The Sea-Based X-band radar (SBX-1) is a floating, self-propelled, mobile active electronically scanned array early-warning radar station designed to operate in high winds and heavy seas. It was developed as part of the United States Department of Defense Missile Defense Agency's (MDA) Ballistic Missile Defense System. The radar is mounted on a fifth-generation CS-50 twin-hulled semi-submersible oil platform. Conversion of the vessel was carried out at the AmFELS yard in Brownsville, Texas; the radar mount was built and mounted on the vessel at the Kiewit yard in Ingleside, Texas. It is nominally based at Adak Island in Alaska but has spent significant time at Pearl Harbor in test status.
Specifications Vessel length: 389 feet (119 m) Vessel beam: 238 feet (73 m) Vessel height: 279 feet (85 m) from keel to top of radome Vessel draft: approximately 33 feet (10 m) when in motion or not on station; approximately 98 feet (30 m) when on station Vessel stability: remains within 10 degrees of horizontal on station (fully passive stabilization) Vessel speed: 9 knots (17 km/h; 10 mph) Cost: US$900 million Crew: Approximately 75-85 members, mostly civilian contractors Radar height: 103 feet (31 m) Radar diameter: 120 feet (37 m) Radar weight: 18,000 pounds (8,200 kg) Radar range: 1,200 miles (2,000 km) Displacement: 50,000 short tons (45,000,000 kg)
Details SBX-1 is part of the Ground-Based Midcourse Defense (GMD) system under development by the Missile Defense Agency (MDA). The decision to place the system on a mobile sea-based platform was intended to allow the vessel to be moved to areas needed for enhanced missile defense. Fixed radars provide coverage for a minimal area due to the curvature of the Earth. Even though the same limitation applies to the SBX, its moving ability mitigates it. SBX's primary task is to discriminate enemy warheads from decoys, followed by precision tracking the identified warheads. Testing has raised doubts about the system's ability to perform these tasks, deal with multiple targets, and report accurately to command authorities. The vessel has many small radomes for various communications tasks and a large central dome that encloses a phased-array, 1,800-tonne (4,000,000 lb) X-band radar antenna. The small radomes are rigid, but the central dome is not - the flexible cover is supported by positive air pressure amounting to a few inches of water. The amount of air pressure is variable depending on weather conditions. The radar antenna is 384 m2 (4,130 sq ft). It has 45,000 solid-state transmit-receive modules mounted on an octagonal flat base, which can move ±270 degrees in azimuth and 0 to 85 degrees elevation (although software currently limits the maximum physical elevation to 80 degrees). The maximum azimuth and elevation velocities are approximately 5–8 degrees per second. In addition to the physical motion of the base, the beam can be electronically steered off bore-sight (details classified). There are currently 22,000 modules installed on the base. Each module has one transmit-receive feed horn, and one auxiliary receive feed horn for a second polarization, totaling 44,000 feed horns. The base is roughly 2/3 populated, with space for the installation of additional modules. The current modules are concentrated toward the center to minimize grating lobes. This configuration allows it to support the very-long-range target discrimination and tracking that GMD's midcourse segment requires. The radar never points at land for the safety of the inhabitants. In addition to the power consumed by the radar, the thrusters that propel the vessel are electric and require substantial power. The maximum speed is approximately 8 knots (9.2 mph; 15 km/h). The vessel has six 3.6-megawatt generators (12-cylinder Caterpillar diesel) to support this and all other electrical equipment. The generators are in two compartments, one port and one starboard.
The radar is derived from the radar used in the THAAD theater ballistic missile defense system. It is a part of the layered ballistic missile defense system (BMDS) program of the United States Missile Defense Agency (MDA). One important difference from Aegis is using the X band in the SBX. Aegis uses S band, and Patriot uses the higher-frequency C band. The X band frequency is higher still, so its shorter wavelength enables finer resolution of tracked objects. The radar was described by Lt. Gen Trey Obering (former director of MDA) as being able to track an object the size of a baseball over San Francisco in California from Chesapeake Bay in Virginia, approximately 2,900 miles (4,700 km) away. The radar will guide land-based missiles from Alaska and California, as well as in-theater assets, depending on the mission. The vessel is classed by ABS and has the IMO number of 8765412.
The first such vessel is scheduled to be based in Adak Island, Alaska, part of the Aleutian Islands. From that location, it will be able to track missiles launched toward the US from both North Korea and China. Although her homeport is in Alaska, she will be tasked with moving throughout the Pacific Ocean to support her mission. The hull code number given to the SBX vessel, "SBX-1", indicates the possibility of further units of the class. When a vessel must be continually on duty over a long period, common naval practice is to have at least three units of the type available to allow for replenishment, repair, and overhaul. Three further CS-50/Moss Sirius design vessels were under construction or contract at the Severodvinsk Shipyard in Russia as of early 2007 but were configured for oil production. On 11 May 2011, Col. Mark Arn, the SBX project manager for MDA, said that the "SBX is the only one of its kind and there are no current plans for another one". In July 2011, a Missile Defense Agency spokesman explained that other, smaller radars in the Pacific will "pick up the slack" while SBX is in port with its radar turned off.
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