WASHINGTON — A super-fast interceptor rocket conceived as a means of destroying missiles as they lift off has effectively been reassigned to a job for which there is no immediate opening within the U.S. missile defense architecture. The U.S. Missile Defense Agency (MDA) has de-emphasized the boost-phase defense role of the Kinetic Energy Interceptor (KEI), couching the system instead as a one that will engage missiles during their mid-course phase of flight.

That leaves boost-phase missile defense to the Airborne Laser, a Boeing 747 aircraft modified to carry a high-power chemical laser.

In recent years, MDA officials have juxtaposed the KEI and Airborne Laser as competing boost-phase systems, with their performances in upcoming flight tests to determine which would go forward to deployment. Unlike the KEI test, which would simply involve a flight of the interceptor’s first two stages, the Airborne Laser demonstration involves an attempt to shoot down a target missile.

But in spite of the fact that its shoot-down demonstration is now delayed from 2008 to 2009 due to what MDA officials characterized recently as unmet programmatic milestones, the Airborne Laser appears to have won the battle.

Rick Lehner, a spokesman for the MDA, said March 5 that barring unforeseen difficulties, the Airborne Laser is the primary boost-phase defense system in the evolving U.S. missile defense architecture. The KEI is now viewed as an eventual replacement for the primary midcourse defensive element, the Ground-based Midcourse Defense system, he said.

Installation of the Ground-based Midcourse Defense interceptors is under way at Fort Greely, Alaska, and Vandenberg Air Force Base, Calif.

The KEI is the first U.S. missile defense system that does not fall under the constraints of the U.S.-Russian Anti-Ballistic Missile Treaty of 1972. Some of the KEI’s key attributes, including its mobility and ability to be cued directly by space-based assets, were barred by the pact, which the United States abandoned in 2002. Along with the high-acceleration rate, these capabilities were incorporated into the KEI design with one thing in mind: hitting enemy missiles during their vulnerable boost and ascent phases of flight.

Northrop Grumman Mission Systems of Reston, Va., won the $4 billion prime contract to develop the KEI in December 2004.

For the past few years, KEI proponents have been touting its potential for engaging missiles in their midcourse as well as the boost phase of flight.

The primacy of the midcourse defense role for KEI became official with the release of the MDA’s 2008 budget request of $9 billion, which is $500 million to $600 million less than agency officials had anticipated. As was the case two years ago under similar circumstances, the KEI program bore the brunt of the impact: the request for the program in 2008 is $227 million, or about 50 percent of what agency officials had expected at this time last year.

As a result, the MDA has halted work on the mobile KEI platform — critical for getting the interceptors close enough to enemy launch sites to be able to engage missiles in their boost phase — and instructed Northrop Grumman to pursue a silo-deployed system. The KEI mobile launch platform was being developed by a unit of Northrop Grumman Electronic Systems in Sunnyvale, Calif.

Craig Staresinich, sector vice president and general manager for KEI at Northrop Grumman Mission Systems, said the long-term vision for the system has not changed despite the new direction. “We’re not forgetting mobile,” he told reporters during a briefing here March 5. The KEI is most valuable as a mobile system, he said.

The KEI is well suited for deployment at sea, particularly aboard the U.S. Navy’s futuristic CGX warship, Staresinich said. Missile defense is among the missions for the CGX, which under current plans would be deployed sometime around the middle of next decade. Northrop Grumman’s KEI contract does not include support for a sea-based version, although the company is studying the concept with internal funds, he said. The MDA and the Navy, meanwhile, are studying options for basing the KEI on existing surface ships, he said.

At roughly 12 meters in length, the KEI is about twice the size of the Standard Missile 3, the primary U.S. sea-based interceptor, and half the size of the Ground-Based Midcourse System interceptor, Staresinich said. Three KEI interceptors could be deployed inside a single Ground-based Midcourse System silo, he said.

Lehner said deployment of silo-based KEI interceptors could begin sometime after 2014, although he could not be specific about where they might be placed. Prior to the latest program restructuring, plans envisioned the mobile interceptors being deployed that same year.

Staresinich said work on the first- and second-stages of the three-stage KEI booster interceptor is proceeding and that the 2008 flight test is still on track. The program requires no new technology, he said. “It’s an engineering program,” he said.

The MDA has abandoned plans for a unique KEI kill vehicle.

Lehner said the interceptor would be topped with the Multiple Kill Vehicle, a system now under development that would eliminate the thorny problem of discriminating between missile warheads and decoys by taking out both. The KEI also could accommodate unitary kill vehicles, such as those currently used on the Ground-based Midcourse Defense interceptor and Standard Missile 3, for the boost-phase mission, Staresinich said.

Staresinich acknowledged, however, that there is little or no work being done right now to integrate the KEI booster with a kill vehicle. The first flight test of a fully integrated KEI could take place around 2010.

James Hackett, who was acting director of the U.S. Arms Control and Disarmament Agency during the Reagan administration and who frequently writes about missile defense, said the KEI is a solution in search of a problem. Even as a mobile system, he contends, the KEI could not have been deployed close enough to likely launch sites in places like China or Iran to catch missiles during their boost phase.

“The original rationale didn’t make a lot of sense and so now they’re looking for new ones,” said Hackett, who believes MDA resources would be better spent deploying and developing evolutionary upgrades to the Ground-Based Midcourse Defense system.

“I’m not sure what the benefit will be” of replacing the current interceptors with the KEI Hackett said. He added that if the U.S. Minuteman 3 ICBM fleet is any guide, the Ground Based Midcourse interceptors could last up to 30 years with maintenance and refurbishment.