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I can't imagine being able to establish multiple spatially separated beams between satellites that are hundreds or thousands of miles apart. If the beam were sm

I can't imagine being able to establish multiple spatially separated beams between satellites that are hundreds or thousands of miles apart. If the beam were small enough to not 'paint' the entire receiving satellite, it would be ridiculously sensitive to alignment. Even the tiniest movement would break the link. Realistically, using optics, I can only see one spatial path to another satellite. You can use various wavelengths of light to establish multiple carriers, and probably get upwards of 1-2 Tb/s of speed. But nothing near what is possible in the same space with fiber optics. A 288 strand optical fiber cable, with jacket and armor is about 2cm in diameter. And each one of those 288 strands can carry terabits per second of data. It will be a very long time before free-space optics can match that kind of density.

mulmen 9y ago
I realize that space is big but those optical links also become susceptible to obstruction. This is not a problem with cables.
- sathackr 9y ago
  Agreed, but I'd say the likelihood of something in space disrupting an optical path between two satellites for any significant duration is quite small, much smaller than the potential for a cable to be physically damaged. But I'm still quite certain that satellites nor free-space optics will not be coming anywhere near the capacity of fiber in the foreseeable future.
mjevans 9y ago
Doesn't really matter (yet). Satellites presently still need to downlink any transferred data and that's going to be the rate-limiting factor.
lolc 9y ago
I agree that alignment and interference are problems if one wants multiple beams. If you're using lasers one way I see is to split each signal beam into a grid so it's many rays in a grid pattern where a few rays will hit the target sensor array. Multiple grids can then be overlaid without interference. The sensor grid at the target must be able to detect which sensor is receiving which beam and adapt over time. Overall that doesn't sound infeasible to me. But then I don't do optics, so maybe I'm ignorant of a basic limitation.
walrus01 9y ago
a 288 strand cable wouldn't really be the best comparison vs satellite, in the context of submarine fiber. long distance submarine fiber is usually 2 to 8 strands maximum. the huge amount of throughput possible is achieved through a combination of high-powered, dense channel spacing, DWDM systems on the terrestrial ends of the fibers (google "ITU 25 GHz DWDM grid"), and modern high density modulation systems like 100/200/400GbE coherent (QPSK, 8PSK, 16QAM + FEC) links.
- dx034 9y ago
  But even a submarine cable with <8 strands can have 40tbit/s. And they are still considerably cheaper to install than satellites (esp including long-term maintenance). EDIT: As an example, the new Atlantic cable "MAREA", partly sponsored by Facebook and Microsoft, has a capacity of 160tbit/s. http://www.datacenterknowledge.com/networks/facebook-and-microsoft-s-high-capacity-submarine-cable-europe-complete http://www.datacenterknowledge.com/networks/facebook-and-mic...

mulmen 9y ago

I realize that space is big but those optical links also become susceptible to obstruction. This is not a problem with cables.

sathackr 9y ago
Agreed, but I'd say the likelihood of something in space disrupting an optical path between two satellites for any significant duration is quite small, much smaller than the potential for a cable to be physically damaged. But I'm still quite certain that satellites nor free-space optics will not be coming anywhere near the capacity of fiber in the foreseeable future.

mjevans 9y ago

Doesn't really matter (yet). Satellites presently still need to downlink any transferred data and that's going to be the rate-limiting factor.

lolc 9y ago

I agree that alignment and interference are problems if one wants multiple beams. If you're using lasers one way I see is to split each signal beam into a grid so it's many rays in a grid pattern where a few rays will hit the target sensor array. Multiple grids can then be overlaid without interference. The sensor grid at the target must be able to detect which sensor is receiving which beam and adapt over time. Overall that doesn't sound infeasible to me. But then I don't do optics, so maybe I'm ignorant of a basic limitation.

walrus01 9y ago

a 288 strand cable wouldn't really be the best comparison vs satellite, in the context of submarine fiber. long distance submarine fiber is usually 2 to 8 strands maximum. the huge amount of throughput possible is achieved through a combination of high-powered, dense channel spacing, DWDM systems on the terrestrial ends of the fibers (google "ITU 25 GHz DWDM grid"), and modern high density modulation systems like 100/200/400GbE coherent (QPSK, 8PSK, 16QAM + FEC) links.

dx034 9y ago
But even a submarine cable with <8 strands can have 40tbit/s. And they are still considerably cheaper to install than satellites (esp including long-term maintenance). EDIT: As an example, the new Atlantic cable "MAREA", partly sponsored by Facebook and Microsoft, has a capacity of 160tbit/s. http://www.datacenterknowledge.com/networks/facebook-and-microsoft-s-high-capacity-submarine-cable-europe-complete http://www.datacenterknowledge.com/networks/facebook-and-mic...