The towering Sea-Based X-Band Radar is back at sea after nearly four months in Pearl Harbor, during which $24 million in repairs and upgrades were made, the Missile Defense Agency said.

“SBX is underway for regular operations,” agency spokeswoman Heather Cavaliere said in an email. “We cannot comment on duration.”

The Missile Defense Agency previously said the floating radar would return to sea for operations and testing following the maintenance period.

The more than $2 billion radar, which operates from Ford Island in Pearl Harbor, is 240 feet wide and 390 feet long. It measures more than 280 feet from its keel to the top of the radar dome and displaces nearly 50,000 tons when ballasted. It left Pearl Harbor late last month.

Inside its Kevlar-like inflated dome are more than 45,000 transmit/receive radiating elements. The radar is capable of seeing an object the size of a baseball at 2,500 miles.

The radar returned to Hawaii on May 31 after spending 582 days at sea — its longest deployment — watching for North Korean, Chinese, Russian and other-nation missiles and participating in missile defense testing.

SBX traveled 6,140 nautical miles during the deployment, which saw winds of more than 130 mph and seas over 60 feet.

“These conditions required additional mitigation by the crew, but did not result in any mission failures,” the agency said.

Built on a former oil rig, the SBX can track and discriminate warheads from rocket debris hurtling through space. However, the radar has a very narrow field of view.

That limitation and operating gaps created by the SBX needing to travel to and from the vicinity of Midway Atoll will be improved on by a series of planned land-based sensors, including the $1 billion Homeland Defense Radar-Hawaii, which is expected to have initial operating capability in late 2023.

“With the addition of the long-range discriminating radar in Alaska, the homeland defense radar in Hawaii and the future Pacific radar, we will have in place a diverse sensor architecture in the Pacific to provide an improved and persistent” missile-tracking capability, former Missile Defense Agency Director Lt. Gen. Sam Greaves testified in April.

The Pacific radar, eyed for Japan, would be part of what the military calls a “birth-to-death” tracking custody chain for missiles heading toward Hawaii and the mainland and is tied into the 44 ground-based interceptors in Alaska and California that theoretically would shoot them down.

All told, the three powerful land-based radars will cost more than $3 billion, an expenditure being made to tackle a proliferation of increasingly sophisticated long-range ballistic missiles.

In the meantime, improvements continue to be made to the SBX.

The Pentagon announced Sept. 23 that Raytheon Integrated Defense Systems was being awarded a $501 million contract modification to continue to perform research and development support for the SBX and the Army Navy Transportable Radar Surveillance Control Model-2, increasing the contract ceiling to $962 million.