The Double Asteroid Redirection Test will be the first time humanity has sent a spacecraft to measurably change the orbit of a celestial body. The mission will also be the first full-scale demonstration of diversion technology that can protect the planet.
The DART spacecraft is headed to Dimorphos, a small moon orbiting the near-Earth asteroid Didymos. The asteroid system poses no threat to our planet and is an ideal target for kinetic impact testing, which may be necessary if an object is on track to hit Earth.
The double asteroid system is visible to ground-based telescopes as a single point of light, but DART will provide our first look at Dimorphos in exquisite detail. The mission will allow scientists to better understand the size and mass of each asteroid, which is critical to understanding near-Earth objects.
Near-Earth objects are asteroids and comets that orbit within 30 million miles (48.3 million kilometers) of Earth. Detecting the threat of near-Earth objects that could cause serious damage is the main focus of NASA and other space agencies around the world.
Currently, there are no asteroids directly impacting Earth, but there are over 27,000 near-Earth asteroids of all shapes and sizes.
The valuable data collected by DART will help in planetary defense strategies, especially in understanding what forces might change the orbit of a near-Earth asteroid that could collide with our planet.
The DART vehicle was launched on a Falcon 9 rocket in November 2021. With its large solar array, DART is about the size of a school bus. Its total mass will be approximately 1,260 pounds (570 kilograms) when it enters Dimorphos.
The spacecraft has two Roll-Out Solar Arrays, called ROSA. The flexible wings are lighter than traditional solar systems, despite being 27.9 feet (8.5 meters) long each. Solar cells and reflective concentrators provide DART with three times more power than standard solar arrays on other spacecraft. These rollable arrays have been tested and installed outside the International Space Station, but this is the first time that DART will be used by NASA on a spacecraft.
Another first on board the DART is its Evolutionary Xenon Thruster-Commercial propulsion system, or NEXT-C. Testing this technology, which improves DART’s fuel efficiency, will help researchers evaluate how well it works for future deep space missions. The solar power system is based on an ion drive that bombards xenon gas with electrically charged atoms.
The spacecraft will guide itself through small-body maneuvers using a real-time autonomous navigation or SMART Nav system. This system synchronizes with DART’s eyes, the Didymos Reconnaissance and Asteroid Camera for Optical Navigation, or DRACO, to help the spacecraft identify the double asteroid system and distinguish which space object to impact.
In addition, DRACO will serve as a high-resolution camera that can measure the size and shape of its target to determine where the asteroid will impact the moon, while capturing stunning images of the two asteroids that will crash into Earth in real life. time at the rate of one image per second.
DART serves as a videographer for the Italian Space Agency’s Light Italian CubeSat for Imaging of Asteroids, or LICIACube. This briefcase-sized CubeSat carried DART into space and was launched from the spacecraft on 9/11.
There are two cameras on the CubeSat called LUKE (LICIACube Unit Key Explorer) and LEIA (LICIACube Explorer Imaging for Asteroids). Together, they will collect images and help guide LICIACube on its journey. The small satellite follows DART to record what happens.
Astronomers discovered Didymos more than two decades ago. It means “twin” in Greek, meaning the asteroid forms a binary system with a smaller asteroid or moon.
Didymos is approximately 2,560 feet (780 meters) wide. Meanwhile, Dimorphos is 525 feet (160 meters) in diameter, and its name means “two forms.”
Dimorphos was chosen for this mission because its size is comparable to asteroids that could pose a threat to Earth. An asteroid the size of Dimorphos could cause a “regional catastrophe” if it were to hit Earth.
About four hours before the September 26 impact event, the spacecraft will become autonomous. At that point, DART will be targeting Didymos because it won’t be able to see the little Dimorphos yet. The spacecraft will still be 56,000 miles (90,000 kilometers) from the asteroid.
About 50 minutes before impact, Dimorphos will appear and DART will shift its field of view slightly to focus on the small moon. Dimorphos will slowly change from being a small point of light to growing larger in the frame of DRACO’s camera.
Scientists will be able to see the moon for the first time, determining its shape and structure and how rocky or smooth it is. Each image will reveal more detail as the DART approaches.
The SMART Nav system will guide the DART until about 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 100 times smaller than Dimorphos, so it won’t obliterate or break the asteroid. Instead, DART will try to change the speed and path of the asteroid in space. The mission team compared the spacecraft’s impact on the small asteroid to that of a golf cart crashing into one of the great pyramids—hitting with enough energy to leave an impact crater.
Three minutes after impact, LICIACube will fly past Dimorphos to capture images and video of the ejecta cloud as it ejects from the asteroid and possibly spy on the impact crater. The mini-satellite will also see the opposite hemisphere of Dimorphos, which DART will not see until it is obliterated. The CubeSat will turn to keep its cameras pointed at Dimorphos as it flies.
The video, while not immediately available, will return 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 is what scientists believe is the most “technologically mature”.
The fast impact will only change Dimorphos’ speed by 1% as it orbits Didymos, which doesn’t seem like much, but it will change the moon’s orbital period.
The thrust will change Dimorphos slightly and more gravity will be attached to Didymos; therefore, the collision will not change the binary system’s path around Earth or increase the chances of it becoming a threat to our planet.
Dimorphos completes an orbit around Didymos every 11 hours and 55 minutes. After impact, this can vary between 73 seconds and 10 minutes. Follow-up observations will determine how much change has 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 is a success. Scientists can compare observations before and after the impact.
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-based telescopes such as Hubble, Webb and NASA’s Lucy mission will also observe the event.
The first full-frame LICIACube images will be returned and processed a couple of days after the impact. The satellite’s unique perspective will provide impact and insight into Dimorphos that scientists would not otherwise be able to see.
To study the effects of the impact, the European Space Agency’s Hera mission will be launched in 2024. The spacecraft, along with two CubeSats, will arrive in the asteroid system in 2026, about four years after DART completes its mission. Once there, Hera will study the two asteroids, measure the physical properties of Dimorphos, and study the DART impact crater and the moon’s orbit, continuing with the overall goal of establishing an effective planetary defense strategy.