Earlier quoted context omitted.
SpaceX is proposing putting them @ 1,100km. The speed of light is faster in space than it is in optical fibre.
The speed of light is faster in space than it is in optical fibre. Could you elaborate? Thanks
[deleted]
Musk files to provide Internet service from space
21–30 of 129 posts
Re: Musk files to provide Internet service from space
#22Earlier quoted context omitted.
SpaceX is proposing putting them @ 1,100km. The speed of light is faster in space than it is in optical fibre.
The speed of light is faster in space than it is in optical fibre. Could you elaborate? Thanks
The speed of light in an optical fibre is about 35% slower than in vacuum -- it depends on the index of refraction.
https://en.wikipedia.org/wiki/Speed_of_light
The same is true for light traveling through water, air, and so forth.
Re: Musk files to provide Internet service from space
#23My first thought, here, was "Well what about the speed of light? Wouldn't that cause satellite internet service to suck, just like it does now? And isn't that why news correspondents are always delayed?" But then I did the math: Speed of light = 186 miles per millisecond. Satellites orbit at about 380 miles above earth (Source: Hubble). So it only takes ~4 ms for a round trip to a satellite directly above? I did not…
Good question. The vast majority of satellite communications today are conducted via geostationary orbit, 35,786 km above the earth. This is the distance at which a satellite orbiting around the equator moves with the same velocity as the surface of the earth, keeping the satellite in a fixed position. This is good for communicating via the ground, since you can just set up your dish pointing in the direction of the satellite. Additionally, such a satellite can cover a wide swath of the earth since it is so far away; see, for example, the coverage of AsiaSat-8 (http://www.spaceflightinsider.com/wp-content/uploads/2014/08...). The disadvantage (especially for internet) is that the round-trip time of a signal at the speed of light is on the order of 250 ms.
As described in this article, the SpaceX constellation would be in a much lower orbit. The advantage is a much faster ping time (say, around 10 ms). The disadvantage is you need a large number of satellites to provide continuous coverage for the entire earth...but that's less of a disadvantage if your company also launches rockets.
Re: Musk files to provide Internet service from space
#24I wonder how it would compare to Exede Satellite service. I have Exede, it's the only thing available here in High Desert :( The speed is very good for what it is, I am getting 16-20 mbps down and 3mbps up. But, the latency is a huge issue for me. Most servers, even once in US, ping at 800ms, this makes it such a pain to do any kind of SSH server admin!
With low orbit devices I would imagine the latency should be better, I am guessing, but how much better.
Re: Musk files to provide Internet service from space
#25I was Director of Marketing with Teledesic, Craig McCaw and Bill Gates's Internet-in-the-Sky from 1995 to 2000. I'm a huge fan of what Musk is doing, with order of magnitude cheaper launch costs and satellite hardware. AMA.
How will devices on the ground communicate with the satellites? i.e. do we still need fixed dishes, or are we looking at something new so an iPhone can get signal right from the satellite?
Re: Musk files to provide Internet service from space
#26Musk claims to want to launch 4,000 or so satellites. The Goddard Space Flight Center indicates that there are 2,271 satellites in orbit now. I'm wondering to what degree this would make it more likely to have a negative feedback loop of satellite destruction in the case of a satellite being hit by space junk.
The problem has to do with cross-section -- these satellites will each be small, a few hundred kilograms each. In comparison, cubesats are 1-3 kg, and big satellites, which are most of the existing ones, are a few tons of mass each. https://en.wikipedia.org/wiki/Kessler_syndrome Also, with satellites at 1,100 km, they'll be above all the crap in LEO.
and solves the other problem of Big High internet, which is latency. At 1000km you could have single-hop round-trips in <10ms.
Re: Musk files to provide Internet service from space
#27I wonder how it would compare to Exede Satellite service. I have Exede, it's the only thing available here in High Desert :( The speed is very good for what it is, I am getting 16-20 mbps down and 3mbps up. But, the latency is a huge issue for me. Most servers, even once in US, ping at 800ms, this makes it such a pain to do any kind of SSH server admin! With low orbit devices I would imagine the latency should be bet…
> With low orbit devices I would imagine the latency should be better, I am guessing, but how much better.
Your satellite's 22,000 miles above the earth. If you were directly under it, round trip latency would be 236ms.
If these satellites are 684 miles up, and you were directly under one, round trip latency would be just 7ms.
The distance between satellites, and between the satellites and whatever ground stations actually connect them to the 'net, will all be smaller because of the lower orbits. Latency should be much better.
Re: Musk files to provide Internet service from space
#28My first thought, here, was "Well what about the speed of light? Wouldn't that cause satellite internet service to suck, just like it does now? And isn't that why news correspondents are always delayed?" But then I did the math: Speed of light = 186 miles per millisecond. Satellites orbit at about 380 miles above earth (Source: Hubble). So it only takes ~4 ms for a round trip to a satellite directly above? I did not…
The Iridium constellation is 485 miles above. I've used it for both voice and data at sea via a motorola handset. Voice was very responsive with no delay, though the compression was very apparent. Data is painfully slow at 2.4 kbps. We needed to use a specialized email client that compressed email, handled the duplex connection, and recovered from errors very gracefully.
I'm curious the reason for such slow data too. Looks like the design was optimized to maximize the number of voice connections for a minimal number of satellites. Combined with the age of the design (first launched in '97) gives pretty poor data connections.
Re: Musk files to provide Internet service from space
#29Great, another pipe-dream to sell to his investor fan club.
As opposed to current pipe dreams: * gigafactory under construction * freemont factory producing ~50K vehicles/year * spacex successfully, repeatedly delivering payloads to orbit (and successfully demonstrating their crew escape vehicle recently)
Just because something is being built with other people's money does not make something a success. None of the companies Elon has been involved with have ever actually generated a profit -- they have largely just taken advantage of speculative investors and their willingness to buy into his ideas.
Re: Musk files to provide Internet service from space
#30My first thought, here, was "Well what about the speed of light? Wouldn't that cause satellite internet service to suck, just like it does now? And isn't that why news correspondents are always delayed?" But then I did the math: Speed of light = 186 miles per millisecond. Satellites orbit at about 380 miles above earth (Source: Hubble). So it only takes ~4 ms for a round trip to a satellite directly above? I did not…
Good question. The vast majority of satellite communications today are conducted via geostationary orbit, 35,786 km above the earth. This is the distance at which a satellite orbiting around the equator moves with the same velocity as the surface of the earth, keeping the satellite in a fixed position. This is good for communicating via the ground, since you can just set up your dish pointing in the direction of the…
Hmm, interesting. Well, I have Exede Satellite service as my ISP (best I can get) and my best latency, to any server, is 800ms. The way I figure it, 35,786 km / 300 miles per ms would be 120ms up * 4 for the round trip. So that's 480ms, plus another 20ms-100ms to a google or another large server. So that's theoretical latency of 600ms, so where are the other 200ms of latency coming from! :(
I am wondering because I maintain some linux servers for some of my projects, and any time I need to do something serious, I have to drive to a coffee shop and borrow their connection. SSH over 800ms latency is frustrating, to say the least.