W and Re ion emitter-crowns and needles for μN space thruster elements manufactured by MIM

Abstract

For very accurate positioning of satellites μN-thrusters are required. These thrusters consist of ion emitters, which are typically made of W or Re. This study focuses on the investigation of needles (diameter 200–400 μm) and emitter-crowns manufactured by MIM. Realizing extremely high aspect ratios (up to 1:200) in combination with controlling of porosity and density gradient in the material is essential for this application and needs to address the following topics: advanced binder system, suitable starting powders, carefully adjusted injection molding parameters. After the development of the injection step, the sintering process and its influence on the densification behavior was studied. The above described application of a space propulsion system needs precise control of porosity and resulting capillary effects within the manufactured W and Re structures. Distinctive open porosity and density gradients were realised including denser cores and porous outer layers. The produced needles and crowns are currently tested for the use in ultra-precise formation flying space systems and terrestrial applications.