Performance Study Of Very Low-power Arcjet Thruster

In recent years,the aircrafts are developing constantly toward miniaturization,micro-scale technology and high performance because of rapidly developing and application of information technology and miniaturization technology,steady increase of request for various space mission and the limitation of weight and overall dimension of aircrafts.It also puts forward higher requirements on propulsion systems.Comparing with traditional chemical combustion propulsion,the space electric propulsion has lots of advantages such as high specific impulse,smaller thrust,long service life,significantly improving the quality of the spacecraft payload ratio,long working time and low fabricating cost.Based on this background,our team set up a set of very low power arcjet experiment system in order to study the arcjet that is suitable for small satellites.This paper realized the stable operation of very low power arcjet experiment system and measuring system with nitrogen and argon as propellant.The paper researched discharge conditions in the thruster's nozzle,change of plasma components with different experiment conditions and impact for performance of some factor for very low power arcjet such as gas flow rate,input power,nozzle expansion ratio and the distance between the cathode and anode.This article mainly discusses two thruster's nozzle with different expansion ratio.The work parameters mainly include thrust,arc current,arc voltage,inlet pressure and vacuum chamber pressure.The performance parameters mainly include specific power,specific impulse and thrust efficiency.The experiment result shows thrust would increase with the increase of the specific power and the variation would become more obvious with large gas flow rate.With nitrogen as propellant,the thrust increased 0.14 m N with thruster A,throat length 0.5mm,throat radius 0.3mm and expansion ratio 300,in the gas flow rate of 200 m L/min condition when the arc current increases from 80 m A to 110 m A.With The same arc current increment,the thrust increased 1.3m N in the gas flow rate of 600 m L/min condition.The variations of specific impulse with specific power are similar to variations of thrust with specific power and specific impulse peak would appear with the increase of gas flow rate.The maximum specific impulse is about 196 s with nitrogen as propellant and maximum specific impulse is about 105 s with argon as propellant.Thrust efficiency is reduced with the increase of specific power and maximum thrust efficiency is about 30% with nitrogen as propellant and maximum efficiency is about 17% with argon as propellant.Arc voltage is reduced with the increase of arc current.Arc voltage shows downward trend in small gas flow rate and shows upward trend with the increase of gas flow rate.Through the analysis of various parameters,the results show that the very low power arcjet's discharge might be a hybrid discharge model.It has both glow discharge and arc discharge.The discharge would occur between cathode and anode nozzle contraction under the small gas flow rate and occur between cathode and anode nozzle expansion under the large gas flow rate.Using propellant with low effective molecular mass and low specific heat ratio can make higher cold thrust under the same gas flow rate.The hot specific impulse of thruster is proportional to radication of product of specific power and efficiency.Adopting propellant that has more hydrogen contents is easy to obtain high input power and high specific impulse.The propellant stayed for longer in the anode nozzle expansion with larger expansion ratio under the same expansion cone half angle.It is helpful that high temperature gas becomes full expansion and the electricity more fully change into gas kinetic energy.So use the nozzle with large expansion ratio can promote thruster's thrust,specific impulse and efficiency.If appropriate increase the distance of cathode to anode,the thruster's performance can be improved because it can improve the input power and make the propellant get more electric energy.