UAVs—The Next Generation

Feb. 1, 2007

The dazzling success of unmanned aerial vehicles in the Global War on Terrorism has opened military eyes to the potential of robotic systems. The MQ-1 Predator, with its phenomenal surveillance and strike capabilities, seems to point the way to broader and more sophisticated UAV operations.

For all that, Predator also has been seen to suffer some crippling shortcomings. Being small, it cannot carry much onboard fuel, which limits range and endurance. It cannot refuel in air, as do manned aircraft. Because Predator operates alone, it often winds up watching targets already being watched by others. The Predator, flown by humans, is subject to poor human judgment.

Each weakness highlights a need for certain technologies, report Pentagon and industrial officials. Developers are therefore pushing forward with several next generation capabilities aimed at satisfying specific needs.

Foremost among these is the need for unmanned aerial refueling capability. Research into autonomous refueling is well advanced. The end result will be an unmanned aircraft that flies up to a tanker and uses various sensors to sink its fuel line into a trailing tanker receptacle.

The Defense Advanced Research Projects Agency has demonstrated the capability using the probe-and-drogue method, in which a UAV’s probe uses newly developed optical sensors to find its way into a basket on the tanker. (See “Aerospace World: Midair Refueling Tests Successful,” November 2006, p. 20.)

50-Hour Missions

Air Force Lt. Col. James McCormick, DARPA program manager, said the service needs autonomous aerial refueling capabilities to extend the endurance of unmanned aircraft. USAF, referring to the Joint Unmanned Combat Air System program, “used to talk about a 50-hour mission limited by the need to change the oil,” noted McCormick.

The test aircraft relies on GPS-based navigation and an off-the-shelf digital camera image of the basket, or drogue, to determine its location relative to the tanker.

This 15-month program ended last October after successful flight tests of an F/A-18 modified to simulate an unmanned aircraft. (A pilot was in the cockpit for safety reasons, but the aircraft was flying autonomously.) The program was then extended for flight tests with realistic environmental factors such as turbulence and an aircraft turning during refueling.

The technology could also be applied to manned aircraft. McCormick said manual refueling is tedious and taxing for pilots because the aircraft must be flown in precise formation close to the tanker. DARPA is working with the Air Force, Navy, various combatant commands, and Air Mobility Command to develop the autonomous refueling capability.

“We used existing off-the-shelf technology so, technically, the capability is here today,” said McCormick. Delay in fielding such a capability would come from standard testing and integration periods.

McCormick estimated that it could take as little as three years to field UAVs that can autonomously refuel, but a more realistic goal is 10 years. The need to develop a concept of operations, determine the aircraft to which the technology would be applied, and to come up with funding will slow things down.

There is at least the potential for rapid results, however. Both the Predator and Global Hawk UAVs began their lives as DARPA projects and were rushed into wartime service for their unique capabilities.

Meanwhile, the Air Force Research Laboratory’s Air Vehicles Directorate at Wright-Patterson AFB, Ohio, is in the fifth year of a six-year program to develop autonomous aerial refueling capability based on USAF’s preferred “boom and receptacle” method, which works much like gassing up an automobile.

An aircraft flies directly behind a tanker, where a boom operator connects a long hose to the aircraft. This program was initially part of an advanced technology demonstration associated with the J-UCAS program, which was dissolved last February.

The program has a series of flight tests scheduled over the next year, culminating in a major event in the fall in which multiple aircraft will fly in formation off the wingtip of the tanker and drop back one by one to refuel. That flight test will also involve an autonomous emergency breakaway from the tanker.

The reliability of GPS data is a particular challenge for both refueling programs because of the high safety margins. AFRL Program Manager Jake Hinchman said the goal is to establish a level of integrity at which there is only a one-in-a-million chance that the refueling aircraft will bump into the tanker.

The intensity and duration—as long as 23 minutes—of the formation flight required for aerial refueling is another major challenge.

See and Avoid

Equally important is the need for technologies that allow UAVs to see and avoid what is in their way so they can better operate in congested airspace.

Despite the successes of unmanned aircraft over the past several years, UAVs still have one major pitfall: They are flown by humans. They can’t autonomously see or avoid obstacles in their path, which can lead to collisions with buildings and other aircraft.

A see and avoid, or sense and avoid, capability is ranked as one of the top objectives for unmanned aircraft systems in the Pentagon’s 2005 unmanned aircraft roadmap. (See “Will We Have an Unmanned Armada?” November 2005, p. 54.)

Gen. William T. Hobbins, commander of US Air Forces in Europe and director of NATO’s Joint Air Power Competency Center, discussed the air traffic hazards created by the proliferation of unmanned aircraft in a recent speech in Germany.

Hobbins said that, in August 2004, an unmanned German aircraft flying over Afghanistan came within 50 feet of an Afghan Airbus carrying more than 100 passengers. The airline pilot’s quick reflexes and a “bit of luck” prevented a collision, he said, but the unmanned aircraft still crashed due to turbulence.

The airspace below 3,000 feet is crowded with tactical UAVs and helicopters, according to Hobbins, who said three collisions have occurred between UAVs and helicopters since the conflict in Afghanistan began.

AFRL has therefore placed a high premium on see and avoid capabilities, said Bruce Clough, chief of strategic planning at the lab. “Human beings can look around them so they don’t crash into things,” said Clough. “How do you build a system that will do that?”

A major facet of the capability is the need to give unmanned systems the ability to “orient.” Orient is the capability to understand the meaning of what is seen—something a pilot or soldier with years of experience does instinctively.

For example, Clough said, a human might say, “There’s a tank there. Oh, I’m being attacked by a mechanized division.” The challenge of giving a machine that kind of understanding is significant.

DARPA’s Organic Air Vehicle program has been flight-testing an obstacle avoidance capability that enables a micro UAV to sense what’s in front of it and modify its preset flight plan accordingly. The program’s small ducted-fan UAV, which flies like a helicopter, has performed well in ongoing tests, according to Daniel Newman, program manager.

Finally, a key requirement is for far more effective command and control linkages. Improved integration is needed to realize the military’s dream of network-centric warfare. Without it, the advance of UAV capabilities will be blocked.

The integration should be so thorough that combat forces treat unmanned systems like any other piece of equipment.

Like Manned Aircraft

Unmanned aircraft need to “act like manned aircraft,” said Hobbins. “We need unmanned aircraft to be tasked like manned aircraft. We need unmanned aircraft to fly in strike packages with manned aircraft. … We should be capable of flying both manned and unmanned platforms together, to include multiple unmanned airframes controlled by one operator. And we need commanders to have the confidence that—unmanned or manned—it doesn’t make any difference, as they are equally effective.”

Toward that end, Hobbins’ NATO joint competency center is developing a “flight plan” to guide the alliance in the development of unmanned aircraft systems. NATO is pursuing unmanned technology as voraciously as the United States military—Hobbins said there are 32 nations developing more than 250 models of UAVs.

Dyke Weatherington’s Pentagon task force, meanwhile, is preparing an updated roadmap, to be released this year, to guide the integration and interoperability of all US unmanned systems.

Major technology challenges already identified include: bandwidth and processing speed; air traffic control (domestically and in war zones where collisions between UAVs and manned aircraft are a constant threat); cooperative control of multiple UAVs by a single operator; and getting formations of unmanned aircraft, ground vehicles, and underwater vehicles operating as a team.

Weatherington said C2 is a significant issue because most UAVs are still operated independently of one another.

Air Force Capt. Nidal Jodeh, program manager for an AFRL effort that would put multiple small and micro UAVs under the control of a single operator, said the lack of coordination among UAVs being used in Iraq and Afghanistan can create redundancies, misinterpretation of facts on the ground, and radar interference.

Rapid Growth in UAV Operations

The ongoing wars in Iraq and Afghanistan have led to a rapid and dramatic increase in UAV flight hours.

UAV flying hours have increased from less than 20,000 in 2001 to more than 160,000 in 2006, according to the Office of the Secretary of Defense’s Unmanned Aircraft Systems Task Force.

The biggest gains have come not from the Air Force but from the Army, which logged 80,000 UAV flight hours in 2006—compared to 60,000 for the Air Force. (These totals exclude small UAVs weighing less than 10 pounds.)

By comparison, the Air Force flew two-thirds of the 60,000 flight hours that DOD UAVs logged in 2004.

Meanwhile, the Pentagon’s overall UAV inventory has grown from 217 aircraft to 3,428 over the past four years. The task force attributes the growth to rising demand for smaller UAVs, which account for 2,908 of the UAVs in the US inventory. The Defense Department had just 90 small UAVs in 2002.

For example, three different UAVs sent out by separate commanders may all be tracking the same target, creating a costly waste of resources and potential confusion.

The AFRL Cooperative Operations in Urban Terrain, or COUNTER, program that Jodeh leads is designed to enable a single operator to control four micro UAVs and one small UAV in a coordinated mission. This should improve situational awareness for ground forces in urban environments.

The human interface remains a major challenge. Can a single operator handle five video streams? What tasks can be automated to relieve stress on the operator

Another factor that limits coordination is that the aircraft must stay above the tops of buildings—in part because of the lack of a sense and avoid capability that would prevent collisions with those buildings. Urban UAV navigation is a hot topic of research at several universities, said Steven J. Rasmussen, a General Dynamics consultant working on the COUNTER program.

For its part, Northrop Grumman, builder of the Global Hawk, believes the ability of one unmanned aircraft to operate autonomously but in conjunction with other unmanned systems may bring the greatest gain to combat forces.

Gene Fraser, vice president of the company’s unmanned systems division, said Northrop is developing technology to let UAVs flying in formation reconfigure themselves according to mission needs. The company has been demonstrating the capability on several unmanned platforms, including a small helicopter and two fixed-wing aircraft.

Where Now

The technological advance of unmanned systems goes far beyond these three general areas. While some of the needs may be obvious, others are not.

“What do cars need? What do boats need?” asked Thomas J. Cassidy Jr., president of General Atomics Aeronautical Systems, which builds the highly successful Predator.

Indeed, just as for cars and boats, the needs of unmanned aircraft depend on who’s driving (or not driving in some cases); what kind of vehicle; and where. Those details have become increasingly varied as the military invests heavily in systems of all sizes and capabilities—from micro unmanned aircraft weighing less than a pound to aircraft weighing more than 40,000 pounds.

Some of the primary areas of research are:

Urban Navigation. Researchers at the University of California, Berkeley, are leading military-funded research into development of swarms and formations of unmanned aircraft able to navigate in and around buildings and cityscapes. The effort involves high-level autonomy, multisensor integration, and multiaircraft coordination.

Long-Range Strike. The Air Force wants a next generation bomber by 2018 and it could be unmanned. Taking the human out of the bomber could improve mission durations, reduce the aircraft’s radar signature, and eliminate risks to pilots. (See “The 2018 Bomber and Its Friends” October 2006, p. 24.)

Heavy Fuel Engines. Many UAVs are powered by conventional gasoline engines, which pose logistical and safety issues because most other military vehicles use heavy fuels. Gasoline is also more volatile than diesel.

Precision Strike. Northrop Grumman’s Fraser says the company’s work to make existing UAVs more lethal tends not to focus on free-fall bombs.

Contingency Response. Unmanned aircraft flying in formation will eventually be able to reconfigure themselves and respond to contingencies. This will require them to disrupt their flight plan without human interference.

Muzzle-Flash Detection. General Atomics is working on sensors to detect flashes from rifles and other weapons. The capability is particularly applicable to urban conflict.

HDTV. High-definition television is not just for sports. General Atomics is adding HDTV to its sensor packages, a move that will offer better resolution of the images transmitted by its UAVs.

For UAVs, as for manned aircraft, technological advance is assured. The only question is when the new systems and capabilities will move out of the factory and into combat operations.

Catherine MacRae Hockmuth is a San Diego-based freelance writer and former managing editor of the Inside the Pentagon defense newsletter. Her most recent article for Air Force Magazine, “The Promise and Problem of Laser Weapons,” appeared in the December 2001 issue.