The U.S. is exploring options to increase the range of its newly fielded Terminal High-Altitude Area Defense (Thaad) anti-ballistic missile system.

The addition of a larger, 21-in.-dia. booster appears to be the option of most interest. The Thaad interceptor is now 14.5 in. in diameter. "The concept behind the 21 inches is that it significantly increases the interceptor range, and by increasing range that significantly--three to four times--increases the defended area we have on the ground with the system," says U.S. Army Col. William Lamb, the Missile Defense Agency's Thaad project manager. He says the MDA is reviewing a concept from prime contractor Lockheed Martin for possible inclusion in the Fiscal 2011 budget, which is in the early stages of development.

Another benefit of the larger booster is the time it would add for commanders to consider firing a salvo of missiles, if needed, to destroy a target. Doctrine now calls for a "shoot-look-shoot" process in which, ideally, a commander can check the effectiveness of the first interceptor and launch only when a second is needed to ensure a kill.

"It allows you to shoot one interceptor, assess whether or not you have killed the incoming reentry vehicle, and [possibly] precludes having to ripple-fire to launch several interceptors," Lamb says. "So, you shoot, assess and then--if you didn't get it--you would shoot again."

This could help from an inventory management perspective by not wasting interceptors, he notes.

Aerojet, Lockheed Martin's Thaad motor supplier, conducted static-fire trials of a 21-in. prototype as well as a second "kick stage" to full duration in 2006, according to Lockheed Martin Vice President Tom McGrath. "Both motors were successful and delivered performance within a few percent of the expected final design requirements--one slightly more than the requirement and the other slightly less," he says. During this trial, the motor nozzles were vectored to represent the "worst-case," or most stressing, flight path, and small changes would be needed to the motor design to enter development. One change for operational use would involve the flex seal, which connects the nozzle to the motor. The seal design was tested, but improvements are envisioned for use in cold environments, says McGrath.

Both stage designs were crafted using Lockheed Martin's internal research and development funding from 2006-08, he says.

Click on the image above to view a full size version of the Thaad timeline.

The two-stage concept would provide more divert capability, which can offer more lateral movement during an engagement, notes McGrath. The 21-in. concept would provide more velocity at burnout, offering greater range for the kill vehicle upon separation.

With both concepts, Lockheed Martin does not envision any hardware changes to the Thaad kill vehicle; only software updates would be needed.

If MDA proceeds with development of a new Thaad booster, the ground-based launcher system would have to be modified. Five 21-in.-dia. interceptors would fit in the launcher that now carries eight of the current Thaad missiles. Each Thaad battery can control up to nine launchers; currently each battery is expected to have three launchers.

Lamb says the Army would assess whether a mix of interceptors could be attached to a single battery. "One possible approach could be--given that you are reducing from eight to five interceptors--you could add . . . a fourth launcher to that battery configuration," he says.

No MDA funding has yet been set aside for the project. However, Lamb says the 21-in. booster could be readied for flight testing about three years after receiving approval. MDA officials have cost estimates, but did not provide them.

A shift to a 21-in. diameter would show an evolution for the land-based system similar to the path that MDA chose for the Aegis-based SM-3 booster made by Raytheon. The U.S. and Japan are jointly developing a 21-in. SM-3 Block IIA, which would greatly add to the capability now planned by a 13.5-in. SM-3 Block IA and B.

Thaad launcher photo credit: Lockheed Martin