I imagine it's a bigger problem than most will admit. That balloon must have had a problem. It was flying far to low. You wouldn't spot one at 90,000- 100,00 feet, and the radar signal would be minimal if it showed up at all. Perhaps they could program low earth orbit satellites to watch for them. That or better radar detection. https://scontent-yyz1-1.xx.fbcdn.net/v/t1.15752-9/329569925_1585337941933536_6628224597549576506_n.jpg?_nc_cat=100&ccb=1-7&_nc_sid=ae9488&_nc_ohc=kJbqQ8kX_1UAX8vuxzv&_nc_ht=scontent-yyz1-1.xx&oh=03_AdTEfcgXCxHJAjyczp9SE29SNcgT3T0r9xj8fQz5qhmklQ&oe=640CB356