How Things Work: Phased-Array Radar

It takes a big eye to see a missile coming

The SBX, shown here on a cargo vessel in Texas, practiced two days of "weather avoidance" when Hurricane Emily arrived in the Gulf of Mexico during 2005 testing. The range of the array inside the dome is limited only by Earth's curvature. (Boeing)
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At 282 feet in height, two football fields in area, and 50,000 cubic tons in volume, the Sea-Based X-Band Radar inspires description in the mold of “Your mama” jokes: SBX is so fat it couldn’t fit through the Panama Canal. SBX is so tall it could straddle the Goodyear Blimp. SBX is such a superstar, it has its own self-propelled, semi-submersible oil-drilling platform as a ride.

The near-$900 million structure, operated by the U.S. Missile Defense Agency (MDA), is by far the largest phased-array radar system on Earth. It is 16 times more powerful than the previous champ—its own prototype—and capable of determining if a baseball-size object thrown into space from another continent is a slider, a curve, or a knuckleball.

This summer it will leave Pearl Harbor, where it is being painted, and voyage to its home port of Adak, Alaska, for the first time. After being integrated into the battle management systems of long-range interceptor missiles located in Alaska and California, the SBX will be able to move throughout the Pacific Ocean, or anywhere else it’s welcome, for training or actual defensive operations.

Once active, it will identify enemy missiles outside the atmosphere, at the highest point of their ballistic trajectories, so that the interceptors can take them out.

With the same frequency of radiation that your microwave oven uses to warm Lean Cuisines, SBX probes the nooks and crannies of “threat complexes”—the cloud of warheads, decoys, and debris such as loose nuts and bolts, spent booster stages, and unburned fuel that surround an enemy missile.

“We can differentiate between very tightly spaced objects, small and large objects, and the like,” says Army Colonel John Fellows, MDA’s project manager for X-band radars. “We can tell [which] is the threatening object.”

At the frequencies used by X-band radars, ranging from 8 to 12 gigahertz, relatively short wavelengths enable sharp, high-resolution radar images.

“You might be able to see rivets and seams and joints and fins, and [that] allows you to form a very accurate representation of what is there,” says Larry

Briggs, who as Raytheon’s program director for ground-based radars oversaw the design and construction of the SBX’s radar array.

Before catching a ride to Hawaii on the back of the Blue Marlin, the world’s largest cargo vessel (which had to be widened for the job), the SBX spent the summer of 2005 on a 52-day shakedown cruise in the Gulf of Mexico. After the platform outran hurricanes, it tested its 10-story array by turning it skyward to track satellites.


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