During the launch replay, I kept seeing a tank filled with some sort of liquid. Was that the fuel tank or was that some sort of experiment?
That was the inside of the second stage.
Amazing that instrumentation has advanced to the point where they can get video from inside a propellant tank. Wasn't too long ago that putting any camera at all on launch vehicles was too expensive in terms of mass penalty and allocated telemetry bandwidth. I'm guessing the Columbia accident spurred the advance.