Test Procedure for locally assessing potential risks of sputter damage due to thruster plumes

Abstract

An important issue in the use of thrusters on a satellite is the need to minimize the interaction of the plume with components of the satellite such as solar panels, antennas etc. Part of the danger in case of ion thrusters is the bombardment of the components with atomic particles of the neutralized beam which may, as a primary effect, cause material erosion by physical sputtering and, as a secondary effect, redeposition of the sputtered material on the components. Both may lead to malfunctions such as short-circuits or opaque contamination of solar panels etc. We have designed microstructured test chips for probing the effects of erosion in the plume of an ion thruster which may be used as add-ons in terrestrial lifetime testing in large vaccuum chambers at distances comparable with the dimensions of satellites. The test chips are 5mm×5mm in size on a silicon substrate. A regular pattern consisting out of titanium microstructures, which serve as etch masking during ion bombardment, i.e. protect the underlying silicon in the etching process, is defined on the surface of the test chip by lithographic methods. Removing the remainder of the titanium after the test chip has been exposed to the ion beam and removed from the vacuum chamber allows one to study the height differences between silicon areas which were protected by titanium in the etching process and those directly exposed to the ion bombardment. Such depth profiles are easily obtained by AFM or stylus profilometer measurements and allow one to determine the etch depth into the silicon with great accuracy and with a high lateral spatial resolution and thus to assess the damage caused by the thruster plume. This test chip design is very versatile and can be easily extended to erosion studies of other materials used for components of satellites.