How fast can a launcher be retargeted?

Question

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.

Answer 1

It depends, on how much testing you want to do, etc. Each launch has a specified vibration testing that is done to ensure that there won't be any problems. Swapping out a payload, depending on the type, can actually be fairly easy with many of today's spacecraft, that have a modular design. It depends somewhat on the type of payload, mind you.

As for the launch itself, it could be done within a matter of a few days. The most difficult thing about changing the launch is to ensure that the "Expected Casualty" figures are still met by the flight path, and if there was something truly important, that might even be bypassed.

The military is rumored to have the capability to launch spy satellites in a very short period of time, through a contract with ULA.

For an interplanetary object, there are a lot more concerns. Launch windows, figuring out the trajectory, etc. These would likely take priority.

For reference, the book "The Martian" does a reasonably good example of what it would take to launch a payload really quickly, and that likely involved items already in place.

Bottom line, this kind of re-direction could probably be done, but it might be difficult.