as best I can remember they circle the earth in various geocentric orbits and occasionally they catch the sunlight and flash. Leaving one to think they are ufos or meteorites or any of a number of strange phenomena.. it seems they are often seen in he North sky. But.. my memory may not be on the game so to speak.
Rosie ----- Original Message ----- From: "Matson, Robert" <[EMAIL PROTECTED]> To: "'Marco Langbroek '" <[EMAIL PROTECTED]>; "'meteorite list '" <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Saturday, October 19, 2002 2:00 PM Subject: [meteorite-list] OT: Iridium flares > Hi Marco and List, > > For those not interested in more info on Iridium flares, delete now. > (This is a bit off-topic for the Meteorite List, but since many > meteorite afficionados are also interested in bolides, there is > a tenuous connection.) > > Marco wrote: > > > For those who do not know, this is a series of artificial > > communication satellites, initiated some years ago (I believe > > we started to first see them in 1997) ... > > This is correct -- summertime of '97. > > > ... in order to provide for (expensive) satellite telephone > > from anywhere in the world. > > Expensive is right. The marketing plan for Iridium was questionable > at best. The phones are bulky and very expensive themselves, and > the per-minute telephone charges were many dollars per minute. Of > course, if you're working in Antarctica on some research project, > you aren't likely to have a nearby cellular site! ;-) > > > The network entailed as much as 70 satellites, most of which > > have indeed been launched. > > Over 90 have been launched -- perhaps around 95 by now. About > a dozen of these have failed, and of that dozen several have > already reentered the atmosphere. 91 remain in orbit at the > present time. > > > The project failed as the company in question got bankrupt, > > but the satellites are still there although they should be > > phased out and re-enter as was the plan some time ago when > > the company was dismantled and the network closed. > > Actually, the DoD bought out Iridium ILC's interest in these > satellites (for pennies on the dollar) and they continue to > operate to this day. The DoD was the primary customer of > the system, so they had a vested interest in keeping it alive. > > > They carry a large antenna panel which reflects beams of > > sunlight. > > There are 3 main mission antennae (MMA), any of which is > capable of reflecting solar glints down to the ground depending > on the geometry. These MMAs are quite large -- door-sized (and > a large door at that). Under the most favorable geometry, an > antenna can produce a glint as bright as magnitude -8.5, and > thus are quite visible in daytime. (I've seen several dozen > of these daytime Iridium flares). > > Back in the summer of 1997, shortly after the first 5 satellites > were launched, the "flare phenomenon" was serendipitously > discovered by an amateur satellite observer. The flares were > totally unforseen by the satellite builders. Working with a > network of observers and the spacecraft designers, I was able > to quickly cobble together a program that would predict future > flares for any observer. As more flare observations came in, > the brightness curves were tweaked until I finally had a very > reliable flare predictor. Indeed, you can set your watch by > these flares -- they're that reliable. > > What makes the flares predictable is that the satellite orientation > is very accurately maintained and thus predictable for weeks into > the future. Marco mentioned that there is a website for predicting > flares -- this is the Heavens-Above site. Its predictions should > be quite compatible with those of my program (IRIDFLAR) as the > program author used my model for photometric brightness. The > Heavens-Above site is handy in that you don't need to know how > to run a flare prediction model. You just plug in your coordinates > or your city name, and it does all the work for you. The only > drawback is that you have to be logged onto the internet. > > Anyway, for the few people left in the world who have never seen > an Iridium flare, make the effort to see one. They are fabulous, > and great for getting kids interested in astronomy. > > Cheers, > Rob > > > ______________________________________________ > Meteorite-list mailing list > [EMAIL PROTECTED] > http://www.pairlist.net/mailman/listinfo/meteorite-list ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
