Back in 1997, Iridium Communications launched a network of 66 communication satellites into low earth orbit (LEO) over a 6 year period, creating the Iridium satellite constellation. Currently there are 66 operational satellites spread equally across 6 planes (11 in each plane) and 6 spares (1 spare in each plane).
In total, 95 units were launched with the remaining 23 replacing older units that either malfunctioned, lost control, or simply fell out of orbit and burned up on re-entry into earth’s atmosphere. The most notable incident occurred when Iridium 33 collided with Kosmos-2251, a defunct Russian communication satellite.
The project originally was intended to have 77 functional satellites in orbit split between 7 planes (hence the name ‘Iridium’ from the Periodic Table), but the company soon discovered that 66 satellites provided more than enough coverage for seamless communication globally.
One of the unique features of these first generation satellites are the 3 very reflective, door-sized main mission antennas (MMA) split 120 degrees apart from each other.
When Iridium launched these Block 1 units, they were quite excited and intrigued by the fact that their satellites’ MMAs were reflecting sunlight at very bright magnitudes compared to other installations such as the Hubble or ISS. With 66 satellites in orbit, flares occur quite often, with an average of 3-5 flares every week either usually during dusk or dawn periods when the sky is dark but where the sun is still at an angle to direct light off the panels to us on Earth.
Traveling at an average speed of 7.8 km/s, flares generally last for just a few seconds. As they make their pass, they go from being dim to very bright and then dim again.
Unfortunately, Iridium Block 1 satellites are reaching their maximum lifespan and can no longer provide the bandwidth needed to support today’s communication needs.
As a result, Iridium has developed a next generation network of replacement satellites called Iridium-NEXT which can transmit data at 1.5Mbps via L-band and up to 8Mbps on on the Ka-band. The first two are estimated to be launched this month (after being delayed due to a bug in the Ka-band transmitter/receiver).
In total, 72 Iridium-NEXT satellites will be launched over the next few years and split into 6 orbital planes (12 per plane) while 9 others will be kept on Earth and launched should any of the 72 need to be replaced.
The 2nd generation bus features only one main mission antenna (along with two solar panels). Unfortunately, the MMA is no where near as reflective as the first gen antennas, meaning that the age of Iridium flares most likely will come to an end after 20 years. The company opted for this simpler design because fewer parts were needed. The MMA’s surface also does not need to be as reflective as before.
Once enough Iridium-NEXT units make it into orbit, the company plans to de-orbit its Block 1 units into a satellite graveyard starting from 2017, bringing an end to Iridium flares as we know it.
Satellite flares on the whole are not a dead concept though as others like the Hubble, COSMO-SkyMed, and MetOP satellites also make their appearances from time to time, even though these occurrences are so few and far apart due to the fact that these are just a handful of units compares to 66 Iridium satellites.
Here’s my long exposure shot of Iridium 11 taken some weeks ago.
[Image: Brocken Inaglory/Wikipedia]