Testing Green Propellants with Existing Systems

Currently, hydrazine is the most commonly used propellant in satellite thrusters. Hydrazine is a toxic and corrosive fuel that is dangerous to handle and store. In a quest to replace hydrazine with a more environmentally friendly fuel, ESA initiated the study of green propellants and propulsion systems that can provide better performance than hydrazine without the toxicity. These propellants could help lower costs by eliminating infrastructure needed for handling toxic fuels and reducing processing time, consequently making it less expensive, safer and easier to launch spacecraft. A high performance green propulsion system will keep both the environment and the workforce safe from contamination at reduced mission costs.

An ESA activity with European Astrotech Ltd in the UK has investigated the compatibility between a variety of current and future materials and weld combinations with these promising new green propellants.

By using materials already present in propulsion systems, the activity is anticipating that it will help to reduce the modifications needed in current systems, keeping costs lower and development times shorter.

The activity assessed five propellants in detail and many more in less depth. Overall, the testing was combined with extensive materials tests to successfully identify the compatibility of up to ten welded materials with two green propellants called LMP-103S and HTP.

The activity showed that LMP-103S had good compatibility with all 10 of the chosen welded materials, it was also easy to handle and store, while HTP was shown to be incompatible with Titanium.

The tests assessed the degradation of the welds, materials and the propellants over eight months at an elevated temperature – equivalent to 5.33 years on-orbit (similar to relevant mission durations). Degradation could be anything; from if, the welds broke to if materials lost mass, or were etched or polished by the propellant. Only two material samples decomposes more than the control sample, and even these showed far less degradation than that seen with hydrazine meaning any of the weld and material samples would be suitable for use in a propulsion system, even for a long-duration mission.

T724-405QT closed in November 2020.