# Re: Calculation of Iridium Flares

From: C. Bassa via Seesat-l <seesat-l_at_satobs.org>
Date: Sun, 7 Jun 2015 17:05:28 +0200
```Hi Johannes,

On Fri, Jun 5, 2015 at 8:42 PM, Johannes Bauer via Seesat-l
<seesat-l_at_satobs.org> wrote:
> Is there a good introduction that I could follow to get the calculations
> done? I'd like to calculate some of this stuff with a pen & paper method
> so I understand what I'm doing and can replicate the results.

The SGP4/SDP4 documentation is a good start on how to compute
satellite positions from two-line elements. You'll also need
algorithms to compute the position of the Sun and the observer. There
are several books explaining that. The best is probably Astronomical
Algorithms by Jean Meeus. I've used his algorithms in my own software:
https://github.com/cbassa/sattools So far it does not (yet) compute
iridium flares, but I might add that in the future.

To find iridium flares I'd start by picking an Iridium satellite,
compute its cartesian position. Compute the position of the Sun and
then take the known orientation of the three mirror surfaces to
reflect the vector from the satellite to the Sun and see if the
reflected vector passes through the Earth. If it does, you'd probably
have to use a bit of iteration to converge on the latitude and
longitude of the point on Earth. Looping through time and the list of
Iridium satellites will allow you to find out which satellites have
the ground trace of the solar reflection pass closest to your
location.

Regards,
Cees
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Received on Sun Jun 07 2015 - 10:06:00 UTC

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