Sea-based X-band Radar (SBX)

The Sea-Based X-band Radar (SBX) is a unique radar housed on a decommissioned North Sea oil rig. The SBX produces very high resolution images of incoming threat clouds, which helps BMD interceptors discriminate between lethal objects and debris. The SBX has contributed to 12 tests of the GMD system and provided tracking and kill assessment for Operation Burnt Frost in 2008 when an Aegis BMD destroyer shot down a potentially toxic satellite falling out of orbit.¹

It has also been deployed on numerous occasions to monitor North Korea’s long range missile tests and routinely contributes to USAF flight tests of U.S. intercontinental ballistic missiles.²

MDA Director Lt Gen Ronald Kadish approved the SBX program in October 2002. Sea trials began in 2005 and SBX has been in service ever since.

The SBX’s high resolution comes with certain tradeoffs, however. One such limitation is its relatively narrow 25 degree viewing arc, which has been likened to looking through a “soda straw.” Because of this, SBX has a limited ability to track an incoming missile and relies on other sensors to provide the target’s location and trajectory, meaning that it cannot be used as a standalone sensor. As a general principle, the higher resolution a radar has, the smaller its viewing arc is, though it can provide greater discrimination. Tracking radars, such as the U.S. system of Early Warning Radars, project a lower radar bandwidth and have a wide coverage area, but little or no discrimination capability. Aegis BMD radars use the S-band, which is often described as a providing a balance between tracking and discrimination capabilities.

SBX’s mobility, while in some cases an asset, also presents a drawback, as it must sail out from its port in Hawaii to the western Pacific for optimal positioning. This requires significant notice prior to the launch of an enemy missile. Weighing in at over 4 million pounds, SBX’s operating costs while at sea are high.

In 2013, MDA moved SBX from operational status to limited test support status due to budget constraints.³

The radar can be reactivated in the event of an ICBM threat to the United States or for testing support. The FY2016 National Defense Authorization Act contained provisions directing MDA to prepare for a potential redeployment of SBX to the U.S. East Coast by 2020 upon completion of the Long Range Discriminating Radar in Alaska.⁴

In November 2016, media reports indicated that SBX had been deployed to the waters off of North Korea to gather information on North Korean testing of its Musudan (BM-25) IRBM.