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Plasma particles and waves are important observation targets in space plasmas for understanding the mechanisms of energy and momentum transfer between waves and particles because space plasmas are essentially collisionless. Multi-point observations are crucial for understanding the spatial–temporal variations of space plasmas. To realize such observations by a large number of satellites, onboard instruments should be miniaturized to reduce their required resources. This paper proposes a small amplifier for plasma particle detectors onboard satellites. This charge-sensitive amplifier converts an electron cloud emitted from the detector, for example a microchannel plate, to a current pulse that can be handled by a time-of-flight measurement circuit to determine the particle velocity and thus mass. The amplifier is realized using application-specific integrated circuit technology to minimize size. Its dimensions are estimated to be $$2120, mathrm{ mu m }times 1680, mathrm{ mu m}$$, which are much smaller than those of a conventional amplifier. The response time of the proposed amplifier has a variation of less than $$1.2, mathrm{ ns}$$ over the range of expected input levels. The amplifier can handle up to $$2times {10}^{7}$$ signals per second and has a sensitivity of $$1.5, mathrm{ V}/mathrm{pC}$$ at $$20, mathrm{^circ{rm C} }$$.

Plasma waves are an important target for satellite-based in situ observation to understand electromagnetic phenomena in space. Recent scientific satellites have carried fast Fourier transform (FFT)-based spectrum receivers; however, such receivers have a disadvantage because they use wideband analog parts. The new receiver overcomes the disadvantage by adding bandlimiting in the first stage of the analog part, and it covers the entire observation frequency range of each band by switching its cutoff frequency. In order to miniaturize circuit size, the new receiver comprises application-specific integrated circuits (ASICs) and a field-programmable gate array (FPGA). The ASIC chip includes the analog part of the receiver and the analog-to-digital converter, and the FPGA includes an FFT module and the controller of the receiver. The proposed spectrum receiver was successfully implemented with a size of 55 mm × 80 mm × 35 mm and a total power consumption of 948.3 mW. The time resolution of the receiver was 112 ms, and the frequency resolutions for frequency bands from 10 Hz to 1 kHz, from 1 kHz to 10 kHz, and from 10 kHz to 100 kHz were 13 Hz, 130 Hz, and 1.3 kHz, respectively. Overall, the developed receiver showed sufficient performance for plasma wave observation.

Plasma waves are important observational targets for scientific missions investigating space plasma phenomena. Conventional fast Fourier transform (FFT)-based spectrum plasma wave receivers have the disadvantages of a large size and a narrow dynamic range. This paper proposes a new type of FFT-based spectrum plasma wave receiver that overcomes the disadvantages of conventional receivers. The receiver measures and calculates the whole spectrum by dividing the observation frequency range into three bands: Bands 1, 2, and 3, which span 1Hz to 1kHz, 1 to 10kHz, and 10 to 100kHz, respectively. To reduce the size of the receiver, its analog section was realized using application-specific integrated circuit (ASIC) technology, and an ASIC chip was successfully developed. The dimensions of the analog circuits were 4.21mm × 1.16mm. To confirm the performance of the ASIC, a test system for the receiver was developed using the ASIC, an analog-to-digital converter, and a personal computer. The frequency resolutions for bands 1, 2, and 3 were 3.2, 32, and 320Hz, respectively, and the average time resolution was 384ms. These frequency and time resolutions are superior to those of conventional FFT-based receivers.

Background: Since conventional one-point observations of plasma phenomena in space cannot distinguish between time and spatial variations, the missions on the basis of multiple-point observations have become the trend. We propose a new system for multiple-point observation referred to as the monitor system for space electromagnetic environments (MSEE). Findings: The MSEE consists of small sensor probes that have a capability to measure electromagnetic waves and transfer received data to the central station through wireless communication. We developed the prototype model of the MSEE sensor probe. The sensor probe includes a plasma wave receiver, the microcontroller, the wireless communication module, and the battery in the 75-mm cubic housing. In addition, loop antennas, dipole antennas, and actuators that are used for expanding dipole antennas are attached on the housing. The whole mass of the sensor probe is 692 g, and the total power consumption is 462 mW. The sensor probe can work with both inner battery and external power supply. The maximum continuous operation time on battery power is more than 6 h. We verified the total performance for electric field measurements by inputting signal to preamplifier. In this test, we found that analog components had enough characteristics to measure electric fields, and the A/D conversion and the wireless transmission worked correctly. In the whole performance for electric fields, the sensor probe has equivalent noise level of - 135 dBV/m/√Hz. Conclusions: We succeed in developing the prototype model of the small sensor probe that had enough sensitivity for electric field to measure plasma waves and the ability to transfer observation data through wireless communication. The success in developing the small sensor probe for the measurement of plasma waves leads to the realization of the multiple-point observations using a lot of small probes scattered in space.