Warplanes: Robots Allowed To Mingle With Airliners


July 31, 2007: U.S. Air Force RQ-4 Global Hawk UAVs recently flew their thousandth sortie. In the last six year, RQ4s have flown 15,135 hours, 71 percent of that combat missions. Some of the more recent models have been able to 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 RQ-4 has also been authorized to fly in civilian air space.

Earlier this year, the U.S. Air Force has ordered five more Global Hawks, at a cost of $58 million each. This is the B version, which is larger (wingspan is 15 feet larger, at 131 feet, and it's four feet longer at 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 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. These 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. 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.

The Global Hawk is the only UAV qualified to fly in civilian airspace. It has a transponder, and when its controllers file a flight plan, civilian flight controllers can maneuver it through air space also used by airliners. The controllers for Global Hawks (a pilot and one or more sensor operators) work from a base in the United States. The UAV uses satellite communications with its controllers, and to transmit data (radar and video) it generates. Last year, a high resolution radar was installed in a Global Hawk. This Active Electronically Scanned Array (AESA) radar consists of thousands of tiny radars that can be independently aimed in different directions. A new AESA radar for JSTARS enables them to spot smaller, man sized, objects. AESA type radars have been around a long time, popular mainly for their ability deal with lots of targets simultaneously, and produce a more accurate picture of what is out there.

There are about half a dozen Global Hawks in service, and nearly fifty are on order.




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