scihouse

I don't believe they're functional anymore.

The satellites pass twice per day, so about 12 hours. Yes the size is proportional to capture time, so technically the max size is however long you can keep receiving the signal. It's a live view.

Not as far as we can tell. The map overlay is the most tempermental part of the program and only works on exceptionally clean signals.

Hubble puts out a massive amount of data that's well beyond the capabilities of any cheap SDR. And the data stream is encyrpted. Look at the satNOGs progect for science satellites that are less high tech. You can get radiation measurments off them in theory.

Technically, yes. But the signals are usually really wide band and/or you need a really big dish to pick them up. This means you'd need a lot of special equipment to do it. Also a lot of them are encrypted so you're forced to pay for access to them. There are however several amateur accessible satellites that have scientific instruments on them. We're working on receiving data from them. Once we have it working, we'll make another instructable.