DART MISSION DEMONSTRATES NASA’S PLANETARY DEFENSE STRATEGY

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 of about 50 metres in diameter entered Earth’s atmosphere and exploded into pieces over Tunguska, Siberia.

It 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 the asteroid Didymos and its tiny moonlet Dimorphos. Dimorphos is only about 160 metres in length, and it’s roughly 11 million kilometres from Earth.

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 mission deployed LICIACube fifteen days prior to the rendezvous with Dimorphos. It’s a comparatively simple spacecraft with a small antenna, so it will take a few weeks to transmit all its images 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.”

Now, dozens of observatories around the world have aimed their telescopes at Dimorphos. They, and even some space telescopes, will be observing the debris from the impact and measuring Dimorphos’s orbital change.

DART MISSION HAS PROVEN FEASIBILITY OF PLANETARY DEFENCE

Even if Dimorphos doesn’t budge as much as expected, the DART mission has already proven the feasibility of using kinetic impact for planetary defence. The findings from the telescopes will enable scientists and engineers to better plan the mass and speed needed to redirect a real-life hazardous NEO.

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 wrapped things up by saying, “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.”

We always have more to learn if we dare to know.

Learn more:

NASA’s DART Mission Hits Asteroid in First-Ever Planetary Defense Test

NASA Smashes Into an Asteroid, Completing a Mission to Save a Future Day

Report on Near-Earth Object Impact Threat Emergency Protocols

James Webb Space Telescope Photos are Spectacular

NASA Discovery Program – 4 Bids to Explore Solar System

Mars Helicopter ‘Ingenuity’ Takes Flight