  In this paper we review the main issues that are relevant for the detection
of Extensive Air Showers (EAS) from space. EAS are produced by the interaction
of Ultra-High Energy Cosmic Particles (UHECP) with the atmosphere and can be
observed from an orbiting telescope by detecting air fluorescence UV light. We
define the requirements and provide the main formulas and plots needed to
design and optimize a suitable telescope. We finally estimate its expected
performances in ideal conditions.
