NASA's DART Mission: Why a Doomed Spacecraft Just Crashed Into an Asteroid
Can we defend Earth from a cataclysmic asteroid collision one day? DART may have the answer.
Monisha RavisettiFormer Science Writer
Monisha Ravisetti was a science writer at CNET. She covered climate change, space rockets, mathematical puzzles, dinosaur bones, black holes, supernovas, and sometimes, the drama of philosophical thought experiments.
Previously, she was a science reporter with a startup publication called The Academic Times, and before that, was an immunology researcher at Weill Cornell Medical Center in New York. She graduated from New York University in 2018 with a B.A. in philosophy, physics and chemistry.
When she's not at her desk, she's trying (and failing) to raise her online chess rating. Her favorite movies are Dunkirk and Marcel the Shell with Shoes On.
The DART, or Double Asteroid Redirection Test, wasn't destined for decades of solar system science. The spacecraft launched in November 2021 and, well, just straight up crashed into an asteroid on Monday. It's now totally destroyed -- but its death was the purpose of its existence.
DART is NASA's test run of a planetary defense system intended to nudge incoming asteroids away from Earth by literally smashing spacecraft into them. Asteroids, which range in size from refrigerators to automobiles, collide with our planet more often than you might think. Thankfully, these impacts aren't generally too menacing because most of the rock burns up in Earth's atmosphere. But nearly 66 million years ago, as you may recall, dinosaurs were wiped out by a massive space rock by the name of Chicxulub.
The objective was simple: NASA wanted to understand if we can crash into an asteroid to prevent such a calamity from also wiping out humans. So, as a proof of principle the spacecraft struck a little asteroid called Dimorphos, which is orbiting a larger asteroid, Didymos.
On Monday, the DART spacecraft autonomously navigated toward and collided with Dimorphos when the rock was about 7 million miles from Earth -- its closest point to our blue planet. The target asteroid is about as big as the Washington Monument is tall, and upon impact, the team behind the DART launch hoped the rock's trajectory and speed were slightly altered.
To be clear, this particular floating rock never posed a threat to our planet. But if the DART team managed to knock Dimorphos off course, we'll know we may have a workable tactic for one day fending off asteroids that are actually dangerous. The take-home message is that this is basically a technology demonstration -- a way for NASA to get valuable insight on how we may one day deflect a scary asteroid really on a collision course with Earth.
Target acquired: Dimorphos
Cruising through our solar system is a grayish space rock about a half mile wide known as Didymos, which, with a gentle gravitational pull, keeps a companion asteroid on a leash. That second, smaller fragment orbiting Didymos was DART's target: Dimorphos.
Scientists behind the DART selected Dimorphos for the test because its orbit around Didymos mimics how potentially threatening near-Earth asteroids orbit around the sun. Asteroids are gravitationally bound to our star, which could put them on a collision course with Earth. But Dimorphos' orbit isn't locked to Earth or the sun but rather to Didymos. This makes it a perfect testing ground for NASA -- they tried to crash DART into the tiny rock to see how that changes its orbit around its larger companion.
NASA predicted the crash would be strong enough to adjust Dimorphos' orbital period by a few minutes. More specifically, calculations show the impact will bring Dimorphos closer to Didymos.
Now that impact is complete, the agency will begin sifting through data of the spacecraft's trajectory and final moments as well as of Dimorphos' new route of travel to see whether those calculations were correct. "Mostly, what we're looking to do is change the speed of the incoming object by a centimeter per second or so. That's not very fast, but if you do it enough seconds in advance, you can cause it to miss the Earth entirely," according to the mission overview by Johns Hopkins University's Applied Physics Laboratory.
This approach -- one of many ideas for saving humanity from asteroids -- is known as "deflection by kinetic impactor." According to the team, this was the first time the method had been employed intergalactically.
"This technique is thought to be the most technologically mature approach for mitigating a potentially hazardous asteroid," NASA's planetary defense officer, Lindley Johnson, said in a statement. "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."
The way it works is pretty intuitive.
Quick, throw something at it!
Let's say your buddy is riding a skateboard extremely fast and is headed toward your dog. One (chaotic) way for you to save your dog is to run into your skateboarding friend. When you collide with your friend, the energy you've built up changes their direction and lowers their speed. You've just become a kinetic impactor, designed to throw your skateboarding buddy off-course and save your dog.
The DART mission is expected to work in a similar way, but the aim isn't to protect any canines, it's just trying to knock the skateboarder off course. The spacecraft, which is about the size of a school bus, flew into Dimorphos at a speed of about 4.1 miles per second. That's roughly 14,760 miles per hour (23,760 kilometers per hour).
Following the impact, NASA says, the small asteroid's, or moonlet's, orbital speed should change by a fraction of a percent, which would lead to an orbital period that's several minutes slower.
Though Dimorphos poses no threat to Earth, Earth-based telescopes can easily catalog the bump's effects, because at just about 7 million miles away, the impact was close enough for scientists to observe any changes in the rock's orbit around its companion. Such observations will ultimately help scientists perfect future planetary defense weapons based on valuable information retrieved from DART's prototype.
The brave spacecraft's specs
The DART spacecrafy was a relatively inexpensive metal box with two roll-out, extendible solar arrays for power, a single camera and a smaller satellite, or CubeSat, that was deployed right before impact. The limited number of tools made sense, as the spacecraft was doomed to die in a suicide mission.
Here are some specifics about the DART spacecraft:
Weight: 1,345 pounds (610 kilograms) at launch / 1,210 (550 kg) pounds at impact.
Box dimensions: 3.9 by 4.3 by 4.3 feet (1.2 by 1.3 by 1.3 meters).
Solar array dimensions: 27.9 feet each (8.5 meters).
Extra instrumentation: DRACO camera and one CubeSat.
Engine: Ion propulsion technology/xenon thrusters.
While the DART's spacecraft payload was hyper-minimal, the team's programming behind the course was highly advanced. That's because the brave little craft behaved autonomously throughout the mission.
Until the end, DART
The spacecraft's tools might've been few, but they were key. The Didymos Reconnaissance and Asteroid Camera for Optical navigation, or DRACO, device was an ultra-high-resolution camera that measured the size, shape and geologic composition of asteroids in its vicinity.
The DART also had a metal-oxide semiconductor and image processor that helped the spacecraft determine the precise positioning of Dimorphos and stream information back to Earth in real time, by way of an antenna attached to the machine.
In addition, the DART was armed with a navigational toolkit with state-of-the-art directional coding, including the star tracker, which is my personal favorite NASA tool, to ensure it hit Dimorphos at exactly the right moment -- ding, ding: the 7 million miles (11 million kilometers) checkpoint. Ten days before DART's spacecraft smacked into its target, it sent a CubeSat out. That offshoot will preserve the kinetic impact's chronicle, despite DART now being nothing more than a pile of rubble somewhere in the cosmos.
Though right up until the very end, the DART performed its duty. NASA was able to catch the collision's juicy details before, during and after impact.
"In its final moments," the Johns Hopkins University overview says, "DART's DRACO camera will help characterize the impact site by providing high-resolution, scientific images of the surface of Dimorphos."
Then: boom. "Pour one out for the dinos," said the DART craft. Probably.
This piece was originally posted when DART launched in November 2021.