Iridium Satellite Flares

The Iridium Corporation which finished putting together their satellite version of a cellular telephone network in june 1998. The Iridium communications constellation now consists of 72 or so satellites built and controlled by the this consortium led by Motorola.

This is the first of some 9 proposals to clutter low Earth orbit with systems of communications satellites. The desired orbit is circular, 782km high, and inclined 86.4 degrees to the equator. The 72 required satellites have been launched, and though 4 are already duds for one reason or another, most are working fine. The company has been offering services since October 1998.

Soon after the initial launch it came to the notice of amateur satellite observers that one got some very bright reflections from these satellites (magnitude -8), in certain parts of the sky. Occasionally an antenna will directly reflect sunlight down to the Earth, creating a predictable and quickly moving illuminated spot of about 10 km diameter. To an observer this looks like an extremely bright flare in the sky with a duration of a couple of seconds.

Some of the flares are so bright (up to -8 magnitude) that they can be seen at daytime, but they are most impressive at night. This flashing has been of extreme annoyance to astronomers as the flares occasionally disturb observations and can damage sensitive equipment.

When not "flaring" the satellites are often still just visible to the naked eye - a typical magnitude is 6, similar to a dim star.

Since the satellites are rotating once per orbit, so that the orientation relative to the local vertical is always the same, the directions of satellite surfaces are thus known all the time. The main mission antennae (MMA) have a silver-coated teflon surface of area about 1.6 square meters, so it is reasonable to assume they are the surfaces involved.

To find out when to see an Iridium Flare over Waterford Click Here