Hera at Didymos: Plan for Two CubeSats and a Close Asteroid Look

ESA's Hera spacecraft and its two CubeSats, Juventas and Milani, are arriving at Didymos and Dimorphos, a double asteroid system. Dimorphos was the target of NASA's DART mission, which crashed into it on purpose in September 2022 to test whether humanity can divert asteroids by giving them a shove.

What Hera will look for

In November, Hera will begin its investigation from a relatively safe distance. It will measure gravity, track orbital motion and map the shape of Dimorphos after the impact. The questions are whether the impact formed a giant crater, cracked the asteroid apart, or changed it in ways no one expected.

A closer approach

Around Christmas, Hera will edge in for a better view, closer than an airliner flying above Earth. It will need to tread carefully: Didymos is the size of a mountain and spins so fast it is almost tearing itself apart.

Releasing the CubeSats

In early 2027 Juventas and Milani will fly the nest. Out at millions of kilometers from Earth there is no mission control to help, so Hera is on its own. The CubeSats will first only part deploy, giving Hera time for one last systems check before letting them go.

Juventas goes first, separating at just a few centimeters a second. In the low gravity, any faster and the CubeSat could drift away for good. Right after separation there is silence: at such close range even a radio signal would be too powerful, so Hera must wait until a signal returns.

The CubeSats at work

Juventas then uses the smallest radar ever flown into space to probe beneath the surface of Didymos. A few weeks later it is Milani's turn, collecting tiny dust particles suspended around Dimorphos to learn about its composition and history.

Both CubeSats report to Hera over a special inter-satellite communication link. Hera relays the data across millions of kilometers back to Earth.