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


  • DART is 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 is 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, is the first space mission to test this or any other asteroid deflection technique. DART launched in November 2021 and will arrive at near-Earth asteroid Didymos in September 2022. The spacecraft won't slow down, intentionally crashing into the asteroid's small moon Dimorphos. The crash should change the time it takes Dimorphos to orbit Didymos, proving the kinetic impactor technique works.

Didymos and Dimorphos are 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 will change 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 does 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.

Radar images of asteroid Didymos
Radar images of asteroid Didymos These 14 radar images of Didymos and its moon Dimorphos were captured by Arecibo Observatory in Puerto Rico in November 2003. Didymos is the small speck above Dimorphos moving between each image.Image: NASA

How does DART work?

DART is a relatively small spacecraft. Its core consists of a box barely a meter wide on all sides, with two roll-out solar arrays that give the spacecraft a width of about 12 meters (40 feet). DART's electric propulsion system generates 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 will loop around Earth multiple times, using its electric thruster to gain the speed needed to escape orbit. From there it will head to Didymos, possibly flying past another asteroid named 2001 CB21 on the way.

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

Five days before arrival, DART will deploy an Italian Space Agency-built CubeSat to observe the impact. The main spacecraft will be too far from Earth for flight controllers to control in real-time, so it will switch to an autonomous navigation mode 4 hours before impact. Images from DRACO will help the spacecraft's computer differentiate between Didymos and Dimorphos and steer into the latter.

And then it's over. DART will crash into Dimorphos at a speed of 6.6 kilometers (4.1 miles) per second. The impact should change 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.

DART spacecraft
DART spacecraft NASA's DART spacecraft cruises through space in this artist's illustration.Image: NASA/Johns Hopkins APL

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