5 ms·

How close are we to space-based laser ISPs? I imagine that you squeeze terabits of optical bandwidth into a single mirror "dish"..

kbar13 12y ago
imagine a world where this was the norm. You wouldn't need to worry about outages due to falling trees or utility poles exploding or people screwing with your wires. Then you step outside to look up at the sky and you lose your eyesight
- deleted 12y ago
  [deleted]
- mnw21cam 12y ago
  Day of triffids scenario aside, no you won't lose your sight from a 2.5W laser pointing downwards from 260 miles up. The power level is too small. People think that lasers produce a parallel beam. They don't - they are diffraction limited by the width of the beam. The narrower the beam, the more it spreads out. For example, a 1cm wide beam produced by a perfect laser would spread out to around 20m wide when it hits the ground from 260 miles away. That's assuming visible green light - if it's infra-red (or even just red) then the spread will be wider.
- kahirsch 12y ago
  But it wouldn't work on a cloudy day, presumably.
awda 12y ago
Latency is a real problem. Distances to satellites in orbit are very long. Also, there is a scalability problem. How many ground targets can a satellite simultaneously provide service to? My guess is, not a lot. This could be an incremental bandwidth (but not latency) upgrade over existing satellite internet service to remote areas (by transmitting to a single ground receiver that serves a local area), but that's about it.
- throwaway_yy2Di 12y ago
  "Distances to satellites in orbit are very long." That's not a fundamental limit. Existing satellites have high latency, because they're sited at insanely high altitude -- ~36,000 km (6 earth radii; 120 light-milliseconds (-> 240 ms minimum round trip)). This is for engineering and economic reasons which aren't solid: one, because geostationary [0] orbits allow dumb dishes that can't track moving objects; and two, because it allows small satellite networks -- i.e. one satellite covering a whole continent -- commensurate with the small size of the market. If instead you had a network of satellites at say 500-1,000 km (unjustified guess), the latencies could be no worse than a direct optical fiber. edit: Here's a sophisticated diagram, https://i.imgur.com/t1SOVpZ.png https://i.imgur.com/t1SOVpZ.png [0] https://en.wikipedia.org/wiki/Geosynchronous_orbit#Geostationary_orbit https://en.wikipedia.org/wiki/Geosynchronous_orbit#Geostatio...
  - mbreese 12y ago
    If you're talking lasers though, don't forget to factor in the time needed to reacquire a new satellite in once the existing one goes over the horizon. The shorter the orbit, the more often you'd have to do this.
    - throwaway_yy2Di 12y ago
      I actually have zero idea how such a thing could work, which is why I'm asking here. :)
    - sneak 12y ago
      Fuck everything, we're doing five (simultaneous) lasers.
      - esbonsa 12y ago
        and we are using drones to deliver them, whether you like it or not
  - derekp7 12y ago
_mulder_ 12y ago
The big problem is getting through the Earth's Atmosphere. Space observatories are nearly exclusively located on mountains or areas with little atmospheric 'pollution'. I'd imagine even the OPALS system can only be used when it's not too cloudy/rainy. This technology does exist on land however. Free Space Optics[1] has been around for a while but hasn't taken off in a big way because it's less reliable than sending light down a fibre cable, even though it is cheaper. [1] http://en.wikipedia.org/wiki/Free-space_optical_communication http://en.wikipedia.org/wiki/Free-space_optical_communicatio...

kbar13 12y ago

imagine a world where this was the norm. You wouldn't need to worry about outages due to falling trees or utility poles exploding or people screwing with your wires. Then you step outside to look up at the sky and you lose your eyesight

deleted 12y ago
[deleted]
mnw21cam 12y ago
Day of triffids scenario aside, no you won't lose your sight from a 2.5W laser pointing downwards from 260 miles up. The power level is too small. People think that lasers produce a parallel beam. They don't - they are diffraction limited by the width of the beam. The narrower the beam, the more it spreads out. For example, a 1cm wide beam produced by a perfect laser would spread out to around 20m wide when it hits the ground from 260 miles away. That's assuming visible green light - if it's infra-red (or even just red) then the spread will be wider.
kahirsch 12y ago
But it wouldn't work on a cloudy day, presumably.

awda 12y ago

Latency is a real problem. Distances to satellites in orbit are very long. Also, there is a scalability problem. How many ground targets can a satellite simultaneously provide service to? My guess is, not a lot. This could be an incremental bandwidth (but not latency) upgrade over existing satellite internet service to remote areas (by transmitting to a single ground receiver that serves a local area), but that's about it.

throwaway_yy2Di 12y ago
"Distances to satellites in orbit are very long." That's not a fundamental limit. Existing satellites have high latency, because they're sited at insanely high altitude -- ~36,000 km (6 earth radii; 120 light-milliseconds (-> 240 ms minimum round trip)). This is for engineering and economic reasons which aren't solid: one, because geostationary [0] orbits allow dumb dishes that can't track moving objects; and two, because it allows small satellite networks -- i.e. one satellite covering a whole continent -- commensurate with the small size of the market. If instead you had a network of satellites at say 500-1,000 km (unjustified guess), the latencies could be no worse than a direct optical fiber. edit: Here's a sophisticated diagram, https://i.imgur.com/t1SOVpZ.png https://i.imgur.com/t1SOVpZ.png [0] https://en.wikipedia.org/wiki/Geosynchronous_orbit#Geostationary_orbit https://en.wikipedia.org/wiki/Geosynchronous_orbit#Geostatio...
- mbreese 12y ago
  If you're talking lasers though, don't forget to factor in the time needed to reacquire a new satellite in once the existing one goes over the horizon. The shorter the orbit, the more often you'd have to do this.
  - throwaway_yy2Di 12y ago
    I actually have zero idea how such a thing could work, which is why I'm asking here. :)
  - sneak 12y ago
    Fuck everything, we're doing five (simultaneous) lasers.
    - esbonsa 12y ago
      and we are using drones to deliver them, whether you like it or not
- derekp7 12y ago

_mulder_ 12y ago

The big problem is getting through the Earth's Atmosphere. Space observatories are nearly exclusively located on mountains or areas with little atmospheric 'pollution'. I'd imagine even the OPALS system can only be used when it's not too cloudy/rainy. This technology does exist on land however. Free Space Optics[1] has been around for a while but hasn't taken off in a big way because it's less reliable than sending light down a fibre cable, even though it is cheaper. [1] http://en.wikipedia.org/wiki/Free-space_optical_communication http://en.wikipedia.org/wiki/Free-space_optical_communicatio...