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22 août 2011 1 22 /08 /août /2011 05:54


source defense-update.com


August 21, 2011: STRATEGY PAGE


Several years ago, the U.S. Air Force ordered a new sensor package for the RQ-4 Global Hawk that would match many of the capabilities of the existing J-8 JSTARS (whose AESA radar could identify and track vehicles moving on the ground below). The new RQ-4 sensor has arrived and is getting its first combat test in Libya. Called SAR-MTI, the radar can spot moving (on the ground) objects a hundred kilometers (62 miles) in every direction. Combined with infrared and vidcams, the sensors can record vehicle size (six meter/20 feet long) objects on a path below it 37 kilometers (23 miles) wide. There is also a spot mode, where the sensors can concentrate on a ten square kilometer area and see anything 1.8 meters (six feet) long or larger. In short, the new RQ-4 sensors can spot vehicles moving about anywhere in Libya, in any weather (even sand storms).


The older JSTARS radar (carried beneath a four engine jet, actually a militarized Boeing 707) has two modes; wide area (showing a 25 by 20 kilometer area) and detailed (4,000 by 5,000 meters). The radar can see out to several hundred kilometers and each screen full of information could be saved and brought back later to compare to another view (to see what has moved). Operators can track movement of ground units, or individual vehicles, over a wide area. Operators can also use the detail mode to pick out specific details of what's going on down there, like tracking the movement of vehicles fleeing the scene of an ambush. JSTARS is real good at picking up trucks moving along highways on flat terrain.


Development of the RQ-4 began in the 1990s, as a DARPA research project. The RQ-4 was still in development on September 11, 2001, but was rushed into action. The first production RQ-4A was not delivered until August, 2003. Although the RQ-4 could stay in the air for up to 42 hours, all of them have only amassed about 4,000 flight hours by 2004. But most of those 4,000 hours, which were originally planned to involve testing of a new aircraft, were instead used to perform combat missions. Global Hawk also got to fly under difficult conditions, something an aircraft still being developed, would not do.


The RQ-4A can cross the Pacific non-stop, flying 12,000 kilometers, from California to Australia, in 23 hours. Current models can fly 20 hour missions, land for refueling and maintenance, and be off in four hours for another twenty hours in the sky. The RQ-4 has been very reliable, with aircraft being ready for action 95 percent of the time. The U.S. Air Force has been buying them at the rate of five a year, at a cost of $58 million each.


The current B version is larger (wingspan is 13 percent bigger, at 42.2 meters/131 feet, and it's nine percent longer at 15.5 meters/48 feet) than the A model, and can carry an additional two tons of equipment. To support that, there's a new generator that produces 150 percent more electrical power. The B version is a lot more reliable. Early A models tended to fail and crash at the rate of once every thousand flight hours, mostly because of design flaws.


The first three RQ-4Bs entered service in 2006. At 13 tons, the Global Hawk is the size of a commuter airliner (like the Embraer ERJ 145), but costs nearly twice as much. Global Hawk can be equipped with much more powerful, and expensive, sensors than other UAVs, which more the double the cost of the aircraft. These spy satellite quality sensors (especially AESA radar) are usually worth the expense, because they enable the UAV, flying at over 60,000 feet, to get a sharp picture of all the territory it can see from that altitude.

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