Magnetoplasmadynamic Thruster Research.

This program is a follow-on study to a 3-year feasibility investigation of lithium propellant in a steady state electric plasma thruster for eventual use in space propulsion. During the earlier program, accelerator development was largely empirical. The present research is aimed at obtaining a detailed knowledge of the mechanisms in the accelerator, and using this information to design and then test engines operating near their optimum capability. The ALPHA thruster evolved from a large body of practical experience with MPD arc jets and from analytical studies, the results of which have correlated well with experimental measurements. The basic engine mechanism is the electrostatic acceleration of ions through trapped electrons by means of the interaction between applied and induced fields and azimuthal Hall currents. ALPHA differs from most other MPD thrusters in its extended magnetic field, its use of anode-fed lithium as propellant, its use of a buffer, and its replacement of conventional insulators by a device called an isolator. In its most advanced configuration, designated RC-1, the ALPHA thruster is completely radiation cooled. Author