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| ERG (Arase) | |
|---|---|
| Name | ERG (Arase) |
| Namesake | Exploration of energization and Radiation in Geospace |
| Operator | Institute of Space and Astronautical Science |
| Launch date | 2016-12-20 |
| Launch site | Tanegashima Space Center |
| Mass | 350 kg |
| Orbit | Elliptical Earth orbit (apogee ~32,000 km) |
| Instruments | PWE, MGF, S-WPIA, XEP-e, HEP-e, HEP-i, LEP-e, LEP-i, SOKOL |
ERG (Arase) ERG (Arase) is a Japanese satellite mission developed to study Earth's radiation belts, magnetosphere, and space weather processes. Managed by the Institute of Space and Astronautical Science and launched by JAXA using an H-IIA rocket from Tanegashima Space Center, the spacecraft carried a suite of instruments to observe energetic particles, electromagnetic fields, and plasma waves. ERG's data complemented observations from international missions and ground networks to advance understanding of particle acceleration and loss in geospace.
ERG (Arase) was conceived within Japan's space science community, with leadership from ISAS and contributions from the National Institute of Polar Research, University of Tokyo, Tohoku University, Kyoto University, Nagoya University, Osaka University, Chiba University, Kanazawa University, Rikkyo University, Kyushu University, Ibaraki University, Kwansei Gakuin University, Hokkaido University, and industry partners such as Mitsubishi Heavy Industries. The mission focused on dynamics in the Van Allen radiation belts, wave–particle interactions related to chorus and hiss emissions, and coupling between the magnetosphere and the ionosphere. ERG complemented missions like Van Allen Probes, THEMIS, Cluster (spacecraft), MMS (spacecraft), Geotail, and ACE (spacecraft).
Primary objectives included measuring acceleration mechanisms for relativistic electrons in the high-energy particle environment, characterizing plasma wave modes responsible for particle energization, and determining loss processes to the atmosphere. ERG aimed to quantify interactions involving whistler-mode chorus, electromagnetic ion cyclotron waves, and plasma waves observed in coordination with ground arrays such as SuperDARN, Pi2 networks, ATHENA, Jicamarca Radio Observatory, CARISMA, IMAGE (satellite), and facilities like Sakigake and Kaguya (SELENE) for comparative studies. Objectives referenced theoretical frameworks from researchers affiliated with NASA, ESA, CNSA, Roscosmos, and academic centers like Stanford University, MIT, Princeton University, University of California, Berkeley, Imperial College London, and University of Colorado Boulder.
The ERG spacecraft bus integrated payloads developed by multiple institutions: the Plasma Wave Experiment (PWE), the Magnetic Field experiment (MGF), and particle instruments including High-Energy Particle (HEP-e, HEP-i), Low-Energy Particle (LEP-e, LEP-i), X-ray Electron Plasma (XEP-e), and the SOKOL sensor. Data processing electronics and telemetry were built with contributions from NEC Corporation, Mitsubishi Electric Corporation, and research labs at ISAS, JAXA Institute of Space and Aeronautical Science, University of Electro-Communications, Kobe University, Tohoku University, and Nagoya University. Instrument capabilities targeted electron pitch-angle distributions, ion composition, wave electric and magnetic fields, and energy spectra to probe mechanisms proposed in studies by investigators at University of Maryland, Boston University, University of California, Los Angeles, Dartmouth College, University of Iowa, Leeds University, Max Planck Institute for Solar System Research, and CNRS.
ERG was launched on an H-IIA vehicle from Tanegashima Space Center into a high-apogee elliptical orbit with perigee in low Earth altitudes and apogee near the outer radiation belt. The orbit enabled repeated traversals of the outer Van Allen belt, interaction regions near the plasmapause, and passages through the magnetotail. The mission operations used tracking and data relay with stations including Usuda Deep Space Center, Uchinoura Space Center, Svalbard Satellite Station, KSAT, and international partners such as NOAA, EUMETSAT, ESA, KSAT (Kongsberg Satellite Services), and ground magnetometer arrays coordinated with INTERMAGNET.
ERG yielded measurements clarifying rapid electron acceleration through nonlinear wave–particle interactions, confirming theoretical predictions about relativistic electron flux enhancements linked to chorus wave activity. Observations identified localized microburst precipitation into the upper atmosphere consistent with loss to the atmosphere, and quantified pitch-angle scattering by EMIC waves during storm times. ERG data supported joint analyses with Van Allen Probes and MMS (spacecraft) revealing cross-scale coupling between plasma waves and particle dynamics, and provided case studies that matched simulations from groups at Los Alamos National Laboratory, NASA Goddard Space Flight Center, Southwest Research Institute, JHUAPL, University of California, Los Angeles, and Sandia National Laboratories. Results influenced models used by agencies including NOAA Space Weather Prediction Center, JMA, and UK Met Office for space weather forecasting.
Post-launch commissioning included instrument calibrations, mode testing, and initial science operations coordinated by ISAS and mission teams at JAXA. Key mission phases involved baseline science, targeted campaign periods during geomagnetic storms observed by ACE (spacecraft) and DSCOVR, coordinated observations with THEMIS and Cluster (spacecraft), and extended operations focused on seasonal and solar cycle variability. ERG operations adapted to spacecraft health management practices developed in collaboration with Mitsubishi Heavy Industries and control centers at ISAS and JAXA. The mission produced long-term datasets archived for community access and cross-mission synergy with repositories managed by NASA CDAWeb, SPDF, European Space Agency archives, and institutional data centers at ISAS and partner universities.
ERG was a collaborative endeavor with international science teams from USA, Europe, Russia, China, India, and Australia, interfacing with projects like Van Allen Probes, THEMIS, Cluster (spacecraft), MMS (spacecraft), ACE (spacecraft), and ground campaigns involving SuperDARN, INTERMAGNET, CARISMA, and IMAGE (satellite) legacy data. Data sharing policies enabled coordinated analysis through workshops at institutions such as ISAS, ESA, NASA Goddard, University of California, Los Angeles, Stanford University, Imperial College London, and University of Tokyo. ERG datasets remain accessible via science archives maintained by JAXA, ISAS, and international data services to support ongoing research in magnetospheric physics.
Category:Japanese space probes