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Comment by fallingknife | Hacker News Reader

This will get us to Mars orbit, but don't we have to go to radio anyway to relay through the atmosphere to the surface?

Mars atmosphere can barely be called that. It's less than one percent of earth's pressure. People just have a wrong perception of it because of wildly inaccurate depictions in movies like The Martian. And even if you want to transmit using radio between the surface and low orbit, it's far less of a bandwidth issue than transmitting over millions of kilometers. Deep space transmissions of the future will use optical wavelengths instead of radio, there's no question about it.

It’s not just the atmosphere that’s an issue though, having a laser in earth’s orbit track something on mars’ surface and vice versa would require some incredible tracking, it would be easier to go from orbit to orbit

It's not that hard with modern electronics. Telescopes with adaptive optics have been doing that since the 90s. Also beware that a laser doesn't remain perfectly coherent over many kilometers (let alone millions). So it's not like you need to perfectly hit a satellite dish area of a few m^2 on the surface of mars from earth. It's not really any harder to do from the surface than from orbit. In fact it might actually be easier since you don't just have to account for the rotation and orbit of earth but also for the orbital velocity of the relay.

The laser experiment in the OP terminated at a ground-based optical telescope in California.

If you wanted a solution robust against clouds, I don't know if it'd make more sense to have a optical->radio relay satellite in earth orbit, or to have a redundant network of ground-based optical receivers in multiple places.

(There's a quirk of physics that transmitting and receiving aren't symmetric in these setups. All of the atmospheric distortion happens in the few kilometers of atmosphere, out of tens of millions of km path lengths. Because the angular distortion happens at the start of their optical paths, laser signals going from Earth–outwards will have much larger absolute distortions, than signals being received on Earth from space).

Aren't photos and radio waves basically the same thing?

I guess the only issue that could happen is the scattering due to atmosphere, but as others have noted it's barely existent.

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