zlacker

>>alden5+(OP)
My understanding of the state of the art of inter-satellite optical links is that they have only been used between satellites that are basically in the same orbital plane and in more or less the same orbit. That is, the angle from one satellite to the other changes very very slowly, so that the optics don't have to do much tracking -- and consequently satellites can only form an optical link with other satellites that are ahead or behind themselves in ~ the same orbit.

Cross-plane optical links would have a trickier tracking problem.

While there's no explicit mention of same-plane vs cross-plane optical links, I assume that the first time people have a public cross-plane optical link, they will make a big deal out of it. :)

The article also mentions that SpaceX would need to do further study before using laser links between satellites and ground stations-- this kind of optical link would require both more angular tracking and probably atmospheric correction as well.

>>ble+c55
Tracking is an issue, but doppler can also be a thing. At orbital speed (actually up to 2x orbital speeds) the doppler effect between two satellites can change the frequency enough to cause interference. Moving a scope to track a moving target is one problem, allowing the algorithms to adapt at the frequency shifts on the fly another.

>>sandwo+z65
Doppler is not a big problem with lasers because the carrier frequency is so much higher than RF that it doesn't matter; it's bang-bang AM modulated.

I'm assuming two things: That something like Manchester coding is being used so that some clock skew is tolerable, and that the laser carrier is not in fact being frequency or phase modulated. Last I checked FM and PM of optical frequencies was not yet practical outside of laboratories, but I'm happy to be corrected.