The interceptor booster is the missile that launches the kill vehicle into space. (The kill vehicle is the part designed to home in on and destroy an incoming warhead.) All the intercept tests to date have used a surrogate, or substitute, two-stage booster in place of the planned three-stage booster for the interceptor. As a result, the speed of the kill vehicle has been much lower than would be expected in the operational system. Currently the interceptor has a top speed of about 2.2 kilometers per second, compared to a planned speed of 7 to 8 kilometers per second for the operational interceptor. This increased booster speed could cut in half the time available for the kill vehicle to attempt to discriminate the warhead from decoys and maneuver to hit the warhead.

In addition, an independent panel that was set up to review the missile defense program, headed by retired General Larry Welch, noted that the three-stage booster intended for the deployed system is expected to subject the kill vehicle to shock forces that are more than ten-times greater than those produced by the two-stage surrogate booster being used in the tests. The panel questioned whether the kill vehicle will be able to withstand these greater forces¹.

The interceptor booster being developed for the operational system is at least a year and half behind schedule, and is not expected to be ready to be used in intercept tests until late 2003 at the earliest. It is not clear why the Missile Defense Agency has chosen to use a two-stage surrogate booster rather than a faster three-stage booster. A three-stage booster is used in the current tests to launch the mock warhead from Vandenberg Air Force Base in California, and could presumably be used for the interceptor as well.

The two-stage surrogate booster lifts off from Meck Island in the Kwajalein Island Atoll, carrying the kill vehicle. This photo is from IFT-8, the ground-based midcourse test on March 15, 2002.

Photo: Boeing