The balloon was at a very high altitude (66,000ft). The F-22 launched its missile at 58,000 feet, probably right at the edge of its loaded service ceiling, and

The balloon was at a very high altitude (66,000ft). The F-22 launched its missile at 58,000 feet, probably right at the edge of its loaded service ceiling, and the missile travelled rest of the way up. Given the height, I don't think it would've been easy to shoot it down with a cannon.