DART — Double Asteroid Redirection Test

Artist’s impression of the aftermath of the DART impact on Dimorphos. The illustration shows the ejection of a cloud of debris after NASA’s DART spacecraft collided with the asteroid Dimorphos. The image was created with the help of the close-up photographs of Dimorphos that the DRACO camera on the DART spacecraft took right before the impact. Credit: ESO/M. Kornmesser

The Double Asteroid Redirection Test (DART) mission was the first mission designed to evaluate the kinetic impact technique by striking an asteroid with a spacecraft at high relative velocity and observing the resulting change in orbit. The test involved flying the DART spacecraft at high relative velocity into the smaller of two asteroids that are co-orbiting in a binary pair, and using Earth-based observations before and after the impact to study the effects on the orbit. It also carried the LICIACube CubeSat, which was released prior to the encounter to image the impact and its result.

   Developed and led for NASA by the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, the DART spacecraft, which launched on November 24, 2021, slammed into an asteroid Dimorphos, the secondary member of the (65803) Didymos binary asteroid system, on September 26, 2022. Telescopes on Earth and in space observed the asteroid system and measured the change in Dimorphos’ orbit around Didymos. DART’s impact altered Dimorphos’ orbit around Didymos by 32 minutes, shortening the orbit to 11 hours and 23 minutes.

   The primary mission objective was to assess kinetic impact as a method for redirection of any future asteroids found to be on a trajectory to impact Earth, with the primary goals:

1. perform a full-scale demonstration of the spacecraft kinetic impact technique for deflection of an asteroid;
2. measure the resulting asteroid deflection, by targeting the secondary member of a binary Near-Earth object and measuring the resulting changes of the binary orbit; and
3. study hypervelocity collision effects on an asteroid, validating models for momentum transfer in asteroid impacts. 

Illustration of NASA’s DART spacecraft and the Italian Space Agency’s (ASI) LICIACube prior to impact at the Didymos binary system. Credits: NASA/Johns Hopkins, APL/Steve Gribben

Inside SpaceX’s Payload Processing Facility at Vandenberg Space Force Base in California, both halves of the Falcon 9 rocket’s protective payload fairing move toward NASA’s Double Asteroid Redirection Test (DART) spacecraft on Nov. 16, 2021. Credit: NASA/Johns Hopkins APL/Ed Whitma
 

   The DART spacecraft was a box-shaped main bus with two large solar panel wings and a total mass at launch of approximately 610 kg. The spacecraft was 18 meters across its two solar panel wings and the main bus box was 1.14 × 1.24 × 1.32 meters. The bus was 2.6 meters high with the thruster and equipment mounteded on the top and bottom, and structures on the sides extended to a width and depth of 1.8 x 1.9 meters. Propulsion was be provided by the NASA Evolutionary Xenon Thruster (NEXT-C) ion engine. The spacecraft carried a single instrument, the Didymos Reconnaissance and Asteroid Camera for OpNav (DRACO), which provided images for the Small-body Maneuvering Autonomous Real-Time Navigation (SMARTNav) algorithm used for guidance, navigation, and control operations in targeting the asteroid, assisted by a star tracker and 5 Sun sensors. Orientation and propulsion were provided by 12 hydrazine thrusters. Communications were provided by a gimbaled high-gain radial-line-slot array antenna and two low-gain antennas. DRACO used a 20.8 cm aperture, F/12.6 telescope with a field of view of 0.29 degrees providing images at a resolution of about 0.5 arcsec/pixel. The two Roll Out Solar Arrays (ROSA) extended from opposite sides of the bus, had a total area of 22 square meters, and were designed to produce 6.6 kilowatts with battery storage.

   The LICIACube (the Light Italian Cubesat for Imaging of Asteroids) wass a 6U CubeSat provided by the Italian Space Agency. It was carried along with DART to Didymos and was released on September 11, 2022, before the DART impact. LICIACube performed a separation maneuver to follow about three minutes behind DART and returned images of the impact, the ejecta plume, and the resultant crater. It will also image the opposite hemisphere from the impact. LICIACube was 3-axis stabilized and had a propulsion capability of 56 m/s. It had two optical cameras, the LICIACube Unit Key Explorer (LUKE), and the LICIACube Explorer Imaging for Asteroid (LEIA). LUKE had a focal length of 70.55 mm and a field of view of 5 degrees, with an IFOV of 16 arcsec/pixel, giving a spatial resolution of 4.31 meters at 55.3 km distance. The LEIA imager had a 220 mm focal length, a 2.06 degree field of view, and an IFOV of 5 arcsec/pixel giving a resolution of 1.38 m/pixel at 55.3 km distance. The CubeSat had dimensions 10 cm × 20 cm × 30 cm, and a mass of 14 kg.

   Didymos is a sub-kilometer asteroid and binary system that is classified as a potentially hazardous asteroid and near-Earth object of the Apollo group. The primary asteroid is about 765 meters in diameter (849 × 851 × 620 m). It was discovered on April 11, 1996 by the Spacewatch survey at Kitt Peak National Observatory in Arizona, and its small 160-meter moon, named Dimorphos, was discovered in 2003. The moon orbits about 1.2 km from its primary. Due to its binary nature, the asteroid was then named Didymos, the Greek word for 'twin'. Didymos orbits the Sun with a semi-major axis of 1.64 au, a perihelion 1.01 au and an aphelion 2.28 au. The orbital period of Didymos is 2.11 years. The minimum distance between the orbit of Earth and the orbit of Didymos is currently 0.04 au (6.0 million km). 

The SpaceX Falcon 9 rocket launches with the DART, spacecraft onboard, November 24, 2021, from Space Launch Complex 4E at Vandenberg Space Force Base in California. The mission was built and is managed by Johns Hopkins APL for NASA’s Planetary Defense Coordination Office. Credit: NASA/Bill Ingalls

Infographic showing the effect of DART's impact on the orbit of Dimorphos. Credit: NASA/Johns Hopkins APL

  DART was launched on a Falcon 9 from Vandenberg Air Force Base on November 24, 2021. The LICIACube was released from DART on September 11, 2022. Impact on Dimorphos took place on September 26, 2022 at 23:14:24 UTC. In the last 4 hours before impact, DART employed the Didymos Reconnaissance and Asteroid Camera for OpNav (DRACO) and the Small-body Maneuvering Autonomous Real-Time Navigation (SMARTNav) algorithm systems to target the asteroid. During this time it also returned detailed images of the surface (better than 20 cm/pixel at impact) of Dimorphos to pinpoint the exact impact site within one meter and to determine the local surface geology for later impact modelling. SMART Nav first detected Dimorphos 73 min before impact, and at 50 min before impact, SMART Nav began manoeuvring towards Dimorphos. As planned, SMART Nav manoeuvring ended at 23:11:52 UTC, 2.5 min before impact, to give the spacecraft time to settle to minimize jitter and smear in the final images.

   The spacecraft flew into Dimorphos at 6.145 km/s with an impact mass of 579.4 ± 0.7 kg. It struck within 25 m of the centre of moon's figure. The final full image was acquired 1.818 s before impact and has a pixel scale of 5.5 cm. The final image received on the ground was a partial image acquired 0.855 s before impact with a pixel scale of 2.6 cm. The LICIACube flew 165 seconds after impact at a distance of 56.7 km, recording details of the impact plume and surfaces at resolutions up to 2 meters per pixel. Data were taken from 71 seconds before the impact until 320 seconds afterwards. After impact, Earth-based observations continued in order to characterize the resulting change in orbit of Dimorphos induced by the impact. The distance to Earth at impact was approximately 11.2 million km.

Asteroid Didymos (bottom right) and its moonlet, Dimorphos, about 2.5 minutes before the impact of NASA’s DART spacecraft. The image was taken by the onboard DRACO imager from a distance of 920 kilometers. This image was the last to contain a complete view of both asteroids. Didymos is roughly 780 meters in diameter; Dimorphos is about 160 meters in length. Didymos’ and Dimorphos’ north is toward the top of the image. Credit: NASA/Johns Hopkins APL

Asteroid moonlet Dimorphos as seen by the DART spacecraft 11 seconds before impact. DART’s onboard DRACO imager captured this image from a distance of 68 kilometers. This image was the last to contain all of Dimorphos in the field of view. Dimorphos is roughly 160 meters in length. Dimorphos’ north is toward the top of the image.  Credit: NASA/Johns Hopkins APL

The last complete image of asteroid moonlet Dimorphos, taken by the DRACO imager on NASA’s DART mission from ~12 kilometers from the asteroid and 2 seconds before impact. The image shows a patch of the asteroid that is 31 meters across. Dimorphos’ north is toward the top of the image. Credit: NASA/Johns Hopkins APL 

     The mass of the Didymos system is estimated at 528 billion kg, with Dimorphos at 4.8 billion kg. The impact targeted the center of figure of Dimorphos and should decrease the orbital period of Dimorphos around Didymos. Details of the surface structure, impact, and changes in the orbit recorded by ground-based observatories and the DART and LICIACube images were used to determine the efficiency of impact kinetic energy transfer.

   Analysis of data obtained in the weeks after the DART impact showed the spacecraft's kinetic impact successfully altered the asteroid’s orbit. Prior to DART’s impact, it took Dimorphos 11 hours and 55 minutes to orbit its larger parent asteroid, Didymos. The spacecraft’s impact altered Dimorphos’ orbit around Didymos by 33 minutes, shortening its orbit to 11 hours and 22 minutes. This measurement has a margin of uncertainty of approximately plus or minus 1 minute. This large change indicates the recoil from material excavated from the asteroid and ejected into space by the impact (known as ejecta) contributed significant momentum change to the asteroid, beyond that of the DART spacecraft itself. The impact ejected over 1 million kilograms of debris into space, producing a dust plume that temporarily brightened the Didymos system and developed a 10,000-kilometer-long dust tail that persisted for several months.
 
   Ground-based observations showed that the Didymos system brightened by a factor of 8.3 after the impact because of ejecta, returning to the preimpact brightness 23.7 days afterwards. The ejecta plume was a cone with an aperture angle of 140 ± 4 degrees. The inner region of the plume was blue, becoming redder with increasing distance from Dimorphos. The ejecta plume exhibited a complex and inhomogeneous structure, characterized by filaments, dust grains and single or clustered boulders. The ejecta velocities ranged from a few tens of metres per second to about 500 metres per second.

   The European Space Agency’s Hera mission, launched on October 7, 2024, will arrive at Dimorphos in late 2026, to observe the aftermath of DART’s impact and evaluate the kinetic impactor method for deflecting a near-Earth object.
 
Post-Impact LICIACube image showing Didymos-Dimorphos and the plume. Distance LICIACube-Dimorphos = 56.7 km. Credit: ASI/NASA

LICIACube satellite acquired these images just before and after its closest approach to the Dimorphos asteroid, after the Double Asteroid Redirect Test, or DART mission, purposefully made impact on Sep. 26, 2022. Didymos, Dimorphos, and the plume coming off of Dimorphos after DART impact are clearly visible. Credits: ASI/NASA
 
These images from NASA’s Hubble Space Telescope, taken (left to right) 22 minutes, 5 hours, and 8.2 hours after NASA’s Double Asteroid Redirection Test (DART) intentionally impacted Dimorphos, show expanding plumes of ejecta from the asteroid’s body. The Hubble images show ejecta from the impact that appear as rays stretching out from the body of the asteroid. The bolder, fanned-out spike of ejecta to the left of the asteroid is in the general direction from which DART approached. These observations, when combined with data from NASA’s James Webb Space Telescope, will allow scientists to gain knowledge about the nature of the surface of Dimorphos, how much material was ejected by the collision, how fast it was ejected, and the distribution of particle sizes in the expanding dust cloud.
Credits: Science: NASA, ESA, Jian-Yang Li (PSI); image processing: Alyssa Pagan (STScI)

Two days after DART’s impact, astronomers using the 4.1-meter NSF’s NOIRLab’s SOAR telescope in Chile captured the vast plume of dust and debris blasted from the surface of the asteroid Dimorphos by NASA’s DART spacecraft when it impacted on 26 September 2022. In this image, the more than 10,000 kilometer long dust trail — the ejecta that has been pushed away by the Sun’s radiation pressure, not unlike the tail of a comet — can be seen stretching from the center to the right-hand edge of the field of view.
Credit: CTIO/NOIRLab/SOAR/NSF/AURA/T. Kareta (Lowell Observatory), M. Knight (US Naval Academy). Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Zamani & D. de Martin (NSF’s NOIRLab)

This Hubble Space Telescope image of the asteroid Dimorphos was taken on 19 December 2022, nearly three months after the asteroid was impacted by NASA’s DART mission. Hubble’s sensitivity reveals a few dozen boulders knocked off the asteroid by the force of the collision. These are among the faintest objects Hubble has ever photographed inside the Solar System. The ejected boulders range in size from 1 m to 6.7 m across, based on Hubble photometry. They are drifting away from the asteroid at around 1 km per hour. Credit: NASA, ESA, D. Jewitt (UCLA)


The final five-and-a-half minutes of images leading up to the DART spacecraft’s intentional collision with asteroid Dimorphos. The DART spacecraft streamed these images from its DRACO camera back to Earth in real time as it approached the asteroid. This replay movie is 10 times faster than reality, except for the last six images, which are shown at the same rate that the spacecraft returned them. Both Didymos and its moonlet Dimorphos are visible at the start of the movie. At the end, Dimorphos fills the field of view. The final image in the movie shows a patch of Dimorphos that is 16 meters across. DART’s impact occurred during transmission of the final image to Earth, resulting in a partial picture at the end of this movie. Didymos is roughly 780 meters in diameter; Dimorphos is about 160 meters in length. 
Credit: NASA/Johns Hopkins APL
 
 
 
© 2025, Andrew Mirecki 

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