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Zuccaro Marchiev aa St. Kliment Ohridski University of Sofia, Bulgaria ba Laboratoire de l’Acc´el´erateur Lin´eaire, Univ Paris Sud-11, CNES/IN2P3, Orsay, France bb APC, Univ Paris Diderot, CNRS/IN2P3, CEA/Irfu, Obs de Paris, Sorbonne Paris Cit´e, France bc IRAP, Universit´ede Toulouse, CNRS, Toulouse, France ca ECAP, University of Erlangen-Nuremberg, Germany cb Karlsruhe Institute of Technology (KIT), Germany cc Ludwig Maximilian University, Munich, Germany cd Institute for Astronomy and Astrophysics, Kepler Center, University of T¨ubingen, Germany ce Institute for Theoretical Physics and Astrophysics, University of W¨urzburg, Germany da Istituto Nazionale di Fisica Nucleare - Sezione di Bari, Italy db Universita’degli Studi di Bari Aldo Moro and INFN - Sezione di Bari, Italy dc Dipartimento di Fisica e Astronomia - Universita’ di Catania, Italy dd Consiglio Nazionale delle Ricerche - Istituto Nazionale di Ottica Firenze, Italy de Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Frascati, Italy df Istituto Nazionale di Fisica Nucleare - Sezione di Napoli, Italy dg Universita’ di Napoli Federico II - Dipartimento di Scienze Fisiche, Italy dh INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica di Palermo, Italy di Istituto Nazionale di Fisica Nucleare - Sezione di Roma Tor Vergata, Italy dj Universita’ di Roma Tor Vergata - Dipartimento di Fisica, Roma, Italy dk Istituto Nazionale di Fisica Nucleare - Sezione di Torino, Italy dl Dipartimento di Fisica, Universita’ di Torino, Italy dm Osservatorio Astrofisico di Torino, Istituto Nazionale di Astrofisica, Italy ea Chiba University, Chiba, Japan eb National Institute of Radiological Sciences, Chiba, Japan ec Fukui University of Technology, Fukui, Japan ed Kinki University, Higashi-Osaka, Japan ee Hiroshima University, Hiroshima, Japan ef Kanazawa University, Kanazawa, Japan eg Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Japan eh Kobe University, Kobe, Japan ei Konan University, Kobe, Japan ej Kyoto University, Kyoto, Japan ek Yukawa Institute, Kyoto University, Kyoto, Japan el National Astronomical Observatory, Mitaka, Japan em Nagoya University, Nagoya, Japan en Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan eo Institute of Space and Astronautical Science/JAXA, Sagamihara, Japan ep Aoyama Gakuin University, Sagamihara, Japan eq Saitama University, Saitama, Japan 2 er Hokkaido University, Sapporo, Japan es Interactive Research Center of Science, Tokyo Institute of Technology, Tokyo, Japan et University of Tokyo, Tokyo, Japan eu High Energy Accelerator Research Organization (KEK), Tsukuba, Japan ev RIKEN Advanced Science Institute, Wako, Japan fa Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Republic of Korea fb Korea Astronomy and Space Science Institute (KASI), Daejeon, Republic of Korea fc Ewha Womans University, Seoul, Republic of Korea fd Center for Galaxy Evolution Research, Yonsei University, Seoul, Republic of Korea ga Universidad Nacional Aut´onoma de M´exico (UNAM), Mexico gb Universidad Michoacana de San Nicolas de Hidalgo (UMSNH), Morelia, Mexico gc Benem´erita Universidad Aut´onoma de Puebla (BUAP), Mexico ha Jan Kochanowski University, Institute of Physics, Kielce, Poland hb Jagiellonian University, Astronomical Observatory, Krakow, Poland hc National Centre for Nuclear Research, Lodz, Poland hd Cardinal Stefan Wyszy´nski University in Warsaw, Poland he Space Research Centre of the Polish Academy of Sciences (CBK), Warsaw, Poland ia Joint Institute for Nuclear Research, Dubna, Russia ib Central Research Institute of Machine Building, TsNIIMash, Korolev, Russia ic Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Russia ja Institute of Experimental Physics, Kosice, Slovakia ka Consejo Superior de Investigaciones Cient´ıficas (CSIC), Madrid, Spain kb Instituto Nacional de T´ecnica Aeroespacial (INTA), Madrid, Spain kc Instituto de F´ısica Te´orica, Universidad Aut´onoma de Madrid, Spain kd Universidad de Alcal´a(UAH), Madrid, Spain ke Universidad Carlos III de Madrid, Spain kf Universidad de Santiago de Compostela, Spain kg Instituto de Astrof´ısico de Canarias (IAC), Tenerife, Spain la Swiss Center for Electronics and Microtechnology (CSEM), Neuchˆatel, Switzerland lb ISDC Data Centre for Astrophysics, Versoix, Switzerland lc Institute for Atmospheric and Climate Science, ETH Z¨urich, Switzerland ma Space Science Laboratory, University of California, Berkeley, USA mb University of Chicago, USA mc Colorado School of Mines, Golden, USA md University of Alabama in Huntsville, Huntsville, USA me University of Wisconsin-Milwaukee, Milwaukee, USA mf NASA - Marshall Space Flight Center, USA mg Vanderbilt University, Nashville, USA 1Corresponding authors: Mario Bertaina (E-mail address: [email protected]), Kenji Shinozaki (E-mail address: [email protected]) Abstract We evaluate the exposure during nadir observations with JEM-EUSO, the Ex- treme Universe Space Observatory, on-board the Japanese Experiment Module of the International Space Station. Designed as a mission to explore the extreme energy Universe from space, JEM-EUSO will monitor the Earth’s nighttime at- mosphere to record the ultraviolet light from tracks generated by extensive air showers initiated by ultra-high energy cosmic rays. In the present work, we dis- cuss the particularities of space-based observation and we compute the annual 3 exposure in nadir observation.