a rocket engine in which the working fluid is accelerated in the plasma state. The ejection velocities of the working fluid that can be attained in a plasma engine are substantially higher than the limiting speeds for ordinary gas-dynamic (chemical or thermal) engines. An increase in the ejection velocity makes possible generation of the required thrust with lower consumption of the working substances; this reduces the mass of the rocket system.

As of 1975, electric-arc jet engines had found practical application in Soviet and American space vehicles. In such engines, electric current from an on-board source is passed through the working fluid, leading to the formation of plasma at temperatures of tens of thousands of degrees. The plasma is then accelerated either gas-dynamically or by the Lorentz force, which arises from the interaction of a current with a magnetic field.

The possibility of designing plasma engines based on other principles is being studied. Models of plasma engines exist in which the acting force is the reactive force from the escape of products of decomposition and vaporization of the surfaces of solids irradiated by high-energy pulses of laser radiation or by pulsed electron beams. A design for a nuclear rocket engine based on a nuclear reactor with gas-phase (more accurately, plasma) fuel elements is also being discussed. The fissionable material in the reactor must be in a plasma state at a temperature of several tens of thousands of degrees. Upon contact with the plasma, the working fluid—for example, hydrogen—will be heated to a corresponding temperature, which will make possible the attainment of ejection velocities of several tens of km per sec.