Motivation and background

The Iridium Catalysed Electrolysis (ICE) thruster concept is a microscale chemical propulsion system utilising gaseous hydrogen and oxygen propellants fed via a water electrolyzer. The immediate benefits of the system are the ease of storage of a non-hazardous propellant in compact, lightweight tanks as well as the very favorable performance of gaseous hydrogen/oxygen. Water electrolysis also requires only a fraction of the power to achieve the same thrust as comparable electric propulsion devices (0.15 mN/W). However, the most efficient use of electrolysis dictates a stoichiometric mixture ratio of H2/O2 which leads to an exceptionally high flame temperature. This challenging thermal environment has prompted a rethink of conventional designs, with a focus on developing a reliable and cost-effective means of incorporating high-temperature materials. A novel fabrication approach has been developed which utilizes MEMS based manufacturing techniques commonly used in the production of micro-electronics. 

This experimentally quantified fabrication process presents an inherently scalable means of manufacturing a high-performance chemical thruster which can be manufactured in bulk with a reliability and cost which is unattainable by any other means.


The present work experimentally validates the feasibility of this concept, addressing the involved difficulties of regulating efficient combustion while maintaining thermal control in microscale reactor geometries. A numerical model, combining compressible flow dynamics with surface chemistry, heat transfer and friction, has been developed to better understand the unique constraints of the system. This model was then used in the detailed design of two ICE thruster variants which can cater for a wide variation of thrust levels, from 1-2N (ICE-200) to 5mN (ICE-Cube). 

Rendering of ICE-200 and ICE-Cube micro-chemical thrusters and size comparison against a one-pound coin
Figure 1: To-Scale Render of ICE-200 (left) and ICE-Cube (right) Micro-thruste

Both thrusters were fabricated utilizing an in-house developed MEMS fabrication process which uses reactive ion etching to shape refractory metal and silicon wafers to micrometre precision.

These etched features are then sputter-deposited with iridium which serves as an ignition catalyst as well as providing oxidation protection to the walls. Thruster wafers are then joined through diffusion bonding, producing a single component thruster ‘chip’. 


 Obtained and/or anticipated results

An experimental performance campaign has been carried out on the manufactured ICE-200 thruster chips with a series of cold flow and hot fire tests.

These tests involved a plena tank blowdown from a maximum inlet pressure of 85bar with full propellant ignition while recording thrust balance data, thermal imaging, exhaust plume composition as well as the pressure, temperature and mass flow rate of the propellant feed lines. A nozzle efficiency in excess of 90% and a specific impulse of 318s at 50bar was obtained which demonstrates a significant performance advantage over current state-of-the-art hydrazine thrusters.

These primary performance results serve as an initial concept validation for the system architecture and MEMS fabrication approach. The performance testing of the ICE-Cube thruster is currently underway.

Relevant publications

  1. Muir C., Ma C., Knoll A. The design, fabrication and test progress summary of the iridium catalysed electrolysis thruster. Space Propulsion Conference 2020+1, 17 - 19 March 2021.
  2. Muir C., Knoll A. Catalytic Combustion of Hydrogen and Oxygen for an Electrolysis Micro-Propulsion System. Journal of the British Interplanetary Society, ISSN: 0007-084X

Main contact

Charlie Muir