Re: Iridium orientation/predict

Bjoern Gimle (
Fri, 10 Oct 1997 21:19:52 +0100

Donald Baker asked about how the structure of Iridiums could be
explained (and a little further), and Leigh Palmer how they could
be calculated.

The following information provided to me by Rob Matson on a similar
question is a very good explanation on the first part of the problem.
Randy John's reply goes a long way to describe the rest.

>Hi Bjorn,
>Let me see if I can do a better job of describing how the Iridium antennas are
>pointed.  Start with three vertical panels (relative to the ground) with
>normals all in the same plane, but with each pointing 120 degrees away from
>its neighbors.  (Think of the surfaces of a prism that has an equilateral
>triangle as a cross-section.)
>Now, make sure one of the panel surface normals is pointing in the same
>direction as the satellite velocity vector (i.e. the "ram" direction).  So
>far, so good.  Finally, tilt each panel 40 degrees "down" so that each panel
>normal points 50 degrees from nadir (and 130 degrees from zenith).  That's how
>it looks.
>I've run predictions for you for Iridiums 4 through 20.  Unfortunately, one
>flare has just happened for you (Iridium 16, 9/30 17:22:10 UTC), and another
>will probably happen before you get this message (Iridium 20, 9/30 18:48:10
>The remainder you've still got time for.

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