First Test Results of the 1 to 15 kW Coaxial HEMP 30250 Thruster

We present a new type of HEMP (High Efficiency Multi Stage Plasma) thruster with a coaxial discharge channel. While maintaining the extreme throttle ability of the cylindrical HEMP thruster concept, the extension towards a coaxial geometry will allow for scaling up to high power and thrust levels as required for orbit raising and station keeping of medium to large geostationary satellites. The first version of a laboratory model named HEMP30250 shall provide a nominal thrust and specific impulse of 250mN and 3000s at an anode efficiency of 55%, respectively. Based on the experience made with our cylindrical HEMP3050 type thrusters models, we expect a wide operational range in applicable discharge voltages from 200 to 2000 V and xenon propellant mass flows from 1 to 15 mg/s, resulting in anode power levels from below 1 up to 15 kW and thrust values of up to 500 mN with only small variations in thrusters efficiency. This is mainly due to the effective plasma confinement provided by the HEMP thruster specific magnetic field topology, where by means of a system of periodically arranged permanent magnets a high density discharge is maintained along the median of the coaxial discharge channel keeping the plasma off the channel walls. As a consequence, thermal losses typically amount only 10% of the electrical input power and are mainly dissipated at the anode rather than at the discharge channel which in addition is kept free from erosion. At this conference we will review the concept of a coaxial HEMP thruster and show design aspects of our HEMP30250 laboratory model DM1. First operational characteristics will be presented and an outlook to future works will be given.