DART, NASA's test to stop an asteroid from hitting Earth

Highlights

• DART was the first planetary defense mission to test a method of deflecting an asteroid on course to hit Earth.
• The threat from asteroid impacts is small but real — and preventable. Missions like DART are essential to help us understand how to stop dangerous asteroids.
• The Planetary Society works to improve asteroid detection and reconnaissance, mature deflection technologies, and develop global response strategies.
  

What was DART?

What should we do if we find a dangerous asteroid on course to hit Earth? There are a number of possible deflection techniques, ranging from extreme (a nuclear blast) to benign (a heavy spacecraft uses gravity to nudge the asteroid off-course).

Somewhere in between is the kinetic impactor technique. The concept is simple: Slam one or more spacecraft into the asteroid at high speed to change its orbit and move Earth out of the crosshairs. This technique works particularly well if used far in advance, since small nudges can add up to big changes later on.

DART, NASA's Double Asteroid Redirection Test, was the first space mission to test this or any other asteroid deflection technique. DART launched in November 2021 and arrived at near-Earth asteroid Didymos in September 2022. On Sept. 26, the spacecraft intentionally crashed into the asteroid's small moon, Dimorphos. The crash changed the time it takes Dimorphos to orbit Didymos by 33 minutes, proving the kinetic impactor technique works.

Didymos and Dimorphos were particularly well-suited targets for DART. Although they are relatively small — Didymos measures just 780 meters (a half-mile) across and Dimorphos measures only 160 meters (525 feet) across — they pass in front of each other as seen from Earth. Optical ground-based telescopes see them as a single point of light that fluctuates in brightness as Dimorphos circles Didymos; the interval of those fluctuations should have changed after DART's impact. Additionally, Didymos and Dimorphos do not come close enough to Earth for DART to inadvertently send them hurtling towards our planet.

Two years after DART's fireworks at Dimorphos, the European Space Agency will launch a mission called Hera to study Didymos and Dimorphos in depth. This will allow scientists to analyze DART's impact crater and understand the mission's full effect.

How much did DART cost? 

The DART project cost $324.5 million. $308 million was spent on spacecraft development, $68.8 million for launch services, and $16.5 million is expected to spent on operations and data analysis. 

For additional context, read our analysis of NASA's planetary defense budget.

How did DART work?

Before it impacted Dimorphos, DART was a relatively small spacecraft. Its core consisted of a box barely a meter wide on all sides, with two roll-out solar arrays that gave the spacecraft a width of about 12 meters (40 feet). DART's electric propulsion system generated a flow of charged ions to create a gentle but continuous push.

DART launched in November 2021 aboard a SpaceX Falcon 9 rocket from Vandenberg Space Force Base in California. The spacecraft looped around Earth multiple times, using its electric thruster to gain the speed needed to escape orbit. From there it headed to Didymos, possibly flying past another asteroid named 2001 CB21 on the way.

DART's single science instrument was a high-resolution camera called DRACO that was also used for navigation. It was based on a similar camera aboard NASA's New Horizons spacecraft.

On Sept. 11, DART deployed an Italian Space Agency-built CubeSat to observe the impact. The main spacecraft was too far from Earth for flight controllers to control in real-time, so it switched to an autonomous navigation mode four hours before impact. Images from DRACO helped the spacecraft's computer differentiate between Didymos and Dimorphos and steer into the latter.

And then it was over. On Sept. 26, DART crashed into Dimorphos at a speed of 6.6 kilometers (4.1 miles) per second. The impact should have changed Dimorphos' orbital period around Didymos from 11.9 to 11.8 hours — a difference of just 4.2 minutes. This will pull Dimorphos slightly closer to Didymos.

You can see some of DART's final images before impact here.

Learn more

• Read about asteroids, comets, and other small worlds
• View the locations of asteroids in the inner Solar System
• Learn about asteroid close calls

Academic resources

• Rivkin, A. S., Chabot, N. L., Stickle, A. M., Thomas, C. A., Richardson, D. C., Barnouin, O., Fahnestock, E. G., Ernst, C. M., Cheng, A. F., Chesley, S., Naidu, S., Statler, T. S., Barbee, B., Agrusa, H., Moskovitz, N., Terik Daly, R., Pravec, P., Scheirich, P., Dotto, E., … Hirabayashi, M. (2021). The Double Asteroid Redirection Test (DART): Planetary defense investigations and requirements. The Planetary Science Journal, 2(5), 173.