Ear plugs?
jd
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of Nels Anderson
Sent: vrijdag 30 september 2016 16:06
To: arocket@xxxxxxxxxxxxx
Subject: [AR] BFR Noise
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.
