The European Space Agency’s (ESA’s) first planetary defence spacecraft, Hera, was launched on a SpaceX Falcon 9 rocket from Cape Canaveral Space Force Station in Florida on 7 October 2024 at 10:52 local time.
The automobile-sized Hera will carry out the first detailed survey of a ‘binary’ – or double-body – asteroid, 65803 Didymos, which is orbited by a smaller body, Dimorphos. Hera’s main focus will be on the smaller of the two, whose orbit around the larger asteroid was changed by NASA’s Double Asteroid Redirection Test (DART) mission in 2022, which demonstrated asteroid deflection by kinetic impact.
The Hera mission is to sharpen scientific understanding of the ‘kinetic impact’ technique of asteroid deflection, thus making Earth safer by turning terrestrial asteroid impacts into a fully avoidable class of natural disaster.
The 7 October launch put Hera on a direct departure trajectory away from Earth, beginning its two-year cruise phase. A scheduled manoeuvre next month will be followed by a swing-by of Mars in March 2025, which will give the spacecraft added velocity for its eventual rendezvous with Didymos. During the Mars gravity assist, Hera will perform a survey of Martian moon Deimos, deploying its instruments for scientific use for the first time. Hera’s arrival at Didymos is expected in the autumn of 2026.
“Planetary defence is an inherently international endeavour, and I am really happy to see ESA’s Hera spacecraft at the forefront of Europe’s efforts to help protect Earth,” ESA Director General Josef Aschbacher was quoted as saying in an ESA press release. “Hera is a bold step in scaling up ESA’s engagement in planetary defence,” he added.
Hera will also perform challenging deep-space technology experiments, including the deployment of twin shoebox-sized CubeSats, called Juventus and Milani, to fly closer to the target asteroid, manoeuvring in ultra-low gravity to acquire additional scientific data before eventually landing. The main spacecraft will also attempt ‘self-driving’ navigation around the asteroids based on visual tracking.
The mission’s launch and journey into deep space is being overseen from ESA’s European Space Operations Centre in Darmstadt, Germany.
ESA, together with NASA and other partner agencies, maintains a watch on the sky to identify and track dangerous asteroids that could threaten Earth. On 26 September 2022 NASA’s DART spacecraft performed humankind’s first asteroid deflection by intentionally crashing into Dimorphos, the Great-Pyramid-sized moonlet of the larger, mountain-sized asteroid Didymos, shifting its orbit.
Based on observations from Earth, DART succeeded in shrinking the orbit period of Dimorphos around Didymos by 33 minutes, nearly 5% of its original value, while also casting a plume of debris thousands of kilometres in space.
However, many unknowns remain about the event, which scientists need to resolve in order to help turn this ‘kinetic impact’ method of asteroid deflection into a well understood and reliably repeatable planetary defence technique. Questions that need answering include ‘How big was the crater left by DART’s impact, or did the entire asteroid undergo reshaping?’ and ‘What is the mineralogy, structure and precise mass of Dimorphos?’
An essential component of the Hera mission is the Inter-Satellite Link (ISL) technology supplied by European advanced unmanned aerial technology provider Tekever. The ISL capability deploys a unique communications and relative positioning infrastructure, enabling Hera and the two CubeSats to communicate among themselves and make precise position determinations.
