CALET, an acronym for CALorimetric Electron Telescope, is a Japanese led international space mission by JAXA (Japanese AeroSpace Agency) in collaboration with the Italian Space Agency (ASI) and NASA.  The payload will be launched from Japan by an H-IIB vehicle and will reach the International Space Station (ISS) utilizing the Japanese developed HTV (H-II Transfer Vehicle).





The CALET instrument will be robotically emplaced upon the Exposure Facility (JEM-EF), an external platform of the Japanese Experiment Module (KIBO) on the ISS. Orbiting at an altitude of about 400 Km, the JEM-EF facility allows long-term observations of charged particles (cosmic rays) and high energy photons (gamma rays) coming from space, before they impinge on the upper atmosphere.






The CALET instrument is designed to identify incoming (fully stripped) cosmic nuclei and gamma-rays and to provide high resolution measurements of their energy. With these capabilities, CALET can address many of the outstanding questions in High Energy Astrophysics, including the origin of cosmic rays, their acceleration and propagation in the galaxy and the yet unclear nature of dark matter.  


Long-term observations on the ISS open the possibility to collect rare events at high energies, where the fluxes are remarkably low. Thanks to its energy resolution and discrimination power between hadrons and electrons and between charged particles and gamma rays, CALET will be able to extend and verify the work of predecessor missions on balloons (e.g.: ATIC, CREAM, TRACER) or in space (e.g.: FERMI, PAMELA, AMS).


One of the main scientific goals of the CALET mission is to measure the inclusive spectrum of cosmic electrons and positrons in the energy range from few GeV to about 10 TeV. This measurement might unveil the presence of possible "nearby" sources of high energy electrons located in our Galaxy (within approximately 1 Kpc from the solar system).  


In addition to electron and gamma observations, CALET will be able to extend and improve the presently available direct measurements of the energy spectra and elemental composition of charged cosmic rays pushing the energy frontier to the PeV scale. It will also measure the flux ratios of secondary versus primary cosmic rays (secondary-to-primary ratios) providing crucial information to discriminate among different models of particle propagation in the galaxy. To reach this goal, CALET is equipped with two independent detector systems to measure the electric charge of the incident particle.






On September 18th 2009, after a successful launch, the HTV docked for the first time on the ISS (see picture above) and delivered two scientific payloads (SMILES and HREP) to the JEM-EF.  It was followed by the successful berthings on the ISS of HTV-2 (launched in Jan 2011), HTV-3 (July 2012) and HTV-4 (August 2013).


The foreseen sequence of operations to install CALET on the JEM-EF includes the launch, orbiting and  berthing phases followed by the pick-up and placement of the payload by the robotic arm, as described in the pictures below. 






The CALET payload is in the final phases of preparation for a launch to the ISS where it is expected to take data for 5 years. The instrument will be installed on port #9 of the JEM-EF (picture below).