The field of UHECRs (Ultra-High energy cosmic Rays) and the understanding of particle acceleration in the cosmos, as a key ingredient to the behaviour of the most powerful sources in the universe, is of outmost importance for astroparticle physics as well as for fundamental physics and will improve our general understanding of the universe. The current main goals are to identify sources of UHECRs and their composition. For this, increased statistics is required. A space-based detector for UHECR research has the advantage of a very large exposure and a uniform coverage of the celestial sphere.
The aim of the JEM-EUSO program is to bring the study of UHECRs to space.
The principle of observation is based on the detection of UV light emitted by isotropic ﬂuorescence of atmospheric nitrogen excited by the Extensive Air Showers (EAS) in the Earth’s atmosphere and forward-beamed Cherenkov radiation reﬂected from the Earth’s surface or dense cloud tops. In addition to the prime objective of UHECR studies, JEM-EUSO will do several secondary studies due to the instruments' unique capacity of detecting very weak UV-signals with extreme time-resolution around 1 microsecond: meteors, Transient Luminous Events (TLE), bioluminescence, maps of human generated UV-light,
searches for Strange Quark Matter (SQM) and high-energy neutrinos, and more.
The JEM-EUSO program includes several missions from ground (EUSO-TA), from stratospheric balloons (EUSO-Balloon, EUSO-SPB1, EUSO-SPB2), and from space (TUS, Mini-EUSO) employing fluorescence detectors to demonstrate the UHECR observation from space and prepare the large size missions K-EUSO and POEMMA. A review of the current status of the program, the key results obtained so far by the different projects, and the perspectives for the near future are presented.