And why do we know this?

The Air Force says a missile-intercept test failed when a long-range missile launched from California missed a target missile launched from a Pacific island because of radar problems.

A statement posted on the Vandenberg Air Force Base Web site says the target missile was launched from the Kwajalein Atoll in the Marshall Islands on Sunday at about 3:40 p.m. and the long-range interceptor missile was launched from California’s central coast shortly after.

The statement says both missiles launched and flew without trouble but the system’s sea-based X-band radar did not perform as expected and the interceptor missed its target.

The statement says officials from the Missile Defense Agency that conducted the test will conduct an extensive investigation to determine the cause of the failure.