FAREWELL TO THE FLARES
The 50 or so glinting Iridium satellites in low Earth orbit have garnered a cult following. Now it’s time farewell writes Jamie Carter
As the Iridium satellite network is deorbitted, the race to catch the final flares is on.
Have you ever seen an Iridium flare? When the Iridium fleet of 66 communications satellites was launched in the late 1990s, no one thought that the sunlight glinting off their panels would become a stargazing staple. Yet anyone regularly observing the night sky in the few hours after dusk and before dawn will probably have seen the unmistakable waxing and waning of an Iridium satellite’s glint; they tend to last between five and 20 seconds and can reach mag. –8, brighter than Venus.
Iridium flares are caused by the satellites’ three reflective panels catching sunlight, but the 50 or so that remain in orbit won’t do so for much longer. Over the coming year, Iridium Communications – the company that owns the satellite network – is replacing it with a constellation of newer, smaller satellites. And to the dismay of the astronomers and astrophotographers who’ve grown used to spotting and photographing the Iridium satellites, these new ones don’t flare.
Who cares? Iridium flare-hunters, that’s who. For amateur astronomer Steve Brown, from Stokesley in North Yorkshire, Iridium satellites have become
part of his regular observing routine and he’s been taking photos of them for the past three and a half years. “When I saw my first one I was amazed by the beauty of it – a star-like point of light moving against the dark sky that gradually brightened over a few seconds to become almost dazzling, before fading again,” he says. Although Brown’s neighbours are used to seeing him out with his camera, he frequently has to explain to them what he’s taking a picture of. “For people who haven’t heard of them before, the response is usually ‘Iridium what?’ But they’re always amazed when I explain and then they see the flare.”
What comes next
Although Iridium flares will soon be missing from the night sky, hobbyists such as Brown have been granted a long goodbye (or should that be flarewell?). Iridium Communications is now halfway through a launch programme with SpaceX to replace its entire fleet with new Iridium NEXT
“I so badly want to photograph the entire Iridium network, it’s become quite an obsession” Mary McIntyre
“I went outside and saw my satellite go across the sky. It was a fantastic sight and I got emotional about it” Matt Desch
satellites, a process that involves de-orbiting all of its older hardware.
“As we continue to launch, we’ll continue to de-orbit,” says Matt Desch, CEO of Iridium Communications. “The final launch will be in June 2018 and by the fall of 2018 we won’t need any more of the original satellites, so the last one to predictably flare will be around the end of 2018.”
That news has caused something of a rush among flare-hunters to complete their observations before the old fleet burns up in the atmosphere. “I so badly want to photograph the entire Iridium network, it’s become quite an obsession,” says Mary McIntyre, an amateur astronomer who’s been observing the satellites for about seven years from her garden observatory in Oxfordshire. She only has eight to go to get the set. “I’m gutted that the new Iridium satellites won’t flare; it’s going to be really sad,” she says.
More function, less flare
The current fleet of Iridium satellites provides voice and data coverage to satellite phones and transceivers around the globe from a near polar orbit, at an altitude of 786km and an inclination of 86°. They’ve been operating since May 1997.
The new fleet of Iridium NEXT satellites are being launched to bring new services online such as Iridium Certus (a 1.4Mbps broadband connection for the entire planet) and Iridum Aireon (an aircraft surveillance and flight tracking network) but they have a flat bottom and a phased array antenna, so they don’t flare. “When we chose the new, more efficient design, we realised they wouldn’t flare, which was a bit disappointing because we feel the same way as the enthusiasts do,” says Desch, who recalls hearing reports of flares from the original Iridium satellites shortly after their launch. “I was in North Carolina and I computed exactly where a flare was going to occur, then went outside and saw my satellite go across the sky. It was a fantastic sight and I got emotional about it.”
Iridium flares aren’t easy to spot, however. At least, not without first doing some research. And they shouldn’t be confused with the steadily bright International Space Station, which can be seen from the whole of the UK. “The flares are very locationspecific because their reflective panels are so small,” explains McIntyre. “The viewing track is about 70km wide and if you look on www.heavens-above. com it’ll tell you exactly how far you are from the flare centre. If it’s faint, you know you’re near the limit.” McIntyre also recommends an app called SatTrack, which not only gives the orbital path of each Iridium satellite, but also provides an exact alt azimuth position, alongside a countdown to the nearest second of when the flare will peak.
Although Iridium is committed to de-orbiting its entire fleet to minimise space junk and the majority will be gone by the end of 2018, all is not completely lost for flare-hunters. “You might see some tumbling flares for a period of time into 2019 and some of the satellites might take as long as 20 years to come down,” says Desch. Either way, the predictable yet fleeting wax and wane of an Iridium flare will soon be consigned to stargazing history.
Follow the end of the Iridium era with the hashtag #flarewell on Twitter, and share your images with us @skyatnightmag