Why does Price say "good" after doing something "evil"?

Some spoilers, if you haven't yet played MW2.

Throughout MW1 and MW2, Price seems to be a good guy. However there is a short part of MW2 where he seems to turn bad. After launching the Russian nuke at America, someone frantically informs him that the missle is launching, and he simply replies "Good". One of the many things in the MW2 plot that totally threw me.... What was the explanation for shooting a nuke at his allies?

Solution 1:

It's part of his plan. He planned for the missile to explode above the atmosphere, creating an EMP that disabled vehicles and electronics. The Americans still had the advantage in this situation.