— The U.S. Missile Defense Agency (MDA) is seeking $368 million in 2010 that could be used to begin modifications to its existing Aegis sea-based interceptor system that will allow it to engage enemy missiles while they are still in the ascent phase of flight, according to a congressional source.

Currently the system, which features the ship-based Aegis radar and fire control system and Standard Missile-3 (SM-3) interceptor, is designed to knock down short- and intermediate-range missiles in the midcourse portion of flight. Unlike the existing Aegis Ballistic Missile Defense system, an ascent-phase variant would draw data directly from airborne and possibly space-based missile warning assets, the source said.

When the MDA sent its 2010 budget request to Congress in May, it officially canceled plans to develop any operational systems to destroy ballistic missiles in the early boost phase, when they are most vulnerable. The primary boost-phase program, the Boeing-built Airborne Laser platform, was reduced to a research and development effort due to concerns about the cost of deploying an operational system and questions about its concept of operations. The Kinetic Energy Interceptor, which at one time was being developed as a boost-phase option, was terminated entirely.

MDA Executive Director David Altwegg said May 7 the agency would instead pursue a new system to intercept missiles in their post-boost ascent phase, meaning after their motors have burned out but while they are still rising. He said the system would leverage existing technologies but declined to be specific.

Firm plans for the ascent-phase system are not yet in place, and an extensive review of all possible options is scheduled for later in June, MDA spokesman Rick Lehner said in a written response to questions June 5. He said “the upgraded SM-3 and airborne sensors are just two of the technologies that will be evaluated for ascent phase intercept.”

MDA officials have briefed lawmakers on the idea of upgrading the sea-based system, which features the Lockheed Martin-built Aegis Weapon System and the SM-3, built by Raytheon Missile Systems of Tucson, Ariz., according to the congressional source.

The Aegis radars typically do not have the range to track missiles in their early stages of flight. The upgrades would enable the SM-3 and its firing system to receive missile tracking information directly from forward-deployed unmanned aerial vehicles and possibly satellites. The MDA has proposed a development plan for the upgraded system that would culminate in a full-scale demonstration in three years, the source said.

Unveiling its budget request, the MDA did not provide a budget figure for the ascent-phase interceptor. The congressional source said the proposed $368 million would be drawn from various MDA accounts.

The House Armed Services strategic forces subcommittee, meanwhile, is scheduled to mark up the defense authorization bill June 11, with its Senate counterpart following suit June 16.