Spacesuit Requirements

a. A space suit must perform several functions to allow its occupant to work safely and comfortably. It must provide:
A stable internal pressure. This can be less than earth's atmosphere, as there is usually no need for the spacesuit to carry nitrogen. Lower pressure allows for greater mobility, but introduces the requirement of pre-breathing to avoid decompression sickness.

b. Mobility. Movement is typically opposed by the pressure of the suit; mobility is achieved by careful joint design. See the Theories of spacesuit design section.

c. Breathable oxygen. Circulation of cooled and purified oxygen is controlled by the Primary Life Support System.

d. Temperature regulation. Unlike on Earth, where heat can be transferred by convection to the atmosphere, in space heat can only be lost by thermal radiation or by conduction to objects in physical contact with the space suit. Since the temperature on the outside of the suit varies greatly between sunlight and shadow, the suit is heavily insulated, and the temperature inside the suit is regulated by a Liquid Cooling Garment in contact with the astronaut's skin, as well as air temperature maintained by the Primary Life Support System.

e. Shielding against ultraviolet radiation
f. Limited shielding against particle radiation
g. Protection against small micrometeoroids, provided by a Thermal Micrometeoroid Garment, which is the outermost layer of the suit

h. A communication system
i. Means to recharge and discharge gases and liquids
j. Means to maneuver, dock, release, and/or tether onto spacecraft
k. Means of collecting and containing solid and liquid waste (such as a Maximum Absorbency Garment)