EUSO-SPB (Extreme Universe Space Observatory - Super Pressure Balloon) is the first path- finder mission of the JEM-EUSO program aiming at the detection of the fluorescence light emitted by Extensive Air Shower (EAS) produced by cosmic ray particles in the atmosphere. EUSO–SPB has flown in Spring 2017 from the Wanaka base in New Zealand on board a NASA Super Pressure Balloon planning to reach up to a 100 days of flight, giving, therefore, the opportunity
to observe for the first time a bunch of cosmic ray events with the fluorescence technique from the edge of space. By means of the ESAF (EUSO Simulation and Analysis Framework) package, which is one of the official simulation tools to study the performance of the different pathfinder missions of the JEM-EUSO program, prior to flight, extensive simulations have been carried out
to determine the expected number of detectable events as a function of several parameters related to the detector performance itself (i.e. trigger logic, optics and electronics efficiency), to the
different environmental conditions (i.e. night-glow level, presence of clouds at different heights with variable optical depth) as well as to the launch season and duration of the flight. The main
results of these simulation studies are presented.