Boeing is developing an exoatmospheric kill vehicle for the Army's Ground-Based Interceptor test program, a key element of America's proposed National Missile Defense system The GBI would be launched on demand to intercept threatening missiles in outer space. Its EKV will separate from the booster, detect attacking missiles and destroy them. Army officials said that recent tests proved that Boeing's EKV sensor performance was outstanding and that the integrated navigation system performance exceeded expectations.