The U.S. Missile Defense Agency (MDA) is buying four fewer Standard Missile-3 Block 1B interceptors than originally expected under a 2011 contract, a change that reflects cost growth related to “resolving technical and production transition issues,” according to a release from the Defense Department July 9.

The MDA will now buy 20 of the sea-based interceptors, rather than 24 as called for in the contract awarded in March 2011. The move is expected to save about $49 million. 

The four interceptors, manufactured by Raytheon Missile Systems Co. of Tucson, Ariz., will be bought at a later date, according to a contract modification.

About half of the savings, or $24 million, will go toward fixing technical issues with the sea-based interceptor, which failed in a 2011 test but has since racked up three straight successes. The change reduces the total value of Raytheon’s contract by nearly $25 million, to $1.907 billion.

The technical issues are “related to the engineering investigation and minor fixes to the third stage rocket motor,” said Richard Lehner, an MDA spokesman. “This motor is a common part with the SM-3 1A that failed for the first time in the first flight of the SM-3 Block 1B.  It has performed well in all subsequent tests.”

The SM-3 Block 1A is an earlier generation of the sea-based interceptor that is operationally deployed on Navy ships.

Full-scale production of the SM-3 Block 1B has been delayed by problems in developmental testing. The MDA has been criticized for moving the system into production prematurely following a September 2011 test failure and Congress members have pushed for a “fly before you buy” purchasing philosophy.

The modification is separate from a contract announced in June, when the MDA authorized Raytheon to begin ordering long-lead components for 29 additional SM-3 Block 1B interceptors. That modification is valued at $126 million.