13:45 〜 14:00
[PCG18-05] Development of fundamental mode orthogonal fluxgate as a small-sized, highly precise magnetometer for future space science missions
★Invited Papers
キーワード：磁力計、磁気センサ、磁場観測、太陽系探査
Magnetic observation from spacecraft plays an important role in space science missions exploring electromagnetic phenomena taking place in space. Spacecraft-borne magnetometers for science missions must satisfy performance requirements often as precise as nT in resolution or lower, while fulfilling strict resource limitations and severe operation conditions. Up to now, parallel fluxgate magnetometers with permalloy ring-core sensors have been the most typical option for vectorial measurement of DC and low frequency magnetic field in space, owing to their low noise characteristics and output offset stability against temperature. Those parallel fluxgate magnetometers bear a lot of heritages from the past missions, yet they are close to technical limitation for further miniaturization of sensors while keeping sufficient performance for scientific objectives. Aiming the upcoming MMX, Comet Interceptor and other future missions where diversifying spacecraft designs and instruments accommodation are assumed, further miniaturization and resource reduction of on-board magnetometers will be of great importance for realization of those missions.
We are now developing a new kind of magnetometer called fundamental mode orthogonal fluxgate (FM-OFG) as a small-sized, highly precise magnetometer for future space science missions. FM-OFG sensor is built simply with one thin pickup coil wound around fine Cobalt-based amorphous wire cores. This simple setup enables the sensor to be small and extremely lightweight (≈1g/axis). FM-OFG sensor is operated with unique “DC-biased AC” sinusoidal excitation current directly passed through the wire core to create circumferential magnetization in the wire, and the pickup coil around the wire cores detects the induced signal reflecting the strength of external magnetic field along the wire’s longitudinal direction. Owing to the DC component in the excitation, circumferential magnetization appearing in the wire becomes unidirectional and saturated, and thus the sensor can avoid picking up Barkhausen noise, which is known to arise during magnetization reversal processes. This is how FM-OFG achieves low-noise characteristic even with a small sensor design. We have employed suitable annealing of the wire cores and proposed novel adjustment methods for ideal sensor operation conditions. Now the sensor obtained temperature stability of 0.013 nT/℃ in wide range of temperature from -60 ℃ to +70 ℃ with low-noise characteristic of ≈12 pT/Hz1/2 @ 1Hz.
The FM-OFG that we developed will be first boarded on Martian Moons Exploration (MMX) mission as one component of instrument called MSA (Mass Spectrum Analyzer). Two sets of tri-axial FM-OFG sensors (named MG-S1 and MG-S2) will be placed separately on the MMX spacecraft panel and will provide background magnetic field information for ion analysis around Phobos. Based on those heritages, we are now designing magnetometer onboard Comet Interceptor (CI) mission. In CI mission, the magnetometer will be boarded together with an ion mass spectrometer as “Plasma Suite” package to observe the unique magnetic phenomena around the target comet, such as diamagnetic cavity appearing in the vicinity of the core and electromagnetic waves excited by cometary plasma. The small and light-weight FM-OFG is especially appreciated in CI mission where several scientific instruments are packed into 24-U cubesat probe. Our challenge not only focuses on to miniaturization of the sensor but also the electronics to operate the sensor. In S-310-46 sounding rocket mission, we will be demonstrating FM-OFG sensor with our newly developed ASIC (Application Specific Integrated Circuit) chip for FM-OFG signal processing circuit. It will contribute to observing Sporadic E layer appearing in the ionosphere, in cooperation with other on-board instruments measuring neutral and charged particles. Employment of ASIC chip will bring further reduction of total size and power consumption of the magnetometer.
We are now developing a new kind of magnetometer called fundamental mode orthogonal fluxgate (FM-OFG) as a small-sized, highly precise magnetometer for future space science missions. FM-OFG sensor is built simply with one thin pickup coil wound around fine Cobalt-based amorphous wire cores. This simple setup enables the sensor to be small and extremely lightweight (≈1g/axis). FM-OFG sensor is operated with unique “DC-biased AC” sinusoidal excitation current directly passed through the wire core to create circumferential magnetization in the wire, and the pickup coil around the wire cores detects the induced signal reflecting the strength of external magnetic field along the wire’s longitudinal direction. Owing to the DC component in the excitation, circumferential magnetization appearing in the wire becomes unidirectional and saturated, and thus the sensor can avoid picking up Barkhausen noise, which is known to arise during magnetization reversal processes. This is how FM-OFG achieves low-noise characteristic even with a small sensor design. We have employed suitable annealing of the wire cores and proposed novel adjustment methods for ideal sensor operation conditions. Now the sensor obtained temperature stability of 0.013 nT/℃ in wide range of temperature from -60 ℃ to +70 ℃ with low-noise characteristic of ≈12 pT/Hz1/2 @ 1Hz.
The FM-OFG that we developed will be first boarded on Martian Moons Exploration (MMX) mission as one component of instrument called MSA (Mass Spectrum Analyzer). Two sets of tri-axial FM-OFG sensors (named MG-S1 and MG-S2) will be placed separately on the MMX spacecraft panel and will provide background magnetic field information for ion analysis around Phobos. Based on those heritages, we are now designing magnetometer onboard Comet Interceptor (CI) mission. In CI mission, the magnetometer will be boarded together with an ion mass spectrometer as “Plasma Suite” package to observe the unique magnetic phenomena around the target comet, such as diamagnetic cavity appearing in the vicinity of the core and electromagnetic waves excited by cometary plasma. The small and light-weight FM-OFG is especially appreciated in CI mission where several scientific instruments are packed into 24-U cubesat probe. Our challenge not only focuses on to miniaturization of the sensor but also the electronics to operate the sensor. In S-310-46 sounding rocket mission, we will be demonstrating FM-OFG sensor with our newly developed ASIC (Application Specific Integrated Circuit) chip for FM-OFG signal processing circuit. It will contribute to observing Sporadic E layer appearing in the ionosphere, in cooperation with other on-board instruments measuring neutral and charged particles. Employment of ASIC chip will bring further reduction of total size and power consumption of the magnetometer.