[ableChair]

I understand your point, but my recollection was that the energy levels delivered were also astronomical. Something on the order of 10 exp 21 Joules. That can't be required just to burn metal; it must be either for penetrating a media or for the radius of the beam (as one poster pointed out).

[Dan Evans]

That can't be required just to burn metal; it must be either for penetrating a media or for the radius of the beam (as one poster pointed out).

Yes, and a lot of other things too. Maybe that figure was was the power input to the laser and the laser was very inefficient. Do you have a link to that source? Was it referring to an xray laser? If so, they weren't very collimated. The beam could have expanded a thousand miles wide. And also what does this have to do with atmospheric absorption? SDI was to shoot down missiles during the boost phase after they left the atmosphere.