Is it a bird is it a plane?

While unmanned aerial vehicles are readily used by the military, E&T discovers that it will be some time before we see them flying-high above our towns and cities.

Even if you have only a passing interest in current affairs, there is a fair chance that you'll have read or seen news reports about military missions in Afghanistan and Pakistan involving unmanned aerial vehicles (UAVs), which the US has been using for several years to hunt down senior members of al-Qaeda.

These heavily-armed drones, with names like Predator and Reaper, are controlled by personnel at ground stations on American soil using satellite comms links and onboard cameras, locating their targets then launching missiles or guided bombs from high altitude. These attacks cause such devastation that Osama bin Laden and his deputy have reportedly been forced to replace people in their organisation with men they've never met.

The logic behind using these craft for such tasks is clear. With no pilot on board, human endurance on a flight half way around the world is not an issue, nor can they be killed or captured if the craft is shot down, and if it is shot down the material loss is a fraction of that involved in the downing of a manned fighter or bomber.

But it isn't just these dangerous tasks that UAVs are suited to, there are dull and dirty ones as well - and this is where the civil, rather than the military, sector will become important in the next few years.

While the military necessarily needs these craft for missions such as target acquisition and precision strikes, search and rescue, reconnaissance and target practice, there's a far wider spectrum of potential civil applications such as geological surveys, crop spraying, border patrols, comms relays, and monitoring pollution, hurricanes and forest fires, with some areas of crossover between the two.

In fact, the consensus in the civil UAV fraternity is that the only limitation to their use is in designers' imaginations. And, unusually perhaps for an emerging market, there are equal opportunities for small and medium-sized enterprises (SMEs).

Military and civil

We won't be seeing civil UAVs above our towns and cities for a few years yet, however, because, at least in terms of their control systems, the prevailing issues between the military and civil sectors are very different. And in the civil sector they all come back to one thing - safety.

"For the military, the important thing is for a UAV to complete its mission," says Marko Lukovic, principal aerospace and defence consultant at Frost & Sullivan. "But in the civil sector, you simply cannot afford to have a UAV crash for any reason - it has to be as safe as a manned craft."

At the moment, aviation authorities say UAVs may operate only in a segregated airspace, in areas outside air traffic control (ATC) regimes. Regulations from organisations such as the UK's Civil Aviation Authority (CAA) and pan-European aviation safety body Eurocontrol specify that to enter airspace governed by ATC, UAVs have to match manned aircraft in their ability to interact with ATC and carry out their own "sense and avoid" manoeuvres to maintain separation from other craft - the equivalent of "see and avoid" for manned aircraft.

The challenge here is translating that into a system specification. For it to be equivalent to the see and avoid capabilities of a pilot, the system must be able to sense other flying objects - from hot-air balloons to jet fighter planes - in 360 degrees, since a fast-flying jet could collide with the UAV from any angle. It also has to be capable of operating in diverse environments, such as cloud, rain, day and night, and over a wide temperature range.

The obvious approach here is to use a range of sensors - automotive-type collision avoidance radar, scanning laser-based light detection and ranging (LiDAR) and distance-aware stereo imaging, for example - and combine the data from them in an onboard collision detection computer so it can instruct the UAV's flight control computer to avoid a collision. But, as we'll see, it's not as simple as that.

The UAV also has to be able to do this in all conditions, beyond the line of sight of a human operator and in circumstances where direct manual control may have been lost, as in a comms outage. So some level of autonomy is key here.

The UK has a major initiative in this field at the moment in the form of the ASTRAEA - Autonomous Systems Technology Related Airborne Evaluation & Assessment - programme. It's a civil-only project consisting of a consortium of companies, government agencies and academia to investigate the technical and regulatory feasibility of routine, autonomous, unmanned flight in UK airspace.

"In the UK, the control system for a UAV for civil use needs to comply with CAA regulations," explains Nigel Mills, who's on ASTRAEA's steering board and is technical director of the area leading the work for consortium member QinetiQ on a project to develop UAV handling systems. "It therefore has to demonstrate that it is sufficiently safe, so it needs to have built-in redundancy, up to quadruplex, as you would have in a manned, fly-by-wire aircraft."

Flight envelope protection

Redundancy is not the only option, though; the ASTRAEA programme is looking at other techniques as well as or instead of redundancy - for example, Flight Envelope Protection, which considers the degree of degradation in the system after, say, a bird strike to decide how to keep the craft controllable.

"FEP would limit the manoeuvre demands of the UAV, as the pilot would do in a manned craft," says Mills, "meaning it could carry out fewer tasks but could still fly safely even if the redundant systems couldn't keep the UAV in its normal configuration. It's another layer of complexity that you may not necessarily have in a military system, but it may reduce the need for full quadruplex redundancy.

"But the main issue here is to give the system the ability to have behaviours that a rational pilot would have," he says. "It's a question of having on-board decision-making, replacing the thought processes of a pilot with electronics."

To put it another way, Mills says that if you're looking at a small remotely piloted UAV, which in essence is just a radio-controlled plane, then the control system can be comparatively simple, but if you're looking to build a UAV the size of, say, a twin-prop aircraft then the control system needs to be similar to that in a manned craft but with the added autonomy needed in place of a pilot.

"So the main stages in developing a UAV control system are first, start with the aerodynamics and flight mechanics. Then you need a low-level control system, then higher and higher levels of command and control so that, for example, if the UAV was tasked with a search and rescue mission, as in identifying a person's location, the UAV could plot a route without having to be told individual waypoints and taking into account environmental conditions."

These levels of control correspond to the three levels of the autonomous hierarchy - strategic, tactical, dynamic - which are defined according to the time scale and therefore by the nature of the control problem.

The strategic level operates on the longest time scale and includes missions such as path planning, task allocation, and searching, and is equivalent to the navigation control problem.

The tactical level operates on a shorter time scale and includes missions such as target observation. Here, the time scale is associated with the maneuverability of the UAV and therefore represents the guidance problem.

The lowest or dynamic level operates on the shortest time scale. This is the "inner-loop" control problem that translates guidance orientation commands to actuator signals.

But there are still the technological obstacles to building a sense and avoid system. So why is it proving so difficult? "The challenge in developing a sense and avoid system is that effectively it has to see what a pilot sees and react appropriately, using a combination of trajectory management and sensors - standard visual as well as infrared sensors, for example," says Mills.

"The human eye has a very high spatial resolution and, with training, can pick out small fast-moving objects against the very cluttered landscape background. Implementing this cost-effectively in hardware and software is the difficulty," he says.

In addition to using a range of sensors, Mills says it's also possible to use co-operative systems similar to those installed on some manned aircraft, where the UAV's planned trajectory is continually transmitted so that other air vehicles know its intentions.

But this is not the only main technological obstacle, there's also the issue of the comms link and maintaining its integrity. "One thing that would be very helpful here would be to have a protected UAV frequency band," says Joseph Barnard, managing director of Barnard Microsystems, an SME developing navigation, flight control and sensor systems for UAVs. "There's no unused space in the spectrum, which means taking some of it over.

"The issue here is that you can't guarantee that you won't lose the comms link, so if there is an outage you need robust autonomy and sense and avoid capabilities to enable the UAV to abort its mission or land nearby - or carry on safely.

"You also have to be able to measure or monitor the quality of the link to account for, say, atmospheric conditions and be able to compensate for that. And you have to be able to prevent jamming and hacking," he says.

This issue of bandwidth allocation is another major sticking point, although it's hoped it will be resolved at the World Radiocommunication Conference in 2011/12, where it's on the agenda.

Aviation regulations

And there's yet another hurdle - conforming to aviation regulations. Barnard says: "This is a problem of specifications. The UAV system has to be as good as a pilot but there's no information on how 'good' a pilot is - there are no specs so this is something that's hard to replicate."

Mills has a contrasting view, saying: "UAV manufacturers have to understand the requirements of the regulators, but the current regulations have been written around manned aircraft.

"There are currently no UAV-specific regulations, such as the last-moment collision avoidance function required of pilots in manned aircraft. A remote pilot would not have enough time or situation awareness to carry out the avoidance manoeuvre so there needs to be some function on the UAV to do it.

"But there is some useful guidance, such as the CAA's CAP 722, which means the regulators can make judgments about the acceptability of a solution when they see the actual UAV on a per-application basis. The guidance is being continually improved, partly because of programmes like ASTRAEA, and is expected to lead eventually to mandatory regulations." 

Another important body here is the European Organisation for Civil Aviation Equipment (EuroCAE), which has established the WG73 UAV working group to address the standards needed for civilian UAVs to fly in non-segregated airspace.

Its task is to review all the work resulting from a range of recent activities. Organised into three groups - airworthiness, operations and air traffic management - it is initially delivering an inventory of UAV-related elements concerning the operational concept, a work plan for the development of the concept and the concept itself. After that it will deal with standards and equipment requirements, development, production, deployment and monitoring.

"The good thing about WG73 is that anyone can offer input into it," says Barnard, whose company does just that. "It's also great for networking with people and pooling expertise, and it allows you to get a broader picture of the way the legislation is coming along." 

Where there are regulations and standards of course there is also certification, and here the process labours under the same imponderables as the regulations - how to justify investment in a UAV technology without knowing exactly how likely it is to be certified.

"This is one reason why ASTRAEA partners use virtual certification, especially on UAV subsystems such as Flight Envelope Protection," says Mills. While this process is used in a wide range of industries Mills explains that here "virtual" means undertaking the certification task on the design and implementation of the autonomous system but exercising it in a virtual environment. "In the case of ASTRAEA, it is hoped to exercise it in a synthetic environment and a manned aircraft with the pilot acting as a safety monitor," he says.

"It allows you to develop a system or technology cost-effectively, determine where it does and does not meet certification requirements then develop it further from there," he says.

Barnard broadly agrees, adding, "I think that while there's certainly a place for virtual certification, this needs to be complemented with real flights - build up some flight hours and see how the aircraft performs."

All of which begs the $64,000 question: when will these aircraft be a routine sight in our skies? "Not for a few years yet," says Antony Adie, senior consulting analyst for aerospace and defence, Europe, at Frost & Sullivan. "Suppliers are bullish about UAV prospects but I can't see the technical and regulatory hurdles being cleared until the beginning of the next decade," he says. That ties in roughly with ASTRAEA's provisional target of 2012, although Adie believes this is optimistic.

Commercial product

So, in the absence of a sense and avoid system, UAV-specific regulations, comms integrity and allocated bandwidth, how can developers make any meaningful progress? "It's tricky," admits Barnard, "but these aren't the only things holding up progress at the moment - insurance and reliability, for example, also have to be resolved.

"But until we get bandwidth allocation, for example, it's possible to use the ISM radio bands used by cellphones and RFID systems, and the Intelsat satellite network instead."

In any event, he says, anyone thinking of joining the sector should not expect a commercial product for about three or four years - although by then many of the issues are likely to have been resolved.

But there is still time to get in on the ground floor. "The opportunities are there," says Barnard. "The market is wide open to new technological approaches."

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