During the early hours of September 27 (still the 26th in the United States), at exactly 01:14, Spanish time, NASA’s DART mission (Double Asteroid Redirection Test) will collide head-on with Dimorphosa ‘mini moon’ barely 160 meters in diameter that orbits around a asteroid mayor, Didymos, about 400 meters. The objective of the impact will be to try to change, in a measurable way, the orbit of the small asteroid.
This is the first test of ‘planetary defense’ tried by humanity throughout its history. According to NASA, the time has come to find out whether or not we are capable of deflecting an asteroid that was on a direct collision course with Earth. The impact of DART against the small space rock will be monitored by a small European satellite, LICIACubesat, weighing just 14 kg, manufactured by the Italian Space Agency (ASI). The small spacecraft has traveled coupled to DART since its launch, in November 2021, until just a few days ago, when it separated from the main mission to go, by its own means, to its observation point, located about 55 km away. of Dimorphos.
Later, in 2024, another European ship, Hera, currently under construction, will be launched again towards the same double asteroid to take precise data on its mass and composition. At the same time, it will measure the crater left by DART and help turn this experiment into a truly large-scale method of defense against asteroids.
This Thursday, the European Space Agency (ESA) held an information session to highlight the role played by Europe in this important mission, in which, in one way or another, more than 20 countries have participated.
planetary defense
As explained by Tom Statler, a program scientist at NASA’s Planetary Defense Coordination Office, this is a task that falls on all of us. “The Planetary Defense program aims to locate all potentially dangerous asteroids.” But not only that. Once located, “we will have to see what we can do with them. And that is precisely what the DART mission will do.”
According to Statler, it is an “exciting” experiment during which “two tests will be done in one. The first is to check if the technology is correct, which will be tested in this mission. And the second and more important, seeing what is intended to do has an effect ».
Nancy Chabot, for her part, DART coordination leader, explains that the impact will occur at 6.1 km per second, and that DART, weighing 570 kg, will use its own cameras to locate the point of impact, something that cannot be controlled from the ground. In the last leg of its journey, indeed, DART will rely almost exclusively on its ability to view and process the images it makes of Didymos and Dimorphos to guide the spacecraft toward the asteroid, especially during the last four hours before impact. From then on, in effect, any instructions sent from Earth would take longer to reach the ship than it would take the ship to the asteroid, so DART would have to navigate itself and impact Dimorphos without any human intervention.
During the remaining days until September 26, the ship will carry out observation rounds every five hours, thanks to which the ground team will execute three trajectory correction maneuvers, reducing the margin of error more and more in each one . After the third and final maneuver, which will take place on September 25, about 24 hours before impact, the technicians will know the position of the target with a margin of only 2 km. From there, DART will be entirely on its own to guide itself autonomously to its final collision with the asteroid’s small moon.
What will we see just before impact?
The Dart images will show the double asteroid getting bigger and bigger, until Dimorphos occupies the entire field of view.
As Statler explains, “DART will display everything in real time. The last hour will be spectacular. We will see perfectly Didymos and Dimorphos. Half an hour before, the images will focus on the target, Dimorphos. In the minutes before, Dimorphos will get bigger and bigger as the ship gets closer. We will see photos even a few cm away. It’s all very exciting.”
Meanwhile, and from its vantage point, LICIACubesat will observe everything, from the collision to the crater produced by it, the materials ejected and, of course, the possible variation in the asteroid’s orbit. Simone Pirotta, leader of the LICIACube project of the Italian Space Agency, explains that the images made by the small ship, weighing just 14 kg, can be seen on Earth about 24 hours after impact. “We will have very interesting images of the impact itself, of the dust cloud that it will undoubtedly raise (the plume), but other data will take weeks to verify.”
At what point can the DART mission be said to have been successful? For Statler, “knowing exactly is difficult, we will have to review the data and compare it with that of the ground-based telescopes that will also be observing. We hope to know something in a couple of days, after reviewing the data. But it could take even several weeks to know everything precisely.
Spain, of course, has not been left out of this mission. As one of the three main collaborators of the European Space Agency, our country has contributed with the communications system, and an innovative navigation control system that will allow us to always know exactly the position of the spacecraft with respect to its objective and always have clear “where to fly”. The system, for the first time, will be completely autonomous thanks to the development of new technology.
Later, in October 2024, another European ship, Hera, will be launched towards Didymos and Dimorphos, where it will arrive in December 2026. Its objective will be to provide much more information about the impact and its consequences as well as about the asteroid itself. : its shape, its mass, its composition… Hera will be able to observe the effects of the impact in great detail. By later comparing your data with the real-time data obtained by DART, we will have much more information about the event and the success of the mission.