Performance characteristics and power requirements of existing electron-bombardment thrustors are presented in a form useful to electric-prop ulsion-system analysis and design. This information is based on experimental operation of laboratory thrustor modules of from 5-50 cm in diam and module and array power levels of up to 30 kw. Static and dynamic controls characteristics of electron-bombardment thrustors are summarized. From these data, it is evident that no serious problems should arise in control-syste m design. A thrustor circuit design is described which suppresses electric breakdowns to a magnitude sufficiently small to eliminate damaging interaction between the thrustor and the power-con version system. This circuit design is based on data obtained in operation of single thrustor modules and large thrustor arrays. It is shown that power-con version and thrustor weights and performance penalties could reduce the payload of a 500-kw, 28,500-lb Mars-orbiter vehicle by 5000 to 9000 Ib.