Nasa rocket to be launched on a collision course with comet

Nasa scientists are preparing for what they hope will be a carefully controlled and entirely spectacular crash in outer space. If all goes according to plan, the resulting pyrotechnics of the 23,000mph collision involving a comet and a spaceship should occur on 4 July, Independence Day in America.

Nasa scientists are preparing for what they hope will be a carefully controlled and entirely spectacular crash in outer space. If all goes according to plan, the resulting pyrotechnics of the 23,000mph collision involving a comet and a spaceship should occur on 4 July, Independence Day in America.

Officials at the space agency confirmed this weekend that they expect to launch a rocket from Cape Canaveral in Florida later this month with its navigation system set to intercept a comet called Tempel 1 as it travels just beyond the orbit of Mars at a distance from Earth of about 80 million miles.

The rocket will carry a special module that will be released just in time to make a direct hit on the surface of the comet. The module is called Deep Impact, a name familiar to fans of the 1998 Hollywood blockbuster about a comet that strikes the surface of Earth.

Researchers are gambling that by deliberately smashing the module into Tempel 1, they will open a crater perhaps as large as the Coliseum in Rome to reveal what lies within. The explosion, equivalent to igniting 4.5 tonnes of TNT in space, will send a shower of material into space that will be analysed.

"We'll understand how the comet is put together, its density, its porosity, whether it has a surface crust and underlying ices, whether it's layered ice, whether it's a wimpy comet or whether it's a rock-hard ice ball," explained Donald Yeomans, a researcher at JPL in California that advised on the making of the film. "All of these things will become apparent after we smack it."

The project offers the best way of mining the surface of a comet short of actually landing a spacecraft on the surface of one. That is the aim of the European Space Agency's Rosetta programme. However, delays mean that the agency only expects to achieve such a landing some time in 2012.

By deliberately crashing Deep Impact, Nasa is hoping for more instant scientific gratification. It will be akin to driving a lorry at full speed into an inert object, said Richard Grammier, the manager of the project. "It would be like it's standing in the middle of the road and this huge semi coming down at it at 23,000mph, you know, just bam!" he remarked.

He and his colleagues play down concerns that the collision could break up the nine-mile-long comet or alter its trajectory. He insisted there is no risk of sending it on a new course that could send it hurtling towards Earth. Nasa calculates that to change the comet's course, the impact would have to be 6,000 times greater.

Lift-off is scheduled for 12 January, two weeks later than expected following delays caused by problems with computers and the rocket system. It is vital to send Deep Impact on its way by 28 January - any later and the mother ship will no longer have the chance to catch up with Tempel 1. The chances of the spaceship missing its target altogether are put at less than 1 per cent.

The project's aim is to help find out how to deflect a comet should one fly towards Earth. Nasa also harbours hopes that comets might prove useful space refuelling platforms, with the possibility of robots breaking down water contained in them into hydrogen and oxygen, the ingredients for rocket fuel.

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