Watching the series ‘The Expanse’ a spacecraft’s hatch was knocked open and the pressurised atmosphere was escaping. I thought it took an inordinately long time to decompress the spacecraft.
Accordingly I was hoping for some rough idea of exactly how quickly it would happen. If we think of a volume of 10m^3 how quickly would decompression happen given a 1m^2 hole?
Bloody fast.
That’s what i thought.
Witty Rejoinder said:
Watching the series ‘The Expanse’ a spacecraft’s hatch was knocked open and the pressurised atmosphere was escaping. I thought it took an inordinately long time to decompress the spacecraft.Accordingly I was hoping for some rough idea of exactly how quickly it would happen. If we think of a volume of 10m^3 how quickly would decompression happen given a 1m^2 hole?
I can calculate that. In the meantime, I’m sure that either the 10 m^3 or the 1 m^2 is unrealistic.
mollwollfumble said:
Witty Rejoinder said:
Watching the series ‘The Expanse’ a spacecraft’s hatch was knocked open and the pressurised atmosphere was escaping. I thought it took an inordinately long time to decompress the spacecraft.Accordingly I was hoping for some rough idea of exactly how quickly it would happen. If we think of a volume of 10m^3 how quickly would decompression happen given a 1m^2 hole?
I can calculate that. In the meantime, I’m sure that either the 10 m^3 or the 1 m^2 is unrealistic.
Well what craft is it? Shenzhou has an internal volume of 8 cu metres and the hatch is a little under a square metre.
Using Fleigner’s formula
t= 0.44 * V/(A * T^0.5) * ( ( p1/p2)^(1/7)-1)
p1 initial pressure
p2 final pressure
A area of hole
V volume
T initial temperature
t time
dv said:
Using Fleigner’s formulat= 0.44 * V/(A * T^0.5) * ( ( p1/p2)^(1/7)-1)
p1 initial pressure
p2 final pressure
A area of hole
V volume
T initial temperature
t time
Yes, but don’t take p2 = 0. Use something more realistic like p1 / p2 = 10 or p1 / p2 = 50.
dv said:
Using Fleigner’s formulat= 0.44 * V/(A * T^0.5) * ( ( p1/p2)^(1/7)-1)
p1 initial pressure
p2 final pressure
A area of hole in metres squared
V volume in metres cubed
T initial temperature in K
t time in seconds
So it will theoretically take forever to completely lose all gas but let us say we want the time until pressure is reduced by 99%.
Take A=1 square metres, V=10 cubic metres, T = 298 K
So I get 0.238 seconds.
This gels with my expectations. The air is going to shoot out of there at something like the speed of air molecules, which is like over 1000 km/h…
dv said:
So it will theoretically take forever to completely lose all gas but let us say we want the time until pressure is reduced by 99%.
Take A=1 square metres, V=10 cubic metres, T = 298 K
So I get 0.238 seconds.
This gels with my expectations. The air is going to shoot out of there at something like the speed of air molecules, which is like over 1000 km/h…
Which episode was that?
dv said:
Which episode was that?
1st I think.
Witty Rejoinder said:
dv said:
Which episode was that?
1st I think.
Just checked wikipedia. It was the 2nd episode.
dv said:
The air is going to shoot out of there at something like the speed of air molecules
Air does tend to do that.
Having watched the ep, I would estimate the interior colume of the shuttle to be between 50 and 100 cubic metres and the hatch to be maybe 3 sq metres. It took 45 seconds for them to seal the hwtch.
But the thing is, the problem was that debris had breach the exterior doors of the airlock. Even with the hatch open, the limiting factor is going to be size of that puncture, which is not shown in detail.
dv said:
But the thing is, the problem was that debris had breach the exterior doors of the airlock. Even with the hatch open, the limiting factor is going to be size of that puncture, which is not shown in detail.
Okay. It was a little more complex than I thought then. Thanks.
dv said:
Having watched the ep, I would estimate the interior colume of the shuttle to be between 50 and 100 cubic metres and the hatch to be maybe 3 sq metres. It took 45 seconds for them to seal the hwtch.But the thing is, the problem was that debris had breach the exterior doors of the airlock. Even with the hatch open, the limiting factor is going to be size of that puncture, which is not shown in detail.
So, now calculate the size of the puncture from the spacecraft volume and time to decompress.
mollwollfumble said:
dv said:
Having watched the ep, I would estimate the interior colume of the shuttle to be between 50 and 100 cubic metres and the hatch to be maybe 3 sq metres. It took 45 seconds for them to seal the hwtch.But the thing is, the problem was that debris had breach the exterior doors of the airlock. Even with the hatch open, the limiting factor is going to be size of that puncture, which is not shown in detail.
So, now calculate the size of the puncture from the spacecraft volume and time to decompress.
Well now, I don’t know what the final to initial pressure ratio is.
I mean people were still able to function without difficulty but I mean people can even hold their breath longer than that. They showed no signs of discomfort so I suppose we could say that the final pressure was unlikely to have been less than a third the initial pressure, but it could, for all we know, be 99% of the initial pressure.
BTW, looks like a good old hard sci fi show. Very Asimovian: all politics and conventional physics. And you gotta love Shohreh Aghdashloo.
dv said:
BTW, looks like a good old hard sci fi show. Very Asimovian: all politics and conventional physics. And you gotta love Shohreh Aghdashloo.
I liked it, interesting how people suffer from a lack of gravity related and how medicine is either extremely expensive or they are denied access to it.
I think I done fucked this up. Stand by for corrections.
dv said:
I think I done fucked this up. Stand by for corrections.
tap, tap, tap …
The pressure’s on, no pun intended
Nah … looks like that’s right. False alarm.
dv said:
Nah … looks like that’s right. False alarm.
*NASA breathes sigh of relief *
I was just looking at that 7 and thinking fuck, that’s weird … 7? Is that supposed to be gamma (γ)?
But a bit of rough modelling makes the answers look reasonable.