ASIM is an approved European Space Agency (ESA) project selected in response to a call for flight opportunity issued by the Directorate of Human Spaceflight in December 2002 for external payloads to be flown to and operated onboard Columbus external platforms. The ASIM payload is planned to be taken to the ISS in 2018 and will be in operation observing the Earth atmosphere during two nominal years 2018-20/21. However, since ASIM has no consumables, its operational life time could be extended two more years. ASIM will be carried by the Heavy Transfer Vehicle (HTV), which is a cargo vessel able to carry up to 6 tons of supplies for the space station. The HTV is launched by a rocket, but has its own propulsion system allowing it to maneuver to the space station.

The ASIM instrument will be flown on the Columbus External Platform Facility (CEPF) of the International Space Station (ISS). The ASIM concept was initially proposed by Danish National Space Center (DSNC), with the objective to observe TLEs (Transient Luminous Events) that occur in the Earth's upper atmosphere accompanied by thunderstorms in the lower atmosphere. These TLE events are known as Blue Jets, Giant Blue Jets, Sprites, Halos and Elves and they were first observed in 1989. The ISS at 340 - 400 km altitude is considered a perfect platform from which to enhance our knowledge of them.

When ASIM is mounted on the external pallets of Columbus, the instruments will be turned on by commands sent from the control center in Denmark. The first operational period is used to check if the instruments have survived the violent vibrations experienced during launch. This phase is called the commissioning phase.

If the instruments work properly, the real scientific observational phase can begin. The X and Gamma-ray sensor is on continuously, except during passage of the South Atlantic Anomaly (SAA), where the earth's magnetic field is weak, allowing considerable fluxes of energetic particles to reach the space station. The optical instruments are on during the night time and sunrise/sunset seen from the space station. The instruments capture automatically flashes of activity. Certain observations, such as those taken over the Mediterranean region, are executed as time-tagged commands sent in advance to ASIM.

The ASIM project is headed by the Danish National Space Centre (DNSC) with participation of the Universities of Valencia (Spain) and Bergen (Norway). ASIM was approved for Phase A in 2004, for Phase B in 2006 and for Phase C/D in 2009. The ASIM consortium includes, in addition to the DNSC and the University of Valencia (Spain), the University of Bergen (Norway) and the Universities of Ferrara and Bologna (Italy). The Spanish ASIM team is formed by five groups with more than 30 researchers from five institutions: the Image Processing Laboratory of the University of Valencia (headed by Dr. V. Reglero and co-author of the ASIM original proposal sent to ESA (ASIM/DSRI/PRO/0001), INTA (headed by Dr. M. D. Sabau), University King Juan Carlos (URJC) led by Dr. M. Arrayás, PolyTechnical University of Catalunya (UPC) headed by Dr. J. Montanya and the Institute of Astrophysics of Andalucía (IAA) of the CSIC led by Dr. F. J. Gordillo-Vázquez.

Figure 1: A cartoon with the different types of Transient Luminous Events (TLEs) so far discovered in the atmosphere of the Earth since the first observation in 1989. The occurrence of TLEs is connected to the lightning discharges taking place in the troposphere. The cartoon also includes the Terrestrial Gamma ray Flashes (TGF) discovered in 1994 which origin remain unclear though present theories and observations indicate that electron can be accelerated to large kinetic energies in the electric fields associated with thunderstorms.

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