The Hera Milani Mission: Use of a Nanosatellite for Planetary Defence Purposes

Hera is the European part of the Asteroid Impact & Deflection Assessment (AIDA) international collaboration with NASA who is responsible for the DART (Double Asteroid Redirection Test) kinetic impactor spacecraft. Hera has been launched in October 2024 and will arrive at the binary asteroid (65803) Didymos, which includes the main body Didymos and its small moon Dimorphos, in fall 2026. The Hera mothercraft accommodates two 6U CubeSats, one of which is Milani, named after Professor Andrea Milani, for his unique contribution to asteroid science and visionary role in defining a viable planetary defence technique. The Milani CubeSat is developed by Tyvak International leading a consortium of European universities, research centers and firms from Italy, Czech Republic, Finland. During the cruise to Didymos (ongoing, the total duration is approx. 2 years), the Milani CubeSat is hosted inside the Hera mothercraft, periodically checked for health, and charged. At arrival it will be deployed and commissioned while Hera is performing the Didymos detailed characterization phase, at about 10 to 20 km distance from the asteroid. Milani mission objectives are defined to add scientific value to the Hera mission: i) Map the global properties of Didymos and Dimorphos, ii) Characterize the asteroids' surface, iii) Evaluate the effects of the DART impact on the binary system and support gravity field determination, iv) Characterize the dust environment around the asteroid, enhancing the scientific return of the whole Hera mission. The instruments supporting the mission are "ASPECT" (VTT, Finland), a visible - near-infrared imaging spectrometer,"VISTA" (INAF, Italy), a thermogravimeter characterizing dust particles below 10 mu m, and the NavCam (PoliMi/Tyvak, Italy), providing optical images in RGB bands.