**1. Introduction**

When a satellite is placed on a geosynchronous orbit, the attractions of both the Moon and the Sun disrupt the orbit that must be adjusted. Thrusters are used for space missions with regard to the spacecraft station keeping, rephrasing and orbit topping applications. In addition, these kind of devices have implication in partially ionized plasmas (tokamaks), in ionosphere (base of the solar photosphere), in protoplanetary discs, circum nuclear discs in active galactic nuclei and neutron stars. Let us denote *m*\_ *<sup>p</sup>* is the mass flow rate, the exhaust velocity *U* ! *ex* and *g* is the acceleration due to gravity. The performance of thrusters is usually determined by thrust *T*, which is the total force undergone by the rocket. Thrust also has same unit as a force in newton, which shows the movement of the propulsion system. Thrust, is generated

by the burning of fuel or electrostatic forces. The thrust *T* ¼ *m*\_ *pU* ! *ex*, if the mass flow rate is constant. The specific impulse *Isp*is used to compare the efficiencies of different type of propulsion systems [1]. The specific impulse is expressed as *Isp* <sup>¼</sup> *<sup>T</sup> m*\_ *pg* . In general, the higher the specific impulse the less fuel that is required. Therefore the specific impulse simplifies to *Isp* <sup>¼</sup> *<sup>U</sup>* ! *ex <sup>g</sup>* . The specific impulse has the dimension of time and is a measure for the effective lifetime of the thruster. The high value of the specific impulse reduces the mission time.
