21.   In two of three interception tests, prototype interceptor rockets failed to hit their target in space.

22.   Other similar tests have used interceptor rockets launched from land.

23.   The military has built and tested prototype interceptor rockets for the ground-based system since the first estimate.

24.   The shield, if it works, would fire interceptor rockets at incoming missiles.

25.   The United States plans this weekend to test part of its missile defense program by trying to shoot a mock warhead out of the sky with an interceptor rocket.