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Given that the alloys (typically made of aluminum or titanium) are optimized for being as light and as durable as possible, what is the maximum pressure a rocket like the Falcon 9 would be designed to handle from the outside (considering a rocket as a pressurized cylindrical vessel)?

NOTE: This question is different as it focuses on the maximum pressure a human body can experience, not a rocket body. Also, if the maximum possible pressure a rocket body can experience and/or if that number isn't publicly available, please mention it.

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    $\begingroup$ Are you talking about the maximum dynamic pressure or are you considering rocket to be a pressurized cylindrical vessel ? $\endgroup$ – Amar Nov 21 '18 at 6:41
  • $\begingroup$ This question is too broad as written. You don't ask about maximum pressures historically experienced but what could conceivably ever happen. No one can answer that authoritatively. $\endgroup$ – Organic Marble Nov 21 '18 at 13:57
  • $\begingroup$ I'm trying to focus more on the maximum pressure a rocket is designed to handle, and I'm asking if such a number (which I assume would be found during the testing process) is calculated and/or if it is available to the public. $\endgroup$ – Vivek Nov 21 '18 at 14:27
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    $\begingroup$ and you're talking about pressure from outside influences? Not e.g. the pressure inside the combustion chamber, but on the outside of the propellant tanks? $\endgroup$ – Hobbes Nov 21 '18 at 14:32
  • $\begingroup$ slightly related: Just how much can tall skinny rockets bend? (roughly, safely) $\endgroup$ – uhoh Nov 21 '18 at 15:09
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For this purpose, you can divide a rocket into 3 areas:

  • Non-pressurized sections (like the section that contains the engines). These are vented, so there's no pressure difference between inside and outside
  • Tank sections. These are typically pressurized to a few bar (in the region of 5-10 bar), with a safety factor of 1.2-1.3. So they should be good to about 10 bar of internal pressure. Atmospheric pressure never gets this high, so the outside pressure isn't really a design parameter for the tanks.
  • Habitable sections. These are usually pressurized to 1 bar, with a safety factor (1.3, maybe higher?), so you'll run into trouble above ~2.3 bar of external pressure.

The highest external pressure the rocket encounters during its flight is before takeoff, at sea level, at 1 bar (100 kPa).

At max-Q, dynamic pressure is in the region of 30 kPa at an altitude of 10 km, where air pressure is ~25 kPa, so total pressure is 55 kPa.

The largest amount of stress on the rocket occurs in orbit, where the outside is at 0 Pa and the habitat and fuel tanks are still pressurized to their original values.

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  • $\begingroup$ This is a good answer, but not to the question. It asks what is the maximum a rocket could encounter, which is really not answerable. $\endgroup$ – Organic Marble Nov 21 '18 at 13:24
  • $\begingroup$ @Hobbes Reading your answer it seems that max-Q, with a total pressure of 55kPa is not really a challenge to the rocket structure, given that before take-off pressure is around 100kPa. So why is it so important max-Q? A quick look at Wikipedia says that dynamical pressure is what really counts for "aerodynamic structural load". Maybe some words should be spent on this. This is because even if the question doesn't say "dynamical pressure", it explicitly says how much pressure a rocket is designed to handle - and I guess rockets are designed to handle a certain "dynamical pressure" (my guess). $\endgroup$ – BlueCoder Nov 21 '18 at 15:18
  • $\begingroup$ @Hobbes I will put it in another way: by reading your answer, one might assume that rocket can withstand 100kPa outside pressure (they do it before take-off). However, if the pressure from the outside would be 25kPa of air pressure plus 75kPa of dynamic pressure (instead of the normal 30kPa) the rocket might fail, even though the sum is still 100kPa (my guess - I don't know the safety factor, I'm just assuming that an unexpected more than double the normal dynamical pressure wouldn't be within limits). $\endgroup$ – BlueCoder Nov 21 '18 at 15:25
  • $\begingroup$ Discussion of structural loading due to Max-Q: space.stackexchange.com/questions/22221/… $\endgroup$ – Hobbes Nov 21 '18 at 15:33

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