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The Command and Control of Unmanned Air Vehicles |
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(Source: Rheinmetall De-Tec; issued March 14, 2005)
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Variously referred to in the media as drones, unmanned air (or aerial) vehicles or even flying robots, these aircraft all have one thing in common: there is no pilot on board. This is not to say that the aircraft flies uncontrolled or cannot be influenced from the control station; it is just that the pilot is located elsewhere.
The key elements of a UAV system are the air vehicle itself, the ground station, and the data link between the two. Depending on the mission and operational options and objectives, the various systems differ substantially. They can be broadly categorized as follows:
--Micro or mini UAVs for operations within a one-kilometre radius. These weigh only a few kilos, can fly at altitudes of several hundred metres, and remain aloft for less than an hour. Ideally, they can be launched by hand, and as a rule are-man portable.
--Tactical drones that operate at ranges of 100-200 km and weigh up to 250 kilos. They can fly several thousand metres high and remain in the air for several hours. They are launched with a catapult, a booster launcher or a conventional reinforced ramp. Tactical UAV systems can generally be loaded onto transport vehicles.
--"Medium Altitude Long Endurance" (MALE) and "High Altitude Long Endurance" (HALE) UAVs. These are for operations lasting 30-40 hours and have a take-off weight of several tons. They can attain altitudes of 15 km or more, and their wingspan equals that of an Airbus or Boeing 747. The MALE and HALE systems require runway lengths of several hundred metres to more than two kilometres.
Uniform rules of operation are required
Depending on the mission and design of the systems, they may be tasked with supplying tactical information about the immediate area, or with gathering strategic intelligence from distant regions. The sensor equipment, the areas flown over, the communications links and control of the airspace in which they are operating will all vary.
So will reliability requirements, depending on whether flights are over restricted areas and thinly settled regions, in enemy airspace, or part of normal air traffic.
These aspects are being studied by committees at national and international levels, as well as in working groups with industry participation. The aim is to establish uniform international rules for operating UAV systems, as well as technical standards for manufacturers and users. MALE/HALE air vehicles, of course, pose bigger challenges to mission planning and flight execution than the other UAV categories.
Mission planning and flight execution
Mission planning comprises a mix of sensor, communications and flight-path planning. This interaction results in the mission program, which contains the flight plan. With flight times of thirty hours or more, provisions must also be made to change the ground crew.
The role of the flight control system is to implement the mission program by issuing commands and signals. The status and actions of the air vehicle, including the state of its individual components (e.g. the engine) are continuously reported back to the ground station via telemetry. Intervention from the ground is possible by altering the 4-D waypoints (XYZ coordinates and time), the direction, the altitude and the speed of flight. Or, the air vehicle can be directly piloted, much like a manned aircraft.
Generally, these air vehicles use an inertial navigation system which receives updates (via GPS, for example) to ensure that accurate positioning is maintained. Some techniques do not depend exclusively on GPS data. One is the rho-theta system, in which the direction of flight is determined by measuring the angle of the data transmission antenna and distance is calculated by the signal time delay.
Another is the manual sensor image-map comparison, or terrain-aided navigation. It measures the altitude of terrain features below and compares it with the profile data stored on board the UAV; or, it extracts sensor images of conspicuous lines of communication (e.g. highways and railways), and automatically compares them with a digital map.
Reliability
The reliability of the total system is critically important, since the air vehicle is controlled via a data link. In the line-of-sight zone, i.e. approximately 250-300 km, jamming-proof data links are used; for longer distances, satellites. If the satellite link fails, high-frequency radio serves as a backup. In such cases, reconnaissance data is unavailable, but the status and control of the aircraft is assured.
For example, the Predator B drone is equipped with a triple-redundant flight computer, along with double-redundant bus systems, power supply, control surfaces, and more. These safety measures are supplemented by fail-safe procedures, which react in accordance with standard air safety regulations and assure a predictable response on the part of the aircraft.
For take-offs and landings, special equipment is being tested or is already in use. Infrared sensors and microwave- and/or laser-based devices help in measuring the air vehicle's position in relation to the runway and in transmitting control commands during approach flights. Here, too, the ground station can intervene manually.
Summary
UAVs have been in service for years. Whenever foreign dignitaries visit Kosovo, Afghanistan or Iraq, one or more UAVs are sure to be in the sky above. Given the complex, multifaceted character of the missions involved, and the exacting nature of aviation technology, operators of unmanned air vehicles must be able to count on experienced manufacturers and tried-and-tested hardware and software.
If we are to contribute as a nation to the development of international solutions for controlling unmanned air vehicles, it is imperative that Germany not merely maintain, but also build on, its existing knowledge of complete UAV systems.
-ends-
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