The Pentagon has successfully tested an infrared sensor that will act as the "eyes" of a missile interceptor, which is part of a proposed nationwide defense system against enemy ballistic missiles. The infrared sensors are designed to identify and track re-entry vehicles carrying warheads. With the sensor operating outside the Earth's atmosphere, the interceptor can hit attacking missiles in midflight. In a similar test in January, a rocket booster's failure delayed the project six months and cost millions of dollars. In the second go-around, the sensor successfully identified and tracked a set of threat targets. The next set of sensor tests is slated for January 1998.