Abstract. JEM-EUSO is a space science mission to explore the extreme energies and physics of the Universe. Its instrument will watch the darkside of the earth and will detect UV photons emitted from the extensive air shower caused by an ultra-high energy cosmic ray (UHECR above 10¹⁸ eV), or an extremely high energy cosmic ray (EHECR) particle (e.g. above about 10²⁰ eV). Such a high-rigidity particle as the latter arrives almost in a straight line from its origin through the magnetic fields of our Milky Way Galaxy and is expected to allow us to trace the source location by its arrival direction. This can open the door to new astronomy with charged particles. In its 5 years of operation including the tilted mode, Extreme Universe Space Observatory an Japanese Experiment Module (JEM-EUSO) will detect at least 1000 events with E>7×10¹⁹ eV with the Greisen–Zatsepin–Ku'zmin (GZK) suppression spectrum. It can determine the energy spectrum and source locations of GZK to super-GZK regions with a statistical accuracy of several percent. JEM-EUSO is planned to be deployed by H2 transfer vehicle (HTV) and will be attached to the Japanese Experiment Module/ Exposure Facility (JEM/EF) of International Space Station. JAXA has selected JEM-EUSO as one of the mission candidates of the second phase utilization of JEM/EF for launch in the early-to-mid 2010s.

Received 6 February 2009
Published 30 June 2009