The ability to position several high-performance, complementary sensors over a target area and leave them in place for 24 hours or longer, while controlling the sensors and downloading imagery in real time, is set to become a reality for U.S. and allied forces. What makes it possible is the Northrop Grumman RQ-4A Global Hawk unmanned aerial vehicle (UAV). Among the most successful UAV projects of recent years, Global Hawk has been performing so well in a current military utility assessment (MUA) program that the Pentagon is looking at ways to start production as soon as possible.

Global Hawk has been under development since 1995, when a team led by Teledyne Ryan Aeronautical of San Diego was chosen by the Defense Advanced Research Projects Agency (DARPA) to develop a high-altitude, long-endurance intelligence, surveillance and reconnaissance UAV. It was one of DARPA's first Advanced Concept Technology Demonstration (ACTD) projects. Highlights of the ACTD included an emphasis on rapid development and low cost, a simple requirement which summed up the user's needs, giving Ryan wide latitude in finding a solution; and a real-world operational demonstration at the end of the program.

Northrop Grumman acquired prime contractor Teledyne Ryan in mid-1999. The historic name-Ryan built Lindbergh's Spirit of St. Louis in San Diego-lives on as the Ryan Aeronautical Center, the lead organization for Northrop Grumman's UAV activities.

The prime goal of the Global Hawk program is to create a vehicle which can loiter for 24 hours, 3,500 nautical miles from its base, at an altitude of 65,000 feet-high enough to provide a good slant range for its sensors, above most other traffic and out of range of many missiles. It carries radar, EO (electro-optical) and IR (infrared) sensors simultaneously, and a high-rate satellite and line-of-sight datalink systems.

The Global Hawk air vehicle is about as large as a medium-sized corporate jet, but with a long span, sailplane-like, carbon fiber wing and a V-tail. The AE3007 engine is an off-the-shelf commercial product. The airplane's distinctive, bulbous nose houses a large, steerable satellite antenna.

Global Hawk is not "piloted" from the ground: flight control, navigation and vehicle management are autonomous. One of the two ground stations, the launch and recovery element (LRE), provides precision guidance for take-off and landing, using differential GPS. The LRE deploys to the airplane's operating base. The other ground station, the mission control element (MCE), tells the vehicle where to go, and where to point its sensors to receive the imagery data. It can be located alongside the LRE, at the theater intelligence center, or, indeed, anywhere in the world. The goal is to make the vehicle and its imagery accessible to people whose need is immediate, and Global Hawk also carries back-up datalinks. Both ground stations and a support package can be transported in one C-5 or two C-17s. The vehicle itself needs no airlift: with a straight-line range of 13,500 nautical miles and endurance up to 38 hours, it can fly anywhere.

The first of five air vehicles built under the ACTD contract, UAV-1, made its initial flight from Edwards AFB on February 28, 1998. The bad news in early tests was that some sub-system failures did occur; the good news was that the back-up systems functioned as designed and the UAV landed safely. "We demonstrated all the back-ups," said Col. Craig McPherson, USAF program director. "Not necessarily when we wanted to, but we checked them, and they worked."

The first sensor-equipped aircraft, UAV-2, flew on November 20. But on March 29, as it passed through 41,000 feet at the start of a sensor and communications test mission, UAV-2 abruptly went into a flight termination mode and crashed into the Mojave Desert. A U.S. Air Force report on the accident investigation has not yet been released.

The program recovered from this setback with remarkable speed. An investigation confirmed what the doomed vehicle's telemetry had been telling the crew up to the moment of impact: there was no technical failure, and the design was sound. In little more than six weeks, UAV-1 had been fitted with a radar sensor and was back in the air, and on June 19, it was gathering imagery above the USAF's Roving Sands exercise in northern New Mexico.

By mid-September, the third vehicle was flying, the fourth was undergoing its final checkouts at Edwards AFB and the fifth was being completed in San Diego. Meanwhile, UAV-1 had taken part in five military exercises, performing a number of flights in each of them. "Our original plan was crawl, walk, run," commented Colonel McPherson. "Crawling" was defined as performing one mission a week, 12 hours long, and acquiring some imagery. "Walking" involved longer flights and more imagery. "We moved very quickly out of the crawl, we're heavily into walking, and we're moving into the run stage," he said.

In the "run" stage, the Global Hawk will be making more than one 24-hour flight per week in support of military operations and providing imagery that the exercise commanders have requested. For example, Colonel McPherson stated, "in the last several exercises, we've been able to retask the vehicle to take different images, from different angles and locations. That was something we didn't expect to do until we were well into the walk-run stage."

The imagery is coming in bright and clear. From 56,000 feet, the fire extinguishers next to parked F/A-18s at the Naval Weapons Center at China Lake stand out clearly on the day EO image. IR even shows an airplane that isn't there: a dark shadow is visible where the concrete cooled down in the shadow of a C-130 that had just taken off. "We're very satisfied," said Col. John Wellman, Chief of the Joint Reconnaissance Center at the U.S. Joint Forces Command, and the command's ACTD manager. "It's very good imagery." Admiral Harold Gehman, Commander-in-Chief of the Joint Forces Command, called Global Hawk "the theater commander's low-hanging satellite."

The Global Hawks will take part in a wide range of exercises before the MUA ends in the summer of 2000. Some operations are dedicated to a single exercise; others have supported multiple operations in several states, including one in which the aircraft roamed from Twentynine Palms in California to Mountain Home AFB in Idaho to the Wendover Range in Utah and back over Nellis AFB before returning to Edwards. Scheduled exercises include nonstop missions over Alaska, flights in support of the National Training Center at Fort Irwin and-an important milestone-an operation in which the entire system will be deployed at Eglin AFB in Florida.

"The vehicle is making us work a lot harder than we expected," said Colonel McPherson. "It's reliable. It flies when we say it's going to fly, and it takes pictures when we say it's going to." The Federal Aviation Administration, Admiral Wellman noted, "was initially concerned" about a UAV operating outside USAF ranges. Now, he stated, "the FAA has given us carte blanche to fly in the Western U.S."

The customer's view is echoed by Bob Mitchell, Northrop Grumman's vice president for unmanned systems and head of the Ryan Aeronautical Center. "We live in an information age and Global Hawk is an information system," said Mitchell. It's not complicated, but it's complex. Our objective is to get the information where it is needed and in the right format, and to keep focused on intelligence, surveillance and reconnaissance. We want to be the most accessible, responsive and reliable asset out there."

Global Hawk is based on an approach to reliability, built on decades of high-performance UAV production by Ryan in San Diego, which balances the need for redundancy with affordability. Most of Global Hawk's systems are duplicated with cross-links and redundancy management to ensure that the vehicle survives a single point failure. For example, the ailerons and the rudder/elevator surfaces are divided into two entirely independent segments, each of which is driven by one of the two flight control computers. Even if one system fails and slams a surface into its stops, the flight control system can physically overcome it and maintain control of the vehicle.

Global Hawk's success in flight tests coincided with the USAF's experience in Kosovo, which underscored several lessons that had also been learned in Desert Storm and Bosnia. One lesson is that there are never enough reconnaissance assets, particularly high-altitude platforms, to meet every need. Another is that manned aircraft can be lost, and that the U.S. public wants a casualty-free conflict.

The long Kosovo deployment exacerbated another USAF problem: unscheduled and extended overseas engagements made it difficult for the service to retain pilots and other key personnel. Not only does Global Hawk free experienced pilots for other missions, but it deploys with a very small crew.

These factors have played a part in a top-level Pentagon decision to move forward with Global Hawk. The Pentagon intends to start an accelerated engineering and manufacturing development (EMD) program in late 2000, using MUA lessons to refine the design. The DoD plans to buy two air vehicles in 2000 and two in 2001, to keep assembly moving prior to going into production.

The first production Global Hawk air vehicles will have the same kind of imaging payload as the ACTD aircraft, but the aircraft is earmarked for dozens of applications. It is the most likely platform for the Airborne Communications Node, a DARPA project aimed at developing a flying switchboard that will connect to almost any communications device in a military theater, from a cell phone to a fighter radio. It could be a signals intelligence platform, a jammer, or a relay for almost any other system. Overseas users are showing interest: a Global Hawk is due to ferry itself to Australia in 2001 for tests over the continent's northern coastline.

Even non-military and commercial users are looking at Global Hawk as a platform for communications, environmental monitoring and resource exploration. It may be some time before the FAA is ready to see commercial UAVs roam above major cities. Until then, the Global Hawk has an important role to play as a source of hard information in the conflicts of the coming century.