The biggest hurdle would seem to be electrical power.
That, and the fact that they have to chase them all over hell-and-gone and relaunch them all the time. Just gas for the chase truck would cost many thousands a year.
The idea of powered airships at great height might work. But the technology would be pretty expensive. And actually, if you're going to power the thing, the best would probably be that fixed wing NASA experiment that reached a record height a year or two ago.
NASA's technology would power their airplane with solar cells (it flys so high that clouds never cover it, and it's over the top of thunderstorms). Night flight would be with fuel cells, an interesting idea where the H2O working fluid was regenerated to H2 during the day for use at night. I suppose the O2 is atmospheric (wonder how they keep it from freezing).