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In science fiction, explosive decompression is occasionally used to slow down or provide a nudge for very large spacecraft (for instance, recently in the 2015 movie The Martian, and in this old Star Trek episode). It seems like the mass of the air in a spacecraft would be quite small in comparison to the spacecraft itself. Would such an event really be enough to substantially change the velocity vector of a spacecraft?

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Do a back of the envelope: At normal pressure the air has a density of approx. $1.2kg/m^3$ and it would escape at roughly the speed of sound i.e. $340m/s$. The interior volume of the ISS is approx. $900m^3$, i.e. the total momentum of the escaping air would be

$1.2kg/m^3\times 900m^3\times340m/s\approx 370,000kgm/s$.

The mass of the ISS is roughly 420,000kg, i.e. the delta-v would be slightly less than $1m/s$. That is so not worth blowing that hatch for...

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  • $\begingroup$ I'm curious why we know the air would escape at the speed of sound? $\endgroup$
    – adam.baker
    Sep 6 '19 at 15:49

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