Research & Development

Field Emission Thrusters (FEEP

Field emission thrusters are currently considered for a large variety of space missions in both Europe and the Unites States. They offer low thrust noise and high controllability combined with a very high specific impulse (up to 8000 seconds) enabling ultra-high precision pointing capabilities. Such thrusters are required for scientific drag-free and constellation missions such as

• LISA Lathfinder (sci.esa.int/science-e/www/area/index.cfm?fareaid=40)
• LISA (sci.esa.int/science-e/www/area/index.cfm?fareaid=27)
• DARWIN (sci.esa.int/science-e/www/area/index.cfm?fareaid=28)

This enables the detection of gravitational waves as well as the detection of planets outside of our solar system.

The core of our FEEP thruster is the indium Liquid-Metal-Ion-Source (LMIS). Indium has a number of significant advantages such as being inert on atmosphere, non-toxic and the fact that the propellant is solid during launch due to its melting point at 156°C. The LMIS can therefore withstand high vibration loads which has already been demonstrated during many previous launches. In addition to the ion source, a neutraliser (electron source) is required to maintain the spacecraft floating potential. A single LMIS can produce a thrust up to about 12 µN. Larger thrusts require clustering of LMIS. Together with our industrial partner Astrium (http://cs.space.eads.net/sp/), we are developing a FEEP cluster assembly for the LISA Pathfinder spacecraft that can produce a thrust up to 100 µN.

Basic Performance Characteristics of a Single In-FEEP Thruster Element

* Depending on power supply used, lower values possible
** Using the present reservoir size of 30 g, larger sizes are possible
*** Comparing the current to the emitter with the current in the ion beam (minus extractor and plume shield current losses)

Key achievements of our research so far includes:

• Successful lifetime tests for a cluster of 2 LMIS up to 4800 h and for a cluster of 8 LMIS up to 2000 h. A total impulse of 370 Ns could be demonstrated. Extensive lifetime modelling (erosion of the LMIS needle) shows that our thruster can be operated more than 20000 hours.
• Thrust resolution in the nano-Newton range.
• Extremely low thrust noise compatible with the present LISA requirements.
• Tested together with all available neutraliser options (thermionic, carbon nanotube, field emission).
• Development of focusing electrodes to achieve a half-angle beam divergence of  25° at maximum thrust.

We are also investigating if FEEP thruster can be miniaturized. In 2004 we were the first to demonstrate firing of a MEMS In-FEEP thruster prototype featuring 400 single thrusters on an area of only 5x5 mm (see Fig. 2).

Recent Publications:

• Tajmar, M., Scharlemann, C., Genovese, A., Buldrini, N., Boss, M., Frueholz, H., and Killinger, R., "Indium FEEP Micropropulsion Subsystem for LISA Pathfinder", AIAA Joint Propulsion Conference, AIAA-2006-4826, 2006
  
  
• Genovese, A., Buldrini, N., Andres, K., and Tajmar, M., "5000h Endurance Test of an Indium FEEP 2x2 Cluster", AIAA Joint Propulsion Conference, AIAA-2006-4827, 2006
  
  
• Tajmar, M., "Influence of Taylor Cone Size on Droplet Generation in an Indium LMIS", Applied Physics A, Vol. 81, No. 7, 2005, pp. 1447 - 1450
  
  
• Marhold, K. and Tajmar, M., "Direct Thrust Measurement of In-FEEP Clusters", International Electric Propulsion Conference, IEPC-235, 2005
  
  
• Tajmar, M., "Development of a Lifetime Prediction Model for Indium FEEP Thrusters", AIAA Joint Propulsion Conference, AIAA-2005-4386, 2005
  
  
• Vasiljevich, I., and Tajmar, M., "Development of a Focus Electrode for an Indium FEEP Thruster", AIAA Joint Propulsion Conference, AIAA-2005-4384, 2005
  
  
• Genovese, A., Buldrini, N., Tajmar, M., Tamas, E., Vasiljevich, I., Marhold, K., and Ruedenauer, F., "Indium FEEP Cluster Development", AIAA Joint Propulsion Conference, AIAA-2005-4385, 2005
  
  
• Tajmar, M., "Indium Capillary Liquid-Metal-Ion-Source Operation in the Flow Resistance Regime", Journal of Physics D: Applied Physics, Vol. 37, 2004, pp. 3057
  
  
• Genovese, A., Tajmar, M., Buldrini, N., and Steiger, W., "2000h Endurance Test of an Indium FEEP Microthruster Cluster", AIAA Journal of Propulsion and Power, Vol. 20, No. 2, 2004, pp. 219-227
  
  
• Tajmar, M., Genovese, A., and Steiger, W., "Indium FEEP Microthruster Experimental Charactization", AIAA Journal of Propulsion and Power, Vol. 20, No. 2, 2004, pp. 211-218
  
  
• Tajmar, M., and Genovese, A., "Experimental Validation of a Mass Efficiency Model for an Indium Liquid Metal Ion Source", Applied Physics A, Vol. 76, No. 6, 2003, pp. 1003-1006 (Rapid Communication)