Flight termination system would be a more appropriate term. Your not look for an Michael Bay explosion, just for the balloon to pop so it will hopefully fall to the ground in a safe area and before it’s unwanted course becomes dangerous.
Per FAR 101.35 which includes unmanned balloons:
(a) No person may operate an unmanned free balloon unless -
[URL unfurl="true"]https://www.ecfr.gov/current/title-14/chapter-I/subchapter-F/part-101[/URL]
This is more about balloon legislation than anyone ever cared to know about.
According to most US agencies, space starts around 80km or just over 260,000ft. According to just about everyone else in the world it’s at the Karman Line, 100k ft.
It’s my understanding there really is no agreement of up to what altitude a country can consider their airspace. It seems like the accepted rule of time is that things that are in orbit around the earth are considered in space not in one’s airspace. Anything that’s not in orbit, like an airplane or balloon, must be in the atmosphere and therefore being in one’s airspace.
