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0 pointsmlyle3y ago0 comments

> it's extremely hard to do at those data rates.

> if it wasn't there would be existing examples.

Let's see. NASA downlinked from the moon to the ground, through the atmosphere at OC-12 rates back in 2013-- so about 100x the distance, with the added penalty of traversing the atmosphere. NFIRE did 5.6 gigabit/sec LEO to ground (again through the atmosphere) in 2011-- shorter distances but higher angular rates which is the "hard part". And EDRS does 1.8gbit/sec over longer distances in geostationary orbit. Both flown and proven.

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shaklee33y ago

are you really comparing the moon to the earth with two satellites at much closer distances moving rapidly?

mlyleOP3y ago

> are you really comparing the moon to the earth with two satellites at much closer distances moving rapidly?

I'm comparing to LEO to ground, which has a higher rate of angular movement (e.g. harder to point at) than LEO-to-LEO in the same shell, among other things.

I've built systems that point to sub-arcsecond precision at satellites in LEO. It's not quite an off-the-shelf controls problem (e.g. good luck getting a COTS motion controller to hit-a-fast-moving-target-at-a-chosen-time, rather than follow a track and not care about time) but it's not super hard, either.

shaklee33y ago

you should probably have worked for Facebook a few years back when they threw billions at the problem and couldn't solve it.

mlyleOP3y ago

Citation needed, for Facebook: A) spent billions of dollars on this specific problem (free space optical links in space), and B) couldn't solve it.

Given that there's systems that have successfully flown doing links from GEO to LEO (e.g. high angular rates again), using several year old conservative technology, it's not so bad.

There's a million little details, of course. Just conduction cooling for fast optical transceivers is going to be annoying in space, for instance.

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shaklee33y ago

are you really comparing the moon to the earth with two satellites at much closer distances moving rapidly?

mlyleOP3y ago

> are you really comparing the moon to the earth with two satellites at much closer distances moving rapidly?

I'm comparing to LEO to ground, which has a higher rate of angular movement (e.g. harder to point at) than LEO-to-LEO in the same shell, among other things.

shaklee33y ago

you should probably have worked for Facebook a few years back when they threw billions at the problem and couldn't solve it.

mlyleOP3y ago

Citation needed, for Facebook: A) spent billions of dollars on this specific problem (free space optical links in space), and B) couldn't solve it.

Given that there's systems that have successfully flown doing links from GEO to LEO (e.g. high angular rates again), using several year old conservative technology, it's not so bad.

There's a million little details, of course. Just conduction cooling for fast optical transceivers is going to be annoying in space, for instance.

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j / k navigate · click thread line to collapse