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A comment on Musk files to provide Internet service from space. Parent comment

Re:Musk files to provide Internet service from space by yincrash on Tuesday June 09, 2015 @09:58PM (#9689610)
~250ms RT latency http://en.wikipedia.org/wiki/Satellite_Internet_access#Signa...

Hubble is a pretty low orbit. Geostationary orbits are @ 36,000km

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Re:Musk files to provide Internet service from space by greglindahl on Tuesday June 09, 2015 @10:02PM (#9689623)
SpaceX is proposing putting them @ 1,100km.

The speed of light is faster in space than it is in optical fibre.

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Re:Musk files to provide Internet service from space by coryl on Tuesday June 09, 2015 @10:05PM (#9689631)
The speed of light is faster in space than it is in optical fibre.

Could you elaborate? Thanks

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Re:Musk files to provide Internet service from space by greglindahl on Tuesday June 09, 2015 @10:12PM (#9689660)
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.

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Re:Musk files to provide Internet service from space by toomuchtodo on Tuesday June 09, 2015 @10:11PM (#9689651)
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.

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Re:Musk files to provide Internet service from space by msravi on Wednesday June 10, 2015 @12:23AM (#9690030)
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...
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Re:Musk files to provide Internet service from space by lmm on Wednesday June 10, 2015 @06:36AM (#9691054)
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.
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Re:Musk files to provide Internet service from space by brian_ on Tuesday June 09, 2015 @10:53PM (#9689812)
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.
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Re:Musk files to provide Internet service from space by paulvs on Wednesday June 10, 2015 @12:04AM (#9689973)
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.
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Re:Musk files to provide Internet service from space by Robin_Message on Wednesday June 10, 2015 @04:51AM (#9690717)
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?

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Re:Musk files to provide Internet service from space by yincrash on Wednesday June 10, 2015 @11:54AM (#9693121)
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?
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