DART: Everything you need to know about NASA’s mission to deflect an Asteroid
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DART: Everything you need to know about NASA’s mission to deflect an asteroid

Published: 23rd September, 2022 at 15:32
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On 27 September the space agency deliberately crashed a spacecraft into an asteroid as part of its planetary defence programme.

NASA's DART spacecraft successfully crashed into its target asteroid at 00.14 BST on 27 September. Here's everything you need to know about the first-of-its-kind mission.


What is the aim of the DART mission?

DART, or Double Asteroid Redirection Test, is the first ever mission to attempt to redirect the path of an asteroid by crashing a spacecraft into it.

The mission is part of NASA’s planetary defence strategy and aims to build on our ability to model, predict and prepare for an asteroid that might provide a threat to Earth, should one be discovered.

It was launched on a SpaceX Falcon 9 rocket from Vandenberg Space Force Base in California on 23 November 2021 and made impact on 27 September 2022.

“It's essentially a big science experiment to see if crashing a spacecraft into an asteroid is a good way to change its orbit around the Sun and potentially deflect an Earth-crossing asteroid away in the future should that happen, or rather when that happens,” said cosmochemist and author of Meteorite Dr Tim Gregory.

“It sounds impossible that something as lightweight as a spacecraft, even a spacecraft like DART, which weighs more than half a tonne, could possibly nudge something like an asteroid, which weighs millions of tonnes. But you don't need to nudge an asteroid by very much for it to miss the Earth entirely. Just fractions of a degree, and you'll miss the Earth by millions of miles.”

© NASA/Johns Hopkins APL

What asteroid did DART crash into?

DART’s target was a binary asteroid system made up of a larger asteroid named Didymos, which is Greek for ‘twin’, and a smaller companion asteroid named Dimorphos, which is Greek for ‘two forms', that orbits it roughly every 12 hours. Didymos is around 780m across and Dimorphos is around 160m across.

“It's important to stress that this particular asteroid system doesn't pose a threat to the Earth. It was merely just chosen as a target for this science experiment, and it was chosen from a few different candidates based on its orbit around the Sun,” said Gregory.

The spacecraft collided with Dimorphos when it is around 11 million km from Earth. At the moment of impact, it was estimated to be travelling at around 6.6km/s.

What's on board DART?

© NASA/Johns Hopkins APL/Ed Whitman

DART was designed and built by teams at Johns Hopkins Applied Physics Laboratory (APL) in Maryland, USA. The main structure is a cube roughly 1m across fitted with large, flexible solar arrays on opposite sides that stretch out around 8m each. It has a mass of around 610kg.

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It is powered by NEXT–C, NASA's Evolutionary Xenon Thruster–Commercial, an solar-powered ion propulsion system that produces thrust using xenon as fuel.

On board is a high resolution camera DRACO, or Didymos Reconnaissance and Asteroid Camera for Optical navigation. As well as being used to support navigation, the camera was also used to measure the size and shape of the asteroid target to investigate the geology of the impact site. The images acquired by DRACO before the kinetic impact were streamed back to Earth in real time.

In the final four hours before impact the SMART Nav, or Small-body Maneuvering Autonomous Real Time Navigation, worke alongside DRACO to autonomously maneuver the spacecraft into position for impact.

The spacecraft was also carrying a companion CubeSat named LICIACube (Light Italian CubeSat for Imaging of Asteroids) that was designed by the Agenzia Spaziale Italiana (ASI). LICIACube was deployed on 11 September during the spacecraft's approach to Dimorphos and captured images of the impact.

What will happen after the collision?

Following the impact, the DART investigation team will compare the results of the spacecraft's collision with Dimorphos via observations with ground-based telescopes with sophisticated computer simulations that they have already ran. This way they will be able to assess the efficacy of the kinetic impact and figure out the most effective way to employ it should any future planetary defence scenarios arise.

“The nature of doing any sort of science is sometimes you just don't know what's going to happen," said Gregory.

"And with this mission being the first of its kind, I think the margin for success is very wide. And I guess, to paraphrase the Apollo astronauts, hopefully it will be a success, but it might be a very successful failure.”

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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.


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