Abstract
Accurate measurements of ambient planetary and interplanetary magnetic fields using spacecraft magnetometers typically require accounting for interfering magnetic fields generated by the flight system (FS). The most common method for removing FS-generated time-variable magnetic fields is narrow-band and low-pass filtering of magnetic field data in the frequency domain. However, if fluctuations in the ambient field contain frequencies overlapping those in the FS field, it can be difficult to construct a filter that will not affect both signals. Here we present an alternate method for removing FS time-variable signatures from magnetic field measurements. For spacecraft that make use of a magnetic gradiometer (i.e. with two or more instruments on a boom at different distances from the center of the spacecraft), the dominant frequencies in the FS field can be identified using spectra of the differenced field components. The amplitudes of the FS field at those frequencies can then be suppressed without removing spectral peaks present in the ambient field. We demonstrate the successful application of this method, referred to as gradiometry peak suppression, both to modeled data sets and to 128 Hz Venus Express magnetometer data.
Highlights
Spacecraft magnetic field measurements are fundamental for the study of the solar system magnetism including planetary dynamos, planetary induction fields, crustal remanence, the interplanetary magnetic field (IMF) and space weather
To show the details of the peak suppression method described in section 1, we focused on the aforementiond 394.75–453.19 s interval in Model 1 consisting of four flight system (FS) alternating current (AC) contributions
The only packets that were not cleaned effectively are the two intervals with FS field frequencies separated by ⩽0.05 Hz from the ambient field frequency of 1.85 Hz (1.8 Hz and 1.9 Hz)
Summary
Spacecraft magnetic field measurements are fundamental for the study of the solar system magnetism including planetary dynamos, planetary induction fields, crustal remanence, the interplanetary magnetic field (IMF) and space weather. Major sources of FS field contamination are the alternating current (AC) fields (i.e. having frequency, f, typically >0.01 Hz) generated by permanently magnetized and/or highcurrent components such as stepper motors, reaction wheels, communication components, and heaters [1]. This contamination can be reduced by mounting the magnetometer sensors on a boom at the end of which the FS field will be attenuated and by implementing a magnetic cleanliness program during mission design to limit the magnetic moments of individual FS components. Other methods include time-averaging measurements taken by multiple sensors and time-averaging measurements taken by a single sensor to eliminate high-frequency FS fields [2,3,4,5,6,7,8]
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