DART: NASA's mission to crash into an asteroid

Artist's illustration of DART at Didymos and Dimorphos. Credit: NASA/Johns Hopkins, APL/Steve Gribben

• Launch Date: November 23, 2021
• Launch Site: Space Launch Complex 4 East at Vandenberg Space Force Base California, United States
• Launch Vehicle: Falcon 9 "Block 5"
• Mission Type: Demonstration & Impactor
• Targets: Didymos & Dimorphos
• Dimensions: 1.2 Meters by 1.3 Meters by 1.3 Meters
• Mass: 684 Kilograms (Including Propellant)

You can build a model of the DART spacecraft out of LEGO here.

The Mission

The Double Asteroid Redirection Test (DART) was NASA's first planetary defence mission. Earth isn't currently under threat from any asteroids, but this mission is intended to test out the simplest defence proposal. The idea is to use a kinetic impactor to deflect the trajectory of an incoming asteroid so it misses Earth. Doing this around an asteroid orbiting the sun would be impractical, because the change in orbit would be nearly undetectable, and could turn a harmless asteroid into a dangerous one. So NASA selected a nearby binary asteroid system: Didymos & Dimorphos. Didymos is the larger partner, and is accompanied by the smaller Didymos. DART would smash into Dimorphos, changing its orbit around Didymos. This would be much easier to detect the change in orbital velocity.

DART was launched by SpaceX's famous Falcon 9 rocket on November 23, 2021. DART would act as a demonstrator for several new technologies on its way to Didymos & Dimorphos. DART possesed a new ion engine, the NEXT-C, with more thrust than previous iterations. Unfortunately only 2 hours of engine testing occured during the mission before it was aborted due to heating problems. DART also had two Roll-Out Solar Arrays (ROSAs) which are lighter than previous solar panel designs.

Credit: NASA/Johns Hopkins APL

DART was also equipped with a secondary spacecraft to image its impact. The Light Italian CubeSat for Imaging Asteroids (LICIACube) was provided by the Italian Space Agency. This spaceraft has two cameras known as LEIA and LUKE.

DART first saw Didymos on July 27, 2022, and made minor course corrections to stay on target. LICIACube was released on September 11, 15 days before the impact. DART shifted its lock onto Dimorphos 50 minutes before impact. DART impacted Dimorphos on September 26, 2022, at 23:14 UTC. You can watch the impact from DART's DRACO camera here.

LICIACube's view of the DART impact. Credit: ASI/NASA

DART's last fully transmitted image before impact. Credit: NASA/Johns Hopkins APL

NASA was hoping to alter Dimorphos' orbit by anywhere from 30 seconds to 10 minutes. However the spacecraft overachieved, and Dimorphos had an orbital decrease of 33 minutes! This is quite significant as the orbit of Dimorphos before impact was only 12 hours. This proved that a kinetic impactor was a valid planetary defense technique. This however, is only the case for asteroids less than one kilometre in diameter. Larger asteroids would need to be spotted way in advance, and probably would need a different method.

DART's impact also destablized Dimorphos, turning it into an "active asteroid," with a small tail like a comet. Scientist had proposed that active asteroids could be activated by impacts, but this test proved it under well studied conditions.

The Targets

Didymos with North facing up. Credit: NASA/Johns Hopkins APL

• Date Discovered: April 11, 1996
• Designation: 65803 Didymos (1996 GT)
• Class: Apollo [NEO]
• Radius: 390 Meters
• Rotational Period: 2.26 Hours
• Orbital Period: 768.99 Days (2.11 Years)

Dimorphos with North facing up. Credit: NASA/Johns Hopkins APL

• Date Discovered: November 20, 2003
• Designation: I Dimorphos
• Class: Apollo [NEO]
• Radius: 81.5 Meters
• Orbital Period Pre-Impact: 11 hours and 55 Minutes
• Orbital Period Post-Impact: 11 hours and 22 Minutes