The maximum resolving power of a satellite with a 2.4m (8 foot) lens, at 650 km (400 miles) orbit, is 10 cm (4 inches). The Hubble is in a circular orbit so I don't see how it can do better than that. http://everything2.com/title/Spy+satellites+can%2527t+read+y... Spy satellites often use highly-elliptical orbits to swoop closer, say 320 km (200 miles) for part of their orbit.
edit OK I might have found an answer actually. Using multiple exposures from different angles, you can resolve an object as if you had a lens that spans the entire angle. https://en.wikipedia.org/wiki/Aperture_synthesis I'm sure the movable secondary lens helps with this :) I'd heard of this technique used by ground-based radio telescopes before, and according to Wikipedia, the ability to do this within the visible spectrum has become possible only recently.
Every time I read about this, I instantly wonder whether this means that I can turn my crappy consumer camera into a spy device.
We have windows that span about fifty feet in the office, and a hotel across the street; if someone left the complimentary bible in the window open to a random page, could I combine multiple exposures into an image detailed enough to read the text?
Not using that technique, since it requires that you measure the phase of the incoming light. But there are some super-resolution techniques that might double a noisy digital sensor's performance. https://en.wikipedia.org/wiki/Super-resolution Try the ClearCam iPhone app.
I assume the NRO telescopes had their instrumentation removed before gifting the optics to NASA, yes? Or were they really just "blank casings"? Either way, it's kinda freaky to think that there are such powerful monitoring devices in space...
Since they were never launched, and (according to NASA) the satellite itself is the part that takes the longest to build, it's plausible that the instrumentation was never installed before the mission was scrapped for whatever reason.
100+ meter diameter radio telescopes pointed at the earth. That's the same size as the largest steerable ground-based radio telescopes. Makes you wonder what they can hear.
