Hi Mike,

>> Is there a safe and legal FSO mechanism that works over these distances
>> through atmosphere shell-to-ground? And the power requirements suitable for
>> a StarLink-sized single, solar-powered system?

I don't know if you are aware of the Koruza open hardware project:

http://www.koruza.net/specs/
http://www.koruza.net/scientific/

I'm not sure that is what you are looking for, but might be a good
starting point. I can connect you to Luka Mustafa, who is the lead of
this project - we have provided some grants to the project in its early
days.

Best,
Michiel Leenaars
NLnet foundation