As noted, certainly a passive signals intelligence gathering device (I love how the Chinese doubled down on the weather balloon thing). It flying over the US may have been a bit of a mistake, but if you release a balloon in the jet stream around Japan, it WILL go over the US a lot of the time. The Japanese in WWII used this exact tactic to try to set the Pacific Northwest on fire (and only managed to kill some campers in Oregon)
Letting it float around is likely not a bad thing. I suspect the US flying above it was waiting for it to send a focused data burst to a Chinese satellite, at which point the US knew what frequencies it was using and what satellite it was communicating with, then jamming them. Then I suspect they did a bunch of testing to see what it would take to pick these up on radar etc.
I would suspect the lower altitude ones they found recently are probably weather / research balloons.
Note the typical paths. Also note where this ballon went, and where other balloons have been spotted (at least admitted to have spotted), around Hawaii and skimming Texas over Mexico.
Interesting notes on the shoot down. Use of a sidewinder seems like a bit of overkill, $400,000 a shot (I am a bit surprised it could even lock on to it), but that is explained below. Use of a cannon for lower altitude balloon also cause some potential issues of 20mm shells eventually reaching the ground. I don't know if aerial 20mm have the same self destruct as the C-RAM (Phalanx anti missile / mortar system) but I suspect not. As noted, shooting one down with cannon was done before, but it didn't work so good (shells just went straight through and the holes likely closed up when it descended).
I would guess the US might develop a bit of a lower cost way of taking these down. Maybe using fused 20mm timed to explode as they pass through the balloon?
We’ll let the dust settle for the final list of military assets put into motion to shoot down a simple balloon, but we’re tracking: F-15Cs, F-22s, numerous tankers, an E-3 AWACS, 1 Navy P-8 Poseidon, 1 Coast Guard C-130, 4 Navy ships, and a partridge in a pear tree.
Anyhoo, once the order was given, F-22s lit the burners, climbed above 50,000 feet, and lined up for the shot.
Due to the altitude, the Raptor had to use a missile. Why: the stealthy F-22 is restricted from shooting its gun above 50,000 feet due to the design limits of the gun door (when the trigger is pulled, the door pops open, exposing the gun barrel to shoot).
The balloon was somewhere around 60-65,000 feet, and the lead Raptor took the shot at 58,000 feet.