The design strategy of an Airwatch mission intended to study cosmic rays at energies above1019 eVis presented. Cosmic Rays having so Extreme Energies (EECR) can be studied through the fluorescence light their showers excite in the Earth’s atmosphere, as seen by a detector mounted on a space platform. According to the Airwatch concept a single detector can be used for measuring both intensity and time development of the streak of fluorescence light produced by the atmospheric shower of an EECR. Both an explorative mission on a small free flyer and a high statistics mission are considered. In order to optimize the design of this space mission, preliminary measurements are forseen with the UVSTAR apparatus flying on the Shuttle and looking at the fluorescence light excited in the atmosphere by a laser. These measurements will provide data for signal to background evaluation. A laboratory measurement of the fraction of ionization energy going in fluorescence light in the air, as a function of pressure, temperature and chemical composition, is also planned. A high intensity X-ray beam will be used for the purpose. This measurement is important in order to evaluate the possibility of detecting GRB impacting on the entire atmosphere. ©1998 American Institute of Physics.