Accuracy of the Scalar Magnetometer aboard ESA's JUICE Mission

Abstract. The paper discusses the accuracy of the scalar Coupled Dark State Magnetometer on board the Jupiter Icy Moon Explorer (JUICE) mission of the European Space Agency. The scalar magnetometer, referred to as MAGSCA, is part of the J-MAG instrument. MAGSCA is an optical, omni-directional scalar magnetometer based on coherent population trapping, a quantum interference effect, within the hyperfine manifold of the ⁸⁷Rb D₁ line. The measurement principle is only based on natural constants and therefore, it is in principle drift free and no calibration is required. However, the technical realisation can influence the measurement accuracy. The most dominating effects are heading characteristics, which are deviations of the magnetic field strength measurements from the ambient magnetic field strength. The verification of the accuracy and precision of the instrument is required to ensure its compliance with the performance requirement of the mission: 0.2 nT (1-σ). The verification is carried out with four dedicated sensor orientations in a Merritt coil system, which is located in the geomagnetic Conrad observatory. The coil system is used to compensate the Earth’s magnetic field and to apply appropriate test fields to the sensor. This paper presents a novel method to separate the heading characteristics of the instrument from residual (offset) fields within the coil system by fitting a mathematical model to the measured data. It allows verifying that the MAGSCA sensor unit does not have a measurable remanent magnetisation as well as that the desired accuracy of 0.2 nT (1-σ) is achieved by the MAGSCA flight hardware for the JUICE Mission.