Velocity/duration of re-entries

From: Ed Cannon (
Date: Mon Dec 03 2001 - 00:54:39 EST

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    A while ago I got to see local TV news show video of the Proton 
    re-entry yesterday.  I don't know if they were playing the film 
    in slow motion, or if it was really that slow.  Also, in this 
    video, there appeared to be two parallel and quite separate 
    tracks, both of them large and fragmenting.
    I'm puzzling over some of the re-entry reports and want to pose 
    a question that I'm definitely not qualified to answer.  Here's 
    a sample from about 32 km south of Lincoln, Nebraska, USA, that 
    was forwarded to the Meteorobs list by Gary Kronk:
    > Starting at the SW horizon we followed with our eyes no less 
    > than 50 "shooting stars" streaking  across the sky above us 
    > to the NE horizon where the earths' curvature prevented 
    > further observation of light show. Estimated total time of 
    > sighting from our position was 20-30 seconds.
    I am trying to figure out how a track from SW horizon to NE 
    horizon could only last 20-30 seconds.  Taking it a different 
    way, if the fiery objects were at the expected height for the 
    observing site, how high above the ground would they have been, 
    and how long would it have taken them to traverse the sky from 
    horizon to horizon?  Another question is at what height above 
    the ground would we expect such objects to slow down enough to 
    stop being visible?  I'm wondering if a very low height could 
    be consistent with a fast traverse, but doubting that objects 
    that low would still be visible.  I haven't seen any reports 
    of sonic booms.
    For reference, the Space Shuttle takes something like two 
    minutes to cross from horizon to horizon on a re-entry that's 
    above 30 degrees above the horizon.  I believe at that time 
    that it's something like 80 km up, when it's due north or 
    south of us here.  (Or maybe the range is 80-90 km.)
    One correction to an earlier post.  I wrote that I had seen a 
    report of "east to west" direction on the re-entry over 
    England-France-Belgium, but it was west to east, from an 
    observer in England.
    Ed Cannon - - Austin, Texas, USA
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