[AR] Re: BFR Noise
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: arocket <arocket@xxxxxxxxxxxxx>
- Date: Fri, 30 Sep 2016 19:08:36 -0400 (EDT)
On Fri, 30 Sep 2016, David Summers wrote:
My understanding was that the shuttle had an area off the coast where
the shock waves were actually lethal, and that they had to make sure was
clear before launch.
Not lethal, I believe, but definitely loud -- a significant concern for
anyone planning to eventually launch over land. However, Elon is talking
about launch over water; the problem is the boom from the *return*.
The problem is that if you fly in an arch, you focus the shockwave into
a small area.
Possibly you could alter the ascent trajectory and acceleration profile,
at some penalty in efficiency, to reduce the focusing; I don't think the
matter has ever really been explored. As I recall, shaping the *vehicle*
doesn't help much, because by that time much of the shock wave is actually
coming off the exhaust plume (the engines being, by then, very much
underexpanded, so the plume expands sideways rapidly and is much larger
than the vehicle).
Henry
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