natural movement without obstacles. Almost all designs try to maintain a constant volume regardless of the movements that the user makes. This is because mechanical work is needed to change the volume of a constant pressure system. If bending a joint reduces the volume of the space suit, then the astronaut must do extra work each time the joint is bent, and must maintain a force to keep the joint flexed. Even if this force is very small, it can be very tiring to constantly fight against the suit itself. It also makes delicate movements very difficult. The work required to bend an articulation is dictated by the formula.