Magnetometer in-flight offset accuracy for the BepiColombo spacecraft

Abstract

<jats:p>Abstract. Recently the two-spacecraft mission BepiColombo launched to explore the plasma and magnetic field environment of Mercury. Both spacecraft, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO, also referred to as Mio), are equipped with fluxgate magnetometers, which have proven to be well-suited to measure the magnetic field in space with high precision. Nevertheless, accurate magnetic field measurements require proper in-flight calibration. In particular the magnetometer offset, which relates relative fluxgate readings into an absolute value, needs to be determined with high accuracy. Usually, the offsets are evaluated from observations of Alfvénic fluctuations in the pristine solar wind, if those are available. An alternative offset determination method, which is based on the observation of highly compressional fluctuations instead of incompressible Alfvénic fluctuations, is the so-called mirror mode technique. To evaluate the method performance in the Hermean environment, we analyze four years of MESSENGER (MErcury Surface, Space ENvironment, GEophysics and Ranging) magnetometer data, which are calibrated by the Alfvénic fluctuation method, and compare it with the accuracy and error of the offsets determined by the mirror mode method in different plasma environments around Mercury. We show that the mirror mode method yields the same offset estimates and thereby confirms its applicability. Furthermore, we evaluate the spacecraft observation time within different regions necessary to obtain reliable offset estimates. Although the lowest percentage of strong compressional fluctuations are observed in the solar wind, this region is most suitable for an accurate offset determination with the mirror mode method. 132 h of solar wind data are sufficient to determine the offset to within 0.5 nT, while thousands of hours are necessary to reach this accuracy in the magnetosheath or within the magnetosphere. We conclude that in the solar wind the mirror mode method might be a good complementary approach to the Alfvénic fluctuation method to determine the (spin-axis) offset of the Mio magnetometer. </jats:p>

Error estimate for fluxgate magnetometer in-flight calibration on a spinning spacecraft

“…Modern sensors, which are often double wound and even triple wound, have excellent linearity (typically to an accuracy of about 10 −4 per axis), but this is not always the case. The MAGSAT single-wound sensor (Acuña, 1980;Langel et al, 1982), for example, suffered from about 1 % nonlinearity, and the same sensor design was used more recently on MESSENGER (Solomon et al, 2007;Anderson et al, 2007). With the present thinking about the possibility of deploying large fleets of small-magnetometer CubeSats with just as small sensors one might ask whether nonlinearity issues can arise again.…”

Pick‐Up Ion Cyclotron Waves Around Mercury

“…In Panel (d) the compressibility parameter Q ± reflects the ratio between the compressional and transverse fluctuations of the observed PCWs and is defined as (Schmid et al, 2020):…”

The BepiColombo–Mio Magnetometer en Route to Mercury

“…Uncertainty of the MGF calibration parameters are summarized in Table 3, based on the lessons from in-flight calibration for the spinning spacecraft and offset determination in the spin-axis direction (Plaschke 2019;Schmid et al 2020). Eight parameters (O 1 , O 2 , g, σ Px , σ Py , δθ 1 , δθ 2 , δφ 12 ) can be determined from the in-flight calibration making use of spacecraft spin.…”