TOP > Report & Column > The Forefront of Space Science > 2013 > Geospace Exploration Satellite - ERG Project
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Geospace exploration project to tackle the mysteries of the radiation belt and Geospace storms In order to elucidate particle fluctuation in the radiation belt and the dynamics of the geospace storm, the Exploration of energization and Radiation in Geospace (ERG) satellite project is underway toward a launch in FY2015. The satellite’s orbit is designed to be elliptical, allowing us to directly observe the core of the radiation belt. It will circle the earth in about eight hours. Fig. 2 shows the ERG satellite. The satellite is a scientific one to be launched by Epsilon Launch Vehicle, which launched HISAKI (Spectroscopic Planet Observatory for Recognition of Interaction of Atmosphere) before. ERG will carry a total of nine scientific instruments. As discussed above, plasmas and particles with a wide energy range over six digits are present in Geospace. In order to understand the cross-energy couplings, it is essential to measure the wide energy band. The satellite will measure electrons from 12 eV to 20 MeV and ions from 10 eV to 180 keV per type of ion such as hydrogen and oxygen. This attempt to measure a wide energy range by a single satellite will be almost unprecedented in the world and Japan’s ERG satellite will be the first to realize it. The instrument to observe electrons and ions in the several tens keV energy band will be a pioneering technology developed in Japan and onboard the satellite. The radiation belt where the ERG satellite will fly has a harsh radiation environment because of flying high-energy particles, making it is a tough region to operate and conduct precise scientific observation. The satellite will incorporate various technologies to perform high-accuracy scientific research in such an intense radiation environment. The new technologies demonstrated in the ERG satellite will be utilized in future in even harsher radiation environments such as Jupiter. The satellite will also use instruments to observe various plasma waves and electromagnetic fields in Geospace. The fluctuation of electric fields and magnetic fields in the radiation belt covers a wide range of time scale (i.e. frequency band). The ERG will measure the electric field from the direct current to 10 MHz and the magnetic field up to 10 kHz. In addition, the satellite will include a wave-particle interaction analyzer, the first such device in the world. It is believed that the energy exchange process between plasma waves and electrons, the key to internal acceleration, occurs universally in outer space. Nevertheless, the actual site remains unobserved because the duration of energy exchange is extremely short. For the ERG satellite, we have created a technology to observe electrons at 10 ?sec using original Japanese ideas and techniques. With this technology we will attempt the world’s first direct observation of the energy exchange between plasma waves and electrons and observe the site where high-energy electrons are born. 
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