I've literally just heard here that the days of observing Iridium satellite flares are numbered. Of course it's common sense, but I never thought about it.
Roughly how soon are these going to start diminishing in frequency? In five years they'll be half as often? Or much sooner? Later?
Will the ramp-down be uniform over the globe, or is there a chance that it could be noticeable at some latitudes sooner than at others?
There won't be any privileged locations, we're all in the same sad boat :-) The Iridium constellation is not geo-stationary. The sats are in a LEO polar orbit and pass all latitudes every 100 minutes. Due to the rotation of the earth, all longitudes get covered by each satellite as they go along.
Two time-schedules are relevant:
In order to replace the old satellites, the new ones have to be put into orbit. This will happen in various sequences of ten satellites. The first batch is already up there (launched in Jan 2017), the next one will follow in mid-June, from then onwards app. every 6 weeks (if SpaceX can make it happen).
With the new satellites up, there first is a period of manoeuvering them to their proper slots, then extensive testing, then the new ones take over the functionalities of the old ones. Once the slot-swaps are done, de-orbiting can start. From the first batch, de-orbiting started for one of the satellites about a week ago. Not exactly sure about that, but I assume it will take several months until it burns up. Since most of the old satellites are still under control and stable, I guess they will be flaring even when on the way down.
So get your fair flare share while you can, it's flarewell soon :-)
update:
This comment links to Space News' February 6, 2019 article Iridium ends legacy satellite service, switches all traffic to Next fleet which includes the passage:
(Matt Desch, CEO of Iridium) said Iridium has “deboosted” 52 legacy satellites, a process that involves lowering their orbits to catch the Earth’s atmosphere and burn up. So far, 47 legacy satellites have reentered**, Desch said.
Iridium will deorbit the last 13 legacy satellites over the next few months. Desch said the average time between deboosting and complete deorbiting is 19 days.
To supplement @eerie's answer I'll add Scott Manley's latest video Iridium Flares Are Disappearing From The Skies.
For the last 20 years Iridium Flares have been a regular feature of satellite watching as the iridium network provided a nice predictable set of satellites which just happened to produce satellite flares. However the old network is in the process of being replaced and soon you'll not be able to see this phenomena.
First sentence:
"Hello it’s Scott Manley and I’m here today to warn you that Iridium flares are going extinct!"
