Wednesday, January 21, 2009

Do Your Ears Pop in Space?

Well…do they?

In my ongoing series of articles gleaned from the non-fiction book of the same name by shuttle astronaut R. Mike Mullane, I thought I should address the pressing question posed by the title. The answer? It depends.

Your ears pop when there’s a change in pressure, so generally the only time your ears would pop is if the mission includes a spacewalk or EVA (Extra Vehicular Activity). If there’s no EVA, the cabin pressure is kept at a constant 14.7 psi…so no pop. If there is an EVA, the cabin pressure is decreased a day before the exercise to 10.2 psi to reduce the possibility of the space-walker getting the bends—just like divers do if they ascend too quickly from the ocean depths—when exposed to the spacesuit’s lower psi of 4.3. The bends is caused when the nitrogen in the body comes out of solution due to pressure change.

But then, what about launch? People’s ears pop in an airliner on takeoff, so why wouldn’t they aboard a space shuttle that’s rocketing skyward? The answer again has to do with pressure. Airliners release air as they ascend. This is done so the pressure on the inside of the vessel does not continue to exert a lot of pressure as the plane climbs into thinner air, otherwise the fuselage would have to be much thicker, heavier, and more expensive to build. Because the air is released, the pressure changes inside the cabin, and this causes your ears to pop. Spacecraft are made to withstand the tremendous differences in pressure between the cabin and the vacuum of space, so air is not released as the craft climbs higher.

When passenger jets ascend, they reverse the process and let air back into the cabin. This is why your ears pop on the way down.

So how do you apply these facts to science fiction writing? My muse had a field day with this, because it seems a SFR pilot might become quite alarmed if their ears popped. To heck with sensors and indicators, if your ears pop and you’re in a space-tight craft, you have a definite problem! It would mean the cabin pressure had changed, possibly as the result of a hull breach or a bad airlock seal (although, granted, it would have to be a very tiny leak or they wouldn’t have time to worry about it.) Popping ears on a spacecraft is akin to a dead canary in a coal mine. Time for quick action and damage control.

So there you have it.

(Articles to be continued…)

2 comments:

  1. Well there you go, I knew the psi thing of spacesuits etc, but I didn't realise about the takeoff. Thanks for sharing.

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  2. Genius is in the details, as they say! Good stuff to know.

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