Actually, it's not that easy (to do well, at least). 18Gpix with a 9Mpix camera means 2000 exposures. Steady-state shooting rate for most digital cameras once

Actually, it's not that easy (to do well, at least). 18Gpix with a 9Mpix camera means 2000 exposures. Steady-state shooting rate for most digital cameras once the buffer is full is about 1 shot/s, so that means it would take at least half an hour. (And it's doubtful a robot mount could move that fast.) During that time, the Sun will move significantly and unless you have a completely clear sky some clouds will likely move in front of the Sun. You'll never get a good stitch.