Ceramic reactor for more eco-friendly satellite propulsion systems

Satellite thrusters are used for attitude control and orbit transfer, as well as end-of-life de-orbiting to avoid space debris. These engines are mostly powered by highly toxic and expen­sive propellants, such as hydrazine, which are increasingly being replaced by more environ­mentally friendly alternatives, such as hydrogen peroxide (H₂O₂).

The induction of the necessary decompositionof H₂O₂ into water and oxygen (oxidizing agent in the combustion process) is currently carried out catalytically. Silver nets or granules coated with platinum or MnO₂ are used for this pur­pose. Apart from its high costs, the fact that the process is not very dynamic causes prob­lems, as satellite engines must work in finely tuned pulses to achieve the required accuracy.

Thermally induced decomposition of H₂O₂ as a green alternative

As an alternative to the catalytically induced decomposition of H₂O₂, thermal induction of the strongly exothermic reaction (T > 1000 °C) is also possible; the reaction then continues to proceed in a stable manner without further energy input. This requires temperatures above 150 °C, but no catalytically active materials.

Additively manufactured and functionalized ceramic components offer a promising approach. The reactor developed at FraunhoferIKTS (image 2) combines several properties that offer significant advantages for the appli­cation scenario. The applied heater structureenables a high-performing induction of the decomposition reaction. The Al₂O₃ used for the substrate is superior to metallic materialsin terms of chemical and thermal resistance and also has a low density. The complex component geometry (image 1) results in a directed fluid flow, which ensures very good mixing and prevents overheating of the exter­nally applied heater structures despite the high reaction temperatures inside.

Combining unique IKTS competences

The manufacturing of the reactor relied on a combination of unique competences of Fraunhofer IKTS. The Al₂O₃ substrate is man­ufactured additively through the CerAM VPP technology followed by sintering at 1650 °C. Subsequently, the heater structure includingthe insulation layer and contact pads was applied by means of rotary screen printing in a thick-film process. The functional materials used for this were then sintered at 850 °C in a second thermal processing step. Finally, wires for electrical contacting were joined by means of adapted micro-welding processes and the assembly points were covered in a thermally stable manner.

Reliable operation up to 400 °C has already been demonstrated in the laboratory. Exten­sive real-life tests are planned for the spring of 2023. Additionally, an expansion of the mate­rial portfolio to Si₃N₄ and AlN is in progress.