Introduction to UAV Systems. Mohammad H. Sadraey
number of techniques ranging from conventional takeoff and landing on prepared sites to vertical ascent/descent using rotary wing or fan systems. Catapults using either pyrotechnic (rocket) or a combination of pneumatic/hydraulic arrangements are also popular methods for launching air vehicles. Some small UAVs are launched by hand, essentially thrown into the air like a toy glider.
Nets and arresting gear are used to capture fixed‐wing air vehicles in small spaces. Parachutes and parafoils are used for landing in small areas for point recoveries. One advantage of a rotary‐wing or fan‐powered vehicle is that elaborate launch and recovery equipment usually is not necessary. However, operations from the deck of a pitching ship, even with a rotary‐wing vehicle, will require hold‐down equipment unless the ship motion is minimal.
1.3.4 Payloads
Carrying a payload is the ultimate reason for having a UAV system, and the payload sometimes is the most expensive subsystem of the UAV. Payloads often include video cameras, either daylight or night (image‐intensifiers or thermal infrared), for reconnaissance and surveillance missions. Film cameras were widely used with UAV systems in the past, but are largely replaced today with electronic image collection and storage, as has happened in all areas in which video images are used. Currently, video cameras are the most popular payloads in UAVs.
If target designation is required, a laser is added to the imaging device and the cost increases dramatically. Radar sensors, often using a Moving Target Indicator (MTI) and/or synthetic aperture radar (SAR) technology, are also important payloads for UAVs conducting reconnaissance missions. Another major category of payloads is electronic warfare (EW) systems. They include the full spectrum of signal intelligence (SIGINT) and jammer equipment. Other sensors such as meteorological and chemical sensing devices have been proposed as UAV payloads.
Armed UAVs carry weapons to be fired, dropped, or launched. “Lethal” UAVs carry explosive or other types of warheads and may be deliberately crashed into targets. As discussed elsewhere in this book, there is a significant overlap between UAVs, cruise missiles, and other types of missiles. The design issues for missiles, which are “one‐shot” systems intended to destroy themselves at the end of one flight, are different from those of reusable UAVs and this book concentrates of the reusable systems, although much that is said about them applies as well to the expendable systems.
Another use of UAVs is as a platform for data and communications relays to extend the coverage and range of line‐of‐sight radio‐frequency systems, including the data links used to control UAVs and to return data to the UAV users.
1.3.5 Data Links
The data link is a key subsystem for any UAV. The data link for a UAV system provides two‐way communication (i.e., uplink and down link), either upon demand or on a continuous basis. An uplink with a data rate of a few kbps provides control of the air‐vehicle flight path and commands to its payload. The downlink provides both a low data‐rate channel to acknowledge commands and transmit status information about the air vehicle and a high data‐rate channel (1–10 Mbps) for sensor data such as a video camera and radar.
The data link may also be called upon to measure the position of the air vehicle by determining its azimuth and range from the ground‐station antenna. This information is used to assist in navigation and in accurately determining air‐vehicle location (e.g., altitude). Other flight parameters, such as aircraft speed, climb rate, and direction, are often transmitted by a down link to MPCS.
Data links require some kind of anti‐jam and anti‐deception capability if they are to be sure of effectiveness in combat.
The ground data terminal is usually a microwave electronic system and antenna that provides line‐of‐sight communications, sometimes via satellite or other relays, between the MPCS and the air vehicle. It can be co‐located with the MPCS shelter or remote from it. In the case of the remote location, it is usually connected to the MPCS by hard wire (often fiber‐optic cables). The ground terminal transmits guidance and payload commands and receives flight status information (altitude, speed, direction, etc.) and mission payload sensor data (video imagery, target range, lines of bearing, etc.).
The air data terminal is the airborne part of the data link. It includes the transmitter and antenna for transmitting video and air‐vehicle data and the receiver for receiving commands from the ground.
1.3.6 Ground Support Equipment
Ground support equipment (GSE) is becoming increasingly important because UAV systems are electronically sophisticated and mechanically complex systems. GSE for a long‐range UAV may include: test and maintenance equipment, a supply of spare parts and other expendables, a fuel supply and any refueling equipment required by a particular air vehicle, handling equipment to move air vehicles around on the ground, if they are not man‐portable or intended to roll around on landing gear, and generators to power all of the other support equipment.
If the UAS ground systems are to have mobility on the ground, rather than being a fixed ground station located in buildings, the GSE must include transportation for all of the things listed earlier, as well as transportation for spare air vehicles and for the personnel who make up the ground crew, including their living and working shelters and food, clothing, and other personal gear.
As can be seen, a completely self‐contained, mobile UAS can require a lot of support equipment and trucks of various types. This can be true even for an air vehicle that is designed to be lifted and carried by three or four men.
1.4 The Aquila
The American UAS called the Aquila was a unique early development of a total integrated system. It was one of the first UAV systems to be planned and designed having unique components for launch, recovery, and tactical operation. The Aquila was an example of a system that contained all of the components of the generic system described previously. It also is a good example of why it is essential to consider how all the parts of a UAS fit together and work together and collectively drive the cost, complexity, and support costs of the system. Its story is briefly discussed here. Throughout this book, we will use lessons learned at great cost during the Aquila program to illustrate issues that still are important for those involved in setting requirements for UAS and in the design and integration of the systems intended to meet those requirements.
In 1971, more than a decade before the Israeli success in the Bekaa Valley, the US Army had successfully launched a demonstration UAV program, and had expanded it to include a high‐technology sensor and data link. The sensor and data‐link technology broke new ground in detection, communication, and control capability. The program moved to formal development in 1978 with a 43‐month schedule to produce a production‐ready system. The program was extended to 52 months because the super‐sophisticated MICNS (Modular Integrated Communication and Navigation System) data link experienced troubles and was delayed. Then, for reasons unknown to industry, the Army shut the program down altogether. It was subsequently restarted by Congress (about 1982), but at the cost of extending it to a 70‐month program. From then on everything went downhill.
In 1985, a Red Team formed to review the system came to the conclusion that not only had the system not demonstrated the necessary maturity to continue to production, but also that the systems engineering did not properly account for deficiencies in the integration of the data link, control system, and payload, and it probably would not work anyway. After two more years of intensive effort by the government and contractor, many of the problems were fixed, but nevertheless it failed to demonstrate all of the by then required capabilities during operational testing (OT) II and was never put into production.
The lessons learned in the Aquila program still are important for anyone involved in specifying operational requirement, designing, or integrating a UAS. This book refers to them in the chapters describing reconnaissance and surveillance payloads, and data links in particular, because the system‐level problems of Aquila were largely in the area of understanding those subsystems and how they interacted with each other, with the outside world,