What To Know About NASA's Asteroid Impact Mission To Test Earth's Defences

NASA is completing preparations for the November 23 launch of Earth's first planetary defense system designed to protect us from asteroid impacts. The Double Asteroid Redirection Test (DART) spacecraft has been fueled and final tests are almost complete with rehearsals for the launch ongoing, the space agency revealed on Thursday.

DART will head towards the double asteroid system Dimorphos and Didymos, almost 7 million miles from Earth. Upon arrival, it will crash into Dimorphos while traveling at a speed of around 15,000 miles per hour. The aim of the impact is to test if such a collision can change the orbit of the asteroid system.

Neither the asteroid Didymos nor Dimorphos, the small moonlet that orbits it, poses a threat to Earth. But by striking the latter and measuring the effects of that impact with telescopes here on Earth, NASA researchers can see how effective such an impact would be on an asteroid that is on a collision course with our planet.

NASA's planetary defense officer Lindley Johnson said in a press release: "DART will be the first demonstration of the 'kinetic impactor' technique in which a spacecraft deliberately collides with a known asteroid at high speed to change the asteroid's motion in space.

"This technique is thought to be the most technologically mature approach for mitigating a potentially hazardous asteroid, and it will help planetary defense experts refine asteroid kinetic impactor computer models, giving insight into how we could deflect potentially dangerous near-Earth objects in the future."

If all goes according to plan, DART will launch aboard a SpaceX Falcon 9 rocket at 10:20 pm PT on November 23, from the Vandenberg Space Force Base in California.

When DART separates from its ride it will unfurl its Roll-Out Solar Arrays (ROSA), two solar arrays each almost 28 feet long, which will collect energy from the sun to power the spacecraft's electric propulsion system.

DART is Loaded to Space X Payload
An image showing DART at SpaceX’s payload processing facility at the Vandenberg Space Force Base in California. DART team members carefully removed the spacecraft from its shipping container and moved it to a low dolly. Johns Hopkins APL/Ed Whitman/NASA

This solar-electric system, the NASA Evolutionary Xenon Thruster – Commercial (NEXT-C), represents the next generation of space propulsion systems. It will carry DART to its target, which it will reach at some point between September 26 and October 1, 2022.

The DART craft is also able to redirect itself and navigate using an onboard propellant system. This will help the craft position itself for impact with the moonlet Dimorphos.

When it leaves Earth DART will have a mass of 1,345 pounds, which will have reduced to 1,210 pounds by the time of impact due to the expelling propellant and deployment of the Light Italian Cubesat for Imaging of Asteroids (LICIACube).

LICIACube will capture images of the DART impact on the surface of Dimorphos. The impact will also be recorded by DART's only onboard instrument, the telescope Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO).

DART's Journey
An infographic showing the journey of DART towards its fateful meeting with the moonlet Dimorphos. On the way DART will jettison the LICIACube, which will record the impact. Johns Hopkins APL/NASA

The impact of DART on Dimorphos will constitute what Johns Hopkins Applied Physics Laboratory researcher Nancy Chabot calls a "small nudge." The aim isn't to destroy the moonlet or its parent asteroid but deflect its orbit.

"It's only going to be a change of about one percent in that orbital period," Chabot said, "so what was 11 hours and 55 minutes before might be like 11 hours and 45 minutes."

How much the orbit changes will hinge on how porous the moonlet is. "We are targeting to be as nearly head-on as possible to cause the biggest deflection," Chabot said. "It's like ordinary chondrite meteorites," she said. "It's a fine grain mixture of rock and metal together."

Currently, there are no asteroids on a direct collision course with Earth, but even though over 27,000 near-earth objects are known, NASA's Center for Near-Earth Object Studies is discovering objects all the time. That means it's not implausible to find one that does threaten an impact.

"The key to planetary defense is finding them well before they are an impact threat," Johnson said. "We don't want to be in a situation where an asteroid is headed towards Earth and then have to test this capability."

DART Prepares for Impact
An artist's illustration of the DART impactor as it approaches its target. NASA are making final preparations for the first test of a planetary defence system for asteroids. NASA