The Sea-Based X-Band Radar, known informally as the giant floating golf ball, will be visible on the horizon today as it pulls into Pearl Harbor for maintenance and crew training, the U.S. Missile Defense Agency said.

It is the eye-catching vessel’s 13th visit here since 2006, and Ford Island has become the SBX’s unofficial home port.

The one-of-a-kind, $1 billion missile tracker is 240 feet wide and 390 feet long. It towers more than 280 feet from its keel to the top of the radar dome and displaces nearly 50,000 tons.

The phased array radar inside the inflatable dome tracks U.S. and foreign missile tests with 45,000 transmission and receiving elements, and is so powerful it could see a baseball in space 2,500 miles away, according to the agency.

The SBX made an appearance off Oahu in early September, but did not pull into port.

In August, the Missile Defense Agency wrapped up three months of work on the SBX, including thruster maintenance, in Seattle. Pearl Harbor was ruled out because the work required a minimum 50-foot water depth, and Pearl Harbor is too shallow.

The Missile Defense Agency previously selected Adak, Alaska, as the home port for the SBX, but the vessel only loitered in the vicinity of Adak, a remote region known for its challenging seas.

The agency subsequently decided the SBX operated best in a "nomadic" mode with periodic maintenance and replenishment stops at Pearl Harbor. The radar vessel spends about 300 days a year at sea.

The SBX is the principal sensor for ballistic missile defense while a rocket is in midflight outside the Earth’s atmosphere, but can engage ballistic missile threats in all phases of flight, the missile agency said.

The radar has participated in multiple tests and the successful Feb. 21, 2008, shooting down of a dying U.S. spy satellite.