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A space suit is protective clothing that astronauts wear when they are outside a spacecraft. This suit provides them with air and water while protecting them from radiation, flying debris, and temperature extremes. If need be, the space suit also functions as a mini spacecraft, allowing the astronaut to get back to the space craft or space station if he becomes separated. In order to protect astronaut's eyes from the sun, a special visor is attached to the helmet. These suits are also known as extravehicular mobility units, or EMUs.
To keep the astronaut alive, a special backpack called a primary life support subsystem is provided. This backpack provides oxygen to the astronaut while he is outside the spacecraft and disposes of carbon dioxide as it is exhaled. The backpack also houses a water tank for cooling and generates electricity for the space suit.
Another component of the suit is an attachment that transforms the space suit into a small jet. This is called the simplified aid for extravehicular activity rescue, or SAFER. A SAFER is a precautionary measure that allows the astronaut to get back to the spacecraft or space station if for some reason he becomes separated from it.
The space suit must protect the astronaut from many environmental extremes. Astronauts face temperatures that range 250 degrees Fahrenheit (120 degrees Celsius) to a frigid -250 degrees Fahrenheit (-160 degrees Celsius). A space suit is composed of many layers of specialized fabric, including high strength composite materials, ortho-fabric, dacron, nylon/spandex, neoprene-coated nylon, urethane-coated nylon, tricot, aluminized mylar, and stainless steel.
Each part of the space suit is made separately and then joined together. The chest or upper body of the astronaut is covered with a unit that is made from hard materials. For arm and hand coverings, softer, more pliable fabrics are used to allow greater range of motion. For the head, a specialized helmet is designed to protect the head, while allowing for as much visibility as possible. The lower half of the suit covers the legs and feet.
Astronauts do not wear regular clothing underneath a space suit, they wear specially designed garments that have tubes woven into the fabric. This clothing covers and keeps the body cool by pumping water through the tubes. It fits the astronaut's body very tightly but does not cover the head, hands or feet.