Thank you guys for replying.
I am indeed developing my own mod (for asteroid interception)
I will check MechJeb source code (even though I am not sure if MechJeb has such functionality), but let me give you guys a better idea of what I am looking for..
It's fine and easy to find out all celestial bodies positions at any point in time right, so for instance I can find where Kerbin is going to be at a given epoch (date+hour) related to the other bodies, but I cannot figure it out to where the launch pad will be facing at that epoch.
One possible solution is to find out to were the launch pad was pointing at epoch zero (it is still going to be a challenge finding out where the launch pad was pointing/facing that day) and then do the planet rotation math to find out where the launch pad will be pointing at in the future, that can be done for sure but I guess there must be something done already.