The Pentagon has launched a counter-offensive against critics of the National Missile Defense program, insisting that they do not have access to enough data to judge the effectiveness of the system. As the current controversy surrounds the issue of sophisticated decoys, the Pentagon has specifically addressed this point. Critics have charged that it is impossible to collect enough data to tell a decoy from a real warhead. The Pentagon insists that NMD can acquire enough data. Decoys can be made in various ways, each simulating some of the aspects of a true warhead (heat, speed, radar reflectivity, size, etc.). It is, however, impossible to build a decoy that simulates all of these aspects unless it is the size and weight of a real warhead, at which point the decoy might as well be replaced by a real weapon. (The point of decoys such as metal-coated balloons is that they take up a lot less space and weight than real weapons, allowing a single-warhead missile to carry up to a dozen dummy warheads.) The Pentagon says that the critics are basing their claims that the interceptor cannot pick out a target from this clutter on the original kill vehicle, but that this has been replaced by a new design that has three different sensors. Moreover, the NMD system combines data from several other sensors (not on the interceptor) to improve discrimination.--Stephen V Cole