How does a scuba diver’s oxygen tank last for ~1 hour but an astronaut’s lasts ~6-8 hours when both tanks are around the same size?
In: Technology
Normal air is 78% Nitrogen (inert), 21% oxygen and 1% the rest (important part is carbon dioxide).
With a normal scuba setup, each time a diver takes a breath and exhales, all of the gas is expelled. That’s why you see all of the bubbles leaving the diver’s mouth. This wastes a lot of air. Also, the deeper the diver goes, the more air is needed for each breath – the ocean is pushing on them and more air pressure is needed for the diver to breathe easily. Every 10m / 33ft of depth needs another “atmosphere” amount of air for each breath.
With a space suit, the air is fully recirculated in the backpack. With each breath, only a portion of the oxygen is consumed and replaced by carbon dioxide. The space suit scrubs out carbon dioxide, removes moisture (humans breathe moistly) and a tiny bit of oxygen is put back in to replace what the body absorbed. Also, a space suit provides less air in each breath due to lower air pressure because outside is the vacuum of space, not a lot of water pushing on them. In this way, a space suit can last many hours.
Back in the scuba area, there are more advanced “rebreather” systems that do not dump all of the gas out with every breath, but they are more expensive, more complicated and not common in recreational diving. When diving with a group, everyone would need a rebreather or the dive is limited in length, and no-one wants to sit and wait on the surface for 3 hours after the dive. Navy seals use rebreathers.
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