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Description
The thermal infrared imager TIRI was developed for the ESA Hera mission, which was launched on 7 October 2024 by the SpaceX Falcon9 launch vehicle from the Cape Canaveral Space Force Station. Hera will rendezvous with the S-type near-Earth asteroid binary 65803 Didymos and its moon Dimorphos in December 2026, and perform a six-month-long observations there for the purposes of planetary defense and planetary science. The asteroid binary has been imaged from the NASA Double-Asteroid Redirection Test (DART) spacecraft on 26 September 2022, just before its kinetic impact to Dimorphos, so that the hemispherical features of both asteroids and the up-close local surface features of Dimorphos were observed. The ground-based observations showed that the orbit of Dimorphos around Didymos was successfully deflected by the DART impact, but its efficiency remains uncertain because we do not know some key parameters such as the mass, internal structure, cohesion, orbital and rotational motion of the asteroid, the amount of ejecta by DART impact, as well as the surface properties like porosity, strength and geologic features. Most of these parameters are expected to be investigated by Hera.
TIRI is the successor of the TIR on Hayabusa2 (Okada et al. 2017), and based on an uncooled micro-bolometer array (Lynred PICO1024 Gen2) with 1024 x 768 pixels, and covers the FOV of 13° x 10°. TIRI has an 8-position filter wheel, with one wide band at 8-14 µm for thermographic imaging and six narrow bands centered at 7.8, 8.6, 9.6, 10.6, 11.0, and 13.0 µm to characterize composition, crystallinity, or degree of thermal alteration of the surface materials. TIRI will be used to investigate thermophysical properties of Didymos, for the first time as an S-type asteroid, and map physical and compositional properties of Didymos which has relatively flat area at the equatorial regions and rugged regions at the higher latitude regions. TIRI will be also used to study thermophysical properties and surface materials of Dimorphos, including the remnant crop after the DART impact, whether there is an excavated crater or a completely deformed feature. Up-close DART images indicate that Dimorphos is a rubble pile body but we do not know whether the surface boulders are porous or consolidated, and whether its composition is similar to Didymos or not.
The initial in-flight checkout operations just after the Hera launch show that TIRI is healthy and performs well as was shown in the Earth-Moon images. Observations of the Mars and its moons, Deimos and Phobos, are being planned during the Mars Swing By in March 2025, to be used mainly for the in-flight calibration of the instrument, and hopefully for scientific study of the opposite side of Deimos to Mars. The flight spare of TIRI will be provided for the Rapid Asteroid Mission for SpacE Safety (RAMSES) mission led by ESA, to observe the surface thermophysical properties and constituent materials of the S-type Near-Earth asteroid 99942 Apophis before, during, and after its close encounter to the Earth on 13 April 2029.