[aptwebapps]

Planes don't always fall straight down. From that height they could go a long way. It would be hard to keep them over empty land and still close enough to enough people to use them.

While it's true that we might have had them sooner if we were willing to use RTGs, it seems like solar tech is good enough now.

[electromagnetic]

I would assume if it has to stay above the weather its wings would be very prone to breaking. However at a descent rate of 0.5m/s and a 40:1 glide ratio. Descending the ~20,000ft before hitting weather would mean 150 miles travelled before being at risk of breaking up.

And I don't think an ejectable RTG would go down well with the public, although passive guidance onto a radio source would work and guided munitions sit for potentially decades and have to remain workable.

I wonder how feasible it would be to produce an aerostat that can reach 70,000ft. The DHS(or DEA, the networks shifted hands a few times due to budget cuts, etc) is operating radar based systems with one tonne payloads at 15,000ft. They have a system wide 98% operational efficiency despite being subject to extreme weather.

Carrying on my RTG love, the thermal output of shorter half-life materials could easily out produce the BTUs produced by a hot air balloon burner (800w/kg of vehicle weight) as the space based RTGs can already approach this and have longevities in the centuries. So I wonder if a hot air aerostat would have a longer longevity than the current helium based ones.