Nasa's 'Dart' mission launches tech to deflect asteroids off path to Earth

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  This image provided by the Southwest Research Institute depicts the 'Lucy' spacecraft approaching an asteroid. It will be the first space mission to explore a diverse population of small bodies known as the Jupiter Trojan asteroids. AP Photo

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  Nasa's Double Asteroid Redirection Test 'Dart' spacecraft will crash into an asteroid as part of a planetary defence experiment. The launch is scheduled for November 23. Photo: Nasa

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  This artist's illustration obtained from Nasa shows the 'Dart' spacecraft and the Italian Space Agency’s LICIACube prior to impact at the Didymos binary system. AFP

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  A United Launch Alliance Atlas V rocket carrying the 'Lucy' spacecraft lifts off from Launch Complex 41 at the Cape Canaveral Space Force Station. AP Photo

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  'Lucy' will observe Trojan asteroids, a unique family of asteroids that orbit the sun in front of and behind Jupiter. AP Photo

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  The United Launch Alliance Atlas V rocket with the 'Lucy' spacecraft takes off. EPA

It might sound like a plot from a Hollywood movie, but Nasa is ready to launch tech into space that could one day deflect a dangerous asteroid off its path towards Earth.

A chunk of cosmic debris measuring just a few hundred metres could destroy a continent if it were to collide with our planet.

That is why Nasa is launching a small spacecraft to crash into a small asteroid satellite to see how much its speed and path can be altered.

The Dart spacecraft launch is the first attempt to deflect an asteroid for the purpose of learning how to protect Earth.

The asteroid it is targeting, called Dimorphos, presents no threat.

“Dart will only be changing the period of the orbit of Dimorphos by a tiny amount. And really that's all that's needed in the event that an asteroid is discovered well ahead of time,” said Kelly Fast, from Nasa's planetary defence coordination office.

At 6.20am GMT on Wednesday, a Falcon 9 rocket carrying the Dart spacecraft will blast off from Vandenberg Space Force Base in California.

The $325 million mission will target a pair of asteroids that closely orbit each other. The larger of the two objects, called Didymos, measures around 780 metres across, while its smaller companion, Dimorphos, is around 160 metres wide.

An artist's impression of the 'Dart' spacecraft with its 'roll out solar arrays' extended. Nasa

Objects of Dimorphos' size could explode with many times the energy of a typical nuclear bomb, devastating populated areas and causing tens of thousands of casualties.

Asteroids with a diameter 300 metres or larger could cause continent-wide destruction, while those bigger than 1km would produce worldwide effects.

After Dart launches, it will first escape the Earth's gravity, following its own orbit around the Sun. It will then intercept the binary as it approaches within 6.7 million miles of Earth in September next year.

Dart will smash into the “moonlet” Dimorphos at a speed of around 6.6km per second. This should change the speed of the object by a fraction of a millimetre per second — in turn altering its orbit around Didymos. It's a very small shift, but it could be just enough to knock an object off a collision course with Earth.