Spaceflight Now: Breaking News

Iridium's fall a mixed blessing for astronomers

Posted: September 20, 2000

  Iridium flash
Colin Murray caught this magnitude -7 flash from the Iridium 26 satellite from Liverpool on July 26.
Motorola intends to deorbit all 66 of the satellites owned by its bankrupt offshoot Iridium LLC, after attempts to find a buyer for the satellite phone company failed. Astronomically, the news is a mixed blessing.

It will certainly be well received by radio observers, who have protested that the transmission frequency of the satellites interferes with the 1612 MHz band, used to study the distribution of OH, the hydroxyl radical. OH is one of the most common interstellar molecules, and enables radio astronomers to investigate the evaporation of comets and the birth and death of stars.

Satellite watchers, however, will be less pleased. The imminent demise of Iridium means an end to the bright spectacle of "Iridium flares". Each satellite has three silver-coated Teflon antennae, angled with respect to its body. The antennae act like giant mirrors, reflecting the Sun's rays down to the ground. An observer in the right place at the right time can see this reflection as the satellite passes over--as a flash, lasting only a few seconds but brighter than Venus.

Work has already begun on deorbiting the satellites. So if you've never seen an Iridium flare before, now is the time to start looking. To find out when the next flare will occur near you, see

The last Iridium satellite should drop from orbit in 2002. But the skies won't be clear for long. Bill Gates' Teledesic network--an armada of 288 communication satellites--is all set to take Iridium's place in 2005.