notes from day 14 at annarbor.com
Why was the launch scrubbed this time?
Problem circuit card in the pyrotechnic initiator controller (STS-51)
Perseid meteor shower (STS-51)
I didn't see a complete list of all possible reasons, but there are lots of problems that can happen when you launch into space. I watched two launches in the last few days - the SpaceX rocket which went up without a hitch, and the shuttle which went up on its 6th try, all very exciting to see.