3 ms·

~250ms RT latency http://en.wikipedia.org/wiki/Satellite_Internet_access#Signal_latency http://en.wikipedia.org/wiki/Satellite_Internet_access#Signa... Hubble

~250ms RT latency http://en.wikipedia.org/wiki/Satellite_Internet_access#Signal_latency http://en.wikipedia.org/wiki/Satellite_Internet_access#Signa... Hubble is a pretty low orbit. Geostationary orbits are @ 36,000km

greglindahl 11y ago
SpaceX is proposing putting them @ 1,100km. The speed of light is faster in space than it is in optical fibre.
- coryl 11y ago
  The speed of light is faster in space than it is in optical fibre. Could you elaborate? Thanks
  - toomuchtodo 11y ago
    http://www.rpi.edu/dept/phys/Dept2/APPhys1/optics/optics/node4.html http://www.rpi.edu/dept/phys/Dept2/APPhys1/optics/optics/nod... Speed of light in vacuum > speed of light in optical fiber. Same reason high frequency traders are using microwave between Chicago and New York instead of a fiber connection.
    - msravi 11y ago
      Is it possible to build a multi-mode "fiber" with an air core so that a significant part of the light's path is through air? The outer sheath made of optically dense material would only be used for internal reflection to "guide" the beam...
      - lmm 11y ago
        No. The core has to be denser than the outside for the guiding to work; if you made a "fiber" like you describe the signal would just travel through the sheath - if it was heading towards the core it would internally reflect to stay within the sheath.
  - deleted 11y ago
    [deleted]
  - greglindahl 11y ago
    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 https://en.wikipedia.org/wiki/Speed_of_light The same is true for light traveling through water, air, and so forth.
  - brian_ 11y ago
    My understanding of it is that when light passes through a medium, it does not do so in a straight line. So, while the actual speed of light remains constant, it takes longer to get from one end to the other.
    - paulvs 11y ago
      To be precise, light can travel through a medium in a straight line, but it bends when it passes from one material to another. The light bounces off the inner walls of the fiber in a zig-zag fashion as it propagates, so it cannot possibly travel at the speed of light. It depends on the index of refraction as mentioned.
    - Robin_Message 11y ago
      No, the speed of light decreases in a medium – in fact, the proportional decrease in speed is the refractive index of the material. So much for it being constant huh?
- yincrash 11y ago
  so ~7ms RT. The satellites will be moving in the sky relative to the ground, so users will need to be able to switch satellites often?

greglindahl 11y ago

SpaceX is proposing putting them @ 1,100km. The speed of light is faster in space than it is in optical fibre.

coryl 11y ago
The speed of light is faster in space than it is in optical fibre. Could you elaborate? Thanks
- toomuchtodo 11y ago
  http://www.rpi.edu/dept/phys/Dept2/APPhys1/optics/optics/node4.html http://www.rpi.edu/dept/phys/Dept2/APPhys1/optics/optics/nod... Speed of light in vacuum > speed of light in optical fiber. Same reason high frequency traders are using microwave between Chicago and New York instead of a fiber connection.
  - msravi 11y ago
    Is it possible to build a multi-mode "fiber" with an air core so that a significant part of the light's path is through air? The outer sheath made of optically dense material would only be used for internal reflection to "guide" the beam...
    - lmm 11y ago
      No. The core has to be denser than the outside for the guiding to work; if you made a "fiber" like you describe the signal would just travel through the sheath - if it was heading towards the core it would internally reflect to stay within the sheath.
- deleted 11y ago
  [deleted]
- greglindahl 11y ago
  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 https://en.wikipedia.org/wiki/Speed_of_light The same is true for light traveling through water, air, and so forth.
- brian_ 11y ago
  My understanding of it is that when light passes through a medium, it does not do so in a straight line. So, while the actual speed of light remains constant, it takes longer to get from one end to the other.
  - paulvs 11y ago
    To be precise, light can travel through a medium in a straight line, but it bends when it passes from one material to another. The light bounces off the inner walls of the fiber in a zig-zag fashion as it propagates, so it cannot possibly travel at the speed of light. It depends on the index of refraction as mentioned.
  - Robin_Message 11y ago
    No, the speed of light decreases in a medium – in fact, the proportional decrease in speed is the refractive index of the material. So much for it being constant huh?
yincrash 11y ago
so ~7ms RT. The satellites will be moving in the sky relative to the ground, so users will need to be able to switch satellites often?