A
space suit is a garment worn to keep a human alive in the harsh environment of
outer space,
vacuum and temperature extremes. Space suits are often worn inside
spacecraft as a safety precaution in case of loss of cabin
pressure, and are necessary for
extravehicular activity (EVA), work done outside spacecraft. Space suits have been worn for such work in Earth orbit, on the surface of the
Moon, and en route back to Earth from the Moon. Modern space suits augment the basic pressure garment with a complex system of equipment and environmental systems designed to keep the wearer comfortable, and to minimize the effort required to bend the limbs, resisting a soft pressure garment's natural tendency to stiffen against the vacuum. A self-contained
oxygen supply and environmental control system is frequently employed to allow complete freedom of movement, independent of the spacecraft.