em launch

CEM’s history in Electromagnetic Launch (EML):

1970’s: Pulsed AC Rotating Machines

Research into pulsed alternators at UT-CEM can be traced back to the late 1970’s with the invention of the compulsator (compensated pulsed alternator), a new type of low impedance electrical machine designed for very high power operation. Although it was conceived at UT-CEM to power laser flash lamps for fusion research at Lawrence Livermore National Laboratories (LLNL), the compulsator concept has been successfully applied to electric launchers for the U.S. Army and NASA, and high frequency microwave sources.

1980’s: "Iron-Core Compulsator" (ICC)

In the mid-1980’s, the first compulsator built for the U.S. Army electric gun program was successfully demonstrated. Named the "Iron-Core Compulsator" (ICC), the device is a 6-pole, rotating field machine which stores 40 MJ of kinetic energy at 4,800 rpm, and can repetitively deliver ten 1 MJ, 2 ms pulses. The ICC generated an open circuit voltage of 2 kV and operated at a peak current of 1 MA, resulting in a peak power rating of 2 GW.
In 1988, the Army contracted CEM to build two single-phase, self-excited, air-core compulsators. Very high strength composites not only made for a much lighter machine, but it could be spun faster allowing it to store more energy.  The compulsator for this system was a 2-pole, rotating armature topology. While rated at half the power of the ICC, the small caliber compulsator (SCC) weighed only 8% as much increasing the power density by a factor of six.
In parallel, the U.S. Army desired the capability to fire a large bore railgun at a test range and demonstrate the pulsed power supply at full scale. In reponse, UT-CEM developed a working 9 MJ range gun.

1990’s: Cannon Caliber Electromagnetic Gun System (CCEMG)

In the early 1990’s, the Army and Marine Corps funded the Cannon Caliber Electromagnetic Gun System (CCEMG) is a joint project for the purpose of demonstrating an EM gun system designed from a system/mission prospective. The CCEMG used a second generation single-phase air-core compulsator which represented a factor of 3 increase in energy (3.5 J/g multi-shot) and power density (to 1,500 kW/kg) over the range gun system. The machine powers a rectangular bore railgun to accelerate 185 g launch packages to muzzle velocities far exceeding the conventional state of the art for this caliber. Rated at 4 kV and 850 kA, the compulsator stored 40 MJ and can deliver 15 shots without recharging the rotor.

EML Technology in the world today:

Railgun Shots: The most recent test of a railgun took place on December 10, 2010, by the US Navy at the Naval Surface Warfare Center Dahlgren Division.  During the test, the Office of Naval Research set a world record by conducting a 33 MJ shot from the railgun, which was built by BAE Systems.  A link to a video of the shot can be found here.

Similar technology using a linear induction motor and alternators for energy storage are also being tested by the Navy for launching aircraft through an Electromagnetic Aircraft Launch System (EMALS).  Compared to steam catapults, EMALS weighs less, occupies less space, requires less maintenance and manpower, is more reliable, and uses less energy.  In June 2010, the land-based prototype of the system passed initial tests, video of a ground based fighter jet launch can be seen here.

See Also:
Railgun Armatures
Rotating Machines
Participation and Accomplishments in the US Electromagnetic Launch Program

Mr. Jon Hahne

Jon Hahne


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