JEM-EUSO is a new type of observatory that uses the Earth's atmosphere as a detector. It observes transient luminous phenomena taking place in the Earth's atmosphere caused by particles coming from space. The sensor is a super wide-field telescope that detects extreme energy particles with energy above 3.1019 eV. This remote-sensing instrument orbits around the earth every 90 minutes on board the International Space Station at the altitude of approximately 400km. The figure shows an extreme energy particle colliding with a nucleus in the Earth's atmosphere, where it produces an Extensive Air Shower (EAS), consisting of numerous electrons, positrons, and photons. JEM-EUSO captures the moving track, which is revealed by the fluorescent UV photons and reproduces the space development of the EAS.
The launch is foreseen for the 2017. The Mission will last at least 5 years. JEM-EUSO will be operated for three years in Nadir configuration to maximize statistics at the lowest energies in order to cross calibrate with the current generation of ground-based detectors. Then the instrument will be tilted (about 30 0) with respect to Nadir in order to exploit a larger amount of atmosphere and to maximize the statistics of events at the highest energies. JEM-EUSO will significantly increase the exposure to UHECRs compared to the largest ground-based air shower arrays presently in operation.