The cause of the failure of the recent ballistic missile interceptor test has been traced back to a leak in the interceptor warhead cooling system. Heat-seeking systems have to be cooled to work, and the interceptor's heat-seeking scanner is no different. Cooled by nitrogen, the system developed a small leak and the seeker (having lost its coolant) warmed up and failed just before impact. The problem is reportedly easy to fix, but fixing it will reportedly delay the next test from April into May.--Stephen V Cole