Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!mitel!sce!cognos!geovision!alastair
From: alastair@geovision.uucp (Alastair Mayer)
Newsgroups: sci.space
Subject: Re: Supersonic aircraft and noise pollution
Message-ID: <533@geovision.UUCP>
Date: 29 Jan 89 20:08:24 GMT
References: <8901240814.AA07708@cmr.icst.nbs.gov> <2556@daisy.UUCP>
Reply-To: alastair@geovision.UUCP (Alastair Mayer)
Organization: GeoVision Corp, Ottawa, Canada
Lines: 25

In article <2556@daisy.UUCP> wooding@daisy.UUCP (Mike Wooding) writes:
>In article <8901240814.AA07708@cmr.icst.nbs.gov>, roberts@CMR.ICST.NBS.GOV (John Roberts) writes:
>> 
>> Surely an SR-71 at surveillance altitude doesn't sound too loud from
>> the ground - that would spoil the surprise (:-)
>
> Since it can and probably does fly at several times the speed
> of sound when spying, it probably doesn't matter how loud it is.
> It's been gone long time when it's heard on the ground.

For those that want a quantitative analysis, figure the Blackbird is
going Mach 3 at >70,000'  (although it's generally beleived that the
SR-71 will do Mach 4 and >80,000 feet, these figures aren't officially
confirmed).   By the time it takes the sound the more than a minute
to reach the ground from 70K feet, the plane is 3*70 K feet (horizontal
distance) from where it was when the sound started -- about 40 miles.

Like the man said, it's been gone a long time when it's heard on the ground.
In any case, the boom is going to be somewhat attenuated after travelling
that far.
-- 
"The problem is not that spaceflight is expensive,  | Alastair J.W. Mayer
therefore only the government can do it, but that   | alastair@geovision.UUCP
only the government is doing spaceflight, therefore | al@BIX
it is expensive."                                   |