IIRC I think George Dyson wrote a book or article on Project Mogul at some point... or at least he researched it in depth enough to talk in detail about it for 30 minutes at a lecture of his I went to. My google-fu can't seem to find a citation to him though.
It's actually a very interesting history linked to the U-2, A-12/SR-71, etc. Seismography and atmospheric radioisotopes ended up being an easier and more precise way to detect Soviet nuclear testing. But the balloons developed were then used to spy on and map Soviet installations in Siberia, dropping their camera payloads in the sea of Japan. Of course the same sort of overflights would later be done by the U-2 and then SR-71 until the early Keyhole satellites made the very concept of atmospheric overflight obsolete.
It's actually a very interesting history linked to the U-2, A-12/SR-71, etc. Seismography and atmospheric radioisotopes ended up being an easier and more precise way to detect Soviet nuclear testing. But the balloons developed were then used to spy on and map Soviet installations in Siberia, dropping their camera payloads in the sea of Japan. Of course the same sort of overflights would later be done by the U-2 and then SR-71 until the early Keyhole satellites made the very concept of atmospheric overflight obsolete.