> If I had to guess, I wonder if they are data relay nodes to collect information from Chinese/Russian bugged equipment that cannot transmit over the internet (eg. compromised equipment in secure military facilities).

An interesting theory, although I would be at least a little worried if secure facilities did not already have some form detection of signals they do not expect.

OTOH, you could instead have something gathering data, and the passing balloon could send a signal to the listening device(s), and then quickly dump+relay the data collected over time.

And balloons have the option to loiter longer than say a satellite or other means. I assumed they were doing some sort of RF monitoring more than the photo type monitoring.

A lot of the comments focus on "Why would they use balloons when they have satellites?" But the reality is they are cheaper, can be oriented inexpensively and can loiter. Not to mention the lower radar signal and other detection issues (made clear by the revelation that this has been going on for a while).

Now that launching/steering balloons is down to the hobbyist level...it seems a larger corp or state actor could easily use them in a way that seemed impossible 30 years ago.

At least WRT the first balloon that kicked off all of this hubbub, NYTimes report that the State Department have disclosed it was "equipped with an antenna meant to pinpoint the locations of communications devices and was capable of intercepting calls made on those devices": https://www.nytimes.com/article/chinese-spy-balloon-mission....