Comment Re:This leads me to an interesting question... (Score 2) 52
And only when they weren't docking at the ISS. Basically if they were headed to the station, and something went wrong and they couldn't hook up, sending another shuttle up wasn't going to help.
One time in recent memory that they had two shuttles sitting on the launchpad, was when one was going to service the Hubble. So in this instance, they had a backup, as they would not be docking with the ISS.
Looked it up to find a picture, and found this article with a little more info. Two shuttles were only every visible on launch pads at the same time 4 times. And there was only ever 2 shuttles on launch pads (but not both visible at the same time) 18 times in history.
http://www.space.com/6597-rare-sight-twin-shuttles-launch-pad-time.html