Hera is the European contribution to an international double-spacecraft collaboration. NASA will first perform a kinetic impact on the smaller of the two bodies, then Hera will follow-up with a detailed post-impact survey that will turn this grand-scale experiment into a well-understood and repeatable planetary defence technique.

While doing so, Hera will also demonstrate multiple novel technologies, such as autonomous navigation around the asteroid - like modern driverless cars on Earth, and gather crucial scientific data, to help scientists and future mission planners better understand asteroid compositions and structures.

Due to launch in 2024, Hera would travel to a binary asteroid system - the Didymos pair of near-Earth asteroids. The 780 m-diameter mountain-sized main body is orbited by a 160 m moon, formally christened 'Dimorphos' in June 2020, about the same size as the Great Pyramid of Giza.

Hera will be humanity's first-ever spacecraft to visit a double asteroid, the Didymos binary system. First, NASA will crash its DART spacecraft into the smaller asteroid - known as Didymoon - before ESA's Hera comes in to map the resulting impact crater and measure the asteroid's mass. Hera will carry two CubeSats on board, which will be able to fly much closer to the asteroid's surface, carrying out crucial scientific studies, before touching down. Hera's up-close observations will turn asteroid deflection into a well-understood planetary defence technique.