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About

    Propellant consumption rate of rocket is determined by its exhaust velocity.
    Deep space explorations or future space transport missions require the high exhaust velocity, and it can not be achieved by chemical fuel combustion energy. For these missions, it is necessary to use "Electric Propulsion" which can use electric energy.
    Our laboratory intend to develop the electric propulsion technology with high efficiency and high exhaust velocity using high power.

The Advantage of Electric Propulsion

Fig.1 Chemical propulsion and Electric Propulsion

   The main purpose of rocket engine is to accelerate the rocket by propellant injection and achieve the intended velocity. The requirement of velocity increment DV depends on the missions.
   Electric propulsion enables high exhaust velocity so that it is use for missions required high DV. These engines are able to get high DV with small propellant consumption. In other words, the rate of burden (payload) is increased. (Fig. 1)
   Furthermore, in the missions required extremely high DV such as deep space exploration, it is impossible to get to the destination by chemical propulsion. Ion thruster used for asteroid probe "Hayabusa" returned from Itokawa asteroid in 2010, is one of the electric propulsion systems.

Usefulness of MPD Thruster

Fig.2 Difference of Ion thruster and MPD thruster

   In the electric propulsion systems, the propellant is heated electro thermally, or ionized and accelerated by electric field or magnetic field. Ion thruster can accelerate only ions by Coulomb force in electrostatic field, but it has a limit of current caused by the mutual repulsion of ions.
   Therefore, it can't increase its thrust density. On the other hand, MPD thruster can accelerate both ions and electrons by Lorentz force in the electromagnetic field, so that it can get large thrust density without repulsion. And more, MPD thruster has features compared to other electric propulsion,
   

It has simple configuration

   

Various propellant gases can be used

   

Improvement of thrust is expected when it is applied high-power

For these reasons, MPD thruster is one of the promising candidates for future high-power electric propulsion systems.

Current outcome

Coaxial MPD Thruster	Rectangular MPD Thruster	Rotate Magnetic Field Thruster
We have developed a steady-state, co-axial MPD thruster. Varying propellant mass flow rate, applied magnetic field and discharge current, thruster performance test were conducted. As a result, the thrust efficiency increased under row mass flow rate and high magnetic field. We also find that using co-axial geometry, wear on the cathode is very severe and it influences the thruster operation characteristics.	To prevent cathode erosion, we have developed a MPD thruster using hollow cathode which is durable against ion bombard. Using this cathode, prolonging the thruster life time is expected. Furthermore, we employed rectangular acceleration channel to direct the Lorentz force to the exhaust. To develop a thruster with high thrust efficiency and specific impulse, we are currently working on analyzing thrust efficiency and improving the thruster.	One of our approaches for the problem of erosion of electrode, we developed electrodeless thruster. This thruster has no electrode exposed to the plasma. It can ionize the propellant by inductive heating using high frequency solenoidal coil current. We carefully tune the RF current phase to generate rotating magnetic and make azimuthal current. The interaction between this current and external magnetic field generate Lorentz force and accelerate the propellant.