" EUSO : a Mission from the International Space Station."

O. Catalano 1, A. Petrolini 2, A. Santangelo 1, L Scarsi 1

1 Istituto Astrofisica Spaziale e Fisica Cosmica - CNR, Sezione di Palermo
2 Dipartimento di Fisica dell'Universita' e Sezione INFN , Geneva -on behalf of the EUSO Collaboration.

     The mission "Extreme Universe Space Observatory EUSO" is devoted to the exploration from space of the highest energy processes present and accessible in the Universe, which are directly related to the extreme boundaries of the physical world.

     The observational goal of the mission can be outlined as:

  • Extension of the measurement of the energy spectrum of the Cosmic Radiation beyond the GZK conventional limit (GZK = 5x10^19 eV) to identify possible structural features in the spectral shape. - Increase of the available data-set for E>10^20 eV from the few events available today and the hundreds from the major ground experiments now planned or under construction (Auger) to the several thousands expected from the operational three year lifetime foreseen for EUSO on the ISS.
  • Detailed map of the arrival distribution for the EECRs extended to entire sky (north and south hemispheres).
  • Observation of a possible flux of High Energy Cosmic Neutrinos and opening of the field of high-energy Neutrino Astronomy.
  • Detection and detailed investigation of "Atmospheric Phenomena" such as meteoroids and electrical discharges.

     The corresponding specific goals for science:

  • Nature and source distribution of EECRs at universal scale
  • Information on dark matter distribution
  • Probing of the far/extreme regions of the Universe
  • Information about the validity of the theory of relativity at values of the Lorentz factor >10^11, far beyond the domain reached by the particle man-made accelerators

     EUSO will detect the Extensive Air Showers induced by the Extreme Energy Cosmic Rays and the High Energy Cosmic Neutrino flux looking at the streak of fluorescence light produced within the Earth's atmosphere, and the Cherenkov signal diffused when the shower hits the ground or the top of a cloud.

     Initially EUSO originally submitted to ESA as a Free-Flyer mission in answer to the Announcement of Opportunity for the F2/F3 missions on January 2000, has been approved in March 2001 for a Phase A Study for accommodation on the CEPF (Columbus External Payload Facility) of the ISS EUSO will observe the EAS fluorescence signal looking to Nadir at the dark Earth's atmosphere from its location on the CEPF under a 60j full field-of-view. Fluorescence light will be imaged by a large Fresnel lens optics onto a finely segmented focal plane detector. The segmentation and the time resolution adopted will enable the reconstruction with acceptable precision of the shower energy (< about 30%) and arrival direction (from a fraction of a degree to a few degrees) depending on the energy and on the inclination to the vertical.