The amazing thing about these specialized balloons is that they can reach altitudes upwards of 10 miles--and they usually stay airborne for about 90 minutes. I would have thought they stay up for a longer period of time, but the balloons expand and pop at altitude. There are, however, some balloons that have much longer durations--I think they're referred to as long-duration high altitude balloons. I haven't read much about these high pressure balloons yet, but I seem to recall that they can stay aloft for days. If the normal weather balloons can travel a distance of 150 miles in just 90 minutes, then I wonder what kind of distance a balloon can cover over a few days worth of drifting? And this train of though led me to the question I've been researching for the last hour:
What happens when a balloon crosses international borders into the airspace of another country?
I assumed that the answer would have something to do with the altitudes associated with sovereign airspace, but based on this paper published by the Space and Telecommunications Law Program at the University of Nebraska-Lincoln, there is no universally agreed upon altitude limit for sovereign airspace (though 100km is starting to look like the going rate). But even if the figure is much lower and high altitude balloons are technically sailing in unregulated/unowned airspace, they still come back to Earth at some point. So the next question is:
What if I launch a balloon that ends up landing in China? Is there some kind of international treaty that covers this scenario, as is the case with FAA regulations and domestic weather balloons? Or is this something that long-duration ballooners need to be constantly aware of?