When a spacecraft encounters an asteroid and nobody is there to see it, has it left a crater? The ESA wants to avoid such issues by sending its unmanned Hera orbiter to Didymos' binary asteroids to investigate the effects of the Double Asteroid Redirection Test (DART) mission to test the potential for potentially dangerous asteroids from to distract the earth.

The likelihood that the Earth will be hit by a huge asteroid is small, but the effects of such a collision can reach as far as a planetary catastrophe. Therefore, a number of space agencies collaborate on projects to discover, track and even combat asteroids possible threats.

A promising counter-strategy would be to change the path of the attacking asteroid and put it on a less dangerous trajectory. But that's one of those plans that say you have to blow the flute at one end and brush your fingers up and down the holes – that's not so easy. There are all kinds of variables to consider, including orbital parameters of the asteroid, distance, speed, composition and shape.

And then there's an important sticking point: no one has ever tried to move a celestial object before. To remedy this, NASA launches its unmanned DART mission in June 2020. Their target is Didymos' binary asteroid system, which consists of a 780-meter-wide main body known informally as "Didymain". Surrounded by 1.2 km (3,900 ft), the 160-meter high moon is "Didymoon", which is "only" about the size of the Great Pyramid of Giza.

The idea is that in October 2022 the DART spacecraft will hit the refrigerator at about 13,420 mph (21,600 km / h) in Didymoon. The hope is that this influence shifts the orbit of the smaller asteroid by a fraction of a degree. While Earth's ground stations, 11 million kilometers away, will monitor the effects, a second probe is still needed to study the asteroids and determine the consequences of the event, as well as gather general data on binary asteroids.

"Such a binary asteroid system is the perfect testbed for a planetary defense experiment, but it's also a whole new environment for asteroid investigations," says Hera manager Ian Carnelli. "Although binaries make up 15 percent of all known asteroids, they have never been explored before, and we expect many surprises." The extremely low gravity environment also poses new challenges for the guidance and navigation systems, and fortunately we can count on the unique experience. " ESA's Rosetta Task Force, which is of great benefit to the Hera mission. "

Hera will launch in November 2023 and will provide the required observation platform when she enters orbit in December 2026 at Didymos. The 800 kg spacecraft is about the size of a large desk and powered by a series of solar cells. He uses hydrazine engines for the drive and also has a fully autonomous navigation system, with which he can perform orbital maneuvers in Darmstadt, regardless of the mission control.

In addition, Hera has a range of sensors, including a high-resolution imager, a spectroscope, a laser mapping system, and radio experiments, which allow him to obtain a detailed map of the smaller asteroid, its internal structure, and the 10-m (33- ft) Crater DART will drop – making Didymoon the first natural object in the solar system whose orbit becomes measurable through human effort.

Along with the mapping, Hera will determine some of the basic features of the smaller asteroid, like its mass. Since Didymoon's gravitational force is superimposed on that of Didymain, Hera will take a series of pictures of the larger asteroid to measure how much he wobbles under the influence of the smaller asteroid. This allows astronomers to calculate their exact orbit and thus their mass.

If all of this were not enough, Hera will be the first European mission to use CubeSats in space. At the station, Hera will deploy a pair of minisatellites that will be able to travel into tighter, more risky orbits around the asteroids to make their own observations.

"Essential information is missing after the DART Impact – this is where Hera comes in," says Carnelli. "Hera's close-up will show us the mass of Didymoon, the shape of the crater, and the physical and dynamic properties of Didymoon." "These key data collected by Hera will turn into a well-understood, one-off experiment into a well-understood planetary defense technique: one that will be repeated in principle if we ever have to stop an incoming asteroid. "

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