Research & Development

Ion Sources for Space Applications

ARC is the world-only supplier of space-proven Liquid-Metal-Ion-Sources (LMIS) using indium as propellant. The ion source consists of a needle or micro-capillary covered with Indium which is heated above the Indium melting point (156.6 ºC). Then a sufficiently high electric potential is applied between the emitter and an extractor electrode until a field strength of about 109 V/m is reached at the tip. The equilibrium between the surface tension and the electric field strength forms a so-called Taylor cone on the surface with a jet protruding due to space charge (see Fig. 1). Atoms are then ionised at the tip of the jet and accelerated out by the same field that created them. The expelled ions are replenished by the hydrodynamic flow of the liquid metal. Propellant tank sizes ranging from 0.22 g up to 30 g were developed.

The ion source is presently used for three applications:

• Active Spacecraft Potential Control (ASPOC): A satellite is charged up positively when exposed to sunlight (photoelectric effect). This can be counterbalanced by emitting positively charged ions that will then reduce the floating potential of the satellite. Our indium LMIS is used for this purpose on a number of satellites.
• Ion Source for Secondary-Ion-Mass Spectrometers: The indium LMIS is used as the core element of a mass spectrometer presently flying on board of the ROSETTA spacecraft. It shall perform an in-situ dust analysis of the comet 67P/Churyumov-Gerasimenko. The name of the instrument is COSIMA.
• Field-Emission-Electric-Propulsion: The ion beam produces a highly controllable thrust that can be used for precision pointing capabilities of spacecraft.

The ASPOC team is lead by the Austrian Academy of Sciences
(www.iwf.oeaw.ac.at/english/research/earthnearspace/cluster/aspoc_e.html) and the COSIMA team is led by the Max-Planck-Institute for Solar System Research
(www.mps.mpg.de/en/projekte/rosetta/cosima/).

Developed more than 25 years ago, Indium LMIS were first successfully tested onboard of the Russian MIR spacestation in 1991 and have since flown on a number of satellites (see Table 1). This makes it the only space-proven LMIS logging more than 12000 hours of combined operation in space on 8 different spacecraft. They have also demonstrated excellent robustness surviving an ARIANE 5 launch failure onboard the CLUSTER satellite. After retrieval from the swamps, ion emission was started with characteristics similar to previous ground testing.