Project for geotail observation of the elemental and isotopic abundances of heavy energetic particles in solar flares and galactic cosmic rays

GEOTAIL spacecraft, a part of ISTP program, is scheduled to be launched in 1992. It includes a package of High Energy Particle instruments (HEP). Two instruments called MI (Medium energy Isotope telescope) and HI (High energy Isotope telescope) among HEP instruments will dedicate to measure elemental and isotropic compositions in SEPs and GCRs. These two instruments have following key features; exceptionally high sensitivity, excellent isotope resolution and wide dynamic ranges of energy and species. These distinguished features can be realized by the Si detector telescopes by the use of newly developed position‐sensitive detectors with a good position response and of very large Si wafers.