That looks like a very cool option and effort. Like the Chinese balloons that overflew the US in the last (few?) years, it would likely be challenging to shoot down. Otoh, it might cause some diplomatic disagreements about overflight.
There are a number of competing theories in international law, with varying
criteria, to delineate the upper limit delineating airspace versus outer
space. This debate is unsettled. [0]
There may also be some technical challenges having to do with beamforming rf to the vehicle. Starshield like Starlink has the predictability of orbital vehicles for tracking. It would be interesting to understand how a ground station focuses on the solar glider.
There might be less societal objection to "satellites in space orbiting the planet" than to "planes flying continuously over the same area," even if both can be used for similar purposes. I'd assume it'd also be easier to disrupt suborbital systems like that than satellites, but I could be wrong.
To shoot something down at 70,000 ft (21 km) all you need is a conventional military jet fighter, and a long-range rocket, or even a MiG-31 with a conventional cannon. At best you can make these birds cheaper than the rocket + flight time.
Something that flies at the upper edge of the stratosphere, at 40-50 km (160,000 ft) would be hard to reach with currently available means. You can of course fire a THAAD at it, but you can fire a THAAD at a Starlink satellite as well.
Exactly; it's a limited and very expensive capability. Nobody would want to spend it on a $100k stratospheric flying vehicle, if the latter existed. It does not exist though, if you do not count weather balloons.
0. https://opil.ouplaw.com/display/10.1093/law:epil/97801992316...