[hakuseki]

What's so difficult about optical links from deep space compared to low earth orbit, where 200 gigabit throughput has been achieved? Is it just the attenuation?

I would have imagined that we could upgrade the communication equipment on a space probe much more easily than we could add fuel for a return trip.

[mlyle]

> What's so difficult about optical links from deep space compared to low earth orbit, where 200 gigabit throughput has been achieved? Is it just the attenuation?

Yup; 300km vs 600000000km. Less than a trillionth of the power comes through for the same emitted power and apertures.

So, you end up having to make apertures much larger and point much, much more precisely. You can also increase laser power some, but that's a small part of your solution.

(Or, of course, you can reduce speeds to have more energy per bit).

I don't think anyone is serious about shipping back physical data from deep space, but the station wagons full of tape thought experiment is always fun.

[jvanderbot]

I am semi-serious. But it's more about a periodic backup of an on site science station.

An on site (orbital) station could run all the models and algorithms and analysis you want on the gobs of imagery and spectral maps / cubes you can gather in real time.

Analysis is an excellent compression algorithm. But, you'd want the raw data eventually, and that means either trickling back 0.1%, or waiting a few years for the full set.

https://josh.vanderhook.info/publications.html#josr2022sspe

[canoebuilder]

Hmm

What’s your sense about SETI or the Fermi paradox, if a signal becomes so vastly diluted just within our solar system?

I’m sure the SETI people have thought about this and made various calculations, but with the inverse square law and the vastness of space, maybe “needle in a haystack” is optimistic.

Is it the wrong model to think that anything but maybe a galaxy scale civilization is just going to have it’s signals more or less totally dissolved into seemingly random cosmic fluctuations, relative to our sensors/receivers at least?

[mlyle]

Maybe. Recovering data on interstellar distances is hard.

Integrating a long time to see if there's a signal there above background levels is maybe not so hard (especially if it was intended for detection in this scenario).

The big issue for data recovery is energy per symbol. If you can integrate for hours, that can still be a lot of "special photons" (whether they're on a weird radio frequency or light wavelength).