Successful sea trials of RUFAS II (a towed, unmanned data-gathering submersible capable of operating to a depth of 2,400 feet) were conducted in the Gulf of Mexico. This paper describes the vehicle automatic flight control system, which is designed to follow the terrain of the ocean floor at a constant height above bottom and to maintain a level zero roll flight condition even against strong cross currents. Results showed that an inexpensive digital depth sounder type of sonar is entirely adequate for height above bottom information and that location of the transducer can provide positive or negative feedback. The stabilizing feedbacks used to damp the system are (1) vane position and (2) output rate feedback, which are remotely controlled (from the tow vessel) depending on the time response desired. A preset minimum height above bottom is designed into the control system to prevent the vehicle from accidentally crashing into the sea bottom.
RUFAS II (Remote Underwater Fishery Assessment System) is a towed, unmanned, controlled, underwater vehicle for rapid bottom and midwinter resource survey. The system will collect pictorial data on midwinter and ocean bottom conditions down to 2,400 feet. The vehicle, a vane-controlled, towed, hydrodynamic body, senses pitch, roll, and height above bottom and maintains the height above bottom established by the operator on the towing vessel.
RUFAS II is equipped with two separate camera recording systems. The forward-looking television camera is controlled in pan, tilt, and focus by the shipboard operator. Monitors on the operator's console repeat the picture that is being recorded on video tape. Illumination is furnished by two thallium iodide, forward looking lights that move with the camera.
The permanent record of objects on the bottom is provided by a 35mm motion picture camera that is interval meter controlled.
The operation of the RUFAS vehicle as a towed, underwater camera platform demands stability in the vehicle control system. The vehicle must be stable in roll so that the camera remains pointed at the ocean floor. It also be able to fly at a constant height from the sea bed so that the camera illumination and focus will remain correct. These requirements established the design criteria for the RUFAS control systems.
The Automatic Terrain-Following Control System maintains a desired vehicle height above bottom (which is remotely selected) following the gradual contours of the ocean floor.
Referring to Figure 2, the basic control system consists of the desired height input summed against the actual vehicle height. The resulting error signal is used to control the average vane angle (through the motor amplifier and motor) which positions the vehicle to the proper height. Normally, the sonar provides new vehicle height information once every second.
To prevent the vehicle from bottoming onto the ocean floor, a minimum height feature is included. A diode referenced fixed voltage is summed with the sonar input providing a minimum sonar signal output.
