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The RQ-4 Global Hawk

The RQ-4 Global Hawk is an unmanned aerial vehicle (UAV) used by the US Air Force as a surveillance aircraft. In role and design, it is somewhat similar to the Lockheed U-2, the venerable 1950's spy plane. It is a theater commander's asset to both provide a broad overview and systematically targetsurveillance shortfalls.

The Global Hawk air vehicle is to provide high resolution Synthetic Aperture Radar (SAR)—that can penetrate cloud-cover and sandstorms—and Electro Optical/Infrared (EO/IR) imagery at long range with long loiter times over target areas. Potential missions forthe Global Hawk cover the spectrum of intelligence collection capability to support forces in worldwide peace, crisis, and wartime operations. According to the Air Force, the capabilities of the aircraft will allow more precise targeting of weapons and better protection of forces through superiorsurveillance capabilities.

The "R" is the Department of Defense designation for reconnaissance; "Q" means unmanned aircraft system. The "4" refers to it being the fourth of a series of purpose-built unmanned reconnaissance aircraft systems. "A" or "B" refers to these being the first and second revisions, respectively. See also RQ-1 Predator, RQ-2 Pioneer, RQ-3 Dark Star, RQ-5 Hunter, RQ-6 Outrider, and RQ-7 Shadow.

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 that of unmanned civil passenger airliners.

Integrated system
The Global Hawk UAV system comprises an air vehicle segment consisting of air vehicles with sensor payloads, avionics, and data links; a ground segment consisting of a Launch and Recovery Element (LRE), and a Mission Control Element (MCE) with embedded ground communications equipment; a support element; and trained personnel.

The Integrated Sensor Suite (ISS) consists of a synthetic aperture radar (SAR), electro-optical (EO), and infrared (IR) sensors. Either the EO or the IR sensors can operate simultaneously with the SAR. Each of the sensors provides wide area search imagery and a high-resolution spot mode. The SAR has a ground moving target indicator (GMTI) mode, which can provide a text message providing the moving target's position and velocity. Both SAR and EO/IR imagery are processed onboard the aircraft and transmitted to the MCE as individual frames. The MCE can mosaic these frames into images prior to further dissemination.

Navigation is via inertial navigation with integrated Global Positioning System updates. Global Hawk is intended to operate autonomously and "untethered" using a satellite data link (either Ku or UHF) for sending sensor data from the aircraft to the MCE. The common data link can also be used for direct down link of imagery when the UAV is operating within line-of-sight of users with compatible ground stations.

The ground segment consists of an MCE for mission planning, command and control, and image processing and dissemination; an LRE for controlling launch and recovery; and associated ground support equipment. (The LRE provides precision differential global positioning system corrections for navigational accuracy during takeoff and landings, while precision coded GPS supplemented with an inertial navigation system is used during mission execution.) By having separable elements in the ground segment, the MCE and the LRE can operate in geographically separate locations, and the MCE can be deployed with the supported command's primary exploitation site. Both ground segments are contained in military shelters with external antennas for line-of-sight and satellite communications with the air vehicles.
The Global Hawk is available in two major variants, the RQ-4A, which is the original variant, and the RQ-4B, which is somewhat larger, and has a 50% greater payload capacity. The U.S.Air Force has begun focusing on this newer version. Scaled Composites and Northrop Grumman are also offering a 50% proportional shrink of the RQ-4A, currently known as the Model 396, as part of the USAF Hunter-Killer program.
Other operators
As of February 2004, Australia has committed to 5-6 Global Hawk airframes for maritime and land surveillance, to replace their Lockheed Martin P-3 Orion patrol aircraft and General Dynamics RF-111C Aardvark reconnaissance aircraft, with deliveries in 2004-2005. Joint USAF/RAAF exercises in 2001 demonstrated the utility ofthe Global Hawk in Australian waters. In addition, Australia increased their requirements from merely a maritime role to a land surveillance role after observing American usage in 2003.

Germany is strongly considering a variant of the RQ-4B (dubbed "Euro Hawk") equipped with an EADS SIGINT package to fulfill their desire to replace their aging Dassault-Breguet Dassault_Atlantic electronicsurveillance aircraft. Canada is also a potential customer.

The U.S. Navy has ordered two examples to be used to evaluate maritime surveillance capabilities. The first RQ-4A will be delivered around October 6, 2004, and the second one will be delivered several months later. The initial example will be tested in a naval configuration at EdwardsAir Force Base for several months, and then will be flown to NAS Patuxent River for a future demonstration.[1]
In operation

Global Hawk prototypes have been used in the 2003 invasion of Iraq and in Operation Enduring Freedom. While their data-collection capabilities have been praised, the aircraft did suffer a high number of accidents, with two of the aircraft, more than one quarter of the aircraft used in the conflicts, being lost (implying that there were seven Global Hawks used in this program). According to Australian press reports, the crashes were due to "technical failures or poor maintenance", with a failure rate per hour flown over 100 times higher than the F-16 fighters flown in the same conflicts. The manufacturers stated that it was unfair to compare the failure rates of a mature design to that of a prototype plane, and pointed to a lack of trained maintenance staff and spare parts. There is also something to be said for the fact that no pilot was placed at risk.

The reports also state that the cost of Australia's purchase of the planes has increased at least fivefold (from 150 million AUD to between 750 and 1000 million AUD) over initial estimates, though no explanation was given for the extra cost and the plans may involve the purchase of extra aircraft.

On April 24, 2001 a Global Hawk flew non-stop from Edwards Air Force Base in the US to RAAF Base Edinburgh in Australia, making history by being the first pilotless aircraft to cross the Pacific Ocean. The flight took 22 hours.
General characteristics
Contractor: Northrop Grumman, with EADS participation in European models.
Landing Type: runway
Launch Type: runway
Ceiling: 19.8 kilometers
Endurance: 24 to 36 hours

RQ-4A: 13.4 meters RQ-4B: 14.5 meters

RQ-4A: 11,600 kilograms

RQ-4A: 35.4 meters RQ-4B: 39.9 meters
Velocity: 250 kilometers per hour (cruise); 636 kilometers per hour

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