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 was launched from Japan in 2015 by an H-IIB vehicle and reached the International Space Station (ISS) with the Japanese developed HTV (H-II Transfer Vehicle).
The CALET instrument was 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 is verifying the observation of predecessor missions on balloons (e.g.: ATIC, CREAM, TRACER) or in space (e.g.: FERMI, PAMELA, AMS-02) and extending them to higher energies.
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 is extending in energy and improving 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 is also measuring the flux ratios of secondary versus primary cosmic rays (secondary-to-primary ratios) which provide crucial information for discriminating among different models of particle propagation in the galaxy. In order to reach this goal, CALET has been 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 the 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 sequence of operations that were follwed 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 was launched from the Tanegashima Space Center (Japan) on August 19, 2015 at 20:50:49 (local time) and reached the ISS on August 24. The Transfer Vehicle HTV-5 "Kounotori" docked at the International Space Station at 6:28 (ET). The instrument was installed on port #9 of the JEM-EF (picture below).
