This is a last gasp of President Reagan's Strategic Defense Initiative, written in sorrow by an enthusiast. His dissection of why SDI has faded is perceptive: there never was a commitment, as there was in the space program of the 1960s, to do something. Both the Administration and its opponents could agree to conduct missile defense research and to move to deployment only when-or more accurately, if-exotic technologies became available. Early deployment of existing ground-based interceptors looked like a live prospect but never really was, for the Reagan Administration was not disposed to take on the military services, none of which favored defense, at least not funded out of its own budget. For the author these conclusions are sad ones; others will regard them as prudent.