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The golf ball is back. The Sea-Based X-Band Radar returned to Pearl Harbor on Friday after spending months at sea likely watching for any North Korean missiles that would have come across the Pacific in the direction of Hawaii and the mainland. Read more

The golf ball is back.

The Sea-Based X-Band Radar returned to Pearl Harbor on Friday after spending months at sea likely watching for any North Korean missiles that would have come across the Pacific in the direction of Hawaii and the mainland.

The towering 280-foot-tall floating radar, which serves as the principal U.S. sensor for ballistic missiles in the midcourse of flight, arrived at its home at Ford Island following North Korean intercontinental ballistic missile test flights on July 3 and 28 that landed in the Sea of Japan, and intermediate-­range ballistic missile flights over Japan on Aug. 28 and Thursday.

The military was mum on why the “SBX” returned to Hawaii and when it will go back out again. The U.S. Missile Defense Agency referred questions to U.S. Pacific Fleet, which referred questions to Navy Region Hawaii.

“We will not discuss the specifics of the ship’s operations while deployed,” Navy Region Hawaii said in an email when asked whether the SBX was monitoring North Korean launches.

In June, Vice Adm. J.D. Syring, then director of the Missile Defense Agency, said funds were being sought in 2018 to extend at-sea time for the SBX to 230 from 120 days to address North Korean missile test activity and for the defense of the homeland.

The agency previously revealed that the SBX participated May 30 in the first test intercept of an ICBM target launched from Kwajalein Atoll that was shot down by a ground-based interceptor fired from Vandenberg Air Force Base in California.

The agency said the SBX, “positioned in the Pacific Ocean,” acquired and tracked the target and sent tracking data to the ground-based system.

The $2.2 billion radar left Hawaii in January to monitor potential North Korean ICBM test launches, news agency Reuters reported at the time, citing a defense official in Washington, D.C. According to Reuters, the SBX was to reach its destination about 2,000 miles northwest of Hawaii near the end of January.

Riki Ellison, chairman of the Missile Defense Advocacy Alliance, said the SBX’s value “is in its discrimination of the North Korean ballistic missile threat to Hawaii and to the U.S. mainland, and it monitors our test launches to gather critical data to make our systems and interceptors better.”

Ellison, whose organization seeks a strong missile defense, said the United States has other radar assets to track the early stages of North Korean missile launches, which would be “out of its (SBX’s) range a bit.” “It was out there doing our (midcourse) tracking and (we) would not want to put it out of its range for the defense of the U.S. homeland and Hawaii,” Ellison said in an email.

The SBX has to be cued by forward sensors to focus on the target so that an intercept can take place above it in the Pacific, he said.

“It has flexibility to move to adjust to tests that we do and to the threat from North Korea,” Ellison said. “There is a sweet spot (in the Pacific where) it can defend both Hawaii and the U.S. (mainland).”

The Missile Defense Advocacy Alliance previously recommended deploying an AN/TPY-2 radar to Midway Atoll “to provide persistency when SBX has to return to Pearl Harbor or has testing missions.”

The SBX is topped by an inflated dome that contains a multidirectional panel studded with 45,000 transmit/receive modules that operate together to form a radar beam that can see an object the size of a baseball at a distance of 2,500 miles, according to the U.S. military.

The Union of Concerned Scientists said in a July 2016 report that while the SBX is the most capable radar in the ground-based defense system to discriminate actual ballistic missile warheads from launch debris and decoys, “it has a number of serious limitations, including a very limited electronic field of view, issues with reliability and survivability, and limited coverage” given that it is the only one of its kind.

The SBX’s “lack of persistence” — meaning it has to take breaks for maintenance or other missions — is the main driver behind the decision to locate a medium-range discrimination radar somewhere in Hawaii, Ellison said. The ground-based radar, which could cost $1 billion, is expected to be partially operational in 2023.

“Once that is a program of record, the SBX will most likely go to the East Coast, or (the military) will look at taking it off the platform and putting it on land, but it still remains a tremendous asset to have in the Pacific,” Ellison said.