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GLOBAL HAWK CONVINCES US AIR FORCE

Compared with the Global Hawk, even the legendary Lockheed Martin U-2 is only a short-range jet. At the same altitude and at similar speed, Northrop Grumman's large unmanned air vehicle (UAV) can stay airborne around three times as long and monitor vast expanses of terrain with its sensors. The crucial factor which distinguishes the RQ-4A from many other UAVs is that this aircraft, originally developed by Teledyne Ryan Aeronautical, has already demonstrated its capability.

The five prototypes built in San Diego, California have already flown over 60 times since the first flight on 28 February 1998. At first glance this may not seem a lot, but together it adds up to almost 750 flying hours. Over 300 of these were notched up in FAA-controlled airspace, albeit mainly at altitudes of 15km or more where no other traffic is to be expected.

After the first 21 test flights, which examined the UAV's flight characteristics, performance data and sensor systems in Phase II of the Advanced Concept Demonstration Programme, the Global Hawk entered Phase 3 in the middle of June 1999. The aim of this phase was to demonstrate the practical operational deployment of the RQ-4A and its supporting ground control infrastructure.

The first task in Phase 3 was to participate in the Roving Sands exercise, which is held every year in Texas and New Mexico. Setting off from Edwards Air Force Base in California, the first prototype flew to the White Sands Missile Range to take high-resolution radar images of the manoeuvre area. These were transmitted to the Teledyne Ryan control centre in San Diego.

The most demanding trials to date took place in April and May of this year, when the RQ-4A flew from Edwards to Eglin Air Force Base in Florida to take part in the "Linked Seas 00" and "Joint Task Force Exercise JTFEX 00-02" exercises. The transit across the USA was used as an opportunity to also demonstrate the Global Hawk's capabilities to the US Coast Guard, which received images of shipping activity in the Gulf of Mexico.

On 8 May, prototype no. 4 then flew northwards from Eglin along the east coast of the USA and transmitted radar images directly to a US Army ground station in Fort Bragg, North Carolina and to the aircraft carrier USS George Washington, which was stationed in Norfolk, Virginia.

It then continued its flight across the Atlantic where shipping movements were monitored to the north of the Azores. Above Portugal, the RQ-4A gathered radar images of an amphibious landing operation near Setubal. However, due to technical problems the quality of the imagery was not as good as had been hoped. The UAV flew back over almost the same route and after some 28 hours airborne it was back at Eglin.

During the mission, the Global Hawk flew through three air traffic control zones above the Atlantic. Its progress was monitored from the Joint Warfighting Center in Suffolk, Virginia, while the data was transmitted via RAF Molesworth in the United Kingdom to NATO's SOUTHLANT HQ - proof indeed that the systems also work in complex scenarios.

As well as these tests, which were typical of how the UAV will be deployed in service, a 24.8 hour flight from Edwards AFB to Alaska and back was completed last October - child's play for the Global Hawk. The greatest length of time it has flown to date has been 31.5 hours, which is an endurance record for a jet-powered UAV. During that time the RQ-4A took no less than 459 radar images.

But even the Global Hawk programme is not immune to setbacks. The second prototype spiralled into the earth on 29 March 1999 near the China Lake military training area because it accidentally received a flight termination command. Then on 6 December 1999 prototype no. 3 was badly damaged on landing. Due to a software conflict, the UAV was commanded to taxi at 155kt (290km/h), causing it to veer off the runway. After that the Global Hawk was grounded for three months.

In the circumstances the US General Accounting Office is somewhat sceptical as to whether the programme is sufficiently advanced to proceed to the engineering and manufacturing development (EMD) phase. A decision on this was expected at the beginning of October.

As no major modifications are planned, EMD effort is to be confined to one year and only $75 million is to be spent on it. This sum does not include the cost of any additional aircraft, as prototypes 6 and 7 were ordered back in February for delivery by June 2002. Together these will cost $71.9 million. Altogether the programme has cost $651.7 million to date.

Northrop Grumman hopes that once EMD is complete, production at an initial rate of two Global Hawks per year will follow. Just how many RQ-4's the USAF will procure is not yet clear. Stated requirements for just the reconnaissance role vary between 20 and 50 machines. In addition, the Global Hawk also offers considerable potential as a flying relay station, for maritime reconnaissance or as an AWACS. However, funding remains a critical issue. Instead of the $10 million price tag originally put forward, the unit cost is estimated to have escalated to over $15 million.

But compared with manned systems, this still represents a huge saving. Hence, foreign interest in the Global Hawk is also substantial. The keenest player here has been Australia, which has signed an agreement to perform its own trials with the UAV. A prototype is therefore to be sent over to the fifth continent on a non-stop flight from California in April 2001 and put through around a dozen test flights there.

Northrop Grumman has also put out feelers in Europe. A collaborative agreement on high-altitude unmanned platforms was signed with EADS at the Farnborough Air Show in July. Global Hawk is thus well placed to profit from the current trend towards UAVs of all kinds.

Global Hawk: the system

Commencing in 1995, Global Hawk was developed by Teledyne Ryan Aeronautical in San Diego. Since July 1999 this long-established UAV specialist company has been a part of Northrop Grumman. Initially the programme was managed by the US Defense Advanced Research Projects Agency (DARPA), but programme responsibility was then passed to the Joint Endurance Unmanned Aerial Vehicle System Program Office of the US Air Force's Aeronautical Systems Center at Wright-Patterson, Ohio.

The Global Hawk's mission is to provide commanders in the field with near-real time high-resolution images. The UAV is therefore equipped with an integrated reconnaissance system, whose central computer processes the data from three sensors:

• Side-looking radar from Raytheon (formerly Hughes). It operates in the X-band with a peak output of 3.5 kW. Depending on operating mode, it can produce 2km x 2km spot images or, in wide area search mode, it can scan 138,000km2 per 24-hour period. It can also track moving targets on the ground (minimum speed 7.5km/h) within a 100km circumference.
• Electro-optical camera with a CCD chip for images in the visible range (0.4 to 0.8 microns), combined with a thermal imaging sensor which operates in the intermediate infrared range (3.6 to 5 microns wavelength). Both of these can be laterally steered +/- 80-o and are fitted with teleoptics. Depending on the requirement, either individual areas or a 10km wide "film strip" can be recorded. With the latter option an area of 138,000km2 can be covered in 24 hours.

The digital data captured by the radar and the EO/IR cameras can be transmitted via a Ku band satellite antenna, over UHF SATCOM or directly to the ground station over UHF, as required.

The surveillance system is accommodated in an airframe which can be likened to a giant powered glider. The slender carbonfibre wings have a wing span of 35.35m, while the fuselage, which is a predominantly conventional, aluminium structure, is only 13.4m long. The 11,340kg RQ-4A is powered by a Rolls-Royce (formerly Allison) AE3007H turbofan engine, which provides up to 33.7kN of thrust.

The UAV is controlled from two ground stations. The first is used to prepare the UAV for flight, including mission planning, while the second monitors mission progress and can be hundreds of kilometres away from the base airfield. The entire flight is fully automated. A differential GPS system permits precision take-off and landing to an accuracy of approx. 30 cm.

From page 58 of FLUG REVUE 11/2000