Magnetoplasmadynamic thruster

A magneto- plasma- dynamic drive, also called MPD- drive (English MPD thruster ), is a driving mechanism for spacecraft based on the principle of electromagnetic acceleration. Due to the high electrical power demand but few drives have been tested in space, particularly through the efforts of Japan and the former Soviet Union since the beginning of the development in the 1960s to date.

It utilizes the Lorentz force, which describes the interaction between a magnetic field and electric power, and is therefore Lorentz Force Accelerator (LFA ) mentioned. MPD propulsion is an evolution of the thermal arcjet ( Arcjet ), the electrothermal acceleration will be replaced by the more efficient electromagnetic acceleration. This allows a higher efficiency can be achieved, which is however, only achieved at high power levels, and associated strong magnetic fields. If, in addition, a magnetic field is applied, one speaks of the external field accelerator (English AF -MPD; Applied - Field MPD ), otherwise the self-field accelerator (English SF -MPD; Self- Field MPD).

Technology

MPD thrusters comprise a funnel-shaped anode, in the middle a rod-shaped cathode is provided. When a voltage is applied between the two electrodes that are in the hopper exploiting dividend supporting compound is ionized, allowing a current to flow radially through the gas to the cathode. By the current flow, a strong magnetic field will be generated. The interaction between the magnetic field electrically generated around the combustion chamber and the ionized mass support this accelerated in the axial direction and letting it escape at very high speed. Due to this effective pulse creates the thrust.

As a basis for the plasma mainly argon, lithium and hydrogen are. In experimental laboratory exit velocities were already using an external magnetic field in a MPD driving 144,000 kilometers per hour (40 km / s).

VASIMR

A variation of the magneto- plasma- dynamic actuator is being developed by the U.S. company, Ad Astra Rocket Company. Manager is the former seven-time NASA astronaut and plasma physicist Franklin Chang- Diaz Ramon, who developed the concept in 1979 in his work at MIT.

When done VASIMR or Variable specific impulse magneto plasma rocket

In three separate compartments.

So that a variation of the relation between specific impulse and thrust can be analogous to the transmission circuit of a wheeled vehicle. A spacecraft could be used to produce a high thrust to then travel a long distance at high speed about to leave the gravitational field of a planet.

VASIMR could thus offer a perspective significantly higher efficiency than conventional spaceship drives, shorten travel times for space flight within the solar system on a monthly or even weekly time periods and thus make feasible for humans. The travel time Earth - Mars would be reduced from more than 180 days to 39 days.

Current development status

As a developer of VASIMR the U.S. company Ad Astra operates, which is working currently by increasing the capacity to improve the overall efficiency; therefore currently 67 % can be achieved. The publications on the VX -50 engine, which uses 50 kW radio-wave power, calculate an efficiency of nearly 59 % as follows:

The model VX -100 is expected to reach an overall efficiency of 72 % by improving the NB ion speed boosting efficiency to 80%.

In October 2008, the company reported that the VX -200 helicon - engine, be ready for use in the first stage, a solid-state RF power coupler. The key technology to the DC radio wave conversion ( solid-state DC - RF), reach here an efficiency of 98%.

The helicon discharge used herein 30 kW radio waves to generate an argon plasma. Further 170 kW are used to accelerate the plasma in the second portion, including ion cyclotron resonance heating (see a cyclotron resonance ) is used.

ISS exploitation

On December 10, 2008 Ad Astra Company was awarded the contract to NASA, the installation and testing of an operational VF -200 engine with 200 kW of power at the International Space Station ( ISS) carried out. With the VF -200 engine, the height of the station can be held, as usual without always having to create rocket fuel to the ISS. The launch was expected in 2014, according to a publication of Ad Astra installation is now planned for 2015. The ISS VASIMR engine will work due to the high power in pulsed mode, with 15 -minute load cycles are buffered by battery.

Based on testing of its predecessor VX -100 is expected that the VF -200 engine has an efficiency of 60-65 % and a boost to 5N. The optimum specific impulse to 5000 s expected, the use of this relatively favorable argon. The specific power output is estimated at 1.5 kg / kW, which this VASIMR engine weighs about 300 kg.

Between April and September 2009, further tests were performed on the VX -200 prototype with integrated superconducting magnet. Thus the expansion of the power range on the use of power of 200 kW was demonstrated.

Energy source

The biggest challenge in MPD as well as VASIMR developments is the generation of electric power that would be useful in applications in the megawatt range. A conversion from chemical energy would reduce the overall efficiency again below the level of chemical propulsion; Solar panels or nuclear batteries previous interpretation does not achieve these benefits. The plans thus rely on nuclear fission or nuclear fusion as a future energy sources for space drives.