Monday, 1 October 2012

The Rail-gun, a brief history and potential future

Catapults seem like antiquated machine throwing large objects at the enemy, the 20th century equivalent seems to be a technology that still has a purpose. Instead of a fulcrum arm, sling and counter weight the rail gum uses strong magnetic forces along a certain distance to throw the object.
Although theory had existed since the nineteenth century, no major development occurred until the middle of the twentieth century. Earlier attempts had been reported, one Mr. Benningfield put an advertisement in 1844 in which his "SIVA" or the DESTROYER promised to revolutionize the battlefield. This is surprising as it occurred well before the 1878 date of Lorentz's theories. Either way, Benningfield's promised revolution never happened, and nothing is known of what happened to Benningfield or his electric gun.
Much later French inventor Louis Octave Fauchon-Villeplee invented an electric cannon in 1918, which is an early form of railgun. He filed for a US patent on 1 April 1919, which was issued in July 1922 as patent no. 1,421,435 "Electric Apparatus for Propelling Projectiles". In his device, two parallel busbars are connected by the wings of a projectile, and the whole apparatus surrounded by a magnetic field. By passing current through busbars and projectile, a force is induced which propels the projectile along the bus-bars and into flight.

During World War II the idea was revived by Joachim Hänsler of Germany's Ordnance Office, and an electric anti-aircraft gun was proposed. By late 1944 enough theory had been worked out to allow the Luftwaffe's Flak Command to issue a specification, which demanded a muzzle velocity of 2,000 m/s (6,600 ft/s) and a projectile containing 0.5 kg (1.1 lb) of explosive. The guns were to be mounted in batteries of six firing twelve rounds per minute, and it was to fit existing 12.8 cm FlaK 40 mounts. It was never built. When details were discovered after the war it aroused much interest and a more detailed study was done, culminating with a 1947 report which concluded that it was theoretically feasible, but that each gun would need enough power to illuminate half of Chicago. In the early 1960s, the railgun was investigated by NASA as a potential means for studying hypervelocity impact physics. The NASA work also provided the inspiration for the work that was subsequently carried out in Australia. During 1950, Sir Mark Oliphant, an Australian physicist and first director of the Research School of Physical Sciences at the new Australian National University, initiated the design and construction of the world's largest (500 megajoule) homopolar generator. This machine was operational from 1962 and was later used to power a large-scale railgun that was used as a scientific experiment.
Much later BAE Systems won a contract to deliver a 32 megajoule lab launcher in June 2007 to the Office of Naval Research (ONR) Electromagnetic Launch Facility, located in Virginia at the Naval Surface Warfare Center’s Dahlgren Division Laboratory. On 31 January 2008, test firing began with this launcher. The railgun was fired at 10.64MJ (megajoules) and the 7 lbs. (3.2 kg) test slug projectile attained a muzzle velocity of 8,268 fps (2,520 mps). The following datapage is constructed from public materials released by the US Navy concerning a "Notional Railgun for Destroyers" with a bore of 150 mm (5.9"). In this Notional Railgun design, the projectile is encased within a sabot which provides a means of putting an aerodynamically shaped projectile into a rectangular gun barrel. The sabot together with the propelling armature is discarded after the assembly clears the muzzle.
In early February 2012, BAE Systems delivered the first of two prototype advanced railguns to the US Naval Surface Warfare Center Dahlgren Division (NSWCDD) for testing, two years after being awarded the contract by the Office of Naval Research (ONR). The first of two, month-long test series began later in the month, with each firing testing its extended range capabilities against surface, air and ground targets at various energy levels. The second General Atomics-built prototype launcher was delivered in April 2012 with trials progressing to firing an aerodynamic round developed by Boeing. It achieved speeds of Mach 5, and with zero gun elevation it penetrated a steel plate an eighth of an inch thick 100 yards away, then travelled seven kilometres down range before it stopped. Tom Hun of General Atomics indicted that in discussions with the navy, General Atomics had identified the USS Arleigh-Burke (DDG-51) as a likely candidate test platform for sea trials. For the next phase the ONR recently awarded $10m contracts to Raytheon, BAE Systems and General Atomics to develop a pulsed power system for launching projectiles in rapid succession. Targeting a firing rate of six to ten 50mm rounds a minute, the naval power system is expected to be operational by 2025.
A railgun offers a number of potential advantages over traditional explosive projectile weapons. The accelerating force is applied to the projectile for the entire time the projectile is between the rails of the launch device, as opposed to explosive forces which, however powerful, have a limited duration. This means much higher velocities can be reached - potentially Mach 10 at sea level, or more than three times the muzzle speed of an M16 rifle - than can be achieved through explosive forces. In turn, this could result in it having a range 220 miles, which is around ten times further than any other gun. High speeds mean projectiles are much less affected than conventional weapons by factors such as wind, allowing them to retain pinpoint accuracy across a large distance, rather than needing on-board trajectory correction, making them considerably cheaper.
Railgun projectiles are generally non-explosive, relying on their enormous speed to destroy the target and thus reducing the risk of a fire on board a ship, and comparatively small and lightweight, so they can be more readily transported and stored. The kinetic energy they deliver could do as much damage as a Tomahawk missile, enabling them to travel clean through a ship. Perhaps the future of battleships will almost be carbon free projectiles smashing into the hull of an enemy ship. In any case the railgun may not just be limited to navel weaponry, there is potential for launching payloads into space. Its an idea worth pursuing for NASA, as it offers a economical answer to sending supplies to the international space station. SpaceX currently has a $1.6 billion contract with NASA for 12 unmanned flights to the ISS, which seems like an expensive taxi service...

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