A radiation hardened digital fluxgate magnetometer for space applications

Abstract

Abstract. Space-based measurements of Earth's magnetic field are required to understand the plasma processes responsible for energising particles in the Van Allen radiation belts and influencing space weather. This paper describes a prototype fluxgate magnetometer instrument developed for the proposed Canadian Space Agency's (CSA) Outer Radiation Belt Injection, Transport, Acceleration and Loss Satellite (ORBITALS) mission and which has applications in other space and suborbital applications. The magnetometer is designed to survive and operate in the harsh environment of Earth's radiation belts and measure low-frequency magnetic waves, the magnetic signatures of current systems, and the static background magnetic field. The new instrument offers improved science data compared to its predecessors through two key design changes: direct digitisation of the sensor and digital feedback from two cascaded pulse-width modulators combined with analog temperature compensation. These provide an increase in measurement bandwidth up to 450 Hz with the potential to extend to at least 1500 Hz. The instrument can resolve 8 pT on a 65 000 nT field with a magnetic noise of less than 10 pT/ √Hz at 1 Hz. This performance is comparable with other recent digital fluxgates for space applications, most of which use some form of sigma-delta ( ) modulation for feedback and omit analog temperature compensation. The prototype instrument was successfully tested and calibrated at the Natural Resources Canada Geomagnetics Laboratory.

A miniature, low‐power scientific fluxgate magnetometer: A stepping‐stone to cube‐satellite constellation missions

“…The phase dependence was estimated by using cross power spectral density. No significant loss of sensitivity was observed over this frequency range (Figure 13), reproducing the previously observed flat sensitivity obtained by using an open-loop AC coupled transimpedance amplifier [Miles et al, 2013;Primdahl et al, 1994]. The slight À0.3 dB loss in gain above 10 Hz is likely due to the roll-off of the analog band-pass filter.…”

“…The presented instrument is a power, mass, and volume optimized version of a well-established Canadian fluxgate design [e.g., Narod and Bennest, 1990;Miles et al, 2013;Wallis et al, 2015]. This optimization is fairly straightforward in principle, but in practice, it is increasingly difficult to make the sensor uniform and symmetrical as its size is reduced.…”

“…The CubeSat fluxgate magnetometer described here draws heritage from decades of Canadian instruments, starting with the terrestrial instruments designed by Narod and Bennest [1990]. This design was updated for the Canadian Space Agency Cassiope/e-POP mission as the Magnetic Field Experiment [Wallis et al, 2015] and was further modernized and improved as a principally digital instrument by Miles et al [2013].…”

In situ calibration of offsetting magnetometer feedback transients on the Cassiope spacecraft

“…The MGF is an initial step in adapting a terrestrial fluxgate magnetometer design (Narod and Bennest, 1990) for use in a space application (Miles et al, 2013(Miles et al, , 2017Wallis et al, 2015). The MGF is a classic second harmonic analog fluxgate (e.g., Primdahl, 1979) with the range extended by the application of a variable magnetic offset to the sensor (Fig.…”

“…2). The output of a digital-to-analog converter (DAC) is converted into a temperature-compensated current (Acuña et al, 1978;Miles et al, 2017;Primdahl, 1970) to cancel the majority of the ambient field in the sensor. This allows the forward gain of the instrument to be increased providing 62.5 pT resolution using a 12 bit analog-to-digital converter (ADC).…”