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Astute SSN Design

The role of the submarine in the Royal Navy is changing as Rear Admiral Stevens, Flag Officer Submarines (FOSM), explained. "The services SSN community has made a decisive break away from its Cold War emphasis on anti-submarine warfare (ASW)to embrace the Navy's new operational concept of Maritime Contributions to Joint Operations. The challenge now is to realise the full potential of the SSN across its wider range of taskings. Operations in direct support of surface forces are becoming a far more important part of the submarine service's operations. The introduction of new secure communications links will provide the improved connectivity essential for operating in conjunction with other task force units. Advances in the technological areas of digitisation, miniaturisation and processing of information gathered, will enable the submarine to become an increasingly valuable asset in covert intelligence gathering operations."

Under the "Smart Acquisition" program, Astute was to be built about one fifth more quickly than earlier boats, will have lower running costs and will have a much smaller ship's company. She would also have massively increased firepower and will be equipped from day one to operate cruise missiles.

HMS Astute was launched on 8 June 2007 as the first of class. She displaces 7,800 tonnes dived and is 97 meters long. Astute will be one of the most capable submarines anywhere in the world. At 7200 tons surfaced, she will be the Royal Navy's largest ever attack submarine. As long as a football pitch, at 318ft, and as wide as four double- decker buses, HMS Astute is a third longer than any British sub which has gone before. Her nuclear reactor would propel her at high speed and allow her to remain submerged with a crew of 98 as long as necessary. She will be armed with six torpedo tubes, able to fire advanced weapons including the Spearfish guided torpedo and the Tomahawk Land Attack Missile.

Astute has a larger torpedo room than Virginia (36 weapons vs. 26) and more horizontal torpedo tubes (6 vs. 4), so the net warloads are about the same (36 vs 38). BAE and the MOD had not absolutely ruled out VLS tubes for the later Astute's (ie Batch 2 onwards). The main driver for fitting VLS would have been if it proved impossible to economically adapt the new Tactical Tomahawk LAM for horizontal torpedo tube launch.

While the traditional cylindrical US Navy Virginia looks like it is designed to an efficient hydrodynamic shape, the Astute looks draggy and boxy. The shape of the boat is designed to reduce the signature of its wake -- which can be detected and followed up to 12 hours later. The Astute class submarines have bows with sharp "chines". The boats generally operate with a slight bow-up attitude to generate positive lift. The "chines" could set the location where the boundary layer detaches from the surface and longitudinal vortices are formed. The other odd thing is the pronounced humpback aft of the sail. Contrary to some spuculation this is not related to Tomahawk missiles, but seemingly provide accomodation for the main turbines and the engine room [the reactor is rather forward of the hump].

Specialist engineers working on the design of Astute are undertook complex activities across a vast range of disciplines which are brought together in the creation of a nuclear powered submarine that is in effect three challenging projects in one: a warship, a nuclear power station, and a spacecraft venturing into the planet's most hostile and alien environment:

  • Nuclear engineering: providing safety and performance improvements to a state-of-the-art Pressurised Water Reactor that is fuelled for life. Rather than building a new power plant for Astute, the MoD chose to use the Pressurised Water Reactor 2 (PWR2) from the much bigger Vanguard-class Trident submarines. It was linked to a steam turbine system based on the model used in the older Trafalgar Class attack submarines.
  • Systems engineering: integrating the thousands of sub-systems that add up to 100km of cabling, 23,000 pipes amounting to10km of pipework, 1 million individual components and over 5 million lines of software code.
  • Supply chain management: ensuring the continued existence, co-operation and collaboration of more than 30 main suppliers, many of whom manufacture products used solely on submarines.
  • Marine and mechanical engineering: providing solutions for the propulsive power train, auxiliary systems and life support. Astute must be quiet, vibration free and robust enough to withstand a nearby underwater explosion.
  • Hydrodynamics and control engineering: the design of the submarine hull, hydroplanes and control systems to provide control of depth and good manuverability. The submarine must maintain neutral buoyancy and is literally 'flown' underwater.
  • Human factors: ensuring that every system is safely operable and maintainable in all conditions by a relatively small crew complement compared with previous nuclear powered submarines.

Despite space restrictions every crewman and passenger has his own bunk (unlike in earlier subs when 'hot bunking' was the norm). Astute's state-of-the-art Pressurised Water Reactor is more complex than a power station with more restrictions placed upon it; it must be engineered and operated in the knowledge that almost 100 people live and work in close proximity, with the submarine commander sleeping less than 10 meters away from the nuclear core. Astute can manufacture its own oxygen from seawater and purify the onboard atmosphere even underwater. The thousands of sub-systems built into Astute comprise of 100km of cabling, 23,000 pipes (amounting to10km of pipework) over 1 million individual components and over 5 million lines of software code.

Design and construction of the Astute Class is arguably the most challenging engineering project in the UK and has been described as "more complex than the space shuttle", involving the production of over 7,000 design drawings. And 10,000 separate design and engineering requirements. The nuclear reactor and 4 turbines on board Astute are capable of generating tens of megawatts of power, yet less than a single watt of power is radiated into the sea. Astute is designed not to require refuelling throughout her full service life - over 25 years - and can patrol for 90 days, remaining undetected thousands of miles from home and hundreds of metres underwater.

These are the largest and most powerful nuclear attack submarines ever built for the Royal Navy, equipped with the world's most advanced sonar system, Spearfish torpedoes and Tomahawk cruise missiles capable of delivering pin-point strikes 2,000km from the coast. Able to circumnavigate the entire globe while submerged she will be able to carry 38 torpedoes and missiles - more than any previous RN submarine. When fully stored Astute displaces 7800 tones of sea water (equivalent to 65 Blue Whales or nearly 1,000 London buses). She is 97m long and is 11.2m wide. A nuclear submarine is typically three times more densely packed with machinery and equipment than a surface ship, so spatial constraints of the Astute class are enormous. The pressure hull of the Astute class is a 97 metre long cylinder which when submerged must withstand pressure equivalent to 400 family saloon cars weighing down on every square metre of surface area. Manufactured from steel, the vessel will spend her entire life immersed in sea water - a highly corrosive liquid.

Astute's Captain will never have to hunch over an optical periscope - a range of equipment including thermal imaging cameras and low light video and CCD TV sensors will enable Astute to capture and then analyse surface images. Astute is designed to be fast and stealthy, and in line with customer expectation will play a role in joint and autonomous operations. Fitted with the now proven Sonar 2076 (through the Swiftsure and Trafalgar update programme) Astute can operate and project power without leaving a trace - denying the enemy vital knowledge. It is said that Astute's sonar is so advanced that if she was lying in the English Channel she would be able to detect ships leaving New York harbor 3,000 nautical miles away (although the details of how she can do this are classified).

The Astute program relies heavily on the power of computer aided design and 'virtual prototyping' because with a project as complex as Astute there is no time or budget to produce an actual prototype submarine. Instead, 'virtual' prototyping is relied upon, harnessing the power of computer test and visualisation, along with continuous design and systems analysis. The Devonshire Dock Hall is the largest shipbuilding construction complex of its kind in Europe, covering an area of 25,000m the height of the hall at 51 metres was determined by the need for overhead cranes to clear the raised masts of nuclear submarines. Astute is one of the first nuclear submarines to be designed entirely in a three dimensional computer aided environment and breaks away from the principle that submarine performance should be optimised by designing the smallest boat possible with little regard to cost.

HMS Astute's capacity for sustained high speed combined with almost unlimited endurance enables a truly global reach. Deployed SSNs are inherently at high readiness, they can move over 500 miles in a day, allowing them to redeploy to any theatre in the world within 14 days. The SSN's stealth is a key attribute, allowing it to operate covertly, with little risk of counter-detection, this provides strategic and operational flexibility. The Astute design extends the current SSN capacity to fully exploit the underwater environment, including littoral waters, allowing it to integrate even more closely with other joint forces to deliver a range of effects, some far inshore"

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Page last modified: 22-09-2021 12:59:30 ZULU