What a range!

Unmanned aircraft have come a long way from the camera-carrying radio-controlled model aeroplanes of 30 years ago. Every aerospace manufacturer is after a piece of this booming business, and every military service is trying to gain experience of operating today's drones in order to formulate sensible requirements for the next generation.

The Teal Group placed the global value of the drone market at approximately $ 2.7 billion in 2006, including $1.4 billion in production, the rest representing RDT&E, operations and maintenance funding. The United States currently accounts for about 80% of worldwide drone spending, with Europe in second place.

By 2015 Teal forecasts that the total will have grown to about $ 8.3 billion (in 2006 values), including $ 4.0 billion in production, with the US share easing off to around 70%. These figures represent an annual rate of increase of more than 13% above inflation, which is higher than Teal predicts for any manned aircraft sector over the same period.

Technologies

Although the use of drones is expanding rapidly, it is still constrained by the rate of progress in the underlying technologies, which, in some cases, depends on commercial funding. In the case of electrically powered drones, battery development is driven by the computer and cell phone sectors, fuel cells by the car industry and solar cells by the civil satellite business.

One major objective in drone development is an autonomous system of in-flight refuelling, to further exploit their endurance potential. In August 2006 the first 'hands-off' probe-and-drogue in-flight refuelling was performed in a joint Darpa-Nasa Dryden programme, using an F/A-18 and an Omega Air B707 tanker. This Autonomous Airborne Refuelling Demonstration (AARD) employed GPS-based relative navigation by Sierra Nevada and an optical tracker by Octec.

On a similar timescale, and as a precursor to automated refuelling, Boeing completed flight trials under its Automated Aerial Refuelling (AAR) programme to show that a specially equipped Learjet could autonomously hold station relative to a KC-135R tanker.

Israel Aerospace Industries (IAI) has completed the preliminary design of an autonomous aerial refuelling system. The Maryland-based UAV Refuelling has unveiled its design for a refuelling unit to be mounted in a weapons bay. It includes a patented drogue equipped with an optical guidance sensor and compressed air jets for position control.

As in the case of manned aircraft, a substantial part of drone attrition occurs in the take-off and recovery phases. Several existing systems feature automatic take-off and landing (Atol), but work continues in this area. For example, the US Air Force is supporting development of the Proxy Aviation SkyForce system, which provides Atol without ground-based equipment and is thus at an advantage in operations from austere sites.

The US Air Force Research Laboratory (AFRL) is to study automated ground handling and departure manoeuvre systems to facilitate drones operating 'interleaved' with manned aircraft.

Turning to more radical developments, both Lockheed Martin and Northrop Grumman have interests in drones that can be operated from (and possibly recover to) submerged submarines. The former has already demonstrated the feasibility of recovering its Cormorant drone, simulating splashdown and its retrieval by a remotely operated vehicle.

Northrop Grumman's Stealthy Affordable Capsule System (Sacs) is designed to allow 'non-marinised' drones and weapons to be deployed from the Tomahawk or torpedo launch tubes of submerged submarines using low-cost disposable capsules. Following recent budget cuts, however, Darpa has now terminated its work on submarine-based drones.

Ground Control Stations

Ground stations will pose an interoperability problem, not only on an international scene but also (and even) within a single nation, as manufacturers have so far developed their own standards and proprietary software, meaning that a drone operated by company B will not necessarily speak to a company B ground control station.

A ground control station may range in size from a hand-held computer and display unit to a complex system (as for Global Hawk) that requires two room-size containers with their own power generators and a satellite dish, but the ground control station (GCS) invariably has one facility to control the flight of the drone and another to receive the information that it generates.

Whereas in the Vietnam War, Ryan (now Northrop Grumman) Firebee drones were hand-flown by professional pilots, technological developments have made it possible for modern drones to be programmed to operate autonomously from launch to landing. The role of the GCS may thus be reduced to inserting (and updating in flight) mission plans for the aircraft and its sensors, and downloading and transmitting imagery. However, in the case of expensive drones, there is still a need for pilot inputs in the event of system failures.

The increased autonomy of drones is making it possible for a single pilot to control several drones simultaneously. Another important trend is toward the standardisation of ground control stations, so that one design can control different types of drones. For example, the AAI One System GCS will be employed by the US Army to control not only the AAI Shadow but also the General Atomics Warrior. It has been used for the Northrop Grumman Hunter.

Ground control stations were discussed in detail by Ian Kemp in Armada 1/2006. Subsequent developments include Lockheed Martin's trials of a centralised controller, consisting of a customised hand controller and a touch-screen laptop computer. Meanwhile, Raytheon has adopted ideas developed by the video-gaming industry to design a 'virtual cockpit' GCS. This Universal Control System (UCS) features hand and finger controls in place of the normal keyboard, and a 270[degrees] wrap-around display of the point-of-view from the drone, combining a synthetic image from a terrain database with actual imagery from the aircraft.