Illustration NASA DART about to collide with Dimorphos Asteroid

DART: Everything you need to know about NASA's planetary defence mission

Published: 19th November, 2021 at 04:00
Try 3 issues of BBC Science Focus Magazine for £5!

Scientists are scanning the skies for potential threats to our planet, but what happens if they discover an asteroid on a collision course with the Earth?

NASA's not just about sending robots to Mars and building space telescopes. They are also making plans to keep our planet safe in the event that we discover an asteroid or comet on a collision course with the Earth. A large part of these plans, of course, is studying the sky for any potentially hazardous objects. But that's not all: the planetary defence programme also includes a mission called DART.


First things first: there isn't an asteroid on a collision course with Earth. We're not going the way of the dinosaurs just yet. The aim of the DART mission is to prepare ourselves. What would we do if we did find a dangerous space rock heading our way? And can we be confident our plan would work?

NASA isn't planning to blow up a dangerous asteroid like Bruce Willis in Armageddon. Instead, the idea behind the DART mission is to crash a spacecraft into it, knocking it into a safer orbit. The spacecraft will launch later in November 2021, and arrive at its target asteroid in 2022.

DART is part of the Asteroid Impact and Deflection Assessment (AIDA) mission, a joint collaboration between ESA, NASA, the German Aerospace Center (DLR), Observatoire de la Côte d´Azur (OCA) and the John Hopkins University Applied Physics Laboratory (JHU/APL).

What is the DART mission?

The Double Asteroid Redirection Test (DART) mission is a trial of NASA's planetary defence plans.

An asteroid or comet with a diameter above 140 metres that approaches Earth at a distance of less than 5 per cent of the distance from the Earth to the Sun is called a 'potentially hazardous object' (PHO). Most of these will pose no danger to us – in fact, NASA says that none of the known PHOs have a significant chance of hitting Earth in the next 100 years. However, it estimates that only 40 per cent of these objects are known.

So, just in cast we should discover a PHO that is heading straight for Earth, NASA has a plan: to use a spacecraft to deflect the oncoming asteroid. DART is the first attempt to do exactly that, using a near-Earth binary asteroid called Didymos. Orbiting Didymos is a moonlet called Dimorphos, which the spacecraft aims to knock into a different orbit.

Is it safe?

Yes, the DART mission is safe. Didymos, the target asteroid, is no threat to Earth. When DART reaches it in 2022, it will be roughly 11 million kilometres away, and the aim is only to move the moonlet Dimorphos into a different orbit around the asteroid.

More like this

When will DART launch?

The launch window for DART begins at 10:20pm PST on Wednesday 23 November (6:20am GMT on Thursday 24 November). The spacecraft will be launched aboard a SpaceX Falcon 9 rocket from Vandenberg Air Force Base, California, and will arrive at its target between 26 September and 1 October 2022.

How will DART work?

NASA plans to use the 'kinetic impactor' technique – that is, the spacecraft will crash into the asteroid to alter its course.

DART will manoeuvre using its onboard camera, DRACO, and autonomous navigation software. These will direct the spacecraft to collide with Dimorphos at a speed of about 6.6km/s (14,700mph), altering the moonlet's speed by less than 1 per cent. If all goes to plan, however, the change in its orbit will be big enough for Earth-based telescopes to observe.

Read more about NASA missions:



Sara RigbyOnline staff writer, BBC Science Focus

Sara is the online staff writer at BBC Science Focus. She has an MPhys in mathematical physics and loves all things space, dinosaurs and dogs.


Sponsored content