Design of the Magnetoresistive Magnetometer for ESA’s SOSMAG Project

A prototype of a Service Oriented Spacecraft Magnetometer (SOSMAG) is being developed for European Space Agency´s Space Situational Awareness program, which shall serve as a ready-to-use space weather monitoring system to be mounted on a variety of different spacecraft built without a magnetic cleanliness program. The separation between the natural magnetic field in space and the artificial magnetic field generated by the spacecraft is one of the key issues for its successful performance. The SOSMAG design is based on two types of magnetic sensors. One or two low-noise fluxgate sensors for the required high measurement accuracy will be mounted along a boom of length 1 m, and two anisotropic magnetoresistance (AMR)-based sensors will be used within the spacecraft for detection and characterization of its magnetic disturbances. This paper presents the design and performance of the AMR magnetometer that contains an application-specified integrated circuit (ASIC) and a hybrid sensor as core elements. The magnetometer front-end ASIC, originally developed for National Aeronautics and Space Administration´s Magnetospheric Multiscale mission, is based on a fourth-order sigma-delta A/D converter design. All the active electronics needed for the readout of the AMR sensor and its digitization, as well as for digitizing the magnetometer´s housekeeping data are part of the ASIC. Each of the three-axis hybrid sensors consists of a ceramics circuit board with three HMC1021 sensor elements, one bypass capacitor, a temperature sensor, and a MOSFET driver mounted in chip-on-board technology. A novel approach is used to set and reset the AMR elements. It is done in a narrow-pulsed way at 32 kHz with a pulsewidth of only 238 ns, thus minimizing the required excitation power to 30 mW in total.