The JEM-EUSO instrument is a wide-angle refractive telescope in near-ultraviolet wavelength region being proposed for attachment to the Japanese Experiment Module (JEM) onboard International Space Station (ISS). The main scientific goal of the mission is the study of Extreme Energy Cosmic Rays (EECR) above 5 × 1019 eV. The instrument consists of high transmittance optical Fresnel lenses with a diameter of 2.5 m, a focal surface covered by ∼ 5000 Multi Anode Photo Multiplier Tubes of 64 pixels, front-end readout, trigger and system electronics. The EUSO-Balloon experiment is a pathfinder mission in which a telescope of smaller dimension than the one designed for the ISS will be mounted onboard a stratospheric balloon. The main objective of t...