This article is about something any space enthusiast would have seen many times – the complex looking space-suit.
A space suit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Spacesuits 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.
Three types of spacesuits exist for different purposes –
IVA (intravehicular activity), EVA (extravehicular activity), and IEVA (Intra/extravehicular activity).
IVA suits are meant to be worn inside a pressurized spacecraft and are therefore lighter and more comfortable. SpaceX Spacesuit is one example of an IVA suit.
IEVA suits are meant for use inside and outside the spacecraft, such as the Gemini G4C suit. They include more protection from the harsh conditions of space, such as protection from micrometeorites and extreme temperature change.
EVA suits, such as the EMU, are used outside spacecraft, for either planetary exploration or spacewalks. They must protect the wearer against all conditions of space, as well as provide mobility and functionality.
The first full-pressure suits for use at extreme altitudes were designed by individual inventors as early as the 1930s. The first space suit worn by a human in space was the Soviet SK-1 suit worn by Yuri Gagarin in 1961.
A space suit must perform several functions to allow its occupant to work safely and comfortably, inside or outside a spacecraft. It must provide:
A stable internal pressure. This can be less than Earth’s atmosphere, as there is usually no need for the space suit to carry nitrogen (which comprises about 78% of Earth’s atmosphere and is not used by the body). Lower pressure allows for greater mobility but requires the suit occupant to breathe pure oxygen for a time before going into this lower pressure, to avoid decompression sickness.
Mobility. Movement is typically opposed by the pressure of the suit; mobility is achieved by careful joint design. See the Theories of space suit design section.
Supply of breathable oxygen and elimination of carbon dioxide; these gases are exchanged with the spacecraft or a Portable Life Support System (PLSS)
Temperature regulation. Unlike on Earth, where heat can be transferred by convection to the atmosphere, in space, heat can be lost only by thermal radiation or by conduction to objects in physical contact with the exterior of the suit. Since the temperature on the outside of the suit varies greatly between sunlight and shadow, the suit is heavily insulated, and air temperature is maintained at a comfortable level.
A communication system, with an external electrical connection to the spacecraft or PLSS
Means of collecting and containing solid and liquid bodily waste.
You can check these answers written by a retired US Astronaut on Quora – https://qr.ae/TWyb0Q