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Comment by timmg | Hacker News Reader

> Fun fact: light travels a bit faster in space than in an optic cable.

Doesn't it have to travel farther, tho? Does that cancel it out?

Fiberoptic cables aren't perfectly straight either, and light in space is about 30% faster than light in fiber. Considering the link up&down to space adds about 1100km, the break-even point is at around cross-continental distances.

The speed difference is big enough that high-frequency traders have been using microwave relay networks for years now. Turns out that a relay chain of point-to-point radio links (which also operate at light-in-space speeds) has enough of an advantage over regular fiber links to be worth the hassle.

Starlink is only an extra ~10% of the Earth radius at orbit height, but optic cables slow light by ~30%. So it's actually counterintuitive but "could" be just as fast. (Depending on how far you need to send data, it will regress for intra nation but will theoretically improve long distance communication).

What's the theoretical max bandwidth in LEO's near-vacuum? Could we use a wide 1GHz-1THz channel for directional beams to hit 1Tbps, given a decent SNR?

Cosmic dust and H atoms seem like non-issues for 1000km links? Would power or thermal reqs be an issue here?

I understand it's only about satellite-to-satellite, but still it's interesting.

You're missing the fact that Starlink doesn't take your traffic to the destination. It takes to a nearby downlink station. Then it goes on those same optic cables to the destination.

It can take your data to the destination via inter-satellite laser links. That's how they offer service over water and near/at the poles, where downlink stations are not in line of sight for the satellites.

"can take your data" is not the same as thing as "takes the shortest path". There is no way that Starlink is using precious inter-satellite capacity when your data can go direct to a downlink station and transit on dirt cheap fiber

No one's saying they are, the point was that they're capable of it.

Seems that they operate in various altitudes but taking your approximation of 10% of the earth radius, that is 10% + 10% as the signal needs to travel to and from the satellite to the ground, that increases the total distance travelled

In certain cases low orbit constellations with inter-satellite links (like Starlink) can beat underwater cable for latency:

https://news.satnews.com/2020/10/14/leo-speed-when-milliseco...

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