The Double Asteroid Redirection Test will be the first time mankind has sent a spacecraft to measurably alter the orbit of a celestial body. The mission will also be the world’s first large-scale demonstration of deflection technology that could protect the planet.
The DART spacecraft is heading for Dimorphos, a small moon orbiting the nearby Earth asteroid Didymos. The asteroid system poses no threat to our planet, making it a perfect target to test a kinetic impact — which may be necessary if an object is ever on its way to hit Earth.
The double asteroid system is visible through ground-based telescopes as a single point of light, but DART will provide our first look – in beautiful detail – at Dimorphos. The mission will allow scientists to gain a better understanding of each asteroid’s size and mass, which is crucial to our understanding of near-Earth objects.
Near-Earth objects are asteroids and comets with orbits that place them within 30 million miles (48.3 million kilometers) of Earth. Detecting the threat of nearby terrestrial objects that could cause serious damage is a primary focus of NASA and other space agencies around the world.
There are currently no asteroids directly impacting Earth, but more than 27,000 near-Earth asteroids of all shapes and sizes exist.
The valuable data collected by DART will contribute to planetary defense strategies, especially understanding what kind of force could shift the orbit of a near-Earth asteroid that could collide with our planet.
The DART vehicle was launched aboard a Falcon 9 rocket in November 2021. With its large solar panels, DART is about the size of a school bus. Its total mass will be about 1,260 pounds (570 kilograms) when it collides with Dimorphos.
The spacecraft has two Roll-Out Solar Arrays, called ROSA. The flexible wings are lighter than traditional solar panels, despite the fact that they are all 8.5 meters long. Solar cells and reflective concentrators within the arrays provide DART with three times more power than standard solar panels on other spacecraft. These rollable arrays have been tested and installed outside the International Space Station, but DART is the first time NASA will use them on a planetary spacecraft.
Another first aboard DART is the Evolutionary Xenon Thruster-Commercial propulsion system, or NEXT-C. By testing this fuel-efficiency-enhancing technology on DART, researchers can assess how it performs for possible inclusion in future deep space missions. The solar-powered system is based on an ion propulsion system that bombards xenon gas with electrically charged atoms.
The spacecraft will self-guide using the Small-body Maneuver Autonomous Real Time Navigation or SMART Nav system. This system syncs with the eyes of DART, the Didymos Reconnaissance and Asteroid Camera for Optical navigation, or DRACO, to allow the spacecraft to identify the twin asteroid system and discern which space object it should collide with.
In addition, DRACO will serve as a high-resolution camera that can measure the size and shape of its target to determine where it will hit the asteroid’s moon — all while capturing stunning images of the two asteroids headed for real. the earth will flow in time at the rate of one frame per second.
The videographer of DART is the Italian Space Agency’s Light Italian CubeSat for Imaging of Asteroids or LICIACube. This briefcase-sized CubeSat took a DART ride into space and disengaged from the spacecraft on September 11.
On the CubeSat are two cameras called LUKE (LICIACube Unit Key Explorer) and LEIA (LICIACube Explorer Imaging for Asteroid). Together they will collect images and help LICIACube on its journey. The tiny satellite travels behind DART to record what’s happening.
Astronomers discovered Didymos more than two decades ago. It means “twins” in Greek, a nod to how the asteroid forms a binary system with the smaller asteroid or moon.
Didymos is about 780 meters wide. Meanwhile, Dimorphos has a diameter of 160 meters and the name means ‘two forms’.
Dimorphos was chosen for this mission because its size is comparable to asteroids that can pose a threat to Earth. An asteroid the size of Dimorphos could cause “regional devastation” if it hit Earth.
About four hours before impact on September 26, the spacecraft will become autonomous. At that point, DART will actually target Didymos because it still can’t see little Dimorphos. The spacecraft will still be 90,000 kilometers from the asteroid.
About 50 minutes before the impact, Dimorphos will come into view and DART will slightly change its field of view to focus on the small moon. Slowly Dimorphos will change from a small point of light and get bigger and bigger within the frame of DRACO’s camera.
Scientists will be able to see the moon for the first time, determine its shape and structure, and determine how rocky or slippery it is. Each image will reveal more detail as DART gets closer.
The SMART Nav system guides DART until approximately two minutes before impact.
The spacecraft will accelerate to more than 13,421 miles per hour (21,600 kilometers per hour) when it collides with Dimorphos – effectively ending the DART mission.
The spacecraft is about 100 times smaller than Dimorphos, so it won’t destroy or shatter the asteroid. Instead, DART will attempt to change the asteroid’s speed and path in space. The mission team has likened the spacecraft’s impact on the small asteroid to a golf cart crashing into one of the large pyramids — it will impact with enough energy to leave an impact crater.
Three minutes after the impact, the LICIACube flies past Dimorphos to capture photos and video of the ejected cloud as it bounces off the asteroid and maybe even spy on the impact crater. The mini-satellite will also glimpse the other hemisphere of Dimorphos, which DART won’t see until it’s obliterated. The CubeSat will rotate to keep its cameras pointed at Dimorphos as it flies by.
The video, while not immediately available, will be streamed back to Earth in the weeks and months following the collision.
This kinetic impact is just one way to redirect asteroids that could pose a threat to Earth, but it’s the “technologically most mature,” scientists say.
The rapid impact will only change the speed of Dimorphos as it orbits Didymos by 1%, which doesn’t seem like much, but it will change the moon’s orbital period.
The nudge will slightly shift Dimorphos and make it more gravitationally bound to Didymos – so the collision won’t change the binary system’s path around Earth or increase its chances of becoming a threat to our planet.
Dimorphos completes an orbit around Didymos every 11 hours and 55 minutes. After the impact, that can change between 73 seconds and 10 minutes. Follow-up observations will determine how much of a shift will have occurred.
Astronomers will use ground-based telescopes to observe the binary asteroid system and see how much Dimorphos’ orbital period has changed, which will determine whether DART was successful. Scientists can compare observations before the impact with those after it.
Telescopes around the world will observe Dimorphos as it passes in front of and behind the asteroid. Measuring Didymos’ brightness and how it changes can help astronomers determine how its orbital period has changed.
Space telescopes such as Hubble, Webb and NASA’s Lucy mission will also observe the event.
The first full-frame images from LICIACube will return and be processed a few days after the impact. The satellite’s unique perspective gives a view of the impact and Dimorphos that scientists would not be able to see any other way.
To survey the aftermath of the impact, the European Space Agency’s Hera mission will launch in 2024. The spacecraft, along with two CubeSats, will arrive at the asteroid system in 2026, about four years after DART completes its mission. Once there, Hera will study both asteroids, measure the physical properties of Dimorphos, and investigate the DART impact crater and the moon’s orbit, with the overall goal of establishing an effective planetary defense strategy.