Study report on the in orbit calibration of the EUSO telescope

The purpose of carrying out in-orbit calibration of the EUSO instrument requires a careful design of the optical setup to measure the performance of lenses and detectors during the EUSO lifetime. Several requirements drive the design, such as weight, power consumption and payload structure, as well as the need of decoupling the optical performance of the lenses from the responsivity of the focal surface detectors. This study report discusses some possible optical arrangements, their limits and impact on the mass and power budget. A possible UV source is also described to get spectroradiometric data on the instrument performance and the advantages or limitations of using independent detectors arranged on the focal surface is discussed.