Forty years after man first walked on the moon, I have managed to use a satellite phone to contact PolarTREC...and I owe it all to Iridium!The Iridium system is satellite-based and has 3 components: the satellite network, the ground network and the hardware.
First the hardware: the part you can see: this is the part I am struggling to learn to use, satellite phone, various antennae, modem, computer, and power supplies. There are adapters for every situation from sitting at home in the city to sitting on top of a mountain. Many of the pieces just have numbers, no names, so I spent a lot of time studying each one to figure out the logic of where it must connect. The phone itself is pretty basic for anyone who uses a cell phone or a two-meter hand-held radio. (Besides, it comes with great instructions and pictures.) The computer part is mostly necessary so I can send documents and photos via email, otherwise I can just make voice calls with the phone. The computer has become an extension of my mind and body.
Next, there is the ground network which means the "system control and telephony gateway" or basically, how information sent from computer and sat phone to the satellites and back to earth gets where it is supposed to go. The parts of this system include the TTAC (Telephony Tracking and Command/Control Station) operational support network and SNOC (Satellite Network Operation Center.) This is how important links are managed. I never see this part, but I would be isolated without it.
Part of those ground network gateways are ground-based antennas, electronics that provide voice and data service, messaging and various other customer support services. The part of this I do see and feel the most is a man named Roy Stehle at SRI International in Ravenswood, California. We talk. He calms me down. I try again. He is like my virtual Prozac while learning to work with all this.
The third part of the system is the satellites: 66 active satellites fly in near-polar orbits 485 miles above the planet. There are six orbital planes, evenly spaced, each with 11 satellites equally spaced from each other in each plane. It takes 100 minutes for each satellite to circle the Earth at 16,832 miles per hour. That's about 10 minutes horizon to horizon. When one satellite dips below the horizon signals are handed off to another so there is no interruption in transmission.
Now here is something really cool: I know the Iridium satellites are up there because I have seen proof! One night in Colorado I was called away from the campfire circle to peer into the night sky at a very specific time...11:10 PM maybe....and I witnessed a tiny bright spark several degrees above the horizon when an Iridium satellite reflected the last rays of the sun before passing into Earth's shadow...an Iridium Flare! (Here I thank Peter Modreski of USGS for making it possible. It didn't seem like a big deal at the time, but now it has become mush more important to me!)
So this is how it all works. With the strength of Iridium behind him, ET might have been able to make that famous phone call...really. For any of my afternoon science club, or other students past, present, or future, reading this try, to make a drawing of the Earth and the satellites in their cozy orbital planes (use the mathematical definition for that word). I will pay off in treats in September if you even get close!
For more information go to http://www.iridium.com/about/howitworks.php