Sea-based X-band radar

It is nominally based at Adak Island in Alaska, but has spent significant time at Pearl Harbor in test status.

The decision to place the system on a mobile sea-based platform was intended to allow the vessel to be moved to areas where it is needed for enhanced missile defense.

Testing has raised doubts about the system's ability to perform these tasks, to deal with multiple targets, and to report accurately to command authorities.

[2] 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 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.

In addition to the physical motion of the base, the beam can be electronically steered off bore-sight (details classified).

This configuration allows it to support the very-long-range target discrimination and tracking that GMD's midcourse segment requires.

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.

[4][5] The radar will guide land-based missiles from Alaska and California, as well as in-theater assets, depending on the mission.

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 to allow for replenishment, repair and overhaul.

Three further vessels of the CS-50/Moss Sirius design were under construction or contract at the Severodvinsk Shipyard in Russia as of early 2007, but were configured for oil production.

On 23 June 2009, the SBX was moved to offshore Hawaii in response to a potential North Korean missile launch.

[12] In December 2011, MDA transferred responsibility for the SBX vessel management and physical security to the U.S. Navy's Military Sealift Command.

This reduced amount would be used to maintain SBX in a "limited test support" role, "while also retaining the ability to recall it to an active, operational status if and when it is needed.