Sense-and-avoid technologies are close to ensuring safe UAV flights on a large scale. It's mostly a matter of time, standards and FAA rules.
Unmanned aircraft have proven their capabilities in Afghanistan and Pakistan, undertaking reconnaissance and combat missions without putting the lives of pilots at risk. And now they're coming home. "We are not darkening the skies yet," said Richard Christiansen, vice-president of NASA contractor Sierra Lobo Inc., "but we are poised."
Unmanned aerial vehicles (UAVs) are already used in domestic airspace. Police departments have tested them for surveillance operations, for example, and state environmental departments have used them to survey forests and wildlife. And the Department of Homeland Security has a fleet of eight drones tasked to monitor activity at borders.
So far, however, these deployments have only been permitted under carefully monitored exemptions to Federal Aviation Administration rules. But the FAA plans to integrate unmanned aircraft into civilian airspace by 2015, and it is currently in the process of selecting six locations around the county to explore the potential extent of such integration.
The major barrier to wider deployment is that current FAA rules require the pilot of a UAV to maintain line-of-sight contact with the aircraft. If that limitation is removed, and UAVs are integrated into civilian airspace, analysts expect the market to grow rapidly. An industry trade group, the Association for Unmanned Systems International, projects sales of $90 billion over the next decade.
In the meantime, the rush is on to develop "sense-and-avoid" systems that will allow untethered flights.
Researchers agree that the basic technologies are already available to deliver effective collision warning and avoidance systems. The challenges, they say, are primarily in engineering and systems integration.
"We know we can technically do it," said Sanjiv Singh, research professor at Carnegie Mellon University's Robotics Institute. "The question is whether we can do it within all of the other constraints." And when it comes to UAVs, especially small UAVs, the primary constraints are size and weight.
Whether a sense-and-avoid system uses electro-optical cameras, laser radar (LIDAR) devices or transponders, the challenge is to make the devices small and light enough to be deployed on small UAVs. "It's getting close," said Ian Glenn, CEO of ING Robotic Aviation, a Canadian manufacturer. "We're making them smaller and smaller. Absolutely the technology will get there."
ADS-B taking off
According to Glenn, the simplest way to protect against mid-air collisions — whether the aircraft has a pilot or not — is to require the use of ADS-B transponders on all aircraft. "These transponders can turn an uncooperative environment into a cooperative environment," he said.
ADS-B (automatic dependent surveillance-broadcast) transponders not only broadcast aircraft location in real time, they also deliver information on altitude and velocity. What's more, they can deliver data on other aircraft, weather and terrain to the vehicle that is carrying them. In fact, ADS-B transponders will replace radar as the primary technology for tracking air traffic, and the FAA will require the majority of aircraft operating in U.S. airspace to be equipped with ADS-B by Jan. 1, 2020.
Using ADS-B transponders on many UAVs was infeasible until recently, when Sagetech Corp., an avionics company based in White Salmon, Wash., developed one that weighed only 3.5 ounces.
Last November, ING Robotic Aviation equipped one if its 22-pound Serenity UAVs and manned Harvard Mark IV, a fixed-wing, single-engine aircraft operated by Canada's National Research Council, with Sagetech ADS-B transponders and Clarity receivers. The two aircraft were then flown for 90 minutes above an Ottawa air park.
"We were able to prove that we could fly, and they could see us a long way away," said Glenn. "We were able to pick up [data on] traffic coming to Ottawa even as it was crossing New York's border."
Even better, he said, the Clarity receiver is independently powered, which means that even older aircraft can adopt the technology. "One of the arguments by regulating agencies is, ‘Well, that's great, but we have people flying Sopwith Camels. They don't even have power supplies, and they don't have a radio,'" said Glenn. "Well, here's a little box that you can stick on the dashboard, with a battery that will last longer than your bladder. And it has its own little Wi-Fi and it'll display on an iPad."
One system for all sizes
Until all aircraft are equipped with ADS-B transponders and receivers, of course, UAV sense-and-avoid systems must rely on other technologies to detect other aircraft and to undertake evasive maneuvers.
One of the most ambitious civilian efforts under way to develop an integrated system for UAVs is the Mid-Air Collision Avoidance System (MIDCAS), which is being developed by five European countries — Sweden, Germany, France, Italy and Spain — and 11 industrial partners.
The four-year, $65 million project is expected by 2014 to deliver an automated sense-and-avoid system that will not depend on transponders. While it is being designed to integrate ADS-B, MIDCAS also includes two visible-band electro-optical cameras and one infrared camera for aircraft to use in identifying other aircraft. In addition, the team's developers are designing image-processing algorithms, processing units and integration with on-board avionics.
Key to the project, said Saab Aerosystems' Johan Pellebergs, MIDCAS project manager, is developing a generic set of sensors and processing modules. "By generic, we mean that it should be able to work on any type of UAS," Pellebergs said. "It should be adaptable. So we try to keep all of the vehicle-specific parts well contained so that they can easily be adapted to all the different types. The variety in UAS is very big, ranging from the Global Hawk, which is very big, all the way down to small ones that you can hold in your hand."
Pellebergs said the international team has developed a prototype system and is ready to test it on a manned aircraft. "The collision avoidance part is fully automatic," he said. "The remote pilot does not need to do anything. If the system detects something, it calculates when it needs to activate. And when the aircraft gets to that point, it triggers and executes the moves automatically."
It is the system's control over evasive maneuvers that requires adaptability to each model of UAV. "That's where the vehicle specifics come in," Pellebergs said. "You need to be able to model the performance and limitations of each of the vehicles. There are large differences between air speed and maneuverability in these vehicles."
That's one reason MIDCAS is working closely with manufacturers of UAVs and sensors.
Another challenge has been designing the software to process the various sensor data. According to Pellebergs, "The data fusion module takes the information from different sensors and makes one picture. Then it is sent over to the avoid part, where you calculate the maneuvers and execute them. It also sends information down to the ground control station."
Of course, the hazards for aircraft — manned and robotic — aren't limited to other aircraft.
"There are very few things above 500 feet to run into," Singh said. But landing, taking off or operating under 500 feet — which is where many UAVs are designed to spend most of their flight time — there are many hazards, including trees, buildings and wires. "You have to go up and come down," noted Singh. "I think that last hundred feet is pretty important."
Accordingly, Singh has set his sights, in a sense, lower. "I work on the aspect of UAVs flying intelligently so that they can fly in what we call 'near-earth environments.' They are aware of their environment, they are aware of what they can do, they are aware of environmental conditions like wind, and then they plan their actions in such a way that they can stay safe."
And being closer to the ground introduces other challenges. "Maybe you need to fly close to things, so the GPS is blocked by trees and buildings," he said. "Maybe you need to operate in dusty conditions or at night. The problem is complex.”
As a result, Singh is working to integrate a variety of sensors and to develop the software to make them usable in UAVs. In addition to the visual sensors (cameras and infrared imagers), Singh is working to incorporate far infrared (effective for detecting features through fog or rain), radar (which can penetrate obstacles) and LIDAR (which is effective in detecting contours of objects).
Singh was part of a team that recently enabled a full-size, autonomous helicopter to fly at low altitude, avoid obstacles, choose a landing site in unmapped terrain and successfully land. In June 2010, the team tested the sensor and navigation system at a Boeing test facility in Mesa, Ariz. Employing a laser scanner and 3D mapping software, the unmanned helicopter was able to avoid a 60-foot crane and high-tension wires, as well as other smaller obstructions, such as four-in-high pallets, chain-link fences, vegetation and even people.
Government in the way?
While there is a long way to go before completely autonomous UAVs can safely operate in all environments and conditions, researchers say the basic technologies are already in place that would allow for widespread deployments right now if government would move to set standards.
"The real challenge is not technological," Glenn said. "The real challenge is regulatory acceptance. I think we're close enough. The key is that we are able to be as good as manned aviation. So the issue is how to get federal aviation authorities around the world to get their minds around it."
According to Glenn, if government regulatory agencies would specify the performance standards UAVs need to meet, he can design appropriate equipment. "You tell me what the requirement is, and I will build it," he said.
Pellebergs agrees. "No one really knows what the requirements are for sense-and-avoid for UASes in civilian airspace, so we need to get a set of standards in place," he said. "I think that's what's holding up a lot of the progress in this area."
Unfortunately, the Federal Aviation Administration declined our requests for comment.