The Iridium Satellite Constellation

Gotta remind myself to post something technical in this blog from time to time so that people will remember that this blog belongs to an engineer :p. So, if I say ‘Iridium’, what comes to your mind? A chemical element, no doubt. But since I’m from telecommonication engineering and not chemical engineering, we’re talking about a whole different kind of Iridium here. Yes, we’re talking about the Iridium satellite Constellation.

Why is it called Iridium? Not really sure about this one. My lecturer said that it’s because its constellation is similar to how the Iridium atom’s electrons orbit around the nucleus. It’s just that the Iridium satellite constellation has a total of 66 satellite, while the Iridium atom has an atomic number of 77. If we’re going for consistency shouldn’t it be named Dysprosium instead? Maybe they went for cool name instead?

The Iridium satellites are mainly used for providing voice and data coverage to satellit phones on the earth.

That's some antenna for a phone

The iridium satellites are placed 6 diferrent orbitals with each having 6 satellites. The orbitals are classified as LEO (780 km above earth), which means that the satellites revolve around the earth quicker than the earth’s rotation. Each satellite can completely circles the earth in around 100 minutes, with the orbital speed of around 27000 km/h. Thus, Iridium satellites can go from horizon to horizon within only 10 minutes. This is in contrast to geostationary satellite, which appear as a single stationary point in the sky – that is if you can actually see an object about as big as your car 36000 km up in the sky.

Due to its high orbital speed, the communication system must cope with several factors, such as doppler shifts (hey, it also appears here in telecommunication, not only in the car siren problem you encounter in high school!) and handoffs problem.  Calls are routed between satellites up there without even touching the ground, so the system is immune to anything that happens down below such as earthquakes or tsunamis. Thus, making it ideal for disaster relief support.

-written when I feel that my english is starting to go downhill


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