I remember seeing several instances where spacecraft (i.e. ISS) had small holes in them and they were fine (NASA even didn’t wake astronauts once). Since the pressure difference is so great (space is a vacuum), how come there’s no explosive decompression (all the air is sucked out at once)?
In: Physics
You are correct the pressure “difference” is great, but only in terms of ratio. In fact the ratio of pressures inside and out tends to infinity. But a phenomenon of fluid flows named “choking” puts a limit to how much of the air inside the craft can leave the hole per second, for a given size of hole.
As the pressure ratio grows between inside and outside, gas indeed starts to leave faster and faster. However for a high enough pressure ratio (only about 2 for air!) the gas will reach the speed of sound and you get something called a choked throat. Because any gas leaving the hole then goes faster than sound, it actually has no way to tell the air still inside to leave faster- the expansion wave telling air it hits to go faster just flies away from the spacecraft!
So, even though there is an almost infinite ratio in pressures inside and out, the mass flow is restricted by the usually small size of the hole. The hole doesn’t break open because the pressure difference (not ratio) is not enough to break the strong and rigid material. Spacecraft aren’t balloons!
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