Fluids: Liquids and Gases

Pressure in Gases

Gas Pressures in a Space Station and a Space Suit


Space capsules have higher air pressure than the near vacuum of space. Leaking always occurs from higher pressure to lower pressure. Thus, air will leak out of a spaceship or a spacesuit into space – that is a bad thing. As leaking occurs there will be a pressure decrease, since pressure is directly proportional to the number of molecules of a substance within a container. To keep the pressure steady, a new source of molecules to replace those that have leaked out is necessary. An oxygen tank is one way to provide extra molecules. Then, a spaceship or habitat or spacesuit can maintain its pressure, while the pressure within the supporting oxygen tank will decrease.

Space is nearly a vacuum with pretty much no air pressure, while the space station has a pressure about the same as Earth, 101,000 Pa. Exiting the International Space Station (ISS) to perform an extravehicular activity (EVA) – the fancy phrase for a space walk -  presents the same problem as when a SCUBA diver ascends from the higher pressure of deeper water to lower pressure, shallow water.


To avoid getting the bends - gases dissolved in the blood forming bubbles - astronauts spend several hours breathing pure oxygen and decompressing before a spacewalk. First, they work out while breathing 100% oxygen, to remove the nitrogen gas from their circulatory system. Next, they float into the Equipment Lock portion of the airlock containing the spacesuit. Here, the pressure is gradually lowered to 70,100 Pa. After donning their spacesuits–not a trivial process, since these suits weigh up to 136 kg (300 lbs) on Earth – they spend an additional 60 minutes breathing pure oxygen. After final checks for suit leaks the remaining air in the Crewlock–about 34,500 Pa – is vented to space. The astronauts then unlock the hatch and maneuver out to begin their EVA mission.


For More Information: Preparing for spacewalking is a lot of work, see Even Homes in Space Need a Door



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