Being older than most of you, I remember doing some of these calculations about burn times, laser intensities, etc. more than 20 years ago. (Although Reagan did not announce SDI until around 1983, the topic was widely discussed in the late '70s. "Scientific American" published articles by Prof. Kosta Tsipis, Richard Garwin, and others about the difficulty of intercepting ICBMs with lasers and particle beams. I remember some of these articles from circa 1977-79. I even used one of the them as the basis for a presentation I made to DARPA in Washington on a kill method for satellites.) A lot of the calculations being sketched out here, of watts/cm^2, dwell times, gold coatings, etc. are slightly off-base. We've known for 20+ years that the kill method is to use a short pulse to "push" (not from the photons' momentum) in the thin wall of an ICBM's fuel system. A very short pulse can produce enough ablative heating, a kind of "puff," to trigger buckling of the very thin wall of an ICBM. So the theory goes. Countermeasures to traditional "heating" are so easy to imagine (rapidly spinning the missile, deploying gold-plated shrouds once exoatmosheric, changing the missile coating at random intervals to foil laser frequencies, etc.) that the "punch" method was developed. I'm still skeptical, for the reasons many have outlined over the years. Bill Stewart, most recently, who pointed out that the Macedonian Liberation Army will simply smuggle in a bomb and then demand that the U.S. and NATO stop arming the Albanian terrorists. And so on. For knocking out satellites, particle beam weapons are the way to go. And don't believe Kosta Tsipis' 1978-79 article in Sci Am about how 50 loads of fuel in the space shuttle would be needed for every firing of a particle beam weapon. --Tim May -- Timothy C. May tcmay@got.net Corralitos, California Political: Co-founder Cypherpunks/crypto anarchy/Cyphernomicon Technical: physics/soft errors/Smalltalk/Squeak/agents/games/Go Personal: b.1951/UCSB/Intel '74-'86/retired/investor/motorcycles/guns