Magnetic field oscillation drive

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Ignition of a MOA engine in the vacuum chamber

The Magnetic Field Oscillating Amplified Thruster ( English magnetic field oscillating amplified thruster , MOA ) in the press as a plasma thruster referred to is a versatile electromagnetic thermodynamic system that is capable of any electrically charged gaseous medium ( plasma application) to high outflow velocities and also electrically to accelerate conductive liquids (hydrodynamic application) in principle.

To do this, the system relies on so-called Alfvén waves , a physical principle of magnetohydrodynamics that was first predicted in 1942 by the later Nobel Prize winner Hannes Alfvén and that states that changing magnetic fields in electrically conductive media (e.g. Plasma , salty water etc.) cause density waves. The associated change in pressure and temperature accelerates the medium enclosed in the magnetic field.

Due to the heating mechanism based on adiabatic compression , MOA differs fundamentally from other electrothermal engines , in particular also from the magnetoplasmadynamic or MPD engine with which it is sometimes compared by the collective term as a plasma engine.

application areas

Because of the high outflow velocities that can be achieved and the associated high specific impulse and the high particle energy, there are two main areas of application: space travel and the surface treatment of certain materials ( coating ). In the first case, the high outflow speed means a significantly lower support mass requirement compared to conventional ion thrusters ; in the second application, the high energy causes a great depth of penetration into the material to be treated. This z. B. steel , aluminum , but also glass and plastics can be hardened or adapted to the required properties as required.

Apart from the high particle energies and outflow velocities, the MOA concept also has the advantage that it is largely corrosion-free . The magnetic fields used to generate the Alfvén waves prevent the high-energy particles from coming into contact with the wall or another structural component and causing damage.

Structure of the MOA system

Plasma application

The entire MOA system essentially consists of five sub-elements:

  • Plasma source,
  • Central tube,
  • Primary coil,
  • Secondary coil,
  • Supply and control unit.

The plasma source generates a continuous stream of ionized particles that drift in the central tube towards the outlet nozzle. These particles can e.g. B. nitrogen or hydrogen molecules , but also atoms of the noble gases argon or xenon or any other gaseous material. Since they are ionized, they react to the two magnetic fields that are created by the primary and secondary coils. The primary coil is permanently in operation and forms the magnetic outlet nozzle, while the secondary coil is switched on and off cyclically in order to deform the field lines in the overall system. This deformation creates the Alfvén waves, which are used in the next step to transport and compress the drive medium. The entire system is controlled by the supply and control unit.

Since the MOA concept requires a plasma source to generate the ionized particles, it is basically an electric drive system like other ion drives . Due to the interaction of the magnetic fields, the particle packets are also compressed and heated, which turns the overall system into an electrothermodynamic system . This combination of electrical and thermodynamic system combines the advantages of both areas, because on the one hand it has the high efficiency of electrical drive systems, but it can also accelerate a large number of particles - like a thermal system - and thus generate a relatively high thrust. The combination of high particle energy or outflow velocity and relatively high thrust is exceptional in this form. The high flexibility by changing the mass flow or the electrical power parameters is unique at the present time.

Hydro-dynamic application

The hydrodynamic variant differs primarily in that the plasma source is omitted. However, the prerequisite for the function is the availability of an electrically conductive liquid or an electrolyte from a container or a surrounding reservoir (e.g. sea water).

History and state of development

Theoretically, MOA was designed in 1982 by Manfred Hettmer, who later developed the system and put it into practice. After he first created a numerical simulation from 1998 and built a mock-up in 1999 for the basic representation of the technical components and functions (initially without a plasma source), the first tests with a functional breadboard model in a laboratory of the LRT (chair for Space technology) of the Technical University of Munich in Garching . The first patent application was made in 2003.

In a report by Horst Löb at the Justus Liebig University in Gießen , the MOA concept was also confirmed on the basis of the technical data and the simulation created by Hettmer.

Later, a laboratory at the Graz University of Technology could be used. At the Institute for Communication Networks and Satellite Communication at TU Graz , the prototype of the engine was tested in a vacuum chamber and the measurement results confirmed the feasibility of the project. The data obtained were presented at the International Astronautical Congress in Fukuoka, Japan on October 21, 2005. An article written by Hettmer was published in the journal Raumfahrt Concret (issue 2/2006). The company QASAR Technologieentwicklung Ges.mbH ( HG Wien commercial register number FN 268333h), which was founded by Hettmer in 2003 , was able to further develop the technology and test potential applications, both with regard to a possible use in space travel as well as for surface treatment. In the summer of 2005, the MOA prototype reached the TRL 5 ( Technology Readiness Level ) and thus proved its function in a relevant environmental condition ( vacuum chamber ).

After QASAR Technologieentwicklung Ges.mbH was closed at the beginning of 2009 due to internal difficulties with shareholders and investors, Hettmer continued the project largely with its own resources within the scope of the given possibilities. The implementation of a commercial application is planned.

See also

literature

Web links

Individual evidence

  1. ↑ Competition for rocket propulsion heise.de