One difficulty might be what counts as flying. If it is a balloon and does not include any maneuvering capability the launching country might try to argue that they just released a balloon over their territory. If the upper atmosphere winds take it somewhere else they might say that an act of God and not their problem.
That might seem absurd, but I believe a lot of countries have made a similar argument for pollutants and waste they dump into the air or water. It took decades for instance to get Canada to stop dumping (literal) shit in waters that end up in Puget Sound [1].
A kind of negative of this arises too, when someone takes something out of the atmosphere or water that passes through their territory and someone downstream had been using that thing.
Generally countries don't really do well when it comes to shared resources like atmospheres and oceans and rivers as far as what happens when one does something involving that resource in their territory that affects it in someone else's territory.
That might seem absurd, but I believe a lot of countries have made a similar argument for pollutants and waste they dump into the air or water. It took decades for instance to get Canada to stop dumping (literal) shit in waters that end up in Puget Sound [1].
A kind of negative of this arises too, when someone takes something out of the atmosphere or water that passes through their territory and someone downstream had been using that thing.
Generally countries don't really do well when it comes to shared resources like atmospheres and oceans and rivers as far as what happens when one does something involving that resource in their territory that affects it in someone else's territory.
[1] https://www.king5.com/article/news/victoria-bc-will-finally-...