Pretend a scientist has discovered that a killer asteroid will hit the Earth in a matter of weeks ;

You should have tried to divert the trajectory of the asteroid's orbit LONG before then, when it would have taken the least amount of power (read rocket power) and the least amount of mass and fuel to deflect the asteroid's path. When an asteroid is only weeks away from impact( it would have been observed LONG before it got that close), it's TOO late. Blowing it up will just create a bunch of less massive impactors that will do more damage over more surface area of the Earth when they impact.

Three part plan??? I'm not going to waste my time simplifying it any more than I already have. You obviously don't want to understand the science behind this. (My apologies if you do want to know. Yes. I'm still in grumpy mood, and I'm getting apple juice all over my keyboard from the apple I am eating.Sticky keys. Ughh!)

This is an EXCEEDINGLY unlikely scenario, to the point of abject implausibility, given that killer asteroids tend to be detectable LONG before a potential impact. Example: 99942 Apophis is well short of an extinction event rock, and it was detected in 2004, with the first "potential" impact in 2029. This was later resolved to be a clear miss, with 2036 being the next potential impact date.

The fanciful nature makes precludes a realistic answer.

I smell home work.
How big is the rock? If it is above a certain size and a couple weeks out there is very little that can be done, in which case strap every nuck you got to any rocket you got and blow up all nukes on one side of the asteroid. Blow the nukes up one at a time so that they don't interfere with eacthother. there should be a sweet spot, a distance from the asteroid that will allow you to not break the asteroid and close enough that the nukes will push it away.

we launch a whole bunch of nuclear missiles at it. Knock it off course to it would not hit the earth. You don't want to blow it up. You just want to blow a nuclear bomb up next to it, so that way it would change it's duration. So that way it does not hit the earth.

Watch the movie Armageddon.

lol - nice try at getting us to do your homework for you....

Sorry, but this is *your* assignment - not ours - and its up to *you* to create your own plans.