UK space experts will tomorrow unveil a mission to save the world from a devastating asteroid impact. Leading rocket builders Astrium have drawn up plans to send a space probe to a 250-yard wide space rock called Apophis in 2013.

The asteroid, weighing 25 million tons, will have Earth in its sights twice in the next 30 years. During the first close encounter, in 2029, Apophis will pass closer than geostationary satellites such as those used for TV broadcasts.

Experts fear that the near miss in 2029 could put the asteroid on a collision course with our planet seven years later in 2036. It would strike with the force of many thousands of atom bombs – enough to wipe out a small country and causing havoc around the world.

Astrium engineers at Stevenage are submitting plans for their unmanned mission, called Apex. Their spaceprobe is designed to rendezvous with Apophis to map its surface in details and analyse its physical properties, such as the way it spins.

From the data, they will work out whether the asteroid will fly through a vital “keyhole” in space in 2029 that would lead to a real life Deep Impact in 2036.

Astrium’s proposal, which is being submitted to the US-based Planetary Society, also contains an analysis on how to avert disaster if a collision looks inevitable. This would involve finding ways to nudge it onto a different course, away from Earth. Simply blowing it apart with nuclear missiles is not an option as it could leave us at the mercy of several slightly smaller rocks.

Astrium’s Space Science Director Dr Mike Healy said today: “It is imperative to collect data on Apophis as soon as we can because once we know it’s on a collision course the safest way to avoid disaster is to nudge the asteroid to change its orbit.

“If we leave it too long, it will be impossible to build a spacecraft powerful enough to move its orbit. Ideally we would need to nudge it before 2025 to be sure it misses.”

The Planetary Society is offering a $50,000 prize for the winning proposal on how to tackle Apophis in a contest that has attracted around 100 entries from international teams and individuals. Astrium, who are also designing a robot rover to work on Mars, say they will fund a scholarship at the International Space University if their mission is accepted.

Picture: An Astrium artist’s impression of Apophis heading for the “cosmic keyhole” in 2029.