RQ-4B Global Hawk: Mother of all UAVs?

This UAV can file its own flight plans and fly in commercial avaiation space. US Air Force RQ-4 Global Hawk UAVs recently flew their thousandth sortie. In the last six years, RQ4s have flown more than 15,000 hours, 70 per cent in combat missions.

The US Air Force (USAF) uses the Northrop Grumman RQ-4B Global Hawk as a surveillance aircraft. In role and design, it is somewhat similar to the Lockheed U-2, the famous 1950s high-altitude spy plane that the US used to maintain surveillance over the Soviet bloc countries during the cold war. It can provide both a broad overview and systematic target surveillance.

Some of the more recent models have been able to fly 20-hour missions, land for refuelling and maintenance, and take off within four hours for another 20 hours in the air. It is a very reliable aircraft, being ready for action 95 per cent of the time. More important, the RQ-4B has been authorised to fly in civilian air space.

The Global Hawk carries a high resolution synthetic aperture radar (SAR)-that can penetrate cloud-cover and sandstorms, as well as provide electro-optical or infrared (EO/IR) imagery at long ranges, and is capable of long loiter times over target areas. It can survey as much as 100,000 square kilometres (40,000 square miles) of terrain a day.

At 13 tons, the Global Hawk is the size of a commuter airliner (like the 50-seat Embraer ERJ 145), but costs nearly twice as much. Global Hawk can be equipped with more powerful (and more expensive) 'spy satellite quality' sensors than other UAVs, which more than doubles the cost of the aircraft. They enable the UAV, which can fly at over 60,000 feet, to get a sharp picture of all the territory it can see from that altitude.

The first three RQ-4Bs entered service in 2006. Earlier this year, the USAF ordered five more B version Global Hawks, at a cost of $58 million each. The B version is larger (the wingspan is 15 feet larger, at 131 feet, and the fuselage four feet longer at 48 feet) and it can carry an additional two tons of equipment. To support the extra equipment, a new generator produces 150 per cent more electrical power. There are just about half a dozen Global Hawks in service, but nearly 50 have been ordered.

The 'R' is the Department of Defence designation for reconnaissance, while the 'Q' means it is an unmanned aircraft system. The '4' refers to it being the fourth of a series of UAV systems. 'A' or 'B' refers to the version. The B version is a lot more reliable than the early A models, which had a fail and crash rate of around once every thousand flight hours.

The RQ-4 is powered by an Allison Rolls-Royce AE3007H turbofan engine with 7,050 pounds of thrust, and can carry a payload of 900kg. The fuselage is mostly aluminum airframe construction, while the wings are made of carbon composite.

The Global Hawk can do all kinds of intelligence collection to support forces in peace, in crisis, and in wartime operations. The air force says it allows more precise targeting of weapons and better protection of forces, owing to its superior surveillance capabilities.

The Global Hawk is the first UAV to be certified by the FAA to file its own flight plans and use civilian air corridors in the United States with no advance notice. This potentially paves the way for a revolution in unmanned flight, including the possibility of automatically piloted passenger airliners.

It has a transponder, and when its controllers file a flight plan, civilian flight controllers can manoeuvre it through air space that is 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, regardless of which country the UAV is operating in. Satellite communications connect it with its controllers, and enable it to transmit the data (radar and video) it generates.

Last year, a new 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. Developed for JSTARS, the E-8C Joint Surveillance Target Attack Radar System (Joint STARS) — an airborne battle management and command and control (C2) platform that conducts ground surveillance to develop an understanding of the enemy situation and to support attack operations for air theatre commanders — enables them to spot smaller, man sized, objects. AESA type radars are known for their ability deal with lots of targets simultaneously.