Security 'necessities' for Spaceships

lwcamp · 12-03-2009, 12:08 PM

I will note that a bullet hole in a spacecraft pressure hull is not all that big of a deal. In a compartment about the size of a typical bedroom (3 m wide x 4 m long x 2.5 m high), a 1 square centimeter hole will cause the pressure to fall by half in about 5 minutes. That is plenty of time to finish the firefight and slap an emergency patch over the hole. The air pressure will push the patch tighter against the hole, so even stray bits of debris larger than the bullet hole will tend to significantly slow the loss of air, actual engineered emergency patches with rubber seals behind a rigid plate should essentially stop the air leak until the spacecraft's engineer can apply a permanent fix.

This is certainly a better option than being at the mercy of thugs with body armor.

Now you just need to convince your GM of this. It is one of those "facts" about space that does continue to annoy me, though.

The sidearms section on the Atomic Rocket web page http://www.projectrho.com/rocket/ is gives lots of useful thoughts on weapons carried aboard spacecraft.

The Math: Air moving from a pressure reservoir into vacuum will be ejected at approximately the speed of sound, or C_s = 330 m/s. With a hole of area A and in a time T, a volume V_a of air V_a=A*C_s*T will escape. The room has a volume of V_r. Thus, at a time T=V_r/(A*C_s), the amount of air that escapes through the hole is equal to the amount of air in the room. Plugging in the numbers, V_r = 3 m x 4 m x 2.5 m = 15 m^3, A=0.0001 m^2, and we find T=454 seconds=7.6 minutes.

This ignores that as the air escapes, the pressure drops and the speed of escape decreases, which extends the available time. A more detailed analysis gives a pressure P=1 atm * exp(-T/454 s). Set P=0.5 atm for a loss of half the air, and you find T=315 seconds=5.25 minutes.

Luke

12-03-2009, 12:08 PM	#14
lwcamp Join Date: Nov 2004 Location: The plutonium rich regions of Washington State	Re: Security 'necessities' for Spaceships I will note that a bullet hole in a spacecraft pressure hull is not all that big of a deal. In a compartment about the size of a typical bedroom (3 m wide x 4 m long x 2.5 m high), a 1 square centimeter hole will cause the pressure to fall by half in about 5 minutes. That is plenty of time to finish the firefight and slap an emergency patch over the hole. The air pressure will push the patch tighter against the hole, so even stray bits of debris larger than the bullet hole will tend to significantly slow the loss of air, actual engineered emergency patches with rubber seals behind a rigid plate should essentially stop the air leak until the spacecraft's engineer can apply a permanent fix. This is certainly a better option than being at the mercy of thugs with body armor. Now you just need to convince your GM of this. It is one of those "facts" about space that does continue to annoy me, though. The sidearms section on the Atomic Rocket web page http://www.projectrho.com/rocket/ is gives lots of useful thoughts on weapons carried aboard spacecraft. The Math: Air moving from a pressure reservoir into vacuum will be ejected at approximately the speed of sound, or C_s = 330 m/s. With a hole of area A and in a time T, a volume V_a of air V_a=AC_sT will escape. The room has a volume of V_r. Thus, at a time T=V_r/(AC_s), the amount of air that escapes through the hole is equal to the amount of air in the room. Plugging in the numbers, V_r = 3 m x 4 m x 2.5 m = 15 m^3, A=0.0001 m^2, and we find T=454 seconds=7.6 minutes. This ignores that as the air escapes, the pressure drops and the speed of escape decreases, which extends the available time. A more detailed analysis gives a pressure P=1 atm exp(-T/454 s). Set P=0.5 atm for a loss of half the air, and you find T=315 seconds=5.25 minutes. Luke