Sea-based X-band Radar

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The Sea-Based X-Band Radar underway.

Sea-Based X-Band Radar is a floating, self-propelled, mobile radar station designed to operate in high winds and heavy seas. It is part of the United States Government's Ballistic Missile Defense System.

The Sea-Based X-Band Radar is mounted on a 5th generation Norwegian-designed, Russian-built CS-50 semi-submersible twin-hulled oil-drilling platform. The hull was originally built at Vyborg Shipyard, hull number 101. Conversion of the platform was carried out at the AmFELS yard in Brownsville, Texas; the radar mount was built and mounted on the platform at the Kiewit yard in Ingleside, Texas, near Corpus Christi. It is based at Adak Island in Alaska but can roam over the Pacific Ocean to detect incoming ballistic missiles. The platform is classed by ABS and has the IMO number of 8765412.


[edit] Specifications

  • Platform length: 116 meters (380 ft)
  • Platform height: 85 meters (280 ft) from keel to top of radar dome
  • Platform draft: approximately 10 meters when in motion or otherwise not on station; approximately 30 meters when on station
  • Platform stability: remains within 10 degrees of horizontal on station (fully passive stabilization)
  • Cost: $900 million
  • Crew: Approximately 75-85 members, mostly civilian contractors
  • Radar range: Classified
  • Displacement: 50,000 tons

[edit] Details

The platform is part of the Ground-Based Midcourse Defense (GMD) system being deployed by MDA. Being sea-based allows the platform(s) to be moved to areas where they are needed for enhanced missile defense. Fixed radars provide coverage for a very limited area due to the curvature of the Earth. The primary task SBX will carry out is discrimination (identification) of enemy warheads from decoys, followed by precision tracking of the identified warheads.

The platform has many small radomes for various communications tasks and a central, large dome that encloses and protects a phased-array, 1,814 tonnes (4,000,000 pound) 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 itself is described as being 384 square meters. It has a large number of solid-state transmit-receive modules mounted on a hexagonal flat base which can move plus-or-minus 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, so there are 44,000 feedhorns. The base is roughly 2/3 populated and so there is room for installation of additional modules. The current modules are concentrated towards the center, so as 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 array requires over a megawatt of power.

In addition to the power consumed by the radar, the thrusters which make the platform self-propelled are all electric and require substantial power (maximum platform speed is in the neighborhood of 8 knots). To support this and all other electrical equipment, the platform currently has six, 3.6 megawatt generators (12 cylinder Caterpillar diesels). The generators are in two compartments, one port and one starboard. The maximum power currently drawn is roughly 12 megawatts, and there are plans to expand the number of generators to eight, so that one entire compartment could be lost and the platform would still continue to operate at full capability.

The active electronically scanned array radar is derived from the radar used in the Aegis combat system, and is a part of the layered ballistic missile defense (BMDS) program of the United States Missile Defense Agency (MDA). One important difference from Aegis is the use of 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 is designed and built by Raytheon Integrated Defense Systems for Boeing, the prime contractor on the project for MDA.

The radar is described by Lt. Gen Trey Obering (director of MDA) as being able to track an object the size of a baseball over San Francisco in California from the Chesapeake Bay in Virginia, approximately 2,900 miles (4,700 km). The radar will guide land-based missiles from Alaska and California, as well as in-theatre assets.

The CS-50 semi-submersible platform on which the radar is mounted was built as the "Moss Sirius" at the Vyborg shipyard in Russia for Moss Maritime (now part of the Saipem offshore company, which is a subsidiary of Italian energy corporation Eni S.p.A.). It was purchased for the Sea-based X-band Radar project by the Boeing company, outfitted with propulsion, power and living quarters at the AmFELS shipyard in Brownsville, Texas, and integrated with the radar at the Kiewit yard in Ingleside, Texas.

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 name given to the SBX platform, "SBX-1", indicates the possibility of further units of the class; in circumstances when a vessel is required to be continually on duty over a long period of time, common naval practice is to have at least three units of the type available. Three further platforms of the CS-50/Moss Sirius design were under construction or contract at the Severodvinsk shipyard in Russia as of early 2007, but as of that time it was unknown whether they would be purchased by the US for more SBX radars or sold to other buyers.

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