Just wondering whether SpaceX's BFR could actually be launched from Cape
Canaveral, given how noisy it would be.
As a first approximation, I would think acoustic power would scale as
jet power. Neglecting the fact that nozzles are usually slightly
over-expanded at sea level, this would mean acoustic power scaling as
the product of thrust and Isp. Per Musk's IAC slides, the BFR will have
3.6 times the take-off thrust of the Saturn V. Isp will be 334 s, as
opposed to the Saturn's 265 s. That gives a power ratio of 4.5.
But provisions were made in the design of LC-39 for rockets larger than
the Saturn. To my knowledge, the largest vehicle seriously considered
was the MLV-23(L), which would have had four liquid strap-ons with two
F-1's each for a total of thirteen F-1's. The BFR's thrust is 1.4 times
the 23(L)'s, and the acoustic power is 1.75 times.
If the acoustic intensity follows an inverse-square law, then the BFR's
window-shattering radius is 1.3 times the 23(L)'s. Of course, since the
early 60's, population density has grown and regs likely tightened. And
Musk speaks of multiple launches daily rather than a few per year. And
low-level clouds reflect sound, invalidating the inverse-square
assumption (if Musk wants to launch with high frequency, weather
constraints will have to be loose).
Are there any mitigating factors? Might the gas-on-gas Raptor be
fundamentally quieter than the liquid-on-liquid F-1? I recall a claim
by Firestar that mixing affects noise.
