The Columbia-class submarine, formerly known as the Ohio Replacement Submarine and SSBN-X Future Follow-on Submarine, is a future United States Navy nuclear submarine class designed to replace the Trident missile-armed Ohio-class ballistic missile submarines. The first submarine is scheduled to begin construction in 2021 and enter service in 2031 (some 50 years after its immediate predecessor, the Ohio class, entered service). From there, the submarine class will serve through 2085.
Graphic artist concept (2012)
Although still evolving, the following are some of the ship characteristics for the SSBN(X) design:
Expected 42-year service life (it is planned that each submarine will carry out 124 deterrent patrols during its service life)
Life-of-the-ship nuclear fuel core that is sufficient to power the ship for its entire expected service life, unlike the Ohio-class submarines, which require a mid-life nuclear refueling
Missile launch tubes that are the same size as those of the Ohio class, with a diameter of 87 inches (2,200 mm) and a length sufficient to accommodate a D-5 Trident II missile
Ship beam at least as great as the 42-foot (13 m) beam of the Ohio-class submarines
16 missile launch tubes instead of 24 missile launch tubes on Ohio-class submarines. A recent report (as of November 2012) suggested that the boats will have 12 submarine-launched ballistic missile (SLBM) silos/tubes. However, other sources do not support this.
Although the SSBN(X) is to have fewer launch tubes than the Ohio-class submarine, SSBN(X) is expected to have a submerged displacement about the same as that of Ohio-class submarines
Also, the US Navy has stated that "owing to the unique demands of strategic relevance, [SSBN(X)s] must be fitted with the most up-to-date capabilities and stealth to ensure they are survivable throughout their full 40-year life span."
In November 2012, the U.S. Naval Institute revealed, citing Naval Sea Systems Command, additional design information:
X-shaped stern control surfaces (hydroplanes)
Sail-mounted dive planes
Off-the-shelf equipment developed for previous submarine designs (Virginia-class SSNs), including a pump-jet propulsor, anechoic coating and a Large Aperture Bow (LAB) sonar system.
The boats may also be equipped with a Submarine Warfare Federated Tactical System (SWFTS), a cluster of systems that integrate sonar, optical imaging, weapons control etc.
Main article: Integrated electric propulsion
Electric drive is a propulsion system that uses an electric motor that turns the propeller of a ship/submarine. It is part of a wider (Integrated electric power) concept whose aim is to create an "all electric ship". Electric drive should reduce the life cycle cost of submarines while at the same time reducing acoustic signature.
Turbo-electric drive had been used on US capital ships (battleships and aircraft carriers) in the first half of the twentieth century. Later on, two nuclear-powered submarines, USS Tullibee and USS Glenard P. Lipscomb, were equipped with turboelectric drive but experienced reliability issues during their service life and deemed underpowered and maintenance heavy. Currently (as of 2013), only the French Navy uses turboelectric drive on its nuclear-powered Triomphant-class submarines.
Conceptually, electric drive is only a segment of the propulsion system (it does not replace the nuclear reactor or the steam turbines). Instead it replaces reduction gearing (mechanical drive) used on earlier nuclear-powered submarines. In 1998, the Defence Science Board envisaged a nuclear-powered submarine that would utilise an advanced electric drive eliminating the need for both reduction gearing (mechanical drive) as well as steam turbines.
In 2014, Northrop Grumman was chosen as the prime designer and manufacturer of the turbine generator units. Turbine generators convert mechanical energy from the steam turbines into electrical energy. The electrical energy is then used for powering onboard systems as well as for propulsion via electric motor.
Various electric motors are being or have been developed for both military and non-military vessels. Those being considered for application on future U.S. Navy submarines include: permanent magnet motors (being developed by General Dynamics and Newport News Shipbuilding) and a high-temperature superconducting (HTS) synchronous motors (being developed by American Superconductors as well as General Atomics).
More recent data shows that the US Navy appears to be focusing on permanent-magnet, radial-gap electric propulsion motors (e.g. Zumwalt-class destroyers use an advanced induction motor). Permanent magnet motors are being tested on the Large Scale