Re: double flash for Iridium 75?

From: Bjorn Gimle (
Date: Wed Jun 05 2002 - 10:18:41 EDT

To answer your direct question:

There are on the average two spares in each of the six planes, overtaking
the eleven operational ones (that pass every 9.2 minutes) regularly.

If Ir 21 were typical, passing two operational ones per day, this would mean
there would be about twelve such encounters every night.

But some spares are closer to their companions, meeting them less often.
And many (most?) of the night passes are in shadow.
And some of the sunlit Iridium passes are nowhere close to giving a flare.

Finally, in daylight you have to be within about 5 km of the flare's ground
track, and if the satellite is more than about 15 seconds off its ideal pass
time, it might not be seen (Earth rotation about 350 m/s at mid-latitudes),
so daytime doubles are perhaps 10 times less frequent.

----- Original Message -----
> Ir 21 is faster by about 85 seconds/orbit, so its flare would be 34 km E
> Ir 75's on the following orbit already, and not seen in daytime.
(Near -95.3
> it was just 2.5 km E)
> > that is it. This is my first daytime flare.  Is this on-off phenomenon
> > common for daytime flares?

Unsubscribe from SeeSat-L by sending a message with 'unsubscribe'
in the SUBJECT to

This archive was generated by hypermail 2b29 : Tue Jun 25 2002 - 20:50:33 EDT