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The JAXA’s Martian Moons Exploration (MMX) mission is planned to reveal the origin of Phobos and Deimos. It will remotely observe both moons and return a sample from Phobos. The nominal instruments include the TElescopic Nadir imager for GeOmOrphology (TENGOO) and Optical RadiOmeter composed of CHromatic Imagers (OROCHI). The scientific objective of TENGOO is to obtain the geomorphological features of Phobos and Deimos. The spatial resolution of TENGOO is 0.3 m at an altitude of 25 km in the quasi-satellite orbit. The scientific objective of OROCHI is to obtain material distribution using spectral mapping. OROCHI possesses seven wide-angle bandpass imagers without a filter wheel and one monochromatic imager dedicated to the observation during the landing phase. Using these two instruments, we plan to select landing sites and obtain information that supports the analysis of return samples.

BepiColombo Mio, also known as the Mercury Magnetospheric Orbiter (MMO), is intended to conduct the first detailed study of the magnetic field and environment of the innermost planet, Mercury, alongside the Mercury Planetary Orbiter (MPO). This orbiter has five payload groups; the MaGnetic Field Investigation (MGF), the Mercury Plasma Particle Experiment (MPPE), the Plasma Wave Investigation (PWI), the Mercury Sodium Atmosphere Spectral Imager (MSASI), and the Mercury Dust Monitor (MDM). These payloads operate through the Mission Data Processor (MDP) that acts as an integrated system for Hermean environmental studies by the in situ observation of charged and energetic neutral particles, magnetic and electric fields, plasma waves, dust, and the remote sensing of radio waves and exospheric emissions. The MDP produces three kinds of coordinated data sets: Survey (L) mode for continuous monitoring, Nominal (M) mode for standard analyses of several hours in length (or more), and Burst (H) mode for analysis based on 4–20-min-interval datasets with the highest cadence. To utilize the limited telemetry bandwidth, nominal- and burst-mode data sets are partially downlinked after selections of data based on L- or L/M-mode data, respectively. Burst-mode data can be taken at preset timings, or by onboard automatic triggering. The MDP functions are implemented and tested on the ground as well as cruising spacecraft; they are responsible for conducting full scientific operations aboard spacecraft.

Abstract The Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is a future Japanese space mission with a frequency band of 0.1 Hz to 10 Hz. DECIGO aims at the detection of primordial gravitational waves, which could have been produced during the inflationary period right after the birth of the Universe. There are many other scientific objectives of DECIGO, including the direct measurement of the acceleration of the expansion of the Universe, and reliable and accurate predictions of the timing and locations of neutron star/black hole binary coalescences. DECIGO consists of four clusters of observatories placed in heliocentric orbit. Each cluster consists of three spacecraft, which form three Fabry–Pérot Michelson interferometers with an arm length of 1000 km. Three DECIGO clusters will be placed far from each other, and the fourth will be placed in the same position as one of the other three to obtain correlation signals for the detection of primordial gravitational waves. We plan to launch B-DECIGO, which is a scientific pathfinder for DECIGO, before DECIGO in the 2030s to demonstrate the technologies required for DECIGO, as well as to obtain fruitful scientific results to further expand multi-messenger astronomy.

The Exploration of energization and Radiation in Geospace (ERG) project explores the acceleration, transport, and loss of relativistic electrons in the radiation belts and the dynamics for geospace storms. This project consists of three research teams for satellite observation, ground-based network observation, and integrated data analysis/simulation. This synergetic approach is essential for obtaining a comprehensive understanding of the relativistic electron generation/loss processes of the radiation belts as well as geospace storms through cross-energy/cross-regional couplings, in which different plasma/particle populations and regions are strongly coupled with each other. This paper gives an overview of the ERG project and presents the initial results from the ERG (Arase) satellite.

The Exploration of energization and Radiation in Geospace (ERG) Science Center serves as a hub of the ERG project, providing data files in a common format and developing the space physics environment data analysis software and plug-ins for data analysis. The Science Center also develops observation plans for the ERG (Arase) satellite according to the science strategy of the project. Conjugate observations with other satellites and ground-based observations are also planned. These tasks contribute to the ERG project by achieving quick analysis and well-organized conjugate ERG satellite and ground-based observations.

This study demonstrates the influence of electromagnetic ion cyclotron (EMIC) rising‐tone emissions on relativistic electrons in the inner magnetosphere using data obtained from the Van Allen Probes and Arase satellites. We find that the intense EMIC rising‐tone emissions occur during the increase in the solar wind pressures, creating favorable conditions for triggering nonlinear wave growth. The strong flux drop‐out of relativistic electrons in the parallel directions of the magnetic field, with energies of 0.2–4 MeV, was associated with the wave activity. We calculated the nonlinear triggering conditions and the minimum resonant energy of relativistic electrons interaction with EMIC waves, based on our observations. We conclude that EMIC rising‐tone emissions contribute not only to the rapid loss of MeV electrons through EMIC wave‐particle interactions while extending the resonance energy to a few MeV by broadening bandwidth via nonlinear wave growth but also to interactions with sub‐MeV electrons through the nonresonant effect. Plain Language Summary Electromagnetic ion cyclotron (EMIC) wave‐particle interactions play an important role in controlling the dynamics of the inner magnetosphere, particularly the loss of energetic protons (1–100 keV) and relativistic electrons (several MeV) in the radiation belts. Nonlinear wave growth of EMIC rising‐tone emissions contributes to the rapid loss of relativistic electrons and ring current ions. Remarkably, EMIC rising‐tone emissions meet the nonlinear triggering conditions driven by the compressed dayside magnetosphere. Significant decreases in relativistic electrons in the parallel direction to the magnetic field are associated with the wave activity. The present result provides new insights into the dynamics of the inner magnetosphere, including radiation belts, by EMIC WPI. Key Points Nonlinear EMIC waves observed in the dayside uniform zone, caused by solar wind compression, meet conditions for the nonlinear wave growth The significant flux drop‐out of electrons within energies of 0.6–4 MeV was associated with the intense EMIC rising‐tone emissions Nonlinear EMIC emissions cause a rapid loss of MeV electrons by nonlinear effect and extend scattering to sub‐MeV by nonresonant effect

The medium-energy particle experiments—electron analyzer onboard the exploration of energization and radiation in geospace spacecraft measures the energy and direction of each incoming electron in the energy range of 7–87 keV. The sensor covers a 2π-radian disklike field of view with 16 detectors, and the full solid angle coverage is achieved through the spacecraft’s spin motion. The electron energy is independently measured by both an electrostatic analyzer and avalanche photodiodes, enabling significant background reduction. We describe the technical approach, data output, and examples of initial observations.

This paper reports the design, calibration, and operation of high-energy electron experiments (HEP) aboard the exploration of energization and radiation in geospace (ERG) satellite. HEP detects 70 keV–2 MeV electrons and generates a three-dimensional velocity distribution for these electrons in every period of the satellite’s rotation. Electrons are detected by two instruments, namely HEP-L and HEP-H, which differ in their geometric factor (G-factor) and range of energies they detect. HEP-L detects 70 keV–1 MeV electrons and its G-factor is 9.3 × 10−4 cm2 sr at maximum, while HEP-H observes 0.7–2 MeV electrons and its G-factor is 9.3 × 10−3 cm2 sr at maximum. The instruments utilize silicon strip detectors and application-specific integrated circuits to readout the incident charge signal from each strip. Before the launch, we calibrated the detectors by measuring the energy spectra of all strips using γ-ray sources. To evaluate the overall performance of the HEP instruments, we measured the energy spectra and angular responses with electron beams. After HEP was first put into operation, on February 2, 2017, it was demonstrated that the instruments performed normally. HEP began its exploratory observations with regard to energization and radiation in geospace in late March 2017. The initial results of the in-orbit observations are introduced briefly in this paper.

The medium-energy particle experiments–ion mass analyzer (MEP-i) was developed for the exploration of energization and radiation in geospace (ERG) mission (Arase), in order to measure the three-dimensional distribution functions of the inner-magnetospheric ions in the medium energy range between 10 and 180 keV/q. The energy, mass, and charge state of each ion are determined by a combination of an electrostatic energy/charge analyzer, a time-of-flight mass/charge analyzer, and energy-sensitive solid-state detectors. This paper describes the instrumentation of the MEP-i, data products, and observation results during a magnetic storm.

The extremely high-energy electron experiment (XEP) onboard the Arase (ERG) satellite is designed to measure high-energy electrons in the Earth’s radiation belts. The XEP was developed by taking advantage of our technical heritage of high-energy particle detectors that are onboard Earth observation satellites of the Japan Aerospace Exploration Agency (JAXA) as the radiation monitor. The main target of the XEP is to precisely measure variations of relativistic electrons in the outer radiation belt even during magnetic storms. The measurement is scientifically required to address physical mechanisms of electron acceleration and loss. The XEP consists of five solid-state silicon detectors (SSDs) and a single-crystal inorganic scintillator of cerium-doped gadolinium orthosilicate (GSO) to measure electrons in the energy range of 0.4–20 MeV and has a 20° single field of view (FOV). It is also equipped with a plastic scintillator that surrounds the GSO scintillator to prevent particles from entering the detectors from outside the FOV. The XEP has started its observation of relativistic electrons and has successfully observed dynamic variations of relativistic electron fluxes in the outer radiation belt during magnetic storms. This paper describes the instrumentation of the XEP and presents an example of initial observation results.