The U.S. Navy is betting the future of its submarine force on a secret and revolutionary nuclear drive system that aspires to be more efficient and quieter than anything under the water today.
The heart of the planned ballistic missile Ohio Replacement (OR) program will be built around a drive that will not need to be refueled for the 50-year life of the boats and cuts out potentially noisy direct mechanical connection to the drive train. In other words, the Navy’s next-gen subs could be almost silent, and keep running for a half-century straight.
The Navy’s ballistic missile fleet, or boomers, rely on stealth to hide from rival boats, ships and sub-hunting aircraft. The quieter the boat, the harder it is to find. (And these boats are big: the current Ohio boomer is more than a football field and half long displacing 19,000 tons.)
Now the Navy is developing an innovation that attempts to give OR boomers the quietest nuclear engine yet by “going to [an] electric drive,” Sean Stackley, the Navy’s chief weapons buyer, said in aJanuary interview with the U.S. Naval Institute.
Current boomers have a direct mechanical connection to the props that drive the boat. Steam turbines driven by the nuclear power plant go through a series of mechanical gears that translate the high torque power from the nuclear plant into lower torque energy needed to propel the ship. All of those mechanical connections can generate noise, the bane of the submariner.
Moving forward, the Navy wants to use the power from the reactor to create an elaborate electrical grid inside of the submarine. The reactor power would feed the grid and in turn the electric motors that would drive the boats. Eliminating the mechanical connection would mean less noise under water. The set up would also free up power previously devoted to driving the ship. Currently anywhere from 75 to 80 percent of the power from a nuclear submarine is devoted to driving the ship through the water. Extra power could be routed to other systems like sonars and potentially unmanned underwater vehicles.
This will be the second try for the Navy to use electric drive subs. The service experimented with the technology in the 1960s and 1970s but found the boats equipped with the drives to be underpowered and maintenance heavy.
Unlike other programs, the Navy hasn’t gone out of its way to tout the electric drive technology it plans to use for the OR boomers. A 2010 Analysis of Alternatives for the OR program, then known as the SSBN(X), was closely held by the service. Gene Taylor, the chairman of the Seapower subcommittee of the House Armed Services Committee at the time, demanded publicly that Congress get a chance to evaluate the proposal. He lost his 2010 election and the Navy kept specifics mostly quiet.
Among the details they have discussed, in addition to the electric drive, is the development of a new nuclear power plant for the OR boats.
“There is investment in the front end in the reactor plant to arrive at a core that will last the life of the boat,” Stackley said.
Now, the Navy’s nuclear fleet requires a mid-life refueling and overhaul that can keep a ship or submarine out of commission for almost three years with a cost in the billions.
“By eliminating that midlife refueling, you effectively get greater operational availability out of the boat,” Stackley said.
The standard ratio for ballistic missile submarines on patrol to subs in port is about four to one. Currently the navy fields 14 Ohio-class boomers packing 24 Trident II D5 intercontinental ballistic missiles. (The first four Ohios were converted to carry missiles with conventional warheads).
“There are still going to be midlife upgrades but the refueling portion is effectively eliminated which allows us to reduce from today’s 14 Ohios to reduce down to 12 Ohio Replacements,” Stackley said.
The original Ohio-class builder General Dynamics Electric Boat hasn’t built a boomer in more than 20 years and the durability of the drive and the boats to last until 2080 is a tall order.
Added to the pressure is a Pentagon imposed cost cap that reduce the cost of the boat from about $7 to 8 billion down to $4.9 billion. But the Navy will have little margin for error if they want to keep the price tag that low.
The Navy has already delayed work two years as part of its 2013 budget. Currently the first OR boat is scheduled to begin construction in 2021 for a decade-long construction and development process. The super-silent boat is scheduled to make its first patrol in 2031. After that, you may never hear from it again.