Re: Two Iridium flares right next to each other

From: Rod Sladen (rodsladen@crosswinds.net)
Date: Thu Jan 10 2002 - 19:20:36 EST

  • Next message: Stephen Fels: "Re: Two Iridium flares right next to each other"

    <*** reformatted repost with profuse apologies ***>
    
    (a) I sent the same message twice - finger trouble
    
    (b) the new crosswinds e-mail package is not wrapping
    automatically like the old one did.
    
    Kevin Mangis (kmangis00@yahoo.com) wrote:
    
    > Last night (9 Jan 02) while watching Iridium 42 flare to 
    > -2 as predicted by Heavens-above (19:02:29 local time or 
    > 00:02:29 UTC), I saw a much brighter flare right next to 
    > it in the sky which appeared to be from a nearby Iridium 
    > satellite that was not predicted by Heavens-above. 
    
    This must have been a very pleasant surprise.
    
    > I didn't think that two operational Iridium satellites 
    > would be so close together -- aren't there 11 satellites 
    > spread out evenly in one orbital plane?
    
    Indeed, the operational satellites are evenly spaced around 
    each plane, and the next would not be along for around 
    another 9 minutes.
    
    > Could the second have been a spare?  
    
    Correct.  Iridium 82, in fact, with a flare predicted to 
    peak at mag. -4.1 within a second or so of Iridium 42 
    flaring to mag. -1.8.  Heavens-Above unfortunately omits predictions for some of the spare satellites.
    
    > My understanding was that the spare Iridiums are not 
    > always nadir-oriented like the operational satellites, 
    > and it seems to me to be too much of a coincidence that 
    > the spare happened to be oriented just like the 
    > operational satellite.
    
    The spares are maintained in correct orientation, though 
    possibly not with quite the same accuracy as the 
    operational satellites.
    
    But most of the spares are in orbits around 68km. below the 
    operational sateliites, and thus "lap" the operational 
    satellites roughly every 11 days.  So what you witnessed 
    was a lucky coincidence.
    
    For making your own predictions, I recommend Rob Matson's 
    IridFlar, which you can download from Mike MCants' site at 
    http://users2.ev1.net/~mmccants/programs/index.html
    
    My own Iridium Constellation Status page is at
    http://www.rod.sladen.org.uk/iridium.htm
    
    -- 
    Rod Sladen
    Beeston, Nottinghamshire, UK
    52.923N, 1.219W
    
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