Requirements and Expected Performances of the JEM-EUSO mission

In this paper we describe the requirements and the expected performances of the Extreme Universe Space Observatory (EUSO) onboard the Japanese Experiment Module (JEM) of the International Space Station. Designed as the first mission to explore the Ultra High Energy (UHE) Universe from space, JEM-EUSO will monitor, night-time, the earth's atmosphere to record the UV (300-400 nm) tracks generated by the Extensive Air Showers produced by UHE primaries propagating in the atmosphere. After briefing summarizing the main aspects of the JEM-EUSO Instrument and mission baseline, we will present in details our studies on the expected trigger rate, the estimated exposure, as well as on the expected angular, energy, and Xmax resolution. Eventually, the obtained results will be discussed in the context of the scientific requirements of the mission.