Design, fabrication and testing of miniaturised electrospray thrusters fabricated by two-photon laser lithography

Abstract

The utilisation of electric propulsion systems has become a well-established and integral component of the contemporary space industry, particularly over the past decade. Their enhanced longevity and efficiency render them optimal for use as in orbit propulsion systems for long-term missions and similar endeavours. The number of launches of spacecraft equipped with electric propulsion systems has increased exponentially since 2010 and continues to grow at a steady rate. The necessity for propulsion systems on these satellites is evident; however, established propulsion systems, such as Hall thrusters, are inadequate for the requirements of small- and micro-satellites. It is therefore evident that there is a high demand for specialised micropropulsion systems. One particularly promising technology that may prove capable of satisfying the need for miniaturised propulsion systems are electrospray emitters. Electrospray emitters represent a subcategory of the electrostatic thruster family. The intrinsic design of these devices ensures their compactness, high efficiency, and the ability to circumvent the necessity for external neutralisation. Their operation is based on the extraction of ions from a liquid ion source. The extraction process is facilitated by the application of a strong, localised electric field, which deforms a fluid meniscus into a so-called Taylor cone. At the apex of the Taylor cone, ions are forcibly extracted from the fluid, subsequently exiting the electrospray emitter in the form of a spray of ions, charged droplets, or a jet of charged fluid. The three most common types of emitter are porous, externally wetted, and capillary. The objective of this dissertation is to develop miniaturised capillary emitters. In order to achieve a significant degree of miniaturisation, a micro 3D printing method, referred to as two-photon lithography, is utilised. The emitters and supplementary components of the thruster assembly are manufactured using a polymeric base material. The project entails an investigation of the influence of miniaturisation, as well as the realisation of new emitter designs. Furthermore, an experimental characterisation setup has been designed and implemented for the purpose of testing the fabricated emitters. This encompasses time-of-flight mass spectrometry, optical analysis and current measurements.