TyMoore - 1/3/2007 2:29 AMYou know, maybe something really 'low' tech might work just as well. If a thin mylar sheet were tensily formed into a circular parabolic reflector, say 1km across with a focal length of say 20km--standing off from an asteroid, such a mirror would intercept:1350 W/m^2 * pi*(500m)^2 = 1.060 GW of solar power at 1 a.u. from the sun.If the overall optical efficiency was only 60% and could focus onto a spot say 50m across, the effective irradiance on that spot would be about:0.60*1060MW/(pi*(25m)^2) = 0.324 MW/m^2 or about 240 suns. Going with a higher 'quality' optical system that allows spot size to shrink to 10m across would put the equivalent of 8.10 MW/m^2 or about 6000 suns on the spot. Knowing absolutely nothing else about the composition of the 'asteroid' I would have to say that even though this is formidable, I don't think it is enough to cause significant volatilization of the surface materials unless they were composed of ice, or were very rich in volatiles. 6000 suns sounds like enough to melt iron and silicates but you'd probably need closer to 50,000 suns worth of irradiance to get a good vapor jet going. Just a hunch though...