MPD Thruster Erosion Research

The multimegawatt MPD (Magnetoplasma Dynamic) thruster is an electric engine capable of orbital transfer and maneuvering of large payloads driven by a megawatt class space power supply. The MPD thruster is capable of specific impulses from 1,500 to 8,000 s. The high specific impulse means this system can perform missions using much less propellant than chemical systems. A five MW MPD electric system, propellant and payload from one shuttle launch must be replaced by the equivalent of four fully loaded Centaur G' stages. Thus, the savings in propellant and launch costs are very substantial. This report discusses 3 aspects of MPD thruster Physics: 1) A significant operational problem which has limited the useful operation of the device is discussed. This is severe erosion of the insulator at the cathode insulator junction. A technique which appears to solve the problem has been tested, and is described. 2) A preliminary analyses of anode sheath is presented. 3) Analysis of the discharges two dimensional nature is explored for the case where transverse gradients are considered but transverse velocity is assumed to be zero. This situation applies to high aspect ratio devices. The analyses concludes with: a) a formalish that provides a means to qualitatively evaluate Ohmic dissipation from simple measurements of magnetic Hall effect on magnetosonic choking (where thermodynamics is ignored).