Earth's first mission to a binary asteroid, for planetary defense

The planning of humanity's first mission to a binary asteroid system has entered its next phase of engineering. The Hera mission proposed by ESA would also be Europe's contribution to an ambitious planetary defense experiment.

Named in the honor of the Greek goddess of marriage, Hera would fly to the pair of Didymos asteroids: the main body of 780 m in diameter is adorned with a 160 m moon, Informally called "Didymoon", the same size as the Great Pyramid of Giza.

"Such a binary asteroid system is the ideal test bench for a planetary defense experiment but is also an entirely new environment for asteroids. Although binaries account for 15% of all known asteroids, they do not have the same effect. have never been explored before, and we anticipate a lot of surprises, "says Ian Carnelli, director of Hera.

"The very low-gravity environment also presents new challenges for guidance and navigation systems, but we can always count on the unique experience of the Rosetta operations team in the area." ESA, an incredible asset for the Hera mission.

The smallest Didymoon is Hera's main objective: the spacecraft will perform a visual mapping, laser and high-resolution radio of the moon, which will be the smallest asteroid visited up to here, to build detailed maps of its surface and its interior structure.

By the time Hera reaches Didymos in 2026, Didymoon will have acquired historical significance: the first object of the solar system to have its orbit shifted by human effort in a measurable way.

A NASA mission called Dual Asteroid Reorientation Test, or DART, is expected to collide with it in October 2022. The impact will result in a change in the duration of Didymoon's orbit around the main body. Terrestrial observatories around the world will see the collision, but at a minimum distance of 11 million kilometers.

"The essential information will be missing as a result of the impact of DART – that's where Hera intervenes," Ian adds. "Hera's proximity study will give us Didymoon's mass, the shape of the crater, as well as the physical and dynamic properties of Didymoon.

"These key facts collected by Hera will turn a grandiose but unique experience into a well-understood planetary defense technique: a technique that could in principle be repeated if ever we had to stop an incoming asteroid."

The traditional method of estimating the mass of a planetary body is to measure its gravitational attraction on a spacecraft. This is not feasible in the Didymos system: the gravitational field of Didymoon would be overwhelmed by that of his biggest partner.

Instead, Hera imagery will be used to track key landmarks on the surface on the larger body, "Didymain," such as rocks or craters. By measuring Didymoon's "oscillation" with respect to the overall center of gravity of the overall body system, its mass can be determined with an accuracy greater than 90%.

Hera will also measure the crater left by DART at a resolution of 10 cm, achieved through a series of bold flyovers, giving insight into the surface features and internal composition of the asteroid.

"Hera enjoys more than five years of work dedicated to the former ESA asteroid impact mission," commented Ian. "His main instrument is a replica of an asteroid imager that is already flying in space – the framing camera used by NASA's Dawn mission during the Ceres inspection, which is provided by the German Aerospace Center, DLR.

"It will also include a" laser radar "lidar for surface measurement, as well as a hyperspectral imager to characterize surface properties, and Hera will deploy the first deep space CubeSats in Europe to collect additional scientific data and test advanced multi-spacecraft interstations. connections."

NASA's DART mission has passed its preliminary design review and is about to enter its detailed phase C design phase.

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Image: Asteroid Impact Mission Spaceship