What if an astronaut went on a space walk without wearing a space suit?

By: Marshall Brain  | 
An astronaut performing a space walk.
Performing a space walk without a suit will kill you in seconds. Marc Ward/Stocktrek Images / Getty Images/Stocktrek Images

Key Takeaways

  • Without a spacesuit in space, you would become unconscious within 15 seconds due to lack of oxygen.
  • Your blood and body fluids would boil and then freeze because of the extremely low air pressure, and your tissues would expand from the boiling fluids.
  • You would face extreme temperatures and radiation exposure, and you could be hit by high-speed micrometeoroids or orbiting debris.

The current space suit that's used for spacewalking from the shuttle and International Space Station is called the Extravehicular Mobility Unit or EMU. Because an Earth-like environment is created within the suit itself, a space suit allows you to walk around in space in relative safety. Space suits provide:

  • Pressurized atmosphere - The space suit provides air pressure to keep the fluids in your body in a liquid state -- in other words, to prevent your bodily fluids from boiling. The pressure in the suit is much lower than normal air pressure on Earth (4.3 versus 14.7 PSI) so that the suit doesn't balloon and so that it's as flexible as possible.
  • Oxygen - Space suits must supply pure oxygen, because of the low pressure. Normal air -- 78 percent nitrogen, 21 percent oxygen and 1 percent other gases -- would cause dangerously low oxygen concentrations in the lungs and blood at this low pressure.
  • Regulated temperature -- To cope with the extremes of temperature, most space suits are heavily insulated with layers of fabric (Neoprene, Gore-Tex, Dacron) and covered with reflective outer layers (Mylar or white fabric) to reflect sunlight.
  • Protection from micrometeroids -- Space suits have multiple layers of durable fabrics such as Dacron or Kevlar. These layers prevent the suit from tearing on exposed surfaces of the spacecraft.


What would happen to your body?

The elements in space will kill you within seconds. See more space suit images.
©2007 Microsoft Corporation

Outer space is an extremely hostile place. If you were to step outside a spacecraft such as the International Space Station, or onto a world with little or no atmosphere, such as the moon or Mars, and you weren't wearing a space suit, here's what would happen:

  • You would become unconscious within 15 seconds because there's no oxygen.
  • Your blood and body fluids would boil and then freeze because there is little or no air pressure.
  • Your tissues (skin, heart, other internal organs) would expand because of the boiling fluids.
  • You would face extreme changes in temperature: Shade: -148°F (-100°C); Sunlight: 248°F (120°C)
  • You would be exposed to various types of radiation, such as cosmic rays, and charged particles emitted from the sun (solar wind).
  • You could be hit by small particles of dust or rock that move at high speeds (micrometeoroids) or orbiting debris from satellites or spacecraft.

The human body could tolerate a complete vacuum for a few seconds at the most. So in the scene in "2001: A Space Odyssey" where Dave ejects from the pod into the vacuum of space and dives for the space station -- that might actually work. But beyond a few seconds, things would get ugly fast.