Design of an RF ion thruster

[摘要] ENGLISH ABSTRACT: Recent years have seen a decline in the rate of space exploration due to the inefficiencyof chemical rockets. Therefore alternative fuel efficient propulsion methods are beingsought to enable cost effective deep space exploration. The high fuel efficiency of electricthrusters enable a spacecraft to travel further, faster and cheaper than any other propulsiontechnology available. Thus electric propulsion has become the propulsion of choicefor scientists and engineers. A typically electric thruster contains some sort of electrodeto ionise the propellant. Although this is feasible for short space missions, it becomes impracticalfor more ambitious space missions as electrodes erode over time. The alternativeis to ionise the propellant using electromagnetic fields, which eliminates lifespan issuesassociated with electrode based thrusters.In order to examine methods of improving the lifespan and performance of electric thrusters,this thesis aimed to study the method of microwave discharge ionisation for an electricthruster. This includes the design of an RF Ion Thruster with extraction and accelerationgrids to generate thrust. A 600 W 2.45 GHz magnetron (obtained from a conventionalmicrowave oven), coupled to circular TM010 resonant cavity, was used to ionise neutralargon gas. The process of electron cyclotron resonance (ECR) was used to ensure theefficient ionisation of a high density plasma. The thrust was achieved with a three-gridsystem biased at high voltages to accelerate positively charged argon ions to high exhaustvelocities.Results yielded the success of the designed electromagnetic based thruster, measuringapproximatively 1.78 mN of thrust with a specific impulse of Isp = 3786 seconds. TheECR process produced a high plasma density with a plasma absorption rate of approximately77% of the total input microwave power. The final results obtained were foundto match the predicted results extremely well and resembled results found in literature.This demonstrates the efficiency of the RF ion thruster that was designed in this projectand the future use in space exploration activities. However, future research needs to beundertaken on a controlled feedback system that will ensure optimal operating conditionsfor maximum performance. In addition, the method of grid-less acceleration needs to bestudied to achieve maximum thrust and specific impulse.

[发布机构] Stellenbosch University