The U.S. Missile Defense Agency (MDA) is contemplating modifying the flight-test plan for its Kinetic Energy Interceptor in what could portend a broader role for the high-speed rocket.

The Kinetic Energy Interceptor was conceived as a boost-phase system that would engage enemy missiles as they lift off from the ground. But program advocates also have touted its potential to knock down missiles in the middle portion of flight.

The trajectory required for midcourse intercepts — as opposed to lower-altitude boost-phase engagements — could be reflected in the planned 2008 flight demonstration of the Kinetic Energy Interceptor, according to Kevin Robinson, the MDA’s chief engineer on the program.

If it proves viable in the midcourse defense role, the Kinetic Energy Interceptor could complement the U.S. territorial missile shield now being deployed at sites in Alaska and California, Robinson said Aug. 17 in a speech here at 2005 Space and Missile Defense Conference, which was sponsored by the National Defense Industrial Association, the Air Defense Artillary Association, and the U.S. Army Space and Missile Defense Association. In this capacity, ground-based, mobile Kinetic Energy Interceptors could be deployed around the world and engage enemy ICBMs at slightly lower altitudes than interceptors of the main U.S. shield, known as the Ground Based Midcourse Defense System, he said.

The Ground Based Midcourse Defense System is intended primarily to counter missiles launched from Iran or North Korea and is optimized for that role, Robinson said. Being mobile, the Kinetic Energy Interceptor would have the flexibility to counter emerging threats in other countries, he said.

The MDA awarded Northrop Grumman Missions Systems of Reston, Va., , a contract worth up to $4 billion in December 2003 to develop the Kinetic Energy Interceptor. Major subcontractors on the program include Raytheon Co. of Waltham, Mass., and Orbital Sciences Corp. of Dulles, Va.

The program bore the brunt of a $5 billion reduction in the MDA’s planned spending over the next six years to help pay the cost of military operations in Iraq and Afghanistan. The MDA requested $218 million in 2006 for the program, far less than previously planned request of roughly $1 billion.

To accommodate the reduction, MDA has restructured the Kinetic Energy Interceptor, shelving deployment plans and focusing on the 2008 flight test, which will not involve a missile intercept. The results of that test will factor into the MDA’s decision on whether to continue work on the Kinetic Energy Interceptor or drop the program to focus on another boost-phase system, the Airborne Laser under development by Boeing Co. of Chicago. The Airborne Laser is slated to conduct its first intercept test in 2008.

But Robinson said the MDA would not necessarily pick one and drop the other. Even if the decision is to proceed with the Airborne Laser, the MDA could continue work on the Kinetic Energy Interceptor at a lower level, he said.

Meanwhile, Kinetic Energy Interceptor program officials have begun examining options for a sea-based version of the system, should it ultimately be fielded.

The agency is working with the U.S. Navy to evaluate the potential of cruisers, destroyers and submarines to fire the interceptor, and likely will choose among these options by May or June of 2006, Robinson said. The MDA and the Navy likely would wait until after the 2008 flight test to allocate funds in future-year spending plans for a sea-based version of the weapon, he said.