>
>> What I actually wanted to posit in relation to that is that one could
>> get sooner a c-cabable backbone sibling by marrying two ideas: the
>> airborne concept ongoing as outlined plus what NASA is planning to
>> bring about for the space backbone, e.g [1][2]. It's laser based
>> instead of directed radio-wave only. Sure, both is in the speed range
>> of c, apparantely, laser transmission has in addition a significantly
>> higher bandwidth to offer. "10 to 100 times as much data at a time as
>> radio-frequency systems"[3]. Attenuations to photons in clean
>> atmospheric air are neglible (few mps - refractive index of about
>> 1.0003), so actually a neglible slowdown - easily competing with top
>> notch fibres (99.7% the vacuum speed of light). Sure, that's the
>> ideal case, though, if cleverly done from the procurement of
>> platforms and overall system steering perspective, might feasible.
>
> Todays laser links are in the few km per hop range, with is easily at
> least one magnitude shorter than radio based equivalents.
>
Hold on! This is a severe oversimplifcation, isn' it. The devices you're
probably referring to are in the low-end segment, dillentically and
maybe terrestrially operated only - to mention a few limiting factor
conceivable possibly being perceived.

Certainly, there are range limiting factors when fully submerged in the
near-ground atmospheric ranges. E.g. in the darkest snow storm, one
cannot expect optics to be reliablly working - admitting that.
Nothwithstanding, recent research[1] showed astounding achievements of
FSOs even in harsh atmospheric conditions - "up to 10 gigabits per
second" while in vivid movement, in heavy fog ... for a single pathed laser.

90% mass of the atmosphere  is below 16 km (52,000 ft), therefore also
most of it's randomness[2]. Meaning, one only had to surpass this
distance to more decently unfold the capabilities of an airborne
backbone. Therefore, a hierarchy of airborne vessels might be necessary.
Might smaller, more numerous ones gatewaying the optics out of the dense
parts of the atmosphere to the actual backbone-net borne lasers, might
by doing this relaying not laser beam based. Far more mitigation
techniques are conceivable. From there on, the shortcomings appear
controllable.

> I don't know the physics behind it, but people who have better insight
> than I do tell me "it's hard" to run longer hops (if one wants any
> kind of high bitrate).
If one looks up what is achievable in space, where the conditions
shouldn't be too different from earth atmosphere over 16 km. Thousands
of kilometres for a single hop, single path. Now imagine a decent degree
of multipathing.

Physical intricacies are certainly a headache in this topic, though
shouldn't be decisive, I'd dare to categorize the largest complexity
compartment of such a system into the algorithmics for steering,
converging or stabilizing the airborne components, directing the optics
problerly and in time. The overall automatic or even autonomic
operations to abstract it.

Probably, me forming some papers wrapping this up would be worthwile.

[1]https://phys.org/news/2017-08-high-bandwidth-capability-ships.html

[2]https://arxiv.org/pdf/1705.10630.pdf

-- 
Besten Gruß

Matthias Tafelmeier