[meteorite-list] OT: Iridium flares

From: Rosemary Hackney <ltcrose_at_meteoritecentral.com>
Date: Thu Apr 22 10:07:02 2004
Message-ID: <000701c277b6$fd2e0500$1b7dd6d1_at_default>

as best I can remember they circle the earth in various geocentric orbits
and occasionally they catch the sunlight and flash. Leaving one to think
they are ufos or meteorites or any of a number of strange phenomena.. it
seems they are often seen in he North sky. But.. my memory may not be on
the game so to speak.

Rosie
----- Original Message -----
From: "Matson, Robert" <ROBERT.D.MATSON_at_saic.com>
To: "'Marco Langbroek '" <marco.langbroek_at_wanadoo.nl>; "'meteorite list '"
<meteorite-list_at_meteoritecentral.com>
Cc: <azaware_at_msn.com>; <tracyl@lib.state.hi.us>
Sent: Saturday, October 19, 2002 2:00 PM
Subject: [meteorite-list] OT: Iridium flares


> Hi Marco and List,
>
> For those not interested in more info on Iridium flares, delete now.
> (This is a bit off-topic for the Meteorite List, but since many
> meteorite afficionados are also interested in bolides, there is
> a tenuous connection.)
>
> Marco wrote:
>
> > For those who do not know, this is a series of artificial
> > communication satellites, initiated some years ago (I believe
> > we started to first see them in 1997) ...
>
> This is correct -- summertime of '97.
>
> > ... in order to provide for (expensive) satellite telephone
> > from anywhere in the world.
>
> Expensive is right. The marketing plan for Iridium was questionable
> at best. The phones are bulky and very expensive themselves, and
> the per-minute telephone charges were many dollars per minute. Of
> course, if you're working in Antarctica on some research project,
> you aren't likely to have a nearby cellular site! ;-)
>
> > The network entailed as much as 70 satellites, most of which
> > have indeed been launched.
>
> Over 90 have been launched -- perhaps around 95 by now. About
> a dozen of these have failed, and of that dozen several have
> already reentered the atmosphere. 91 remain in orbit at the
> present time.
>
> > The project failed as the company in question got bankrupt,
> > but the satellites are still there although they should be
> > phased out and re-enter as was the plan some time ago when
> > the company was dismantled and the network closed.
>
> Actually, the DoD bought out Iridium ILC's interest in these
> satellites (for pennies on the dollar) and they continue to
> operate to this day. The DoD was the primary customer of
> the system, so they had a vested interest in keeping it alive.
>
> > They carry a large antenna panel which reflects beams of
> > sunlight.
>
> There are 3 main mission antennae (MMA), any of which is
> capable of reflecting solar glints down to the ground depending
> on the geometry. These MMAs are quite large -- door-sized (and
> a large door at that). Under the most favorable geometry, an
> antenna can produce a glint as bright as magnitude -8.5, and
> thus are quite visible in daytime. (I've seen several dozen
> of these daytime Iridium flares).
>
> Back in the summer of 1997, shortly after the first 5 satellites
> were launched, the "flare phenomenon" was serendipitously
> discovered by an amateur satellite observer. The flares were
> totally unforseen by the satellite builders. Working with a
> network of observers and the spacecraft designers, I was able
> to quickly cobble together a program that would predict future
> flares for any observer. As more flare observations came in,
> the brightness curves were tweaked until I finally had a very
> reliable flare predictor. Indeed, you can set your watch by
> these flares -- they're that reliable.
>
> What makes the flares predictable is that the satellite orientation
> is very accurately maintained and thus predictable for weeks into
> the future. Marco mentioned that there is a website for predicting
> flares -- this is the Heavens-Above site. Its predictions should
> be quite compatible with those of my program (IRIDFLAR) as the
> program author used my model for photometric brightness. The
> Heavens-Above site is handy in that you don't need to know how
> to run a flare prediction model. You just plug in your coordinates
> or your city name, and it does all the work for you. The only
> drawback is that you have to be logged onto the internet.
>
> Anyway, for the few people left in the world who have never seen
> an Iridium flare, make the effort to see one. They are fabulous,
> and great for getting kids interested in astronomy.
>
> Cheers,
> Rob
>
>
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Received on Sat 19 Oct 2002 05:32:11 PM PDT