With a 33-megajoule jolt, Navy scientists fired a projectile from an electromagnetic railgun with a muzzle velocity of Mach 7. Navy officials claim that the Dec. 10 test firing at the Naval Surface Warfare Center at Dahlgren, Va., was a world record.
The concept is pretty simple.
"The rail gun uses electricity instead of gun propellant to fire a projectile from a naval gun," said Roger Ellis, rail gun program manager for the Office of Naval Research (ONR).
When ready to fire, the Dahlgren teams charged up the system's capacitor bank, the size of a small warehouse, using power from the local electric utility. The power builds up in about three to five minutes, but discharges in a matter of milliseconds. Electricity travels down a rail, passes through the aluminum projectile and back down the other rail, creating an electromagnetic field in back of the projectile that propels it out the barrel.
The firing of the 1.5 million amp spark results in a loud bang, like a naval gun.
'Pulse power' allows the gun system to store energy and then release it quickly enough to create the powerful force to propel the projectile," says Ellis.
There are some powerful cost savings. "It costs about $7 to $8 of electricity to do this," Ellis says, referring to the cost of electricity to fire the gun.
There is a big safety benefit, too. The projectiles have no explosive charge to expel them from the gun. And they have no explosive warhead to destroy targets, but instead rely on the kinetic energy of the projectile travelling at hypersonic speeds. That makes the ordnance safer to handle and store.
"The 33-megajoule shot means the Navy can fire projectiles at least 110 nautical miles, placing sailors and Marines at a safe standoff distance and out of harm's way, and the high velocities achievable are tactically relevant for air and missile defense," said Rear Adm. Nevin Carr, chief of naval research.
By comparison, the maximum range of a 5-inch projectile fired by one of the Navy's cruisers or destroyers is 13 nm.
Carr says hypersonics, directed energy weapons and electromagnetic railguns allow for a "deepening of the magazines." He explained how the inert railgun rounds will increase the depth of fire while at the same time be safer to store aboard ship because they have no propellant or explosive charge. "Directed energy weapons can be fired again and again, as long as power is available."
The test firing was conducted with a 10-meter laboratory launcher. This launcher is built to come apart so different types of materials and configurations can be tested. General Atomics and BAE Systems are both making prototype guns for the Navy. Unlike the test launcher, these guns, with barrels made from advanced composites, look very similar in size and shape to naval guns found on combatants today.
The railgun can potentially be used against fixed positions hundreds of miles away, or as a defensive weapon to protect against incoming high speed threats from the air or surface targets.
The next step is re-ratable pulse power, meaning the power system can charge the capacitors, then discharge them quickly to fire the gun in a repetitive manner for multiple firings in a short period of time. The Navy's goal is to demonstrate the thermal and power management for an auto-loading gun capable of a repetitive "firing rate of military significance."
Early barrels wore out quickly, but today's barrel liners can hold up for shots measured in the hundreds rather than tens. Navy officials say the weapon is technically not a gun, but more appropriately referred to as a launcher.
The research effort to date has managed to get more power into smaller capacitors, which is important for shipboard installations. The Navy continues to study compact energy storage and power management, materials for rails and barrels, and compact electronics for projectile guidance that can withstand the very high G-forces associated with railguns.
High speed cameras record the test firing from several vantage points. The "flame" one sees in photos of rail gun shots is the "glow of the air around the bullet turning into a plasma," Ellis says.
Following the shot, test director Tom Boucher and his team "safe" the launcher and make sure everything is grounded.
"We used to fire the round into a sand catchment. This would pretty much destroy the round."
The Dec. 10 test round was fired on a flat trajectory down a range where it was recovered about a mile away, enabling the round to be studied and compared with others. About 45 minutes after the launch, Boucher displayed the round - which was still quite warm - to reporters.
Unlike the test projectile, the real railgun round will be an aerodynamically shaped projectile surrounded by a sabot that serves as the armature. The sabot falls away outside of the barrel as the projectile continues the target.
The lab test used a 1.2 kg projectile. A tactical round would weigh about 11 to 16 kg per projectile for a 100 mm round with a sabot. A tactical round would travel out of the muzzle at 2.5 km. sec., and be travelling 1.5 km/sec. 200 miles later.
The small projectile from the laboratory launcher has a recoil of less than an inch, Ellis says, but that recoil on a tactical gun would be more like 10 to 12 inches.
"The rounds can be guided to GPS coordinates, or can dispense fragmentation munitions just before hitting a target, such as ground forces, ships or radar installations," says Charles Garnett, the project manager at NSWC Dahlgren.
The Navy plans to conduct about 100 firings in this series of 32 megajoule tests, officials say.
Ellis says the technology could be ready for deployment in the 2020-2025 timeframe.
Dr. Elizabeth D'Andrea, strategic director for ONR's Electromagnetic Railgun program, described the record-breaking demonstration as "exhilarating."
"We plan to go through the process of registering this world record with Guinness," says ONR spokesman Peter Vietti.
"Our top priority is to focus on those areas that deliver the biggest payoff for our future and ensure we make every single dollar count for maximum benefit for the war fighters," says Carr, "and to look for science and technology (S&T) that give us that leap ahead 'next big thing' type of capability."
Navy officials say the railgun test demonstrates the tactical relevance of the research and the technology could complement traditional surface ship combat systems in the future. "This demonstration moves us one day closer to getting this advanced capability to sea," Carr says.
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