The air pressure within a space station or spacecraft is maintained equivalent to that on the Earth’s surface, allowing astronauts to carry out normal activities and movement. However, when they need to exit the spacecraft for a specific task in outer space, they are required to wear specialized suits and undergo a 3-hour oxygen pre-breathing protocol before stepping into the vacuum of space. This is to prevent the onset of illnesses caused by the reduced pressure in space.
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What is decompression sickness, and how does breathing oxygen prevent it?
Inside the spacecraft, the air pressure is maintained at a level similar to that on the Earth’s surface, which amounts to approximately 9.8 newtons per square centimeter. With an adult’s body surface area of around 2 square meters, the body would experience a pressure of about 196,000 newtons. However, on Earth, we don’t perceive this pressure because the pressure within our bodies balances it. If the external pressure drops significantly, the gases dissolved in our body fluids (mostly nitrogen) will transform into gas bubbles throughout the body’s circulatory system.
Apart from causing joint pain, more seriously, nitrogen bubbles can obstruct veins and arteries. When these bubbles appear in the brain, they can lead to strokes and seizures. Bubbles in the heart can result in acute heart failure and even death.
While spacefarers wear space suits when venturing into outer space, these suits provide a certain level of atmospheric pressure. However, due to current technical limitations, the suit’s pressure is only about one-third of what is experienced within the spacecraft (equivalent to an altitude of 9-10 km in Earth’s atmosphere). Ground experiments have demonstrated that from an altitude of 8 km and above, humans can develop decompression sickness. Therefore, astronauts need to breathe oxygen before exiting the spacecraft to eliminate nitrogen from their tissues and fluids, preventing decompression sickness. This enables them to successfully carry out tasks outside the spacecraft.