Corrected problem with Iridium Flares missing in GSOC predictions

Chris Peat (
Wed, 25 Feb 1998 14:45:35 +0100

Dear SeeSaters,

I have had some reports recently that certain Iridium flares have not been
predicted by our web site, even though they were observed and were predicted
by other programs such as Iridflar.

I have traced this problem to the criteria we use for selecting operational
Iridium satellites from the database. This was changed a few weeks back to
select only Iridium satellites with a mean motion of 14.342... revs/day, and
this was clearly too restrictive since the mean motion of some of the
satellites occasionally moves outside this range. I have now fixed the
problem (I hope) by manually adding a flag to the valid satellites, and
include all Iridiums except the "rogues" 11, 21 and 27. Newly launched
satellites that are still climbing to their operational orbits (such as
those launched on Feb. 18th) are also included when looking for flares. If
anyone has any comments about whether I should include any of the rogues,
and which ones, I would welcome them. I heard that Iridium 27 is tumbling,
and so I assume it should certainly not be added to the list.

We apologise for this problem and any flares you might have missed.

For your information, I use the following parameters when searching for a

Max. Sun elevation - 0 deg.
Min. flare elevation - 10 deg.
Max mirror angle - 4 deg.

These parameters are fixed at the moment, but we plan to allow users to
specify their own values at some time in the future, probably by requesting
a user name which would then be used to fetch a user's preferences from a
database. This would eliminate the need to enter them every time. Using the
current method of storing parameters in the bookmarked URL only works with a
small number of parameters.


Chris Peat, Anite Systems
Currently working at the German Space Operations Centre near Munich