But the true test for this asteroid deflection technology will come in September 2022, when the spacecraft reaches its destination, to see how it impacts the motion of a near-Earth asteroid in space.
Near-Earth objects are asteroids and comets with orbits that place them within 30 million miles (48 million kilometers) of Earth. Detecting the threat of near-Earth objects, or NEOs, that could potentially cause grave harm is a primary focus of NASA and other space organizations around the world.
Asteroid Didymos and its moon Dimorphos
In Greek, Didymos means “twin,” which is a nod to how the asteroid — nearly half a mile (0.8 kilometer) across — forms a binary system with the smaller asteroid, or moon — 525 feet (160 meters) in diameter — that was discovered two decades ago. Kleomenis Tsiganis, a planetary scientist at the Aristotle University of Thessaloniki and a member of the DART team, suggested that the moon be named Dimorphos, which means “two forms.”
It’s the perfect time for the DART mission to occur. Didymos and Dimorphos will be relatively close to Earth — within 6,835,083 miles (11 million kilometers) — in September 2022. The spacecraft will come speeding in at about 15,000 miles (24,140 kilometers) per hour, targeting Dimorphos, said Nancy Chabot, DART coordination lead at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.
A camera on the spacecraft, called DRACO, and autonomous navigation software will help the spacecraft detect and collide with Dimorphos. DRACO is short for Didymos Reconnaissance & Asteroid Camera for OpNav.
The mission’s aim is to deliberately crash into Dimorphos to change the asteroid’s motion in space, according to NASA. This collision will be recorded by LICIACube, or Light Italian Cubesat for Imaging of Asteroids, a companion cube satellite provided by the Italian Space Agency. It’s the Italian Space Agency’s first deep space mission.
The briefcase-size CubeSat will travel on DART and then be deployed from it prior to impact so it can record what happens. Three minutes after the impact, the CubeSat will fly by Dimorphos to capture images and video.
The video of the impact will be streamed back to Earth, which should be “pretty exciting,” said Elena Adams, DART mission systems engineer at the Johns Hopkins Applied Physics Laboratory.
“Astronomers will be able to compare observations from Earth-based telescopes before and after DART’s kinetic impact to determine how much the orbital period of Dimorphos changed,” said Tom Statler, DART program scientist at NASA Headquarters, in a statement. “That’s the key measurement that will tell us how the asteroid responded to our deflection effort.”
A few years after the impact, the European Space Agency’s Hera mission will conduct a follow-up investigation of Didymos and Dimorphos.
While the DART mission was developed for NASA Planetary Defense Coordination Office and managed by the Johns Hopkins University Applied Physics Laboratory, the mission team will work with the Hera mission team under an international collaboration known as the Asteroid Impact & Deflection Assessment, or AIDA.
“DART is a first step in testing methods for hazardous asteroid deflection,” said Andrea Riley, DART program executive at NASA Headquarters, in a statement. “Potentially hazardous asteroids are a global concern, and we are excited to be working with our Italian and European colleagues to collect the most accurate data possible from this kinetic impact deflection demonstration.”
A mission of firsts
Dimorphos was chosen for this mission because its size is relative to asteroids that could pose a threat to Earth, but the double asteroid system itself is not a threat to Earth.
The spacecraft is about 100 times smaller than Dimorphos, so it won’t obliterate the asteroid.
“This isn’t going to destroy the asteroid, it’s just going to give it a small nudge and deflect its path around the larger asteroid,” Chabot said. This means there isn’t a chance of changing the trajectory of the asteroid to make it more of a threat.
The fast impact will only change Dimorphos’ speed as it orbits Didymos by 1%, which doesn’t sound like a lot — but it will change the moon’s orbital period by more than a minute. That change can be observed and measured from ground-based telescopes on Earth.
Dimorphos completes an orbit around Didymos every 11 hours and 55 minutes. If the impact is successful, it will change that period by at least 73 seconds, said Andy Cheng, DART investigation team lead at the Johns Hopkins Applied Physics Lab.
Measuring the momentum transfer between the spacecraft and Dimorphos will show how much is needed to change the course of an asteroid.
“If one day an asteroid is discovered on a collision course with Earth, then we will have an idea how much momentum we need to make that asteroid miss the Earth,” Cheng said.
Planetary defense strategies
While there are currently no asteroids on a direct impact course with Earth, there is a large population of near-Earth asteroids — more than 27,000 in all shapes and sizes.
“The key to planetary defense is finding them well before they are an impact threat,” said Lindley Johnson, planetary defense officer at NASA Headquarters. “The principle with all of them is just to change the orbital speed of the asteroid just a small amount. Changing that speed of the asteroid in its orbit changes its orbit so in the future, it won’t be in the same place it was going to be to impact the Earth.”
Three years after the impact, Hera will arrive to study Dimorphos in detail, measuring physical properties of the moon, studying the DART impact and the moon’s orbit.
This may sound like a long time to wait between the impact and follow-up, but it’s based on lessons learned in the past.
In July 2005, NASA’s Deep Impact spacecraft launched a 815-pound (370-kilogram) copper impact into a comet, Tempel 1. But the spacecraft was not able to see the crater that resulted because the impact released tons of dust and ice. However, NASA’s Stardust mission in 2011 was able to characterize the impact — a 492-foot (150-meter) gash.
Together, the valuable data collected by DART and Hera will contribute to planetary defense strategies, especially understanding what kind of force is needed to shift the orbit of a near-Earth asteroid that may collide with our planet.
After analyzing the results of the mission, “this technique would be a part of a toolbox that we’re starting to build of capabilities to deflect an asteroid,” Johnson said.