November 24, 2021

— After billions of years of asteroids impacting Earth, NASA has taken its first step to strike back.

The Double Asteroid Redirection Test (DART) launched on Wednesday (Nov. 24) will slam into a small space rock — the "moonlet" of a larger asteroid — to slightly knock it off course. The target, Dimorphos, poses no risk to Earth, but changing its orbit will test technologies and generate data to improve our capabilities when the next asteroid is discovered heading toward us.

"It's our first test of planetary defense," Thomas Zurbuchen, NASA's associate administrator for science, said during a pre-launch briefing on Monday (Nov. 22). "It's an intentional crash of a spacecraft into a rock. What we're trying to learn is how to deflect a threat."

The DART probe lifted off atop a SpaceX Falcon 9 rocket from Space Launch Complex-4E (SLC-4E) at Vandenberg Space Force Base in southern California. The spacecraft is comprised of a body smaller than a car (roughly 3.9 by 4.3 by 4.3 feet or 1.2 by 1.3 by 1.3 meters), two very large roll-up solar arrays (27.9 feet, or 8.5 meters long when deployed) and hypergolic and ion propulsion systems.

The launch, at 1:21 a.m. EST (0621 GMT or 10:21 p.m. PST local on Nov. 23), began the countdown to DART colliding with Dimorphos sometime between Sept. 26 and Oct. 1, 2022.

NASA's DART mission launch. Click to enlarge video in a new pop-up window. (NASA)

"Our mission is to hit an asteroid at 15,000 miles per hour [4 miles per second or 6 kilometers per second]. That's tough, that's hard," said Ed Reynolds, DART project manager at Johns Hopkins University Applied Physics Laboratory (APL). "We've worked really, really hard to design a mission that will hit the moon of an asteroid."

Over the next 10 months, the DART probe will cruise toward it target, a binary system formed by Didymos, an asteroid about the same diameter (2,500 feet or 780 meters) as the height of the Burj Khalifa in Dubai, the tallest building on Earth, and Dimorphos, its moonlet, about the size (525 feet or 160 meters) of the High Roller in Las Vegas, the tallest operating Ferris wheel.

"We're going to be doing a lot of tests using our telescope called DRACO [Didymos Reconnaissance and Asteroid Camera for Optical navigation], calibrate it [and] make sure it all works," said Elena Adams, DART systems engineer. "[We will] also demonstrate some new technologies for NASA."

One of those technologies, the Small-body Maneuvering Autonomous Real Time Navigation, or SMART Nav] will be turned on four hours before the spacecraft hits Dimorphos.

"That's what actually allows us to guide ourselves into the asteroid because we don't see Dimorphos at all until about an hour in," said Adams. "The whole time the spacecraft does everything autonomously. Just follows in and then we hit."

If the impact is successful, then it will slow Dimorphos' orbit around Didymos from its known rate of 11 hours and 55 minutes to something less than that.

"We expect to change the period of that asteroid by about 10 minutes," Reynolds said. "So it will go from 11 hours, 55 minutes to 11 hours, 45 minutes and with that we can do a lot of the analysis to determine the effectiveness of using a kinetic impact as a tool, as one of the strategies to protect Earth from asteroid impacts."

A small satellite provided by the Italian Space Agency, LICIACube, or Light Italian CubeSat for Imaging of Asteroids, will be deployed from DART about 10 days prior to the arrival at Dimorphos to follow the spacecraft in and transmit images of the impact and its aftermath.

From there, it will be up to telescopes on Earth to measure the amount Dimorphos has been redirected by observing the change in its orbit.

"The DART spacecraft, the main body of it, is about 100 times smaller than Dimorphos, the asteroid it is targeting, so this isn't going to destroy the asteroid. It is just going to give it a small nudge," said Nancy Chabot, coordination lead.

Although the first probe to attempt to deflect an asteroid, the $330 million DART is one of several NASA missions currently aimed at learning more about the rocks that orbit between the planets. The OSIRIS-REx spacecraft is now on its way back to Earth with the samples it collected last year from asteroid Bennu; the Lucy spacecraft, launched in October, is the first mission to study the Trojan asteroids; and Psyche, set to launch in 2022, will travel to a unique metal asteroid orbiting the Sun between Mars and Jupiter.