ESA’s first planetary defense spacecraft has departed planet Earth. The Hera mission is headed to a unique target among the more than 1.3 million known asteroids in our Solar System the only body to have had its orbit shifted by human action to solve lingering mysteries associated with its deflection.
By sharpening scientific understanding of the ‘kinetic impact’ technique of asteroid deflection, Hera aims to make Earth safer. The mission is part of a broader ambition to turn terrestrial asteroid impacts into a fully avoidable class of natural disaster.
Developed as part of ESA’s Space Safety program and sharing technological heritage with the Agency’s Rosetta comet hunter, Hera lifted off on a SpaceX Falcon 9 from Cape Canaveral Space Force Station in Florida, USA, on 7 October at 10:52 local time (16:52 CEST, 14:52 UTC) with its solar arrays deploying about one hour later.
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, demonstrating asteroid deflection by kinetic impact, in 2022.
“Planetary defense is an inherently international endeavor, and I am really happy to see ESA’s Hera spacecraft at the forefront of Europe’s efforts to help protect Earth. Hera is a bold step in scaling up ESA’s engagement in planetary defense,” said ESA Director General Josef Aschbacher.
Hera and its CubeSats connected by inter-satellite links
Hera will also perform challenging deep-space technology experiments including the deployment of twin shoebox-sized ‘CubeSats’ to fly closer to the target asteroid, maneuvering 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 by ESA’s European Space Operations Centre in Darmstadt, Germany.
“Hera is finally on its way to Didymos; today we are writing a new page of space history,” said Hera mission manager Ian Carnelli. “This deep space mission took shape from contract signing to launch in only four years, a testimony to the hard work and dedication of the Hera team across ESA, European industry, science, and the Japanese space agency JAXA. But the underlying idea of a planetary defense mission based on one spacecraft impacting an asteroid with a second that gathers data goes back two decades, with a significant contribution made by the late Prof. Andrea Milani, a pioneer in asteroid risk monitoring whose name has been lent to one of Hera’s two onboard CubeSats.”
NASA’s DART mission was created to help answer that question. On 26 September 2022, the 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 kilometers in space.
With a cube-shaped main body measuring approximately 1.6 m across and flanked by twin 5-m solar wings, the Hera spacecraft is ESA’s contribution to this international planetary defense collaboration. Once it reaches the Didymos binary asteroid in two years, the mission will perform a close-up ‘crash scene investigation’ to gather all the necessary knowledge.
“Hera’s ability to closely study its asteroid target will be just what is needed for operational planetary defense,” explains Richard Moissl, heading ESA’s Planetary Defence Office. “You can imagine a scenario where a reconnaissance mission is dispatched rapidly, to assess if any follow-up deflection action is needed. We should soon be practicing this again with our Ramses spacecraft, a proposed planetary defense mission to rendezvous with the Apophis asteroid during its close approach to Earth in 2029.”
Size guide to Hera and its target asteroids
Around 100 European companies and institutes across 18 ESA Member States have been involved in developing the Hera mission. OHB System AG led the industrial consortium, including responsibility for the overall spacecraft design, development, assembly, and testing.
Hera will perform the most detailed exploration yet of a binary asteroid system. Although binaries make up 15% of all known asteroids, none has ever been surveyed in detail. In addition, the Dimorphos asteroid is the smallest body yet visited by a space mission while Didymos is a fast spinner for its size, coming close to the limits of structural stability given its dimensions.
The Milani CubeSat, developed for ESA by Italian industry led by Tyvak International, will survey the mineral makeup of Dimorphos and its surrounding dust, while the Juventas CubeSat, produced by a Luxembourg-led consortium under GOMspace, will perform the first subsurface radar probe of an asteroid. Late in its six-month asteroid survey, Hera will also test out an experimental self-driving mode that will allow it to navigate around the asteroids autonomously based on monitoring of surface features.
The launch put Hera on a direct departure trajectory away from Earth, beginning its two-year cruise phase. A scheduled maneuver next month will be followed by a swingby 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 the Martian moon Deimos, deploying its instruments for scientific use for the first time. The arrival at Didymos is foreseen for autumn 2026 when the asteroid mission will enter its main science and technology demonstration phase.
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