This special issue of Experimental Astronomy summarises the key activities for the JEM-EUSO space mission, to be operated on board the International Space Station. JEM-EUSO is being designed to unveil the nature and the origin of the ultra-high energy cosmic rays from E > 1019 eV to well beyond 1020 eV. JEM-EUSO will detect the UV light emitted by cosmic-ray generated air-showers in the earth’s atmosphere. JEM-EUSO also addresses basic problems of fundamental physics at energies around 1020 eV, unachievable by man-made accelerators and of atmospheric phenomena.

The JEM-EUSO activities consists of the development of the main mission and of a series of pathfinder experiments. While the JEM-EUSO baseline is being improved some pathfinders have already been developed and are in operation, like the EUSO-Balloon program on board of stratospheric balloons or EUSO-TA deployed on ground in coincident operation with the Telescope Array air-shower experiment.

The articles of this special issue deal with crucial design issues, sub-systems and components of the baseline concept. In addition, the special issue include papers presenting results of detailed simulations and test measurements.

Many of the developments around the JEM-EUSO mission in its baseline configuration, described by the studies presented in this special issue, are of universal interest in the field and relevant for any future space based air-shower detector. The emphasis which the JEM-EUSO Collaboration places on designing, engineering, prototyping, simulating and demonstrating the capabilities of such a mission is apparent from the mixture of the included papers.

We hope that you enjoy this summary of the present JEM-EUSO engineering and related activities, and we thank the authors, i.e., the entire Collaboration, the reviewers and the Experimental Astronomy staff for their assistance in producing the volume.

Andreas Haungs

Gustavo Medina-Tanco

Andrea Santangelo

Guest Editors