The Hall effect and rocket flight

Chemical rockets take the random thermal motion of a hot gas generated by combustion and convert it into directed velocity. The maximum speed that can be obtained—usually a few kilometers per second—is limited by the temperature generated by the released chemical energy, typically about 2500 °C. In contrast, plasma rockets, also called plasma thrusters, derive their energy from electricity and expel ions at a velocity that can easily exceed 10 times that of their chemical counterparts. The thrust delivered by the rocket to the spacecraft is equal to the rate of mass discharged from the rocket multiplied by the exhaust velocity. Plasma rockets produce more thrust for a given rate of mass ejection and, hence, transfer more momentum. The plasma advantage is somewhat mitigated by the need to have on-board equipment to generate the electric power. Nonetheless, there has been a dramatic increase in the use of plasma thrusters for...