ESA: Hera asteroid spacecraft assembled

Hera is complete — ESA’s asteroid mission for planetary defence was built and prepared in two halves, but now, through a painstaking operation, they have been mated together to make a single spacecraft, ready for full-scale testing of its readiness for space.

Hera will carry two smallsats – Juventas and Milani. These are Europe’s first deep-space CubeSats; they will get closer to Didymos’s companion, Dimorphos, gathering additional data on the asteroid whilst testing new intersatellite link technology. Each companion spacecraft will be small enough to fit inside a briefcase, as compared to the desk-sized Hera. Image is courtesy of ESA.

The mating occurred at OHB Bremen in Germany, with Hera’s Core Module raised more than 3 meters above its Propulsion Module then gradually and carefully slotted into place, over a three-hour period. The modules had been placed in cages to ensure their correct alignment relative to each other down to a few tenths of a millimetre.

Hera is Europe’s contribution to an international planetary defence experiment. Following the DART mission’s impact with the Dimorphos asteroid last year – modifying its orbit and sending a plume of debris thousands of kilometers out into space – Hera will return to Dimorphos to perform a close-up survey of the crater left by DART. The mission will also measure Dimorphos’ mass and make-up, along with that of the larger Didymos asteroid that Dimorphos orbits around.

*Hera’s propulsion module. Photo courtesy of ESA.*

To make its rendezvous with Dimorphos Hera has to lift off in October 2024 — to maximize working time, the mission was constructed by prime contractor OHB as two separate modules, which could be worked on in parallel.

Hera’s Propulsion Module incorporates its propellant tanks – housed within a central titanium cylinder, the ‘backbone’ of the spacecraft – along with piping and thrusters, which will have the job of hauling the mission across deep space for more than two years, then to manoeuvre around Dimorphos and Didymos.

Manufactured together, the Core Module remained at OHB while the Propulsion Module traveled to Avio near Rome in Italy for the addition of its propulsion system. The pair were then reunited in Bremen to prepare for the mating operation.

Once the tip of the Propulsion Module cylinder met the top deck of the Core Module the mating was complete. Then an initial test bolt was inserted to check the alignment was entirely correct in advance of the two modules being fully bolted together.