The sudden disappearence of a star brings a wealth of information on small Solar System objects. ACROSS targets challeging stellar occultations.By exploiting the the immense accuracy of Gaia stellar data we can now predict and observe events by Near Earth Asteroids. Our projects support the DART and Hera missions, by targeting in particular occultations by the asteroid Didymos. The support of the amateur community and the organisation of specific campaign are at the core of our project.