The race is on to design and produce UAVs for ISR duties with ever-increasing time on station. In future, most likely, UAV endurance will extend to weeks, perhaps even months.

Unmanned aerial vehicles (UAVs) are now operationally deployed or being considered for use in practically every role that manned combat aircraft are capable of. Deadly armed UAVs have been used for years against high-value ground targets in the Afghanistan-Pakistan region and other conflict zones. And it’s only a question of time before an unsuspecting fighter pilot somewhere in the world finds himself locked in combat with an unmanned but lethal adversary. However, this article is about the first and most significant function of UAVs—intelligence, surveillance and reconnaissance (ISR).

The race is on to design and produce UAVs for ISR duties with everincreasing time on station. To begin with, unmanned airborne endurance was measured in terms of hours. Now a handful of UAVs are beginning to demonstrate the ability to operate for days at a time. In future, most likely, UAV endurance will extend to weeks, perhaps even months. Why is the ability of surveillance UAVs to stay aloft for extended periods so crucial? The far higher accident rate of unmanned platforms as compared with manned aircraft is partially attributable to the high number of UAV take-offs and landings. Remaining airborne for a longer duration decreases take-offs and landings. This, in turn, sharply reduces accident risks and associated costs. It also means that round-the-clock target surveillance can be mounted with as little as a pair of UAVs—one remaining on patrol, while the other returns to base for refuelling and maintenance.

High-altitude long-endurance (HALE) UAVs have most of the advantages and not many of the disadvantages of orbiting satellites. Operating in the stratosphere, they fulfil the need for a surveillance capability that never needs to take time out, yet is cheaper to operate and easier to adapt and upgrade than a satellite. Satellites have inherent drawbacks. A low-earth satellite, orbiting at an altitude of 320 km or so, cannot keep a desired target in continuous view. After passing over a point, it revisits it again only after a full orbit. A satellite in geosynchronous orbit can indeed maintain over a designated point, but it needs heavy, expensive telescopes, powerful enough to pick up small objects on the surface of the earth, some 36,000 km away. A minor glitch in a critical onboard system could bring an early end to the mission and the abandonment of a costly satellite. Naturally, therefore, long-dwell stratospheric surveillance by UAVs is a capability coveted by many nations.

Orion on Target

Aurora Flight Sciences is trying to revolutionise the accepted definition of long loiter time with its Orion medium-altitude long-endurance (MALE) UAV, at present in the technology demonstration phase. The Orion was unveiled on November 22, last year, in Mississippi USA, and its first flight is expected mid-year. A decade or so ago, the MQ-1 Predator had top-dog status by virtue of its maximum 30-hour capability. If Aurora’s efforts bear fruit, such performance will soon seem pedestrian. The Orion is designed to fly for 120 hours (five days) at 20,000 ft, carrying a 1,000 pound multi-sensor payload. This too will mark a huge increase over the Predator’s 450 pound payload. The Orion’s long endurance will mean a time-on-station capability ranging from 113 hours at 550 nm range to 47 hours at a distance of 3,000 nm. Alternatively, it can deliver a total mission range of more than 9,500 nm allowing it to be located farther from its target—at a main base where fuel costs much less than when transported to a forward launch location. Its superior performance will be achieved through a combination of a lightweight airframe, efficient aerodynamics and propulsion, reliable systems and autonomous operation. The aim will be to reduce the cost of an hour’s surveillance to around 20 per cent of the cost of currently deployed systems like the MQ-1 Predator, its successor the MQ-9 Reaper, and the manned MC-12W Liberty ISR aircraft.

The Orion flies slowly—barely touching 90 kt as compared with 310 kt for the RQ-4B Global Hawk and 150-170 kt for the MQ-9 Reaper. Its low cruise speed improves fuel efficiency and allows use of a pair of Austro diesel engines rather than more costly and thirsty jet engines. But flying slow may decrease weather tolerance and so a compromise has to be struck. Onboard systems also need to be extremely rugged and reliable to fulfil the 120 hour on-station promise. No single point of failure is acceptable; some components are triple-redundant and others are double. The UAV also features autonomous operation—capability to take-off and land without a pilot in the loop—which means lower overall costs by reducing the number and training of crew required to operate the system.