A Cubesat-optimized Magnetic Field Measurement Concept for Operation Beyond Low Earth Orbit

Abstract. This paper presents a CubeSat-optimized measurement concept for magnetic field, which was designed for missions beyond low Earth orbit targeting novel radiation belt studies. The instrument combines a miniaturized three-axis fluxgate sensor on a low‑mass deployable boom together with a compact sensor control unit that implements fully synchronous excitation, sampling, and digital control. A hybrid feedback module integrates three prototype fluxgate feedback microchips that provide low‑noise current sources with selectable full‑scale ranges (±3/±9 mA), enabling vector measurements over ±70 μT while retaining sub‑nT resolution. The boom provides 65 cm standoff from the CubeSat and pointing knowledge of 1°. The designed boom length limits the tolerable magnetic dipole moment inside the CubeSat to 0.05 Am². Extended housekeeping includes voltage supply and thermal monitoring, an additional magneto‑inductive sensor on the sensor control unit for disturbance discrimination, and total ionizing dose tracking. Laboratory characterization demonstrates noise densities of 20–30 pT√Hz at 1 Hz, with 128 vectors per second science data and linearity suitable for near‑Earth fields. As it is a pivotal element in the instrument, the prototype feedback microchip was tested for its radiation response. Heavy‑ion testing showed no single‑event latch‑up up to 100 MeV cm²mg. Single‑event transients as well as single-event upsets were observed and are consistent with rare functional interrupts in the digital part of the signal chain. They are addressable by standard redundancy techniques. X‑ray tests up to 1 Mrad confirm functionality with worst‑case gain and offset drifts of approximately 600 ppmkrad and 1 μAkrad within 0–100 krad. The prototype meets the performance requirements derived from the Foresail‑2 mission concept and demonstrates a path to high‑quality, resource‑efficient magnetometry on 3U–6U CubeSat platforms suitable for operation in the Van Allen belts and other harsh radiation environments.