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The origin and nature of extreme energy cosmic rays (EECRs), which have energies above the 5 ⋅ 10 19 eV —the Greisen-Zatsepin-Kuzmin (GZK) energy limit, is one of the most interesting and complicated problems in modern cosmic-ray physics. Existing ground-based detectors have helped to obtain remarkable results in studying cosmic rays before and after the GZK limit, but have also produced some contradictions in our understanding of cosmic ray mass composition. Moreover, each of these detectors covers only a part of the celestial sphere, which poses problems for studying the arrival directions of EECRs and identifying their sources. As a new generation of EECR space detectors, TUS (Tracking Ultraviolet Set-up), KLYPVE and JEM-EUSO, are intended to study the most energetic cosmic-ray particles, providing larger, uniform exposures of the entire celestial sphere. The TUS detector, launched on board the Lomonosov satellite on April 28, 2016 from Vostochny Cosmodrome in Russia, is the first of these. It employs a single-mirror optical system and a photomultiplier tube matrix as a photo-detector and will test the fluorescent method of measuring EECRs from space. Utilizing the Earth’s atmosphere as a huge calorimeter, it is expected to detect EECRs with energies above 10 20 eV . It will also be able to register slower atmospheric transient events: atmospheric fluorescence in electrical discharges of various types including precipitating electrons escaping the magnetosphere and from the radiation of meteors passing through the atmosphere. We describe the design of the TUS detector and present results of different ground-based tests and simulations.

The High Energy Ray Observatory (HERO) is a project for a space experiment based on an ionization calorimeter to measure the spectrum and composition of cosmic rays. The effective geometric factor of the installation is not less than 12 m 2 sr for protons and not less than 16 m 2 sr for nuclei and electrons. During ~5–7 years of exposure, this mission will measure the element-by-element spectra of cosmic rays in the energy range 10 12 –10 16 eV/particle with a high energy resolution. A Monte Carlo simulation of the experiment using a borated scintillator as a part of the calorimeter is presented.

The current status of the KLYPVE orbital detector of ultrahigh energy cosmic rays, which is scheduled to be deployed on board the Russian module of the International Space Station, is discussed. The main focus is on describing possible optical systems for the instrument.

The main goal of the TUS experiment was to search for and study extremely high-energy cosmic rays with energies EeV. The TUS detector registered a number of unusual events, the origin of which is unclear. The analysis of not similar to EAS and unique anomalous events is the subject of the study presented in this paper.

The main goal of the TUS experiment was to search for and study ultra-high energy cosmic rays with energies E > 70 EeV. The TUS detector registered a number of unusual events, the origin of which is unclear. Events that are unique and not similar to extensive air shower (EAS) are the subject of the study presented in this paper. Events such as gamma-ray bursts (GRBs), out-of-aperture upward going EASs accompanied by lightning flashes, as well as terrestrial gamma-ray flashes (TGFs) are considered as their possible sources.

The main goal of the TUS experiment was to search for and study ultra high-energy cosmic rays with energies E > 70 EeV. The TUS detector registered a number of unusual events, the origin of which is unclear. Events that are unique and not similar to EAS are the subject of the study presented in this paper. Events such as gamma-ray bursts (GRBs), out-of-aperture upward going EASs accompanied by lightning flashes, as well as terrestrial gamma-ray flashes (TGFs) are considered as their possible sources.

The results of the TUS experiment on search and study ultra high-energy cosmic rays with energies E > 70 EeV are analyzed. The TUS detector registered several unusual events of the unclear origin. The analysis of not similar to EAS and unique anomalous events is the subject of the study presented in this paper.

Two types of orbital detectors of extreme energy cosmic rays are being developed nowadays: (i) TUS and KLYPVE with reflecting optical systems (mirrors) and (ii) JEM-EUSO with high- transmittance Fresnel lenses. They will cover much larger areas than existing ground-based arrays and almost uniformly monitor the celestial sphere. The TUS detector is the pioneering mission developed in SINP MSU in cooperation with several Russian and foreign institutions. It has relatively small field of view (±4.5°), which corresponds to a ground area of 6.4 * 103 km2. The telescope consists of a Fresnel-type mirror-concentrator (∼ 2 m2) and a photo receiver (a matrix of 16 x 16 photomultiplier tubes). It is to be deployed on the Lomonosov satellite, and is currently at the final stage of preflight tests. Recently, SINP MSU began the KLYPVE project to be installed on board of the Russian segment of the ISS. The optical system of this detector contains a larger primary mirror (10 m2), which allows decreasing the energy threshold. The total effective field of view will be at least ±14° to exceed the annual exposure of the existing ground-based experiments. Several configurations of the detector are being currently considered. Finally, JEM-EUSO is a wide field of view (±30°) detector. The optics is composed of two curved double-sided Fresnel lenses with 2.65 m external diameter, a precision diffractive middle lens and a pupil. The ultraviolet photons are focused onto the focal surface, which consists of nearly 5000 multi-anode photomultipliers. It is developed by a large international collaboration. All three orbital detectors have multi-purpose character due to continuous monitoring of various atmospheric phenomena. The present status of development of the TUS and KLYPVE missions is reported, and a brief comparison of the projects with JEM-EUSO is given.

The TUS telescope, part of the scientific equipment on board the Lomonosov satellite, is the world’s first orbital detector of ultra-high energy cosmic rays. Preliminary results from analyzing unexpected powerful signals that have been detected from the first days of the telescope’s operation are presented. These signals appear simultaneously in time intervals of around 1 μs in groups of adjacent pixels of the photodetector and form linear track-like sequences. The results from computer simulations using the GEANT4 software and the observed strong latitudinal dependence of the distribution of the events favor the hypothesis that the observed signals result from protons with energies of several hundred MeV to several GeV passing through the photodetector of the TUS telescope.

The TUS orbital experiment is aimed to study energy spectrum, composition and arrival directions of the Ultra High Energy Cosmic Rays (UHECR) at E ~ 1020 eV. The TUS mission is planned for operation at the dedicated \"Mikhail Lomonosov\" satellite. The TUS detector will measure the fluorescence and Cherenkov light radiated by EAS of the UHECR using the optical system – Fresnel mirror-concentrator of 7 modules of ~2 m2 area in total. Status of the Fresnel mirror production, its optical parameters measurement and the TUS trigger system simulation are presented.