Recent advancements and technology development roadmap of Water Electrolysis Propulsion Thrusters within the Ice2Thrust project

In Water Electrolysis Propulsion (WEP) systems, liquid water is decomposed into gaseous hydrogen and oxygen onboard a spacecraft using an electrolysis unit. Water stands out as a promising, non-toxic green propellant alternative to hydrazine, offering significant potential for cost savings due to easier handling on the ground and better availability. The GH2 and GO2 produced can be used for both chemical (hot-gas & cold-gas) and electrical propulsion, delivering higher performance than other non-cryogenic propellant combinations. With a theoretical chemical specific impulse (Isp) of >400s, additional cost-savings could be achieved through propellant mass reduction. The benefits of using water as propellant can be further leveraged when making use of its simplicity in refilling operations as well as exploiting the in-situ availability of water on celestial bodies. To reap the benefits mentioned, Isp values superior to the hydrazine baseline (~330s) must be demonstrated in practice, which remains a challenge due to the demanding properties of stoichiometric hydrogen/oxygen combustion. Furthermore, reliable and durable ignition is a must to compete with hypergolic propellant combinations. The EU-funded project Ice2Thrust approaches these limitations and to pave the way to establish WEP as a superior alternative to conventional propulsion systems. The activities presented in this paper pertain to the Ice2Thrust project and include the investigation of transpiration cooling as a means to improve the efficiency of the energy conversion in hot-gas thrusters. Following results from a previously published study on the theoretical modelling and performance of the cooling method, an overview of the outcome of a recently conducted transpiration cooling test-campaign is given. An overall agreement between theoretical model and experimental results could be observed. Remaining deviations are discussed and conclusions for the subsequent development roadmap are drawn and presented. Additionally, an analysis of the successfully tested catalytic ignition system is given. A review of the performance achieved and potential for improvement are provided. Repeated ignitions under ambient conditions with good dynamics (ignition delay <50ms) without requiring pre-heating have been demonstrated, while longevity of the catalyst bed remains a challenge. Manufacturing considerations for porous thruster features (required for transpiration cooling) are discussed, and requirements are formulated. First elements of a manufacturing study conducted with industry, including an overview of approach, methodology and results are also provided. A conclusive outlook on the remaining thruster development roadmap within Ice2Thrust and beyond is given, as well as projected performance metrics.