What are Iridium Flares?

Iridium flares are spectacular, bright reflections from satellites in low Earth orbit.

Iridium is a US telecommunications company which used a constellation (group) of relatively small satellites to provide a mobile telephone system with handsets which could work anywhere on the Earth’s surface.

The reflections from these satellites are sufficiently bright that many observers on the ground have claimed that the flares are actually UFO's!

The flares last for between 5 and 20 seconds and can be up to 30 times brighter than the planet Venus, before the satellite once again becomes invisible to the naked eye.

How are they caused?

The Main Mission Antenna (MMA) on each satellite is made from highly reflective aluminium in the form of a flat plate, angled at 40 degrees away from the axis of the body of the satellites. This can provide a specular (direct) reflection of the Sun's disk, which is seen as a flare on the ground. At the Earth's surface, the specular reflection is only tens of kilometres wide so each flare can only be viewed from a fairly small area.

How do you know where to look?

The flares’ time and location can be predicted provided the satellite's position, orientation, the relative Sun angle, the reflective properties of the mirror and the position of the observer on the Earth's surface are known. Certain Internet sites provide predictions for particular locations for the next 7 days.

Unusually for reflective flares, Iridium flares can be sufficiently bright to be visible in daylight. In this case knowing exactly where to look to observe the flare is essential.

How were the satellites launched?

Three satellite carriers launched the satellites:

• Boeing's Delta II rocket launched 45 satellites
• Russia's Proton Rocket launched 21 satellites
• China's Long March 2C/SD launched the rest of the satellites.
  

What's going to happen to the satellites?

Iridium’s initial plan was for mobile telephones which worked anywhere in the world, an idea that seemed feasible both to them and to their leading investor, Motorola. However, the handsets needed were expensive to purchase and incurred high call charges, making them uncompetitive with ground-based networks. As a result the Iridium corporation has announced that it is going into liquidation. Consequently they will have to deorbit their constellation of satellites due to their high maintenance costs, which means that each satellite will be directed to burn up in the Earth’s atmosphere. It has been estimated that this process (there are over 80 satellites) will take up to two years and cost around $50 million.

Once this is complete, no more flares will be seen. However they will be still be visible during the deorbiting process. Unfortunately, it will no longer be possible to predict them.