WASHINGTON — Aerojet and Pratt & Whitney Rocketdyne will design competing steering-thruster mechanisms for a planned next-generation missile interceptor under contracts announced Oct. 3 by the U.S. Missile Defense Agency.

Each company will design a divert and attitude control system thruster assembly for possible use on the planned Standard Missile (SM)-3 Block 2B interceptor, the Missile Defense Agency (MDA) said. The thruster assemblies are used to steer the interceptor’s warhead, or kill vehicle, to its target.

The SM-3 Block 2B, also known as the Next Generation Aegis Missile, is an upgraded variant of the Raytheon-built SM-3 Block 1A interceptor currently deployed aboard U.S. Navy ships. Slated for deployment around 2020, the Block 2B would have greater capability than previous SM-3 variants and is slated for a key role in protecting Europe in a ground-basing mode.

Aerojet of Sacramento will design and test components for its Block 2B steering assembly under a $15.4 million contract. Canoga Park, Calif.-based Pratt & Whitney Rocketdyne’s competing contract is valued at $13.9 million.

The contracts run from September of this year through September 2013. At that point, one company’s control system will be selected by the MDA’s director for the final missile project.

Boeing, Lockheed Martin and Raytheon, the SM-3 incumbent, are developing competing designs for the Block 2B upgrade. The MDA hopes to select a prime contractor for the next-generation interceptor in 2013.

The Senate Appropriations Committee proposed canceling development of the Block 2B missile in its version of the 2012 defense spending bill, which was drafted in September. The committee said the MDA has enough on its hands with two other SM-3 upgrades, the Block 1B and Block 2A, already in development.

The House version of the defense spending bill recommends fully funding the Block 2B program next year at $123.5 million.

MDA spokesman Richard Lehner said in an emailed response to questions that the agency is pressing ahead with Block 2B development despite the budgetary uncertainty.

“There is no [final] defense bill yet, so speculation about future funding for the 2B is pointless,” Lehner said.

The MDA has developed guidelines to ensure the free flow of technical information between the companies competing for the SM-3 Block 2B prime contract and prospective component suppliers like Aerojet and Pratt & Whitney Rocketdyne, Lehner said.

By early 2013, Aerojet and Pratt & Whitney Rocketdyne are expected to have developed and tested parts of the control system. The companies also are expected to deliver prototype designs.

Meanwhile, the MDA awarded a $9 million contract to Alliant Techsystems (ATK) of Minneapolis to develop and test third-stage rocket motor technologies for the Block 2B. That contract runs through December 2012, according to the MDA. The agency has a previously announced contract with Aerojet for similar third-stage design work.

Lehner said the MDA opted to do early risk reduction work on the Block 2B third stage because it is expected to be more technologically challenging than the first two stages of the vehicle.

“Data from both Aerojet and ATK concepts will be made available to all three of the prime contracting teams,” Lehner said. “The prime contractor who eventually gets the missile contract will determine who builds the third stage rocket motor.”