The Yasen may be expensive, but is essential that Russia has an effective force of state-of-the-art SSN hunter-killers in order to order to match the USNs Seawolves and Virginias. Fielding cheaper but less capable frontline units is not an option if you actually want these boats to hold the line in any future hostilities.
I disagree, Yasen are SSGN´s not SSN´s. It would make sense to build a smaller, cheaper and stealthier SSN as a compliment to SSGN´s. A dedicated submarine hunter that can protect the SSGN´s and SSBN´s against opposing submarines. Also it would be as good against surface targets, but with no or limited land attack capabilities.
I for one see the need for such a platform, a small very stealthy and lethal SSN.
Incorrect. Yasen class is most definitely an SNN, but has been given VLS for anti-ship and land-attack capabilities to make them a true multi-role boat. Her advanced sonar system and emphasis on silent operations mark them as hunter-killers, not long-range stand-off missile carriers. The idea that a "Yasen-lite" without VLS will somehow be significantly smaller or cheaper is not really credible. The high cost is due to advanced (ie expensive) on-board systems and any dedicated SSN equivalent will require the same. Elimination of the VLS compartments will reduce boat length and mass, but not by a significant degree. A saving of maybe 15% may be achieved by elimination of the stand-off attack capability (and a big loss in combat capabilities), but will this result in a significant increase of hulls in water? I doubt it...
Small SSNs are possible (ie the Soviet Lira/Alpha class) but nuclear powerplants tend to be big and expensive, and keeping the size/tonnage down requires exotic design solutions like lead-bismuth liquid metal coolant systems and very high automation levels to reduce crew numbers. While possible, its not cheap, and imposes other limitations such as complex and expensive facilities to support core heating (to keep the coolant molten) while the sub is in port. More than one Lira had to be de-commissioned after her core froze...
TR1 is correct in saying that conventional AIP boats SSKs are probably the answer for Russia to defend her coastline and SSBN bastions. Small, silent, deadly and comparatively numerous, they are ideal for coast and littoral defence. They can carry sensor and weapon outfits similar in scope to the big Yasens, and their numbers will allow force concentrations in critical areas such as the bastions while their larger nuclear cousins either join them as "squad leaders" or range further afield hunting HATO high-value surface combatants.
He is also right regarding the low availability of Soviet era SSNs, though how much of this is due to budgetary reasons is hard to tell. I'd like to think that money for refit is the issue and that the boast themselves are basically sound and are capable of serving through the 2020s, but who really knows?