The idea is 20 years old and comes from Manfred Hettmer, president Austrian Mars Society: With the help of “Alfven waves”, based on plasma propulsion, the thrust of a rocket can be drastically increased, at the same time the fuel consumption is reduced.

It was in 1942, when the later Nobel laureate Hannes Alfvén [] published a letter, stating, that oscillating magnetic fields can accelerate ionised matter via magneto hydrodynamic interactions in a wave like fashion. These waves were later called “Alfvén waves []”, in honour of their discoverer. Although the evidence for Alfvén’s hypothesis came already rather early with the observation of certain plasma phenomena, such as being connected with high solar wind Wolf-Rayet stars, more than 60 years had to pass by before a technical implementation of Alfvén waves for propulsive purposes was proposed for the first time.

The name of the concept, utilising Alfvén waves to accelerate ionised matter for propulsive purposes, is MOA – Magnetic field Oscillating Amplified thruster. Alfvén waves are generated by making use of two coils, one being permanently powered and serving also as magnetic nozzle, the other one being switched on and off in a cyclic way, deforming the field lines of the overall system.

It is this deformation that generates Alfvén waves, which are in the next step used to transport and compress the propulsive medium, in theory leading to a propulsion system with a much higher performance than any other electric propulsion system.

Based on computer simulations, which we conducted to get a first estimate on the performance of the system, MOA is a highly flexible propulsion system, whose performance parameters might easily be adapted, by changing the mass flow and/or the power level. As such the system is capable to deliver a maximum specific impulse of 13116 s (12.87 mN) at a power level of 11.16 kW, using Xe [] as propellant, but can also be attuned to provide a thrust of 236.5 mN (2411 s) at 6.15 kW of power.

Although a dual-use system, space propulsion is expected to be the prime application for MOA. As MOA works best in high-power mode and with ionised matter, utilisation concepts range from a high-efficient Nuclear Electric Propulsion System, to an ‘afterburner’ for Nuclear Thermal Propulsion Systems. This wide range of applications makes MOA a unique accessory for any nuclear propulsion system to overcome specific concept drawbacks, allowing a full-fledged hybrid nuclear propulsion system, with attune able thrust / specific impulse parameters, perfectly suited for nearly all types of space missions.

This article will be presented on Friday, October 21 2005, 08h30m at the 56th International Astronautical Congress [] in Fukuoka, Japan.

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