Re: Simultaneous Iridium flares

From: Robert Holdsworth (robbonz1@xtra.co.nz)
Date: Wed Mar 26 2003 - 11:39:29 EST

  • Next message: Edward S Light: "Re: Simultaneous Iridium flares"

    Thanks all.
    
    There is no way I can prove anyone's maths wrong  - way beyond my level of
    expertise.
    
    I have had difficulty getting Iridflar to work - not sure whether this is my
    problem or the system's.
    
    Incidentally Björn you also posted helpful information to the observer of
    the twin flare in  1999!
    
    Robert
    
    Robert.
    
    ----- Original Message -----
    From: "Björn Gimle" <b_gimle@algonet.se>
    To: <SeeSat-L@satobs.org>
    Sent: Thursday, March 27, 2003 2:59 AM
    Subject: Re: Simultaneous Iridium flares
    
    
    >
    > Using IridFlar and the current elset at Mike's site, I get the range
    > difference as 1665.6-1391.3 = 274.3 km and a flare center diff of 3.8
    > seconds.
    >
    > Using SkyMap, their vertical separation was 800.0-693.3 = 106.7 km.
    >
    > There are 17 satellites marked ? (engineering "spare" orbits - I am
    > surprised that HA predicted one of them) in iridium.tle. Their Mean
    .> Motions are 14.36-14.93, vs the operational 14.34215.
    > This means that each one of those 17 will overtake one of the 11 in the
    > same plane 0.24-6.49 times per day, in total 47.6 encounters per day.
    >
    > Actually, the higher the frequency, the shorter the duration of each
    > encounter.
    > "Your" Iridium 94 ? flare ground speed differs from the Iridium 28 ground
    > speed by about 0.27 km/s. If the definition of "close" is +- 1 s, this is
    > about 15 km, or 56 seconds.
    > Since Iridium 94 ? passes an operational one 3.56 times per day, there is
    > a close pass 3.3 minutes/day somewhere on Earth.
    >
    > This duration (longer but less frequent, or in one case shorter but more
    > frequent) times 17 is almost one hour out of 24, or about 24000 km in
    > total.
    >
    > The width of a good/visible flare depends on the elevation, say 150 km at
    > night, 10 km in daytime.
    > The length of the flare track may be almost the full orbit for twilight
    > orbits, a half orbit for "noon orbits" at 10 km width, and perhaps 1/10
    > orbit at 150 km width. At any time, there may be nearly two MMA flares
    > hitting the ground, on the average ??
    >
    > Assuming an average (150,5,15 km) of 25 km, I get 600 000 square km
    > covered by double flares each day. The Earth is 510 000 000 km, so each
    > should have a one-second coincidence in three years.
    >
    > Please prove my math wrong !
    >
    > One way is to run a large number of two-month runs with IridFlar,
    > covering one or more years and a number of latitudes, and let a program
    > count the number of coincidences (or coincidences within a minute and
    > divide by 60).
    >
    >
    > > I have not had any response to my query so far.  However I have done a
    > web
    > > search and can find no mention of any flares in such close proximity
    > since
    > > 1999!  There are a few reports of double flares but these have been
    > much
    > > greater than 1 second apart.
    > >
    > > I would also appreciate it if someone could calculate the separation in
    > km
    > > or miles - it seems from the respective orbits that it may have been
    > less
    > > than 100 km.  I guess I should have stated my elevation in feet or
    > metres
    > ...
    > > > This evening 25 March at 20:15 local (UTC plus 12) I observed with
    > the
    > > naked
    > > > eye simultaneous Iridium flares from a location at Wellington
    > waterfront
    > > > (41.2861 S; 174.779 E at 0 degrees elevation.)
    > > >
    > > > These were from Iridium 28 1997-051-E  and Iridium 94 2002-005-C
    > > >
    > ...
    > > >
    > > > I would be interested to know how rare or otherwise sightings of
    > > > simultaneous flares are.
    > > >
    >
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