High Precision Magnetometer on-board of China Seismo-Electromagnetic Satellite

The China Seismo-Electromagnetic satellite (CSES) is a sun-synchronous orbit satellite with an altitude of 507km, and it is the first platform of Chinese earthquake observation system in space. The High Precision Magnetometer (HPM), which contains two fluxgate sensors and a Coupled Dark State Magnetometer (CDSM), measures the vector of the Earth's magnetic field with a bandwidth from DC to 15Hz. The two fluxgate sensors are in a gradiometer configuration in order to reduce satellite interferences. Additionally, the CDSM sensor measures the scalar value of the magnetic field with higher accuracy and stability, and which can be used to do the in orbit calibration for the vector values.

Several calibration tests have been operated to assess the HPM performances with the standard facility before launching, include the linearity, sensitivity, stability, thermal drift and so on, which can give out the excellent performances of both FGM and CDSM parts. During the commissioning phase, several assessment methods have also been developed for its in-orbit performances, which met the ground calibration results well.

With the benefits of two fluxgate sensors, the ambient magnetic field can be reduced, the vector noise of HPM can be assessed with the difference calculation method. Two main methods were developed to assess the stability of the magnetic field exploration. And the accuracy of vector values and the accuracy of vector directions have been evaluated. With both the ground calibration results and in-orbit assessment performances, the dynamic measurement ranges of HPM is form -70,000nT to +70,000nT. And the vector sensitivity is better than 18pT/Hz^-1/2@1Hz within the bandwidth from DC to 15Hz. With a long term in orbit data analyzing, the vector stability is better than 1nT/month. The vector value accuracy is better than 0.5nT with the vector direction uncertainty is within 0.05 degrees.

All performances show that the HPM can supply the perfect magnetic data both for the earthquake research and space science applications.