2015.B.4.1. Cathode-less gridded ion thrusters for small satellites

Author(s)

Ane Aanesland (1)
Dmytro Rafalskyi (1)

CNRS- Ecole Polytechnique, France

Session

B.4

Keywords

Electric space propulsion, ion thrusters

Abstract

Electric space propulsion is now a mature technology for commercial satellites and space missions that requires thrust in the order of mN, and with available electric power in the order of kW. Developing electric propulsion for Cubesats are challenging due to the small space and limited available electric power (in the order of 10 W). One of the challenges in downscaling gridded and Hall thrusters is the need to neutralize the positive ion beam to prevent beam stalling. This neutralization is achieved by feeding electrons into the downstream space. In most cases hollow cathodes are used for this purpose, but these are fragile and difficult to implement, and in particular for small systems they are in addition difficult to downscale, both in size and electron current.

We describe here a new alternative ion thruster that can provide low thrust and high specific impulse suitable for mission control of satellites as small as 6 kg. The originality lies in the acceleration principles and based on using a set of grids biased with Radio Frequency voltages (RF). In this case, the same RF power supply is used to generate the plasma, accelerate the ions and provide electron neutralization. The acceleration of ions and neutralization by electrons is achieved by applying an RF voltage to the grid system via a blocking capacitor. This blocking capacitor charges up due to an unequal area or loss surfaces for ions and electrons, forming a dc self-bias. The applied RF voltage is thus rectified into a DC and RF voltage such that ions are continuously accelerated by the DC field while electrons are emitted in brief instants within the RF period. This new thruster is called Neptune and provides the same level of thrust as classical gridded ion thrusters, but without the need of a neutralizer. We will present recent experimental results and define the limitations for downscaling.