Characterisation of the dielectric properties of the propellants MON & MMH

Future (commercial) satellites will require accurate propellant gauging systems, in order to meet the end-of-life reorbiting requirement and the need for replacement planning. A capacitive Gauging Sensor Unit is currently being developed for the Meteosat Second Generation spacecraft. Its measurement principle is based on the difference of the dielectric properties of the propellant liquid and vapour. To optimise the sensor accuracy, the dielectric properties of propellants need to be accurately known as a function of the temperature (and pressure). Therefore the dielectric properties of MON (Mixed Oxides of Nitrides) and MMH (Mono Methyl Hydrazine) were to be measured. The test setup and the test results are described in detail.