Design, fabrication and test of the iridium catalysed electrolysis (ICE) thrusters

Abstract

The Iridium Catalysed Electrolysis (ICE) thruster concept addresses the growing need for a microscale chemical propulsion system which can cater for the stringent power, propellant and integration requirements of smallsat platforms. In-situ H2/O2 propellant production via water electrolysis is highly suitable for secondary payload satellites especially when direct feed from electrolysers eliminates any requirement for gas phase storage. Two bi-propellant thruster architectures are presented with a common design and fabrication approach but highly disparate design thrust levels of 4.5 mN (ICE-Cube) and 0.7-1.7 N (ICE-200) which each address identified operational and efficiency drawbacks of current electrolysis system architectures. A MEMS-based fabrication approach has been developed and applied in the realisation of each thruster. This includes the qualification of several novel processes, including bulk reactive ion etching of tungsten to etch depths exceeding 500 µm and sputter deposition of iridium onto refractory metal and silicon substrates to serve as an ignition catalyst. This experimentally qualified fabrication process has enabled the realisation of a fully regeneratively cooled thruster chip with a throat width as small as 13 µm and presents an inherently scalable means of manufacturing high-performance, low unit cost chemical thrusters. A representative experimental performance evaluation was carried out on both thrusters supporting the feasibility of the concepts. Cold flow testing demonstrated exceptional Isp efficiencies in both fabricated micronozzles, exceeding 0.93 ± 0.05 for ICE-200 and 0.89 ± 0.08 for ICE-Cube. Hot fire testing provided a representative operational demonstration, with ICE-200 achieving an Isp range between 298.7-388.6 s ± 33.2 s over short duration firing periods and ICE-Cube demonstrating prolonged firing periods exceeding 200 s and an achieved Isp between 181.2-185.4 s ± 32.4 s. This initial performance characterisation has allowed the feasible envelope of microscale electrolysis and bi-propellant thrusters to be widened and provides a validated methodology applicable to design, fabrication and test of these systems.