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Low earth orbit (LEO) Satcom seems all the rage, with huge corporations planning on mega constellations. How else is Amazon going to take over the entire planet? A funny thing is that the Department of Defense is just going to sit back and watch, and then contract services on these networks. They realize that this innovation will be driven by commercial interests.
Let's start with some definitions, which may be subject to change.
LEO satellites are positioned at an altitude between 160 km and 1,600 km (100 and 1,000 miles) above Earth. The International Space Station is 409 km (254 miles) above Earth, what could go wrong?
MEO satellites operate from 10,000 to 20,000 km (6,300 to 12,500 miles) above Earth.
GEO (geostationary or geosynchronous orbit) satellites are 35,786 km (22,236 mi) above Earth.
When we way "Earth" in this context we are talking about mean sea level.
All that talk about Earth means it's time to review some footage of Earth.
Note that the first satellite collision happened in 2009, so there is already a lot of space debris. Each collision incerases the odds of another collision, and it is possible that we end up destroying our ability to use Earth orbit for anything. Read about the Kessler Syndrome here. As Einstein put it, “I do not know with what weapons World War III will be fought, but World War IV will be fought with sticks and stones.”
Update April 2023: There's a nice summary of the current space debris situation over at the EcoWatch site, including references to several companies trying to find solutions to the problem. Thanks to Annie for pointing it out to us.
Right now (as of January 2020), Starlink, a project by SpaceX, has begun to assemble, with 182 satellites in place so far of a projected 12,000. While Starlink is the first project of this size, it isn't the first LEO constellation. Globallink and Iridium both started launching satellites into LEO in 1998, with a total of fewer than 200 satellites between them. The video below will give you an idea of the scale of the Starlink project:
Starlink
Obviously this animation exaggerates the size of the satellites. Each one is rather flat at about 2.4 meters by 1.1 meter (8 ft by 3.5 ft) and weighs around 260 kg (just under 575 pounds). This is quite small by satellite standards, which is why they can launch them by the dozens. Once they're in place - at about 550 km up - you won't actually be able to see them from Earth without a telescope. There's well-founded concern about the amount of space junk already in orbit around our planet, and what impact adding another 12,000 objects into our night sky over the next few years will have. There is also quite a bit of concern among astronomers that you'll see the glare from the reflections off the solar panels and that glare will interfere with scientific studies of our universe.
Starlink isn't the only "constellation" in progress - there have been announcements by OneWeb, Samsung, Telesat, and even Amazon (who plans to put up 3200 satellites, assuming they get permission from the FCC).
https://www.businessinsider.com/spacex-starlink-user-terminal-flat-round-ufo-stick-elon-musk-2020-1
Notice that this is not electronically scanned. That would cost too much!
One of the main attractions for LEO satcom is low latency because of that pesky speed limit in the universe.
Will the GEO satellites become obsolete? Not for a long time, there is a lot of inferastructure built up around GEO.
But your signal's trip to GEO and back use up a large fraction of a second. If you are a Wall Street tycoon, you'd pay anything to have a fraction of a second advantage over your competitors. Back in 2011, shaving 5 milliseconds off a transatlantic cable was big news.
https://www.popularmechanics.com/technology/infrastructure/a7274/a-transatlantic-cable-to-shave-5-milliseconds-off-stock-trades/
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