India's future S5 SSBN Boasting K-6 SLBMs

On March 22. 2024 Gessler provided some very interesting links, photos and comments along the lines:

"On Pete's note regarding the K-5 SLBM's possible 14m height, something comes to mind:

Photo A - By now we've all seen the first (publicly known) hydrodynamic model (photo above - source https://ibb.co/F3DPCJg ) of the future S5-class full sized Indian SSBN with a prominent missile compartment (or 'hump').

Its hump obviously speaks to the size of the SLBMs it's designed to carry. However, that S5 design (which I'm assuming is only one of many being tested) is now at least 6 years old, considering the first public sighting/leak was in 2018. 

Photo B - More recently I've come across what could be a newer iteration of the evolving S-5 design (see photo above - source https://ibb.co/Wnf9sQK ). This is from an official publication earlier in 2024. Again, there is no context or specific information provided about the program, so we know just as little regarding the program's current status as before.
[Pete comment Wikipedia's drawing apparently from a visit to DRDO supports Photo B being the more likely shape of the S5 class.]

Of note is obviously the fact, at Photo B, that the missile compartment is now far more streamlined into the submarine's hull. Could this be an indication that DRDO's propulsion advancements in ballistic missile development have resulted in a smaller and/or lighter missile being sufficient to reach the same range with the same payload as before? I can only guess.

There are also other differences, such as the dive planes being moved onto the sail/conning tower (which is more in line with how most submarines have them) as opposed to the previous model which had them on the hull in front of the sail (like on UK's Vanguard-class).

Pete Comment

Yes. Ever smaller missiles are achieving longer ranges. This is through use of lighter composite materials, for many parts and casings, rather than using heavier steel. Also solid fuel propellants are being developed that are more energy intensive per kg. 

Furthermore lower throw-weights requiring less boost can be achieved through greater miniaturisation of warheads and MIRV "buses" with no reduction in explosive power. Changing from heavier "old school" boosted fission to 2 staged thermonuclear warheads is one way to achieve smaller, lighter warheads. Increasing accuracy (ie. smaller, lower CEP) can make smaller, lighter warheads (say of 100kT as effective (eg. on deep dug bunkers) as effective as older larger multi-megaton warheads). 

Looking at Wikipedia's entry for the future S5-class SSBN it will be:

-  13,500 tonnes (presumably surfaced)

- it might carry K-5 SLBMs but with severe range limitations of only 6,000km (barely adequate to hit Beijing). This might mean an S5 might need to operate in waters near land. Chinese patrol aircraft based in Myanmar might strike it. Also fixed Chinese undersea sensors might detect it. Or its possible patrol area is within a predictable seaspace for  Chinese SSNs or Pakistani SSKs (lurking near the Vizag current Indian SSBN base) to detect it. 

-  So its better to carry between 12 and 16 much longer range K6 SLBMs . Not yet developed K6s might be just over 12m tall. With a 3,000kg (presumably max) MIRVed payload its range might be the minimum 8,000km for patrolling in a "safe haven" south of Diego Garcia but still in range of Beijing. 
=  With a 1,000kg "light load" a K6 SLBM might have range of 12,000km allowing the S5 SSBN to be safer, far into the southern Indian Ocean, yet still in range of Beijing.