In 2021, a spacecraft was launched on a first-ever suicide mission to try to deflect an asteroid on impact in space in the revolutionary planetary defense experiment: How NASA’s DART mission changed an asteroid’s orbit

In 2021, a spacecraft was launched on a first-ever suicide mission to try to deflect an asteroid on impact in space in the revolutionary planetary defense experiment. NASA’s Double Asteroid Redirection Test, known as DART, was designed to test whether a spacecraft could change the movement of an asteroid by hitting it. DART was launched aboard a SpaceX Falcon 9 rocket from Vandenberg Space Force Base in California. Its target was Dimorphos, a small moonlet orbiting the asteroid Didymos. The asteroid system was not a threat to Earth. The spacecraft reached Dimorphos on September 26, 2022, and deliberately collided with it to measure the change in its orbit.

How NASA’s DART mission was planned?

In 2021, a spacecraft was launched on a first-ever suicide mission to try to deflect an asteroid on impact in space in the revolutionary planetary defense experiment. The mission was called the Double Asteroid Redirection Test, or DART. NASA designed it to test whether a spacecraft could change an asteroid’s movement by hitting it at high speed.


The mission was a test of a planetary defense method called a kinetic impactor. The idea is direct. A spacecraft travels toward an asteroid and collides with it. The force from the collision can change the asteroid’s speed and path.

DART was developed and led for NASA by the Johns Hopkins University Applied Physics Laboratory. NASA’s Planetary Defense Coordination Office sponsored the mission. The spacecraft was launched aboard a SpaceX Falcon 9 rocket from Vandenberg Space Force Base in California.

The launch took place on November 23, 2021, at 10:21 p.m. PST. Because of the time difference, the launch was November 24 at 1:21 a.m. EST. The mission had two science targets in one system. They were the asteroid Didymos and its smaller moonlet, Dimorphos. The planned impact was carried out on September 26, 2022.

Why NASA selected Didymos and Dimorphos?

Didymos is a binary asteroid system. The name Didymos means twin in Greek. The system contains a larger asteroid and a smaller asteroid moonlet. Didymos has a diameter of about 760 meters, or 0.47 miles. Dimorphos has a diameter of about 150 meters, or 492 feet. Dimorphos travels around Didymos.

The centers of the two objects are separated by about 1.2 kilometers, or 0.74 miles. The system was selected because scientists could measure changes in Dimorphos’ orbit from Earth. Didymos and Dimorphos form an eclipsing binary as viewed from Earth. Dimorphos passes in front of and behind Didymos during its orbit. This movement causes changes in the brightness of the combined system. Telescopes can measure these changes and use them to determine how long Dimorphos takes to complete an orbit.

There was also an important safety factor. Neither Didymos nor Dimorphos was on a path that intersects Earth. The asteroid system was not a threat to the planet. At the time of the collision, the system was about 11 million kilometers, or 7 million miles, from Earth.

What happened when DART hit Dimorphos?

DART reached Dimorphos on September 26, 2022. The spacecraft hit the moonlet nearly head-on. The impact took place at 7:14 p.m. EDT, or 23:14:24.183 UTC. Before the collision, Dimorphos took 11 hours and 55 minutes to orbit Didymos. Scientists then used observations from telescopes to measure the change caused by the impact.

Initial measurements showed that the orbital period was shortened by about 32 minutes. Later analysis using Earth-based observations produced a measurement of 33 minutes, with an uncertainty of about one minute. The mission had set a minimum successful change of 73 seconds. The measured change therefore passed that benchmark by more than 25 times.

The spacecraft had a mass of about 580 kilograms, or 1,280 pounds, at the time of impact. Dimorphos itself has not been directly weighed. Its mass was estimated at about 5 billion kilograms using assumptions about its size and density. The impact did not destroy Dimorphos. Instead, it changed the time required for the moonlet to complete its orbit around Didymos.

Why the asteroid moved more than expected?

The collision involved more than the spacecraft striking the asteroid. When DART hit Dimorphos, rock and other material from the asteroid’s surface were displaced and thrown into space. This material is known as ejecta.

The ejecta moved away from Dimorphos. The movement created a recoil effect that added to the force produced by the spacecraft. Scientists compared this effect to the movement of a balloon when air leaves it. The escaping material moves in one direction, while the balloon moves in the opposite direction.

DART struck Dimorphos at about 14,000 miles per hour, or 22,530 kilometers per hour. The resulting change in Dimorphos’ orbital motion showed that the ejecta played a role in increasing the momentum transferred to the asteroid.

Researchers calculated that Dimorphos experienced an instantaneous slowing of about 2.7 millimeters per second along its orbit. The momentum change was estimated to be between 2.2 and 4.9 times the momentum delivered directly by the spacecraft, depending on the assumed mass of Dimorphos. This finding helped researchers understand why the kinetic impactor method can change an asteroid’s motion.

What scientists learned from the impact?

The DART mission was not only an asteroid deflection test. It also provided information about asteroid properties and the behavior of material released during an impact. The spacecraft hit between two large boulders. Its body and its two solar panels interacted with those rocks during the collision.

The spacecraft body, also called the bus, was about 1.3 meters, or 4.3 feet, from front to back. DART also changed Dimorphos into what scientists call an active asteroid. An active asteroid is an asteroid that follows an asteroid-like orbit but produces a tail of material similar to a comet.

Scientists had proposed that impacts could cause activity on some asteroids. Before DART, however, scientists had not observed an asteroid becoming active under a known and controlled impact. The mission provided a controlled case for studying how an impact can produce and move material around an asteroid.

How scientists measured the result?

Scientists around the world observed the Didymos system after the collision. Observations came from ground-based telescopes and radar facilities. These included NASA’s Goldstone planetary radar in California and the National Science Foundation’s Green Bank Observatory in West Virginia. Other facilities included the Swope Telescope at Las Campanas Observatory in Chile, the Danish Telescope at La Silla Observatory in Chile and the Las Cumbres Observatory global telescope network in Chile and South Africa.

The Hubble Space Telescope also observed the material released from Dimorphos. An image taken on October 8, 2022, showed debris from the surface 285 hours after the collision. The Italian Space Agency’s LICIACube also provided images. Scientists used images from DART’s final approach and LICIACube observations to study the shape and mass of Dimorphos. The investigation also examined the impact crater and the material released from the surface.

What DART means for planetary defense?

The purpose of DART was not to protect Earth from Didymos or Dimorphos. Neither object poses a hazard to Earth before or after the controlled collision. The purpose was to test a method that could be considered if scientists discover an asteroid on a collision course with Earth.

The mission showed that a spacecraft can autonomously target and hit a small asteroid during a high-speed encounter. Researchers said an asteroid with a diameter of less than one kilometer can be intercepted without an advance reconnaissance mission, although such a mission would provide information that could help plan the operation and predict the result.

Time is a key part of the method. Researchers said an asteroid-deflection mission would need sufficient warning. Several years would be needed at a minimum, while decades would be preferable.

As of March 2023, scientists had found about 42 percent of asteroids larger than 140 meters. No known asteroid larger than 140 meters had a significant chance of hitting Earth during the following 100 years, according to the supplied NASA material.

This means asteroid detection remains an important part of planetary defense. Finding an object early would provide more time to study it and decide whether a deflection mission is required.

What comes next after DART?

The DART investigation did not end with the collision. Scientists continued to study the data from the spacecraft and observations from Earth. One area of study is the efficiency of momentum transfer. Researchers want to understand how much of the spacecraft’s impact energy changes the asteroid’s motion and how much comes from ejecta.

Scientists also need more information about Dimorphos’ physical properties. Its surface characteristics and strength can affect how an asteroid responds to an impact. The European Space Agency’s Hera project was planned to conduct detailed surveys of Didymos and Dimorphos about four years after the DART impact. The mission is intended to study the crater produced by DART and make a measurement of Dimorphos’ mass. DART data are archived through NASA’s Planetary Data System.

Why the mission matters?

DART provided the first full-scale demonstration of asteroid deflection technology through a kinetic impact. The spacecraft was intentionally destroyed when it struck Dimorphos. The loss of the spacecraft was part of the mission design. The objective was to measure whether the collision could change an asteroid’s motion.

The answer was yes. Dimorphos’ orbital period changed from 11 hours and 55 minutes to about 11 hours and 22 to 23 minutes, depending on the measurement and analysis. The later detailed studies measured the change at about 33 minutes with an uncertainty of about one minute. The result gave researchers data on the kinetic impactor method, momentum transfer, ejecta and asteroid activity.

DART also showed why asteroid defense cannot depend on impact technology alone. A potential threat would need to be detected early enough for scientists and space agencies to study the object and plan a response. The mission therefore became a test of both spacecraft targeting and asteroid science. Its findings provide information that can be used when considering future planetary defense missions.