In recent years, the military has invested heavily in UAVs, which could mark a significant shift in how operations are carried out in hostile environments.
They are able to keep going for far longer than a pilot or driver could, and can be used in locations that could pose a risk to human life.
"Unmanned systems could be a real game-changer," says Captain Robert Dishman of the US Navy, the former programme manager of the Persistent Maritime Unmanned Aircraft Systems Program Office at Naval Air Systems Command.
"UAVs offer endurance and persistence that can exceed the limits of the human body. They can stay aloft for days or even weeks without changing pilots.
They can even operate in hazardous situations where you might not want to risk a human life gathering information. They are ideal for the dull, dirty and dangerous missions."
Dishman, who was in charge of the unit from its inception in 2007 to June this year, suggests that UAVs could have played a major role in monitoring the nuclear disaster in Japan without contamination risk, or could be used to alert merchant ships to nearby pirate activity.
"UAVs are a big step forward in combat, surveillance and humanitarian aid missions, although they won't replace manned aircraft," he adds.
The dark cloud on the horizon
UAVs certainly herald a new era in intelligence, surveillance and reconnaissance (ISR) capability, and the technology is already at an advanced stage.
But the most significant challenge remains - ensuring that an unmanned vehicle can operate safely in airspace used by other aircraft. In a manned aircraft, the pilot can take responsibility for visually monitoring the nearby airspace, but in an unmanned one an alternative but equally reliable system must be put in place.
This issue is one of the challenges being addressed by the US Navy's broad-area maritime surveillance (BAMS) programme and the US Air Force's Global Hawk programme.
The BAMS unmanned aircraft system is designed to increase situational awareness, support coastal operations and provide surveillance when no other naval forces are present.
"The BAMS unmanned aircraft system must operate with 'due regard' and comply with the set of rules used by manned aircraft during ISR missions so that it does no harm when it is the same airspace as other aircraft," says Dishman.
To achieve this goal, stakeholders have come together to develop and certify systems that will define the safety and operational effectiveness of UAVs in the years ahead. For instance, the level of cooperation between the US Navy and the US Air Force is unprecedented. The Office of the Secretary of Defense's unmanned directorate has established an executive committee to look at UAV access to controlled airspace with the Federal Aviation Authority, as well as an integrated product team that meets monthly to discuss technological capabilities. These include the ground-based 'sense and avoid' technology being developed by the US Army and the US Navy's existing surveillance radar.
Dealing with due regard
There are four ways to ensure that aerial operations are conducted with due regard.
Firstly, the pilot in a manned aeroplane can perform a visual check to avoid traffic, which is obviously not an option for UAVs. Secondly, an offboard radar system, operated from a ship or by air traffic control for example, could monitor the airspace around the UAV. The third option is to have an air-to-air radar capability aboard the aircraft. The final one is to stay outside controlled airspace, as the Global Hawk does by flying above it.
"For BAMS, we chose the air-to-air radar system," says Dishman. "That is the incremental element that has come in as a result of the BAMS programme. We also clear flight plans, use ground-based air traffic control, use an automatic dependent surveillance-broadcast transponder to squawk position and altitude, and use the same collision-avoidance systems fitted on manned aircraft.
But air-to-air radar allows us to measure the same volume of airspace as a pilot would monitor visually, and that signal is sent to the pilot on the ground."
The air-to-air radar system provides coverage of ±110° azimuth - from behind the left wing to just behind the right wing - and ±30° elevation. This replicates the volume of airspace for which a pilot is responsible under Federal Aviation Authority regulations. The system, which has just passed a critical design review, actually offers some improvement over the monitoring capability of an onboard pilot.
"Remember that a radar system is more capable than the human eye in detecting objects at greater distances and in different weather conditions," says Dishman.
BAMS assets will fly with this air-to-air radar capability from 2013. It will mark a critical step towards the completely autonomous operation of UAVs.
"In parallel with BAMS, we are working with the US Air Force to develop an algorithm that would allow computers to develop a manoeuvre to avoid a collision based on the radar track, which would give us autonomous control. That is not that hard, given that there are people already working on swarming UAVs, but we need to certify the algorithm with the International Civil Aviation Authority and the Federal Aviation Authority for every instance where aircraft converge," says Dishman.
An algorithm that enables a UAV to autonomously adjust its course to avoid collisions will be a major breakthrough, but the greatest amount of work that needs to be done in this area is not necessarily on the algorithm itself, but on the certification process. Progress is not straightforward when there is no clear definition of success.
"We are working towards fully autonomous operations. Optimistically, I would say that achieving this by the end of 2015 would be good. It may not happen then, but if it doesn't it will be shortly after that," says Dishman.
"We will develop a radar capability to meet the due regard requirements. Then the big challenge will be to convince the authorities about that capability. To do that, we have to satisfy safety specifications that are not necessarily defined, but we believe that we have got it right."
This article was first published in our sister publication Defence & Security Systems International.