Research is being conducted worldwide on environmentally friendly alternatives to the toxic hydrazine (N2H4) which is a commonly used propellant for spacecraft. Various alternatives with different technology readiness levels (TRL) are currently being analyzed. As part of the European Space Agency's (ESA) High Performance Propellant Development project, DLR researchers from the Institute of Space Propulsion investigated a promising combination of nitrous oxide (N2O) and ethane (C2H6). This propellant offers high performance and cost-saving potential. It uses less expensive propellant components than hydrazine and due to the use of non-toxic substances, the handling is considerably simplified compared to hydrazine.
HyNOx - good prospects for application in space
To study the propellant characteristics, the DLR team developed and patented a liquefaction and mixing setup at the M11 test facility complex. The setup allows condensation, pressurization and mixing of N2O and C2H6. The liquid fuel mixture "HyNOx" produced in this way was tested for its thermal stability, its compatibility with various materials such as metal alloys or typical sealing materials, its ignition behavior, and its pressure shock sensitivity (waterhammer). In another series of tests under vacuum conditions, the DLR team demonstrated the ignition of the propellant under high altitude conditions.
An important aspect in the design of satellite propulsion systems is a simple, reliable and lightweight propulsion system. Hydrazine as a single propellant component feeds the thruster from only one tank, thus combining sufficient performance with low propulsion system weight. The "HyNOx" propellant has been tested to meet a similar configuration in hot-run tests with a 22-Newton research thruster. The test setup consisted of a tank, a valve and the thruster and thus resembled a typical hydrazine propulsion system.
The "HyNOx" fuel mixture showed consistently positive test results in all the test series conducted and thus forms a solid basis for further developments in terms of premixed, green propellants. The DLR team of scientists derives two recommendations for action from the project: The sensitivity and stability of the propellant must be analyzed in greater depth as well as investigated with further standard tests. Furthermore, the development of engine and propulsion systems with a higher TRL must be advanced to test and ultimately qualify the propellant mixture with all components.