Vol . 8 No. 5 & 6 October/December 2000
Underwater Weapons Technologies
The underwater weapons technology is multidimensional, encompassing almost all disciplines of engineering and science. Due to technology denial, the scientists face the most challenging task to develop every bit of technology indigenously for which infrastructural and industry backup are lacking. DRDO has been engaged in the development of torpedoes, sea mines, deep mobile target, decoy, fire control system; versatile acoustic target, and simulators. The technologies related to development of light-weight torpedo, wire-guided torpedo, processor-based mine and fire control system have been developed. Thermal propulsion technology, the most guARDEd technology with the developed countries for heavy weight and long range torpedoes, has been realised and will be Integrated with a weapon system soon. To meet the requirement of reduced self noise of torpedoes and to make them more stealthy, a pumpjet propulsion system has been developed and integrated with the torpedo. Many emerging technologies are under development to deliver the most advanced underwater weapons to the Navy. Certain critical technologies related to the development of torpedoes and mines are discussed here.
Torpedo is the most dynamic and lethal underwater weapon. Design of this sophisticated and complex system calls for technologies relating to mechanical engineering, propulsion, power source, electronics, signal processing, control and guidance, hydrodynamic study, aerodynamic study, suspension and release devices, computer and software, explosive, exploder mechanism, etc. Torpedo, being a fire and forget type of weapon, comprises an intelligent homing system which has to perform an optimum search, detect target amongst decoys and eventually guide the weapon on to the target to hit it for exploding the explosive onboard. The shells and mechanical components used in the torpedo are required to be of very high weight-to-strength ratio to enable it to withstand the ambient pressure as well the launch impact at the same time without adding to its weight. It requires very light-weight high-power batteries, motors, homing device, actuators and control devices. Different types of shells, including composites for different torpedoes, sea water activated batteries for electric propulsion, contrarotating motor, propellers, homing head with PZT sensors, electronic . system onboard computers signal processing unit and actuation system have been developed. The first ever indigenously developed anti-submarine light-weight torpedo of air/ship launch version has completed user evaluation and cleared for limited series production. This weapon also contains the first ever homing system to be developed by [3RDO. All sub-systems for the torpedoes have been developed indigenously. Some such important sub-systems are discussed here.
Sea water activated Mg-AgO primary batteries for light-weight torpedoes and Ag-Zn secondary batteries for heavy-weight torpedoes have been developed in collaboration with High Energy Batteries Ltd., Tiruchirapalli. Contra-rotating motors have been developed using rare earth permanent magnets to achieve high degree of efficiency within a. smaller volume. Contra-rotating propellers have been developed to facilitate high-speed, low-noise, cavitation-free and roll-balanced performance for torpedo.
Control & Guidance
A digital control technology has been developed to achieve high degree of accuracy in torpedo control and guidance. It involves development of precision sensor, an onboard computer based on 80486 processor, and high torque and light-weight controllers.
The accuracy and hit probability of any guided underwater weapon depends on its homing capability. Such a system incorporating the latest signal processing techniques, such as constant false alarm rate algorithms, signal adaptive filtering, etc. to counter the reverberation, multipath acoustic propagation, and acoustic countermeasures has been developed. Detection algorithm, post-detection processing techniques and mission requirement are all software-controllable. Low-noise, high-efficiency, compact underwater electroacoustic transducers have been used for the homing system.
Torpedo Propulsion Systems
For increasing the speed of torpedoes, a thermal propulsion system will be required. DRDO is engaged in active research in this area and has made a few significant achievements. Fuel and oxidiser have been synthesized and technology transferred for bulk production. An external servo-controlled swash plate fuel pump and air impulse turbine with transmission systems have been developed.
Contra-rotating propellers are unable to generate high speed due to cavitation at speeds exceeding 45 knots. A pumpjet propulsor has been developed successfully in collaboration with Indian Institute of Science, Bangalore, and Turbo Tech, Precision Engg. Comp., Bangalore. The pumpjet propulsor has been tested to develop more power and low-noise performance.
Decoys & Targets
The submarine under the threat of an attack from a torpedo uses several evasive methods to get away from the attack. One such evasive method is to fire an expendable decoy which is an electronic and acoustic countermeasure against the active-passive torpedo. Decoys have been developed that are housed in a small FRP shell and use lithium-sulphide batteries. These decoys can be ejected through a cartridge. The acoustic system with transducers creates acoustic noise mimicking that of a submarine and decoys the attacking torpedo. The buoyancy of the decoy is critically controlled for slow descent rate. Signal design is implemented to decoy either passive or active homing system. Targets, mobile and static, are generally needed for training the sonar operators and ASW crew in practising torpedo firings. The targets imitate and simulate the submarine acoustically. The targets generate broadband frequencies from very low to high frequencies. Several target parameters can be set to include target strength, pulse-length, Doppler shift, and raDIATed nose level. A static target called versatile acoustic target (VAT) has been developed and extensively used in the evaluation of torpedoes and mobile target called programmable deep mobile target (PDMT).
Mines continue to be a cost-effective deterrent in naval warfare. These
have become more and more intelligent since World War II types of contact and magnetic
mines. State-of-the-art sea mines have been developed that work on the influence of anyone
or a combination of magnetic, acoustic and pressure signals. The pressure transducer used
in the mine has also been developed indigenously. Three types of mines, processor-based
ground mine, moored mine, and processor-based exercise mine developed by DRDO have been
accepted for production after extensive trials by the Navy. The processor-based ground
mine is already under production at KELTRON.
A tripple tube torpedo launcher has been developed and is in use onboard naval ships. Three torpedoes can be loaded and launched from this tube.
Fire Control System
The target parameters measured by a sensor are used to compute the weapon data in the fire control system. A fire control system has been developed to provide complete solution based only on bearing information. The system can track multiple targets and identify six priority threats. It can also generate information on iDEAL manoeuvering of the platform in a particular combat scenario. Contact motion analysis algorithm using square residual innovation process and statistical hypothesis using implemented to declare the manoeuver of the target.