Out-of-control SpaceX rocket set to slam into the moon at a fantastic speed

An out-of-control rocket fired by SpaceX seven years ago is set for a high-speed impact with the surface of the moon.

The Falcon 9 has been drifting between the earth and the moon since February 2015, lacking enough fuel to get back home or to escape the gravity of the planet.

But astronomer Bill Gray said the rocket's aimless drift through space is going to come to a sudden and violent end.

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On March 4 the booster rocket will slam into a crater on the far side of the moon at a speed of 2.58km/second, or 9000km/h.

What complicates Dr Gray's predictions are the impact of sunlight hitting the rocket.

"If this were a rock, I'd be 100 per cent certain," he wrote in his blog.

"But space junk can be a little tricky.

"I have a fairly complete mathematical model of what the earth, moon, sun, and planets are doing and how their gravity is affecting the object.

"I have a rough idea of how much sunlight is pushing outward on the object, gently pushing it away from the sun."

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The rocket was used to launch the Deep Space Climate Observatory.

Dr Gray said this was the first unintentional case of space junk hitting the moon that he was aware of.

If space junk hits the Earth, it is usually burnt up in the atmosphere and largely destroyed before making contact with the ground.

But the moon has no atmosphere.

The rocket booster weighs an estimated four tonnes.