Kinetic Energy Interceptor (KEI)
ATK produces the second-stage motor for the Kinetic Energy Interceptor (KEI), a U.S. Missile Defense Agency initiative to develop an interceptor missile capable of destroying medium-range, intermediate-range, and intercontinental ballistic missiles during the boost and ascent phases of flight.

The KEI missile will initially be deployed using a mobile land-based platform, with a sea-based deployment expected to follow. It will complement other U.S. missile defense systems that target enemy warheads in the midcourse phase of flight, including the Standard Missile 3 and the Ground-Based Midcourse Defense missile, both of which use ATK propulsion systems.

The KEI second-stage motor has been successfully tested as part of a series of static motor firings leading up to the first flight in 2008.