Re: Satellites making supersonic noises.

From: Tony Beresford (starman@camtech.net.au)
Date: Sun Jun 04 2000 - 01:12:07 PDT

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    At 16:09 4/06/00 , RocketKevin@netscape.net wrote:
    >The question has popped in and out of my mind for many years is do
    >very Low Orbiting satellites make supersonic noises until I saw a very fast pass of #13576 over my friends house recently.about 25 seconds after the
    >pass there was a very soft to medium noise almost like a supersonic jet.
    Kevin, firstly a question of applying the right names. Supersonic
    just means fast than sound, nothing else. In relation to your question
    I assume you meant ultasonic, the sound equivalent of ultraviolet,
    the high pitched sounds we humans cant hear ( > 20 kilohertz for most of
    us, and > 14khz for me)
    The upper atmosphere is too low a densiy to progogate sound waves in the
    audible range when you get above 30,000 metres ( 100,000 feet). The circumstances
    are even worse for ultrasonic frequencies. 
    This is shown by the observations that only meteoroids that penetrate below
    this height make a sonic boom.Since the satellite you mentioned would have been
    at at least 150Km, it seems unlikely to be source of the whooshing sound you heard.
    The length of the time delay you quoted is really what kills your
    explanation though. A delay of 25 seconds implies a distance of some 9Km,
    as the speed of sound is about 330 meters/second. 
    Tony Beresford
    
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