lds
02-May-2003, 06:23 PM
You said the photo of the shuttle exploding snagged from Armageddon was "real enough." I read your review of The A-Team in Outer Space (as I retitled the film) and I found a glaring omission of one of my major peeves. That is, you don't get explosions or flames in space.
The billowing clouds you see from an explosion are caused by the earth's atmosphere compressing in on the outrushing gas of the explosion. That produces a bounded front. As the explosion expands, it's pressure drops since it is a finite amount of matter (albeit gaseous) filling a larger and larger volume. "Do the math." As the cloud or flame front doubles its volume goes up 8 times and the pressure drops to 1/8 of the previous value. When it expands 4 times its volume has increased 64 times and its pressure to 1/64. The explosion's cloud slows and stops when it equals the atmospheric pressure.
In space the careering gas molecules would act individually, like tiny shotgun pellets. Nothing stops their scattering. Any light from the flame would be very close to the center of the explosion. In a couple feet the molecules would no longer collide and thus be forced to give off energy as light and heat.
Similarly a flame is compressed by the atmospere pushing back, containing it and making the leaf shape of a candle flame. Some of the flame of an oxy-acetylene torch is caused by the atmospheric pressure. That is, the hot carbon, hydrogen and acetylene molecules and the oxygen molecules are not flying out freely but contained in a volume where they are likely to meet and combine. In a vacuum they would only have a lottery-like chance of meeting and much would fly off uncombined.
In 2001 it is a bit disturbing to watch the ships moved by their rockets and see no flame, but that is correct. You would only see the flame when looking directly into the blast chamber where the walls of the rocket motor provide compression to force the gases to meet.
IIRC, Silent Running showed the nuclear explosion quickly turn to a shower of fragments. That was also correct.
Because I knew these things, one of my major "suspension of disbelief" problems was that despite the spacesuits I could never imagine that they were in a vacuum.
The billowing clouds you see from an explosion are caused by the earth's atmosphere compressing in on the outrushing gas of the explosion. That produces a bounded front. As the explosion expands, it's pressure drops since it is a finite amount of matter (albeit gaseous) filling a larger and larger volume. "Do the math." As the cloud or flame front doubles its volume goes up 8 times and the pressure drops to 1/8 of the previous value. When it expands 4 times its volume has increased 64 times and its pressure to 1/64. The explosion's cloud slows and stops when it equals the atmospheric pressure.
In space the careering gas molecules would act individually, like tiny shotgun pellets. Nothing stops their scattering. Any light from the flame would be very close to the center of the explosion. In a couple feet the molecules would no longer collide and thus be forced to give off energy as light and heat.
Similarly a flame is compressed by the atmospere pushing back, containing it and making the leaf shape of a candle flame. Some of the flame of an oxy-acetylene torch is caused by the atmospheric pressure. That is, the hot carbon, hydrogen and acetylene molecules and the oxygen molecules are not flying out freely but contained in a volume where they are likely to meet and combine. In a vacuum they would only have a lottery-like chance of meeting and much would fly off uncombined.
In 2001 it is a bit disturbing to watch the ships moved by their rockets and see no flame, but that is correct. You would only see the flame when looking directly into the blast chamber where the walls of the rocket motor provide compression to force the gases to meet.
IIRC, Silent Running showed the nuclear explosion quickly turn to a shower of fragments. That was also correct.
Because I knew these things, one of my major "suspension of disbelief" problems was that despite the spacesuits I could never imagine that they were in a vacuum.