To be able to explore and work in space, humans have to take their environment with them because there is no atmosphere to supply the pressure and oxygen necessary to support life. Without sufficient atmospheric pressure, body fluids will start to heat up and boil. Without oxygen, we would be unable to breathe.
Spacesuits serve many functions. Today's spacesuits are pressurized, have an oxygen supply, protect the astronaut from micrometeoroid bombardment while spacewalking, and insulate the astronaut from the severe temperature changes experienced in space.
The Space Shuttle astronauts have more than one “outfit” for space travel. What they wear while on a mission is determined by the job they are doing. During the launch and re-entry, the astronauts wear a partially pressurized suit and a parachute pack. The suit has a helmet, gloves, and boots which all serve as protection for the astronaut. Within the suit are bladders that automatically fill with air at reduced cabin pressures. At low pressure, the blood will pool in the lower body causing the astronaut to black out. The bladders maintain the pressure on the lower body to prevent this from happening. While working in the Shuttle during orbit, astronauts work in comfortable clothes such as knit shirts, pants, or flight suits. In addition, prior to each mission, flight crews are outfitted with lined jackets, sleep shorts, slippers, and underwear.
While working outside of the Shuttle during a mission, astronauts wear an extravehicular mobility unit (EMU). This suit has interchangeable parts so it can be assembled to fit different astronauts. This makes the suit more cost effective since it can be reused. The EMU has a liquid cooling garment, which is a one piece suit made of spandex, and keeps the astronaut cool while in the suit. The unit also contains headphones and microphones, a drink bag which carries water, a life support system containing oxygen, and a urine collection device. Gloves are included with the unit along with a helmet and a visor. All of this is necessary to protect the astronaut from micrometeoroids, solar radiation, infrared radiation, temperature changes, pressure changes, and oxygen deprivation.
To help the astronaut get around freely while performing a spacewalk, a manned maneuvering unit (MMU) can be attached to the EMU. The MMU is a nitrogen propelled backpack that allows the astronaut to fly with precision. The MMU has a 35mm camera attached to it so that the astronaut can take pictures while in flight.