USNI
The ultra-sensitive radar the U.S. uses to track ballistic missile targets was deployed off North Korea in September, according to local press reports.
Sea-Based X-Band Radar (SBX-1) an oil-derrick sized phased array radar was deployed off the Korean peninsula for about a month, according to a report in the South Korean newswire Yonhap.
“[SBX] was sent to an undisclosed location off the Korean Peninsula for a one-month deployment after departing Hawaii in late September,” a South Korean military official told the wire, reported Stars and Stripes.
“It sailed back to its home port in late October.”
The time off the peninsula would overlap with a recent string of North Korean intermediate range ballistic missile launches and would likely be recording key information from the launches.
The SBX-1 is a key component of the U.S. ballistic missile defense system and is sensitive enough to detect an object the size of a baseball at 2,500 miles, according to information from the Missile Defense Agency (MDA).
While U.S. officials did not confirm any details of the Yonhap report. The deployment of SBX-1 mirrors a 2013 deployment in which the radar was deployed off North Korea during a period of ballistic missile tests.
The news of the SBX-1 off of the peninsula comes as a Tuesday report from Fox News quoting U.S. officials that North Korea will conduct a launch of a Musudan intermediate-range ballistic missile within the next 24 to 72 hours.
“The pre-Election Day launch of the Musudan missile would be the ninth test launch this year, in addition to two nuclear tests by the communist nation in defiance of United Nations sanctions,” read the report.
Later this week, the U.S., the U.K. and South Korea will hold a trilateral air exercise centered on the Osan Air Base.
“The Invincible Shield drill is aimed at improving the allies’ capabilities of attacking North Korea’s major military and leadership facilities (if provoked) but also intercepting incoming fighters from the North,” a South Korean Air Force spokesman told Yonhap.
North Korea warned Britain to back out of the drills last month.
“This is a hostile act, openly joining the U.S. and South Korean forces in moves for a new war against us,” said North Korean Foreign Ministry official Pak Yun Sik, according to a report in The Associated Press.
“Britain claims that this military exercise is not targeting us, but the U.S. and South Korea openly say that these military exercises are aimed at launching a strike against our military facilities and our command structure.”
https://news.usni.org/2016/11/01/report-sbx-1-radar-operated-near-north-korea#more-22308SBX-1 is part of the Ground-Based Midcourse Defense (GMD) system under development by the MDA. 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. Fixed radars provide coverage for a very limited area due to the curvature of the Earth. However, the same limitation applies to the SBX. SBX's primary task is discrimination of enemy warheads from decoys, followed by precision tracking of the identified warheads. 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.
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. The amount of air pressure is variable depending on weather conditions.
The radar antenna itself is described as being 384 m2 (4,130 sq ft). It has a large number of 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 feedhorns. The base is roughly 2/3 populated, with space for 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 array requires over a megawatt of power.
In addition to the power consumed by the radar, the thrusters which propel the vessel are electric and require substantial power. The maximum speed is approximately 8 knots (9.2 mph; 15 km/h). To support this and all other electrical equipment, the vessel 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 vessel would continue to operate at full capability.
The radar is derived from the radar used in the THAAD theater ballistic missile defense 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 was designed and built by Raytheon Integrated Defense Systems for Boeing, the prime contractor on the project for MDA.
The radar has been 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 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-theatre assets.
The CS-50 semi-submersible rig on which the radar is mounted was built as the "Moss Sirius" at the Vyborg Shipyard (Выборгский судостроительный завод) in Russia for Moss Maritime (now part of the Saipem offshore company). The vessel is classed by ABS and has the IMO number of 8765412.
https://en.wikipedia.org/wiki/Sea-based_X-band_Radar
