Introduction to UAV Systems. Mohammad H. Sadraey
air vehicle and its subsystems.
1.4.1 Aquila Mission and Requirements
The Aquila system was designed to acquire targets and combat information in real time, beyond the line‐of‐sight of supported ground forces. During any single mission, the Aquila was capable of performing airborne target acquisition and location, laser designation for precision‐guided munitions (PGM), target damage assessment, and battlefield reconnaissance (day or night). This is quite an elaborate requirement.
To accomplish this, an Aquila battery needed 95 men, 25 five‐ton trucks, 9 smaller trucks, and a number of trailers and other equipment, requiring several C‐5 sorties for deployment by air. All of this allowed operation and control of 13 air vehicles. The operational concept utilized a central launch and recovery section (CLRS) where launch, recovery, and maintenance were conducted. The air vehicle was flown toward the Forward Line of Own Troops (FLOT), and handed off to a forward control section (FCS), consisting mainly of a ground control station, from which combat operations were conducted.
It was planned that eventually the ground control station with the FCS would be miniaturized and be transported by a High Mobility Multipurpose Wheeled Vehicle (HMMWV) to provide more mobility and to reduce target size when operating close to the FLOT. The Aquila battery belonged to an Army Corps. The CLRS was attached to Division Artillery because the battery supported a division. The FCS was attached to a maneuver brigade.
1.4.2 Air Vehicle
The Aquila air vehicle was a tail‐less flying wing with a rear‐mounted 26‐horsepower, two‐cycle piston engine, and a pusher propeller. Figure 1.3 shows the Aquila air vehicle. The fuselage was about 2 m long and the wingspan was 3.9 m. The airframe was constructed of kevlar‐epoxy material but metalized to prevent radar waves from penetrating the skin and reflecting off the square electronic boxes inside. The gross takeoff weight was about 265 lb and it could fly between 90 and 180 km/h up to about 12,000 ft.
1.4.3 Ground Control Station
The Aquila ground control station contained three control and display consoles, video and telemetry instrumentation, a computer and signal processing group, internal/external communications equipment, ground data terminal control equipment, and survivability protection equipment.
The GCS was the command post for the mission commander and had the display and control consoles for the vehicle operator, payload operator, and mission commander. The GCS was powered by a 30‐kW generator. A second 30‐kW generator was provided as a backup. Attached to the GCS by 750 m of fiber‐optic cable was the remote ground terminal (RGT). The RGT consisted of a tracking dish antenna, transmitter, receiver, and other electronics, all trailer‐mounted as a single unit. The RGT received downlink data from the air vehicle in the form of flight status information, payload sensor data, and video. The RGT transmitted both guidance commands and mission payload commands to the air vehicle. The RGT had to maintain line‐of‐sight contact with the air vehicle. It also had to measure the range and azimuth to the air vehicle for navigation purposes, and the overall accuracy of the system depended on the stability of its mounting.
Figure 1.3 Aquila air vehicle
1.4.4 Launch and Recovery
The Aquila launch system contained an initializer that was linked to the RGT and controlled the sequence of the launch procedure including initializing the inertial platform. The catapult was a pneumatic/hydraulic system that launched the air vehicle into the air with the appropriate airspeed.
The air vehicle was recovered in a net barrier mounted on a 5‐ton truck. The net was supported by hydraulic‐driven, foldout arms, which also contained the guidance equipment to automatically guide the air vehicle into the net.
1.4.5 Payload
The Aquila payload was a day video camera (Electro‐Optic) with a bore‐sighted laser rangefinder/designator for designating targets. Once locked on to a target, moving or stationary, it would seldom miss. The laser rangefinder/designator was optically aligned and automatically bore‐sighted with the video camera. Scene and feature track modes provided line‐of‐sight stabilization and auto‐tracking for accurate location and tracking of moving and stationary targets. An infrared (IR) night payload was also under development for use with Aquila.
1.4.6 Other Equipment
An air‐vehicle handling truck was part of the battery ground support equipment and included a lifting crane. The lifting crane was necessary, not because the air vehicle was extremely heavy, but because the box in which it was transported contained lead to resist nuclear radiation. In addition, a maintenance shelter, also on a 5‐ton truck, was used for unit‐level maintenance and was a part of the battery.
1.4.7 Summary
The Aquila system had everything imaginable in what one could call “The Complete UAV System;” “zero‐length” launcher, “zero‐length” automatic recovery with a net, anti‐jam data link, and day and night payload with designator. This came at a very high cost, however – not only in dollars but also in terms of manpower, trucks, and equipment. The complete system became large and unwieldy, which contributed to its downfall. All of this equipment was necessary to meet the elaborate operational and design requirements placed on the Aquila system by the Army, including a level of nuclear blast and radiation survivability (a significant contributor to the size and weight of shelters and the RGT mount). Eventually, it was determined that many of the components of the system could be made smaller and lighter and mounted on HMMWVs instead of 5‐ton trucks, but by that time the whole system had gained a bad reputation for:
Having been in development for over 10 years;
Being very expensive;
Requiring a great deal of manpower, a large convoy of heavy trucks for mobility, and extensive support;
What was widely perceived to be a poor reliability record (driven by the complexity of the data link, air‐vehicle subsystems, and the zero‐length recovery system);
Failure to meet some operational expectations that were unrealistic, but had been allowed to build up during the development program because the system developers did not understand the limitations of the system.
Foremost among the operational “disappointments” was that Aquila turned out to be unable to carry out large‐area searches for small groups of infiltrating vehicles, let alone personnel on foot. This failing was due to limitations on the sensor fields of view and resolution and on shortcomings in the system‐level implementation of the search capability. It also was partly driven by the failure to understand that searching for things using an imaging sensor on a UAV required personnel with special training in techniques for searching and interpretation of the images provided. The sources of these problems and some ways to reduce this problem by a better system‐level implementation of area searches are addressed in the discussions of imaging sensors in Part Four and data links in Part Five.
The Aquila program was terminated as a failure, despite having succeeded in producing many subsystems and components that individually met all of their requirements. The US Army Red Team concluded that there had been a pervasive lack of systems engineering during the definition and design phases of the program. This failure set back US efforts to field a tactical UAS on an Army‐wide basis, but opened the door for a series of small‐scale “experiments” using less expensive, less‐sophisticated air vehicles developed and offered by a growing