By BBC News Online science editor Dr David Whitehouse

The tiny Near spacecraft has swept into a trouble-free orbit around the asteroid Eros, becoming the first spacecraft to orbit an asteroid. It fulfilled its Valentine's day date just over a year after its first attempt failed.

A few hours before the manoeuvre, mission officials uploaded the encounter commands to Near's computer. These allowed it to automatically fire its thrusters and settle into a 200 km (124-mile) orbit of the potato-shaped asteroid.

Near will now begin a year-long study of Eros, conducting research that one day may help mankind defend the Earth against a killer asteroid like the one thought to have wiped out the dinosaurs.

Failure at first

"Everything is operating right on time," mission director Robert Farquhar said. "It is working exactly as we expected. We can just sit and wait now."

Eros is 34 km (21 miles) long and 13 km (8 miles) wide. The encounter took place 257 million km (160 million miles) from Earth.

The $224 million spacecraft was launched 17 February 1996 and should have gone into orbit around Eros in January 1999. However, a rocket firing that would have aimed the spacecraft at the asteroid went wrong and shut down automatically.

During its mission, Near will descend into lower and lower orbits. Later this year it may actually brush Eros' surface with a solar panel and photograph the mark it leaves.

"That's one of several options the team is considering for the end of the mission," said Mr Farquhar.

Near has five instruments, including a camera, that will map and probe Eros. The instruments will measure density, chemical composition and magnetic fields.