Electromagnetic propulsion (EMP) is the principle of accelerating an object by the utilization of a flowing electrical current and magnetic fields. The term electromagnetic propulsion (EMP) can be described by its individual components: electromagnetic – using electricity to create a magnetic field, and propulsion – the process of propelling something.
Principle: The electrical current is used to either create an opposing magnetic field, or to charge a field, which can then be repelled. When a current flows through a conductor in a magnetic field, an electromagnetic force known as a Lorentz force, pushes the conductor in a direction perpendicular to the conductor and the magnetic field. This repulsing force is what causes propulsion in a system designed to take advantage of the phenomenon.
Electromagnetic propulsion is utilized in transportation systems to minimize friction and maximize speed over long distances. This has mainly been implemented in high-speed rail systems that use a linear induction motor to power trains by magnetic currents. It has also been utilized in theme parks to create high-speed roller coasters and water rides. Cable-free elevators using EMP, capable of moving both vertically and horizontally, have been developed by German engineering firm Thyssen Krupp for use in high rise, high density buildings.
China’s ‘Breakthrough’ In Electromagnetic Propulsion
In Oct 2022, it was reported that Chinese scientists achieved the pinnacle of electromagnetic propulsion technology when they sent a 1,000-kilogram object at the speed of sound. The ‘electromagnetic sled’ in Jinan City, east China’s Shandong Province, accelerated a one-ton carriage to 1030 kilometers an hour (640 miles), potentially offering speed, reliability, and fossil-fuel independence in a single transport system.
The research and development of ultra-high-speed ground and air vehicles has to address issues with aerodynamics, high strength advanced materials and operation of sensors in super speed conditions. The electromagnet driven facility can provide solutions to those problems with its advantages in strong push power, sensitive reaction and precision control.
China Global Television Network (CGTN) said the project is a collaborative effort between the Institute of Electrical Engineering (IEE) of the Chinese Academy of Sciences (CAS) and the governments of Shandong Province and Jinan City.
Chemical rocket propulsion has limitations when applied to space application, with respect to
specific impulse, delta-v, volume, and stored energy, which can be overcome by an electric propulsion system. Among various types of Electric propulsion systems, electromagnetic propulsion has added advantages for many space applications.
There are multiple applications for EMP technologies in the field of aerospace. One such application is the use of EMP to control fine adjustments of orbiting satellites. One of these systems is based on the direct interactions of the vehicle’s own electromagnetic field and the Earth’s magnetic field. The thrust force may be thought of as an electrodynamic force of interaction of the electric current inside its conductors with the applied natural field of the Earth. To attain a greater force of exchange, the magnetic field must be propagated further from the flight craft. The advantage of such systems is the exact and instantaneous control over the thrust force.
In addition, the expected electrical efficiencies are far greater than those of current chemical rockets that attain propulsion through the intermediate use of heat; this results in low efficiencies and large amounts of gaseous pollutants. The electrical energy in the coil of the EMP system is translated to potential and kinetic energy through direct energy conversion. This results in the system having the same high efficiencies as other electrical machines while excluding the ejection of any substance into the environment.
Magnetoplasmadynamic (MPD) thruster
The magnetoplasmadynamic (MPD) thruster is currently the most powerful form of electromagnetic propulsion. The MPD’s ability to efficiently convert megawatts of electric power into thrust makes this technology a prime candidate for economical delivery of lunar and Mars cargo, outer planet rendezvous, and sample return, and for enabling other bold new ventures in deep space robotic and piloted planetary exploration. With its high exhaust velocities, MPD propulsion offers distinct advantages over conventional types of propulsion for each of these mission applications. MPDs expel plasma to create propulsion. MPDs can process more power and create more thrust than any other type of electric propulsion currently available, while maintaining the high exhaust velocities associated with ion propulsion.
In its basic form, the MPD thruster has two metal electrodes: a central rod-shaped cathode, and a cylindrical anode that surrounds the cathode. Just as in an arc welder, a high-current electric arc is struck between the anode and cathode. As the cathode heats up, it emits electrons, which collide with and ionize a propellant gas to create plasma.
Plasma is an electrically neutral gas in which all positive and negative charges—from neutral atoms, negatively charged electrons, and positively charged ions—add up to zero. Plasma exists everywhere in nature; it is designated as the fourth state of matter (the others are solid, liquid, and gas). It has some of the properties of a gas but is affected by electric and magnetic fields and is a good conductor of electricity. Plasma is the building block for all types of electric propulsion, where electric and/or magnetic fields are used to push on the electrically charged ions and electrons to provide thrust
A magnetic field is created by the electric current returning to the power supply through the cathode, just like the magnetic field that is created when electrical current travels through a wire. This self-induced magnetic field interacts with the electric current flowing from the anode to the cathode (through the plasma) to produce an electromagnetic (Lorentz) force that pushes the plasma out of the engine, creating thrust. An external magnet coil may also be used to provide additional magnetic fields to help stabilize and accelerate the plasma discharge.
NASA is currently researching both pulsed and continuous forms of MPDs with hydrogen or lithium as a propellant. While attractive from an efficiency standpoint, lithium is a condensable propellant and may coat spacecraft surfaces and power arrays. MPD thrusters using noncondensable hydrogen propellant will eliminate these concerns and provide higher exhaust velocities than lithium-fueled thrusters. Glenn is currently developing high-specific-impulse, megawatt-class, hydrogen-fueled MPD thruster technology. Research at Glenn encompasses a combination of systems analysis, numerical modeling, and high-power experiments that investigate pulsed versions of both self-field and applied-field MPD thrusters. Testing for these thrusters has demonstrated exhaust velocities of 100,000 meters per second (over 200,000 mph) and thrust levels of 100 Newtons (22.5 pounds) at power levels of 1 megawatt. For perspective, this exhaust velocity will allow a spacecraft to travel roughly 11 times the top speed of the space shuttle (18,000 mph).
Future power-rich robotic and piloted outer planet missions will require exhaust velocities approaching 100,000 meters per second (over 200,000 mph). These higher velocities can be achieved using noncondensable hydrogen plasmas, which are currently under investigation at NASA Glenn. As research continues, the efficiency of the MPD thruster will be increased, which will allow missions with reduced propellant requirements or increased range. Higher exhaust velocities and thrust levels will lead to shorter trip times and reduced mission cost, which is especially beneficial for cargo and piloted missions. As large amounts of power become available in space, MPD thrusters may become the method of propulsion that carries humans to other planets in our solar system.
The Electromagnetic Aircraft Launch System (EMALS) is a type of aircraft launching system currently under development by General Atomics for the United States Navy. EMALS uses electrical energy to propel Aircraft by converting electric energy into kinetic energy. The system launches carrier-based aircraft by means of a catapult employing a linear induction motor rather than the conventional steam piston. EMALS was developed for the Navy’s Gerald R. Ford-class aircraft carriers and will be used in all future U.S. Navy aircraft carriers. US Navy has finished Load testing of the Electromagnetic Aircraft Launch System (EMALS) aboard the future aircraft carrier PCU Gerald R. Ford (CVN-78). The tests catapult “dead loads” placed on weighted sleds into the river.
EMP and its applications for seagoing ships and submarines have been investigated since at least 1958 when Warren Rice filed a patent describing the technology. The technology described by Rice considered charging the hull of the vessel itself. The design was later refined by allowing the water to flow through thrusters as described in a later patent by James Meng. The arrangement consists of a water channel open at both ends extending longitudinally through or attached to the ship, a means for producing magnetic field throughout the water channel, electrodes at each side of the channel and source of power to send direct current through the channel at right angles to magnetic flux in accordance with Lorentz force
Many concepts for electromagnetic propulsion devices with weapon-like performance have be attempted. Interest in developing an electromagnetic gun has come and gone several times, generally waning due to the lack of a sufficient power source to supply the energy mandated by the gun’s performance parameters. The factors which determine the power supply requirements are the projectile mass, launch velocity, rate of fire, and launcher efficiency.
Australian National University in the late 1970s accelerated a 3-g mass to 5.9 km/sec. Although the equipment utilized in this experiment was huge and not weaponizable, the conversion of electrical energy to more than 50 kJ of kinetic energy at such high velocity was a very significant achievement. A joint Army, Department of the Army Defense Advanced Research Projects Association (DARPA), and Defense Nuclear Agency (DNA) launched a program develop an anti-armor gun with an output of 9 MJ of projectile kinetic energy. Space-based applications of electromagnetic launchers (EMLs) were researched by the Strategic Defense Initiative Office (SDIO) and Air Force laboratories.
COMPONENTS OF AN EML
First is energy generation, fuel is needed to provide energy for conversion to projectile kinetic energy. The fuel is consumed in some prime power engine which drives an electrical generation device. The EML requires far too large an electrical input for the needed electrical power to be generated directly, so some form of energy storage is required.
Energy storage can take many forms. It could, for example, be placed to the left of the generator in the form of a flywheel, which stores a large amount of rotational kinetic energy. Rotational kinetic energy storage may also be integral to the generator in the form of a massive rotor, which also stores energy via rotational kinetic energy. Batteries can be utilized to store large amounts of energy in an electrochemical fashion. Capacitors, which contain an electrically stressed medium, are another choice of energy storage. For short times, inductors may also serve as energy storage devices, storing energy in a volume filled with a magnetic field. Many possibilities exist, including combinations of two or more of the items listed above.
Power conditioning section, may be in several forms. An opening switch for the inductive energy store is one example. A variable inductor coupled to a battery energy store is another. A series inductor with closing and crowbar switches is yet another form of power conditioning In the case of the pulsed alternator or Compulsator, the power conditioning is built into the device by engineering it to operate in a fast pulse-discharge mode.
With the energy generated, stored, and properly conditioned, it must be transmitted to the EML.
In laboratory devices, this is usually done by a set of bus bars. As the path to weaponization is taken, much more flexible power transmission conductors must be found which allow the barrel to be rapidly aimed. The loss mechanisms in this power transmission must be well understood and reduced as much as possible to permit a reasonable sustained rate of fire.
Then the gun itself, with ammunition stowage in a magazine or autoloader. The barrel, of course, must be aimed and fired, either by the soldier or by remote control, if the weapon is mounted outside an armored, airborne, or sea-going vehicle. Since projectiles for EMLs can be radically different from conventional ammunition need separate development.