The DART mission successfully struck an asteroid 11 million kilometres away with a spacecraft. Find out why this achievement demonstrates how humanity could one day protect and preserve life on Earth.
I had the great privilege of taking a course with Professor Emeritus Henry Halls when I was in university. Professor Halls is an eminent geologist.
He’s the person from whom I first learned about the Tunguska incident. In 1908, an asteroid about 50 metres in diameter entered Earth’s atmosphere and exploded into pieces over Tunguska, Siberia.
The explosion flattened over 80 million trees over an area of 2,150 square kilometres, killing at least three people in that isolated and unpopulated region. It was the largest impact event in recorded history, although prehistoric collisions have been much more destructive.
Possibility of Impacts Have Concerned Astronomers
The possibility of future impacts like these have concerned astronomers ever since they discovered asteroids. Although observations show no sign of an imminent impact like the one that killed the dinosaurs, scientists realized that we have no planetary defense strategy.
Near-Earth objects (NEOs), like comets and asteroids, orbit the sun, but their orbits can sometimes intersect with that of the Earth, leading to potential collisions. NASA set up its Planetary Defense Coordination Office to manage these NEO hazards.
As part of that, ten months ago, NASA launched the Double Asteroid Redirection Test (DART) mission. Along with the Johns Hopkins Applied Physics Laboratory (APL), their goal was to demonstrate the feasibility of having a spacecraft collide with and redirect an asteroid away from Earth.
Chose the Asteroid Didymos’ Tiny Moonlet Dimorphos
For their test case, the team chose an asteroid 11 million kilometres from Earth called Didymos and its tiny, 160 metre moonlet Dimorphos. They wanted to see if they could change Dimorphos’s orbit around Didymos.
To be clear, neither Dimorphos nor Didymos are any threat to our planet. The researchers chose the asteroids as a test case to demonstrate how the technique they call “kinetic impact” might work.
NASA Administrator Bill Nelson explained the purpose of the mission this way. “As NASA studies the cosmos and our home planet, we’re also working to protect that home, and this international collaboration turned science fiction into science fact, demonstrating one way to protect Earth.”
Box-Shaped Spacecraft with Camera and Navigation System
The heart of the DART mission was a box-shaped spacecraft that weighed 570 kg and measured 1.2 x 1.3 x 1.3 meters. It carried solar panels, a camera and a navigation system.
The camera was called the Didymos Reconnaissance Asteroid Camera for Optical navigation (DRACO). It was a high-resolution imager with a sophisticated onboard image processor.
The Small-body Maneuvering Autonomous Real Time Navigation (SMART Nav) was a set of algorithms. It enabled DART to tell Didymos and Dimorphos apart and aim for Dimorphos.
Italian Space Agency Provided Cube Satellite
DART was also carrying a tiny sidekick. The Italian Space Agency provided a cube satellite to support the mission.
The Light Italian CubeSat for Imaging of Asteroids (LICIACube) accompanied DART to get a different camera angle and continue taking pictures of DART and Dimorphos after the impact.
The DART spacecraft launched LICIACube fifteen days prior to the rendezvous with Dimorphos. It’s a comparatively simple spacecraft with a small antenna, but its images and data are gradually finding their way back to Earth.
DART’s Accuracy Nothing Short of Amazing
As I watched the impact live on NASA TV, DART’s accuracy was nothing short of amazing. Travelling at around 23,000 kilometers per hour, DRACO took one picture every minute.
Over the course of an hour, Didymos came into view and then resolved into the pairing of Didymos and Dimorphos. Soon, Dimorphos was in the middle of the screen.
Finally, at 7:14 EDT, DART collided dead-centre with Dimorphos. The detailed image of its surface suddenly went blank on impact.
Detailed Image Suddenly Went Blank on Impact
“Normally, losing signal from the spacecraft is a very bad thing,” Dr. Ralph Semmel, APL’s director, told the New York Times. “But in this case, it was the ideal outcome.”
The daunting challenge of “hitting a bullet with another bullet” has now been met. As Dr. Semmel put it, “This first-of-its-kind mission required incredible preparation and precision, and the team exceeded expectations on all counts.”
After the impact, dozens of observatories around the world aimed their telescopes at Dimorphos. They, and even some space telescopes, have been observing the debris from the impact and measuring Dimorphos’s orbital change.
Here’s an image from LICIACube showing the results of the impact on Dimorphos in upper right.
DART Mission Has Proven Feasibility of Planetary Defence
The verdict is in now, and NASA has declared the mission a success. Before the impact, Dimorphos orbited Didymos every 11 hours and 55 minutes.
Now, its orbit takes only 11 hours and 23 minutes, a difference of 32 minutes. The researchers had set a minimum orbital shift benchmark of just 73 seconds, and DART did 25 times better than that.
In about four years, the European Space Agency’s HERA spacecraft will arrive at Dimorphos. It will conduct high-resolution image, laser and radio mapping of the moonlet.
This will overcome the limitations of trying to assess the DART mission’s results from Earth. DART may have raised too much dust for accurate observations.
HERA Mission to Confirm Mass and Crater Size
Also, without HERA’s observations, we don’t know Dimorphos’s mass or the exact size of DART’s crater. Scientists need that information to accurately measure precisely how much DART redirected Dimorphos.
The DART mission represents a different approach to space exploration. Most of the time, the goal is to learn more about the universe and our place in it.
Missions like DART LICIACube and Hera are Hero’s Journeys
In this case, instead of a quest for knowledge, our plucky spacecraft is defending us from danger. Either way, we can think of missions like DART, LICIACube and Hera as hero’s journeys.
Dr. Semmel agreed. “Beyond the truly exciting success of the technology demonstration, capabilities based on DART could one day be used to change the course of an asteroid to protect our planet and preserve life on Earth as we know it.”
“All of us have a responsibility to protect our home planet. After all, it’s the only one we have,” Bill Nelson added. “This mission shows that NASA is trying to be ready for whatever the universe throws at us. NASA has proven we are serious as a defender of the planet.”
We always have more to learn if we dare to know.
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