SIGINT, ELINT, and MASINT. Putting a bunch of radars on a balloon platform is relatively cheap, much cheaper than a satellite. It's also got better plausible deniability than a similarly equipped airplane.
Ground penetrating radar over military bases can yield useful intelligence. So can gauging the response times and radio characteristics of air defense radars. Then there's good ol' photo reconnaissance. Such a huge platform could easily have stabilized mounts for high resolution cameras. Being an order of magnitude closer to the targets makes for better photos.
Ground penetrating radar over military bases can yield useful intelligence. So can gauging the response times and radio characteristics of air defense radars. Then there's good ol' photo reconnaissance. Such a huge platform could easily have stabilized mounts for high resolution cameras. Being an order of magnitude closer to the targets makes for better photos.