In their darkest moments, even the most hardened submariners must wonder where help could possibly come from if they were stranded 600m down on the ocean’s floor.
In the absence of a real-life version of Thunderbird 4 and its intrepid crew, the outlook for stricken submarines is grim. Rescue attempts have a poor record, and historically have nearly always failed because the ability of submarines to go deeper for longer has not been matched by similar advances in rescue systems.
There has only ever been one successful operation, in 1939, when 33 men were saved from the USS Squalus using a diving bell. Ageing rescue technology and the reluctance of navies to co-operate was starkly illustrated by the deaths of 118 submariners in the Russian Kursk disaster four years ago.
Like most submarine-operating nations the UK has its own rescue system, called the LR5. But this has been in operation since 1978 and urgently needs replacing. The technology is out of date and incapable of meeting the demands of a modern navy.
Since the early 1990s NATO has been discussing a joint-nation submarine rescue project that would use state-of-the art technology, and this year things finally began to accelerate. France, Norway and the UK will build the NATO Submarine Rescue System (NSRS), which will replace the ageing LR5 by December 2006 and have the ability to be flown worldwide to help any navy rescue its crews within 72 hours.
The NSRS – a free-swimming submarine rescue vehicle (SRV) – will dive deeper, swim faster and endure longer than any current rescue system, and – despite its multi-national funding structure – will owe its existence to UK expertise.
This summer Rolls-Royce announced it had won the 10-year, £47m contract to lead development of NSRS, beating 16 other companies.
Subcontractors The Engineering Business will provide the portable launch and recovery system, Perry Slingsby Systems will build the vehicles, Babcock Design and Technology will offer support services and Divex will provide the decompression equipment. Once built, the system will operate out of the Clyde Naval base.
Cdr Dickie Burston, a former submarine captain and expert on rescue systems is heading the NSRS project for the UK’s Defence Procurement Agency. ‘The NSRS is unique, because it is the first time nations have worked together to jointly own and operate a single rescue system,’ he said.
The rescue system will be split into three major components – reconnaissance, rescue, and crew decompression. First a smaller reconnaissance sub called a Remotely Operated Vehicle (ROV) will be flown to the disaster area. The ROV will locate the submarine to check for signs of life, provide emergency supplies to any survivors and remove debris. The main part of the rescue system will arrive on the scene within 72 hours. The NSRS, with three crew members, docks with an escape hatch on the sub’s hull and carries the crew back to the surface in batches of 12.
Most new submarines now have a standard flat ‘polo mint’ around the escape hatch to allow a rescue vehicle to dock. A cone-shaped skirt beneath the rescue sub with a rubber lip seal sits on the hatch at an angle of up to 45 degrees. Water is drained out creating hydrostatic pressure so that the SRV clings to the sub’s hull. The internal air pressure between the two is matched and then the hatch can be opened to transfer crew.
The pressure is maintained up to the surface where survivors are transferred into a decompression facility called a Transfer Under Pressure (TUP) chamber, the third element of the rescue system. Rolls-Royce will keep an evolving database of suitable motherships, both civilian and military, from which to launch the rescue. The full cost of the NSRS’s 25-year life is expected to be £120m.
Getting the project to this stage has not been without its problems, however. The NATO group originally involved 12 nations, yet only five provided financial backing for the original feasibility study in 1996.
Shortly after, the US decided to develop its own parallel rescue system (see sidebar) and Italy dropped out because of misgivings about the suitability of motherships operating in its region.
Turkey joined in 2000, but pulled out due to lack of funds. This, and negotiations over an enabling treaty (finally signed last December), delayed the project a further year, and meant the LR5 needed an expensive upgrade to stay in service until the NSRS can completely replace it in 2007.
Burston said: ‘We found the LR5 could actually last another 25 years, although she wouldn’t be as agile, would have poorer communications and less propulsion.’ He said the hope is to sell the LR5 outside NATO, and some Asian countries have already expressed interest in the older system for use in their local waters.
The challenge for engineers working on the NSRS has been meeting NATO’s tough requirements for the system. It needs to be light, compact and air-portable to allow it to arrive on the scene within its strict 72-hour time window. It must then be able to launch from a mothership in conditions of up to sea state six (5m waves) and dive up to 700m coping with pressures of 5 bars. And it may have to make the trip more than 10 times, ferrying up to 150 people between stricken submarine and decompression facilities on the mothership.
Neville Yard, chief engineer on the project for Rolls-Royce, said NSRS will break new ground because every component of the system is designed with nothing but rescue in mind. ‘It’s the first time a rescue system has been designed and built from scratch. All systems at the moment are hybrids – bits of second-hand equipment married together,’ said Yard.
The key difference between the NSRS and the new US system is the free-swimming capability. The US Navy subscribes to the school of thought that pilots should operate the sub from the surface, and is planning an evolution from the current remotely-operated Australian Remora rescue system. This was rushed to meet Australia’s rapid new submarine programme and has proved problematic. The planned US rescue submarine has a thick umbilical cord that offers continuous power and strong, clear communication with the surface – plus a ‘string’ to pull the vehicle back on board. But umbilicals also add drag to the craft, prevent a launch from a support sub and risk wrenching the craft off the sunken sub’s hull mid-transfer if the mothership experiences positioning errors.
Aidan Goldsworth, NSRS project manager at Rolls-Royce explained that the decision to go free-swimming was not easy and needed some clever engineering. ‘We have got rid of the three big handicaps which in the past stopped people from choosing free-swimming subs,’ he claimed ‘Most people would agree that if you can overcome these then free-swimming vehicles are better.’ To match the performance of the US umbilical system, Rolls-Royce needed to find reliable ways to power the craft, communicate with the surface, and get the craft back on board without divers.
Rolls-Royce overcame the problem of power supply by taking battery technology well-established on land on electric vehicles and applying it for the first time in a marine setting. The Zebra battery delivers double the energy at 50 per cent the weight compared with the equivalent lead-acid cell, and can be charged from zero to 80 per cent capacity in just over an hour, Rolls-Royce claimed. Yard said: ‘You cannot tolerate downtime in a rescue â€” the batteries have got to work when they are needed. Our batteries have made a significant step forward to overcoming people’s concerns over lack of free-swimming endurance.’
The key active ingredients are sodium chloride and nickel. The energy is stored by the transfer of sodium ions through a solid electrolyte of beta-alumina ceramic. The cells operate at between 250-350 degrees C so the team’s initial concern was whether they could be air transportable. However, a vacuum-insulated casing shields the hot liquid sodium.
Communication issues were solved by the addition of a 7mm fibre-optic cable connecting the main rescue vehicle to the surface, which is designed to break at strain and can be deliberately jettisoned. Unlike an umbilical, it causes no drag and is neutrally buoyant, but transfers speech, video and text, plus navigation and tracking information at a level comparable to the US system. ‘Through-water comms has always been a problem,’ said Yard.
‘Depending on the saline and particulate content in the seawater it can often give very poor transmission. Submarine rescue however is media-hungry.’
The solution to the third challenge – how to achieve diver-less recovery – is still under wraps. The Engineering Business is currently working on two different systems. Yard explained that to operate at sea state six, it would be dangerous to put divers in the water. The two hook-up methods are both sub-surface where things are much more tranquil, according to Burston – who as the former captain of nuclear submarine Valiant, is in a position to know.
‘There’s a submarine expression that goes “happiness is 500ft in a force 12”,’ he said. ‘While our compatriots on surface ships heave their guts out, we’ve got a white tablecloth and a glass of claret.’ The two methods currently under investigation will either hook the vehicle on the seabed, or mid-water before pulling it to the surface. Burston hinted that the techniques are similar to the way a sewing machine needle picks up a thread, but the Rolls-Royce team was cautious about elaborating further.
An area in which the UK-led team claims it is stealing a march on the US system is the TUP decompression system. Yard said: ‘All eyes fall on the rescue vehicle, but the technological challenge for the TUP is just as significant. You’re trying to mobilise 150 people on to an unknown platform and it’s all got to fit together.’ The TUP can accommodate up to 87 submariners at once in three separate chambers, and will be the highest capacity air-portable TUP system in the world. ‘All the pressure boundaries of the parts have to be finely machined and able to lock together. Airtight integrity is vital because if you lose a seal it could rapidly decompress up to 36 people,’ said Yard.
One major challenge still to overcome is operation in very shallow waters in which tidal currents cause an extra complication. The aim is to work at 20m depth, but that may require divers and careful positioning, and the team is examining methods to lock the vehicle on to the hull.
Weight is also an issue. Clever integration of all the parts is critical – the bigger and heavier the vehicles, the harder they are to air-transport. At the moment the team said the whole system would fit in about 15 Airbus A400m aircraft (the project’s chosen aircraft).
The US system uses lighter weight composites in the main sub but Rolls-Royce rejected these materials in favour of a steel hull, so at 27 tonnes the main rescue sub is around seven tonnes heavier than its US equivalent. The NSRS team said the penalty for using composites was too much to bear, and the materials would not survive the NSRS’s 25-year service life.
‘Going to another type of material may save on weight, but they may need special coatings for example, and those coatings never last as long as the manufacturers say they do. Maintenance costs suddenly become a lot higher than expected,’ said Yard.
According to Yard, the greatest difficulty in the development has been meeting the demands of all the sub-contractors. ‘It’s such a finely balanced thing,’ he said. ‘If you’re forced to make a change it is like putting a grain of sand into a Swiss watch – it can mess up the whole operation. The NSRS success has been wholly dependent on getting the interfaces right.’
Rolls-Royce is confident that its equipment will take a leap forward in submarine rescue technology, and in tandem with the US system will provide worldwide aid for stricken submarines.
The NSRS is now well on track to enter service at the end of 2006, so submariners may soon be able breathe easier.
Sidebar: The US goes its own way
After the NSRS feasibility study in 1996, the US shunned NATO and pursued its own rescue submarine design. The Submarine Rescue Diving and Recompression System (SRDRS) will replace the US Navy Deep Submergence Rescue Vehicle (DSRV) used today.
The US design is similar to the NATO system with reconnaissance equipment, a main rescue vehicle – called the Pressurised Rescue Module (PRM) – and a Transfer Under Pressure decompression system (TUP) on the mothership. Yet it is 3m shorter and weight saving materials – such as aluminium structural extensions, Arimid fibre composite wall panels and titanium HY-100 components – make it seven tonnes lighter.
However, NATO will have a fully working decompression system first. The SRDRS will be rescue-ready by August 2006, but the US TUP equipment will not be ready until summer of 2008 â€” 18 months after its UK-designed equivalent.
According to Capt Thomas Eccles, programme manager for the SRDRS, a key design requirement that pushed the US away from the NATO system was that a civilian pilot controls the main rescue sub from the surface. He refuted the disadvantages of a tethered umbilical compared with free-swimming vehicles like the NSRS.
‘If the umbilical is severed, the PRM has battery back-up power for at least 20 hours for lights, control and communications. The PRM is slightly positively buoyant, so that upon loss of the umbilical it will gently float to the surface.’ The umbilical will break at loads of 50,000lbs.