The Indian SSNs will be fast, Silent and Lethal with Pump jet propulsion.
The hunter-killer under the sea that can wreck carnage in minutes, if the need arises. Fast, Lethal, and silent, this underwater warrior can change the course of any war and shift the strategic balance in no time. Often termed as silent service, the submarine arm of any Navy is one of the prime deterrence against the enemy. The SSNs (Submersible Ship Nuclear) – nuclear-powered general-purpose attack submarine is designed to protect the surface combatants and missile submarines and sinking other submarines, surface combatants, and merchant’s vessels.
Indian nuclear attack submarine program:
The Indian Navy plans to construct six advance new nuclear-powered attack submarines (SSN) under Project 75 Alpha in the coming years. The project was approved by the Government of India in February 2015. It is believed that these boats will be 6000 tonnes or lesser, INS Arihant like hulls but will be faster, stealthier, and will have a capability to dive deeper than Arihant class.
These will be designed by the Navy’s in-house Directorate of Naval Design based on Arihant class the submarines. The project will require comparatively lesser research and development as most of the technologies associated are already proven.
Development of these Submarines:
Though the submarine will be based on the Arihant class sub but the purpose for which these submarines are built is completely different. Thus, its natural design will require modification and optimization. As the power requirement is larger in this faster submarine thus the reactor rating could be higher or this need may be mitigated by a brand-new type of propulsion system. The current Arihant class of submarines uses an 83 MW miniaturized pressurized water reactor.
The government of India allocated INR 100 crore in June 2019 for the initial phase of the project and the preliminary designs phase is now complete. The Directorate of Naval Design and DRDO will now start working on the detailed design and construction phase of the program (Which hasn’t started yet).
The DRDO is currently working on multiple projects which appear to be associated with this project. These projects provide a good sneak peek into the design of the most awaited SSN of the Indian Navy. Let’s have a look one by one:
Sneak-peek into the design of Indian SSN:
1. Pump Jet Propulsion:
The most significant change likely will be in the propulsion system as the submarine is expected to move faster. Though a larger power rating reactor was also studied.
What is Pump jet Propulsion?
A pump-jet is a system that produces a jet of water for propulsion. The system comes in various configurations, but the basic principle is the same. The propeller blades or vanes are shrouded by the cowling. This cowling introduces multiple advantages such as:
- Higher speed before the onset of cavitation, because of the raised internal dynamic pressure.
- High power density (with respect to volume) of both the propulsor and the prime mover.
These advantages make this an obvious choice for the stealth submarines used in the attack mode.
Project 75 Alpha will have Pump jet Propulsion?
DRDO is currently working on Super Conducting Synchronous Motor for a Pump jet Propulsor. The current requirement is to develop a Scale down model for the Electric Motor (525 kW) as a Technology Demonstrator. However, the plan is to scale up to the requirement “upto” 35 MW.
For comparison, the Virginia class submarines of the US Navy also use a pump jet propulsion, and to drive the boat the SG9 reactor is used. The reactor drives a 30 MW pump-jet propulsion built by BAE systems. The Virginia class of submarines is 7,900 tonnes boats.
The SSN which India is building are ~6000 tonne and thus this scaling up likely is for an application. Which likely will be on the Project 75 Alpha.
Why this system is not for S4 and S5 class of submarine?
The S4 class of submarine are already under construction and the design of pump jet is still under prototype phase. On the other hand, the S5 class of submarines will be massive boats and will require far more power than a 35 MW pump jet. The speculated displacement of the boat will be 13,500 tonnes with a 190 MW reactor. Thus, the only available project in which this system can be used is SSN. Also, the pump jet is an obvious choice for a SSN over a SSBN.
2. Material for the Submarine
Mishra Dhatu Nigam or MIDHANI a public sector metal and alloy manufacturer located in Hyderabad is making special alloys in partnership with NMRL for this requirement that will not have any ferro magnetic qualities and will stronger than the current hull material of Arihant class to allow the SSNs dive deeper in the sea.
The possible material could be
- Bulk Metallic glass: Bulk Metallic Glasses (BMG) have been found to exhibit very high strength, high elastic modulus, high corrosion resistance and several unique physical properties not observed in conventional crystalline metallic materials. This makes a potential choice for the outer hull of the submarine.
- High Vibration Damping Aluminium Metal Matrix Composites: NMRL has developed molten flux assisted reaction synthesis foundry technology to produce high vibration damping aluminium metal matrix composites. Ultrafine reinforcement of graphite and ceramic particles such as Titanium Diboride (TiB2), Titanium Carbide (TiC), Boron Carbide (B4 C), etc.
Currently the material is used for the torpedo nosecone application and likely be modified for parts of the internal hull of a submarine to further reduce noise.
3. Stealth Material (Acoustic Stealth Material):
Vibroacoustic Tile: Vibroacoustic tile is used in the sonar dome of submarines to isolate the sonar transducers from structural vibrations and acoustic noise. This tile is also having a multi-layered configuration with perforated layers in the core, which are attached to each other by a specialty adhesive.
Variant of these tiles are also used below the engine and crew space to further shield any noise sneaking out of submarine.
Epoxy Putty: Epoxy-based putty is used for the levelling of surfaces and filling the gaps between metal to metal joints and for adhering metal to rubber surfaces. It provides excellent metal to rubber adhesion and has a service life of more than 20 years and is primarily used to adhere to acoustic rubber tiles onto the underwater surface of marine vessels.
The second generation of acoustic coating materials: These materials will be used to damp the low frequency sound as its these frequencies that let the secrets out.
- Acoustic Rubber Tile MK3
- Reinforced Coating
- Noise silencer
Overall, the submarines under project 75 Alpha are ghosts in making.