Mini-EUSO (Extreme Universe Space Observatory) is a small-scale prototype cosmic-ray detector that will measure Earth‘s UV emission and other atmospheric phenomena from space. It will be placed in the International Space Station (ISS) behind a UV transparent window looking to the nadir. The launch is planned this year (2019). Consisting of a multi-anode photomultiplier (MAPMT) camera and a 25 cm diameter Fresnel lens system, Mini EUSO has a 44° field of view (FoV), a 6.5 km² spatial resolution on the ground and a 2.5 ms temporal resolution. In principle, Mini-EUSO will be sensitive to extensive air shower (EAS) from cosmic-rays with energies above 1021 eV.
A mobile, steerable UV laser system will be used to test the expected energy threshold and performance of Mini-EUSO. The laser system will be driven to remote locations in the Western US and aimed across the field of view of Mini-EUSO when the ISS passes overhead during dark nights. It will emit pulsed 355 nm UV laser light to produce a short speed-of-light track in the detector. The brightness of this track will be similar to the track from an EAS resulting from a cosmic-ray of up to 1021 eV. The laser energy is selectable with a maximum of around 90 mJ per pulse. The energy calibration factor is stable within 5 %. The characteristics of the laser system and Mini-EUSO have been implemented inside the JEM-EUSO OffLine software framework, and laser simulation studies are ongoing to determine the best way to perform a field measurement.