Could parabolic mirrors in low earth orbit be used to melt incoming comets? Power plants focus sunlight to make steam power.
jee, the problem is that mirrors cannot concentrate a diffuse source more than it's peak radiance per unit solid angle (not sure I have the right physical quantity here, but should be close). The Sun appears to be a 6000K black body. So any mirror is going to appear to be at best a 6000K body. The only thing that differs is the apparent size of the mirror to the asteroid.