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Q. Why do astronauts wear space suits? — Doug A.
A. To be able to live in Space.
Human beings must take their environment with them when they fly in Space, because:
  • There is no atmospheric pressure Out There and no oxygen to sustain life,

  • The range of temperatures in Outer Space is extreme,

  • Radiation in the Space environment is very dangerous,

  • High-speed micrometeoroids bombard objects in Space.
How extreme is the temperature range? The outside of a spacesuit facing the Sun could be heated as high as 250 degrees Fahrenheit. On the other hand, when in the darkness of Deep Space, the outside of a spacesuit could be as cold as -250 degrees Fahrenheit. Back down here on Earth, our planet's atmosphere provides oxygen, filters out radiation from sunlight, stabilizes the temperature and shields against micrometeoroids.

So, a spacesuit supplies air to breathe, insulates the astronaut or cosmonaut from extreme temperatures and shields against radiation and tiny penetrating objects.

It's a different situation inside a spacecraft, of course. The inside atmosphere can be controlled so that special clothing isn't needed. Astronauts traveling in U.S. shuttles and cosmonauts working aboard the Mir space station wear flight suits, trousers, lined zipper jackets, knit shirts, sleep shorts, soft slippers, and more-or-less ordinary underwear.

Why is air pressure important?

  • Down on the surface of Earth and on up to about 60-75 miles altitude where Space begins, our planet's atmosphere is 20 percent oxygen and 80 percent nitrogen.

  • On the way up, at around four miles altitude, the atmosphere is half as dense as it is on the ground.

  • At eight miles above the surface of Earth, the air is so thin and the amount of oxygen so small you must wear a pressurized oxygen mask.

  • Above twelve miles altitude, the total air pressure is no longer sufficient to keep body fluids from boiling. So, humans must wear spacesuits that not only supply oxygen for breathing, but also maintain a pressure around the body to keep body fluids liquid.
Spacesuits provide atmospheric pressure.
  • Shuttle spacesuits are pressurized to 4.3 pounds per square inch (psi).

  • International Space Station spacesuits are to be pressurized to 8.3 psi.
The gas in a spacesuit is 100 percent oxygen, so the wearer has more oxygen to breathe than he or she would at sea level without the spacesuit. Before going outside a shuttle to work in space, an astronaut has to spend hours breathing pure oxygen. That removes nitrogen dissolved in body fluids and prevents its release as gas bubbles causing the "bends" when pressure is reduced. Space station spacesuits will be pressurized to 8.3 psi to shorten the amount of time spent in pre-spacewalk breathing of pure oxygen.

If you skip to NASA's Spacesuits Page you will learn more about spacesuits worn by shuttle astronauts.  »»

Right here in Space Today Online, learn more about astronauts living and working in Space.  »»



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