[jonah-archive]

Free-space optical transmission is a thing, though it's environmentally quite challenging. We tested some gear from https://www.koruza.net at the Internet Archive ~10 years ago or so (I've also built some 10G point-to-point links in my garage, though I'd hardly call them reliable). It is pretty cool to see a scratch build rather than using commercial transceivers

[esseph]

Taara is a Google/X moonshot that was recently spun off to do the same thing.

https://www.taaraconnect.com/product

[tgma]

Doesn't Starlink do that already for sat2sat comms?

[eqvinox]

Not quite the same thing as doing it in an atmosphere.

[jonah-archive]

There's not a huge amount of info I've seen on the specifics of Starlink's LISL setup, but there are a couple interesting bits in here: https://www.pcmag.com/news/starlinks-laser-system-is-beaming...

> Brashears also said Starlink’s laser system was able to connect two satellites over 5,400 kilometers (3,355 miles) apart. The link was so long “it cut down through the atmosphere, all the way down to 30 kilometers above the surface of the Earth,” he said, before the connection broke.

(the presentation that's being reported on, which I don't have access to: https://www.spiedigitallibrary.org/conference-proceedings-of... )

[pixl97]

30k would be about 1/3rd MSL air pressure, so that's pretty thin relative to what humanity experiences. Also note it says 'connection broke', not that the connection was way way slower than it would be in a vacuum.

[aerostable_slug]

That's right, the beam pointing problem is far harder when everything is moving.

[eqvinox]

There's this thing called wind that can move your outdoor installations quite a bit ;)

I'd call it a wash, space is hard, but so are atmospheric interactions, weather, foliage, and all the side effects of human habitation (like someone building a house in the middle of your laser link, yes that happens.)

[littlestymaar]

Deterministic space dynamics vs chaotic fluid dynamics (or worse, as the sibling comment by eqvinox illustrates).

Space is hard by many aspects, but on that part it's much easier than on earth.

[oskarkk]

Space dynamics are not that much deterministic. Gravity itself is kinda noisy (Earth isn't an ideal sphere with uniform density), there's the Moon, orbital decay (caused by drag from particles in low orbit, which is variable), solar radiation pressure (also variable), etc. Calculation of the dynamics will only give an approximate result, a prediction. They need constant measurement of the trajectories and frequent correction maneuvers (by ion engines). But yeah, I think that once the satellites accurately know each others trajectory, their movement shouldn't be a big issue for the lasers, as in the timespan of one laser connection it should be predictable with the required precision. And if both satellites would be on the same orbit, their relative movement should be ~0, so the laser beam ideally wouldn't move at all from the satellite's perspective, the angle would be constant.

[connicpu]

Starlink sats do fly just low enough that they experience some mild atmospheric drag. Their next generation sats will fly even lower too. But it's certainly still in the range where simple computer models will be very accurate for at least a few hours out.

[GJim]

Bizarre take.

Atmospheric scintillation is the barrier for free space laser communications on terra-firma; this is one reason we enclose the laser light in optical fibre to avoid this problem.

In space where nobody can hear you scream, scintillation isn't a problem.