Slashdot Mirror
SpaceX Wants Permission To Test Satellite Internet
An anonymous reader writes: SpaceX has filed documents with the FCC asking for permission to begin testing a project to serve internet access from space. "The plan calls for launching a constellation of 4,000 small and cheap satellites that would beam high-speed Internet signals to all parts of the globe, including its most remote regions." This follows news that Facebook and Google had stepped back their efforts in that arena. SpaceX could prove to be a better fit for the project, given that they need only rely on themselves for launching satellites into orbit. "The satellites would be deployed from one of SpaceX's rockets, the Falcon 9. Once in orbit, the satellites would connect to ground stations at three West Coast facilities. The purpose of the tests is to see whether the antenna technology used on the satellites will be able to deliver high-speed Internet to the ground without hiccups."
Google and facebook have realized that some problems are not (economically) surmountable.
The problems are the following: The closer you fly your satelite to the earth, the more resistance it has from the atmosphere. The density of the atmosphere reduces by a factor of 100 each 46 km of height. So at "100km", you have about 10000 times less air than at the surface. Some people call that space. At 200km the air pressure is about 100 million times less than what it is over here. That is enough to have a reasonable decay rate of weeks/months/years. "skylab" came down after a few decades, right?
The further away you fly your satellites, the longer the travel times will be for the signals. This equates to ping-times. Hmm. 200km is 0.6 ms, quite acceptable. Both ways. 1.3ms. Still fine. Double the distance to 400km for slower decay times, and you're still about 10 times faster than a normal ADSL line. Acceptable. Not a problem. (the problem here is the same for everybody. The satellites will then play "pass the hot potato" to one that's flying above the ground station and beam your packet down to earth. Assuming your halfway around the globe, that will be about 10000 km. That's with 66ms (round trip) already more than what you get with a residential ADSL line. Still not too shabby.)
The problem with putting satellites high is that the distance to the user becomes large. You want them as close as possible.
The closer you put them, the more you need. -> 4000 of them. This however is not just a one-time investment: because they are low, their orbits decay and they fall back to earth on relatively short notice. If you need 4000 of them, they are not going to be large. So they are small. If you have a cubesate (10cm cubed) weighing 1kg, its orbit will decay just like a 100kg satellite of 10x100x100cm (flying the wrong side towards the front). But a bigger satellite is likely to be 100x100x100cm and weigh not 100, but 1000kg. The extra weight helps keep it in orbit, the extra size in the flying direction does not make a big difference. So the small satellites decay fast as well!