India Looks to Modify Scorpene Subs With MESMA AIP Propulsion
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Back on September 19, 2005, DID offered in-depth coverage of India’s $3.5 billion local-build deal for 6 SSK Scorpene Class ultra-quiet diesel-electric submarines between 2012-1017, as well as the present status and future plans of the rival Chinese and Pakistani submarine programs. Now the Times of India reports that India’s Navy wants the last 3 submarines to include DCN’s MESMA air-independent propulsion (AIP) systems, changing them from CM-2000 to AM-2000 Scorpene designation.
What’s MESMA, why does it matter, who else builds AIPs, and how does MESMA compare?
The MESMA anaerobic system will change the Scorpene’s ability to operate underwater for sustained periods without having to surface. An AM-2000 is still not in the same league as SSN nuclear subs which can do this indefinitely, but it is a substantial improvement that reduces “indiscretion time” on the surface where the sub can be spotted by radar, and also heard more easily by underwater sensors. A CM-2000 Scorpene can operate underwater for 4-6 days without surfacing or snorkelling to get oxygen to recharge its batteries. An AM-2000 Scorpene, in contrast, will be able to operate for up to 18 days, depending on variables like speed, etc.
Basically, the MESMA approach is closed-cycle steam turbine derivative of French nuclear-propulsion experience using non-nuclear steam generation. A conventional Rankine-cycle turbo-alternator is powered by steam generated from the combustion of ethanol (grain alcohol) and stored oxygen at a pressure of 60 atmospheres. This pressure-firing allows exhaust carbon dioxide to be expelled overboard at any depth without an exhaust compressor.
Each MESMA system costs around $50-60 million, as they require adding a new 8.3 meter (27 foot), 305 tonne hull section to the submarine. The resulting AM-2000 Scorpene AIP is about 70m long and displaces 1,870t. Note that per DID’s earlier article, Pakistan third Khalid Class (Agosta 90B) sub will also be equipped with MESMA.
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Other AIP systems around the world include Kockums’ Stirling-cycle AIPs fitted to Gotland, Sodermanland, and Nacken Class submarines; parent firm HDW also has its own design for U209, U212, and U214 Class vessels that uses Siemens’ PEM (Proton Exchange Membrane). Fellow member of the German Submarine Consortium Thyssen Nordseewerke has a closed-cycle diesel (CCD) system that uses liquid oxygen, diesel fuel, and argon gas, and the Dutch RDM submarine shipyard has advertised a “Spectre” CCD.
An article in Undersea Warfare Magazine notes that: “although MESMA can provide higher output power than the other alternatives, its inherent efficiency is the lowest of the four AIP candidates, and its rate of oxygen consumption is correspondingly higher.”
