Science

With the DART asteroid mission, NASA makes its first foray into planetary defense

The first operation to collide a spacecraft with an asteroid will launch on Wednesday (November 24) and see if humans can deflect a potentially disastrous cosmic impact.

For such an ambitious goal, NASA’s project, called the Double Asteroid Redirection Test (DART), had rather humble origins. “I conceived the idea for the mission that became DART on a winter morning in early 2011 while doing stretching exercises in my basement,” said Andrew Cheng, planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Maryland. and principal investigator for DART, he told Space.com.

DART is targeting a near-Earth binary asteroid called Didymos and its lunar Dimorphos: the largest body is about 2,560 feet (780 meters) across, while its companion is about 525 feet (160 m) in size. The plan is for the spacecraft to reach the pair in September or October 2022, when the asteroids are relatively close to Earth, less than 7 million miles (11.2 million kilometers).

Related: If an asteroid really threatened Earth, what would a planetary defense mission look like?

The objective of the mission is to change the course of Dimorphos through what is called a kinetic impact, with DART ramming its target at speeds of approximately 14,760 mph (23,760 kph), several times the speed of a high-powered rifle bullet. . NASA will use ground-based telescopes to monitor asteroids before and after the collision to see how much the impact changes Dimorphos’ orbit around Didymos.

“DART is the first demonstration of a kinetic impactor on an asteroid, and DART is the first test of an asteroid deflection method,” Cheng said. “There has been no other space mission like DART in either respect.”

Cheng’s idea that winter morning in 2011 was to target a binary asteroid rather than a singleton. A kinetic impactor operation targeting a single asteroid would likely require two spacecraft, one to hit the target and the other to monitor the relatively small effects of the collision on the rock’s orbit around the sun.

In contrast, a mission in which researchers hit the smallest member of a binary asteroid with a probe would lead to relatively large changes in the orbit of that rock around its larger partner, which scientists could monitor from Earth. Such a design could require a single spacecraft, which would be less difficult and more cost-effective.

“With a kinetic impactor, we could hope to deflect an asteroid and prevent it from hitting Earth, but this technique has never been tested,” Cheng said. “We don’t know how an asteroid will respond to a high-speed spacecraft impact or how much deflection it will result. This mission will help us answer these questions, and that’s what I find exciting about DART.”

Although neither Didymos nor Dimorphos pose a danger to Earth, a rock as large as Dimorphos, “if it hit Earth, it would be capable of devastating a region the size of a small state,” Cheng said. “It is good that DART tests the kinetic impactor approach before any specific asteroid impact threat is discovered.”

Initially, the DART was conceived as a single conventional rocket, using chemical reactions to boost propulsion. In 2016, the mission changed to also employ NASA’s Evolutionary Xenon Thruster (NEXT-C), which uses electrical energy to accelerate xenon away from the spacecraft to generate thrust. “DART is the first flight for NEXT-C technology,” Cheng said. NASA added that DART could help pave the way for the use of NEXT-C in future missions.

With electric propulsion, the DART spacecraft needed solar panels large enough to generate the required electrical power, so it acquired the Roll-out Solar Arrays (ROSA), which extend about 62 feet (19 meters) from end to end. when they unfold. DART is ROSA’s first deep space mission, Cheng said.

In 2018, DART was changed again with the addition of the cubesat LICIACube from the Italian Space Agency. This miniature probe will fly over Didymos 167 seconds after the DART impact to provide images of the impact and its aftermath.

The technical challenges in developing the ROSAs, as well as the DRACO (Didymos Asteroid and Reconnaissance Camera for OpNav) camera that the spacecraft will use to guide itself towards its target, helped drive the DART impact window from October to November. of 2022.

“DRACO needed to be beefed up to ensure it withstood the stress of the launch, and ROSAs were delayed due to supply chain impacts that resulted from, but were not limited to, the COVID-19 pandemic,” Cheng said.

If DART is successful, the next step is to hit a variety of different asteroids.

“There are many different types of asteroids, not only in terms of composition, but also in terms of their interior surfaces and structures,” Cheng said. “Does the effectiveness of a kinetic impactor depend a lot on these differences?”

In addition, there are other methods to deflect an asteroid. These include nuclear explosives, as well as gravity tractors, in which a robotic probe flies alongside a space rock for months or years, gradually deflecting it from its course by a slight gravitational tug. “What is the best method to use if an asteroid impact threat is discovered one day?” Cheng said.

Finally, successors to DART should explore the speed at which the Earth can respond to imminent threats. “How long does it take to mount an asteroid mitigation space mission and how will it compare to the amount of warning time we can have?” Cheng pointed out.

DART and its successors may one day help answer these vital questions and in doing so help save the planet.

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