Imagine that an asteroid is detected on an incoming trajectory, or some scientifically very interesting phenomenon occurs somewhere in the Solar System, prompting us to quickly send something there to learn more about it. Something off the shelf, a science probe which already awaits launch for some other intention.
How soon could a planned launcher with a prepared payload be rescheduled to launch on a completely different trajectory than initially intended? I suppose the military can do this within days or hours for their suborbital ICBM's, but I wonder how this could be done with today's most frequent orbital launchers.
Also, how soon can the payload of a prepared launch be changed? Could for example the Osiris-Rex probe (to be launched in about 8 months from when this is written) be put on the next scheduled Delta IV Heavy launcher and sent to a threatening asteroid? Or is everything just too mingled together and optimized for such dramatic changes to be feasible? Such things seem to have been simpler 50+ years ago. If so, maybe it was because of the world war sense of urgency then, and the increasing complexity now.