400-V bus direct driven high power arcjet thruster

Objectives

High power electric propulsion attracts attention because mass transportation to realize massive space transport for building larger structure. An arcjet thruster, which uses Joule heat that is produced by discharge current and plasma resistance, yields higher thrust than the other electric propulsion devices and higher specific impulse than chemical thrusters. The feature provide arcjet thrusters with features of high power electric propulsion .

Moreover, the satellite bus system tend to have larger voltage power supply to effectively transmit electricity, and in the future, the bus voltage will reach 400 V. To drive arcjet, voltage converters are necessary, since conventional arcjet thrusters consumes 100 A class large current with several tens of voltage. Hence, we propose 400-V bus direct driven arcjet thruster; the 10-kW class arcjet thruster is driven by 400-V bus with relatively low current of 30-A class. Now, we vary electrode configuration and structure to design new arcjet thrusters.

Experimental apparatus

Prototype 2-kW class arcjet thruster

A water-cooled arcjet was designed to evaluate dependencies of discharge voltage and power on electrode geometries and flow pattern.

Designed thrust: 200 mN
Propellant: nitrogen (tentative), hydrazine decomposed gas, or ammonia may be used.
Expansion ratio of anode nozzle: 50
Anode: copper, cathode: tungsten, Insulator tubes: ceramic

Vacuum chamber

Figure 1. Vacuum chamber

Figure 1 shows a vacuum chamber 1-m in diam. and 1.5 m in length, in which a pendulum-type thrust stand was placed to evaluate performances (discharge voltage, thruster efficiency, and specific impulse). The thrust stand is a vertical pendulum with the solenoid actuator that damps unnecessary oscillation induced by sudden change in thrust, and the displacement is measured with a laser displacement sensor. From the view point of mechanics, as long as angular displacement is sufficiently small, external forces, aka, thrust is proportional to pendulum angle.

The vacuum chamber simulates the space by reducing back pressure. A dry pump (mechanical booster pump) evacuates the vacuum chamber down to 10 Pa (one to ten thousand of the atmospheric pressure.)

Experimental results

arcjet_impose.mp4

This movie shows the thruster firing at a discharge power of 1 kW with nitrogen propellant.

Google Sites

Report abuse