NASA`s NEAR spacecraft prepares to touch down on Eros asteroid

The US spacecraft NEAR Shoemaker Monday was to attempt a historic unmanned touchdown on the surface of the asteroid 433 Eros, scientists with the National Aeronautics and Space Administration (NASA) said.

NEAR Shoemaker -- NEAR stands for Near Earth Asteroid Rendezvous -- has been orbiting Eros for a year and during that time collected 10 times more data than originally expected during its five-year, 223-million-dollar mission.

Now the craft is almost out of fuel, and its final approach toward the asteroid it has long gazed at -- not originally planned as part of the mission -- is "bonus science," according to NEAR Mission Director Robert Farquhar.

"It might not be a very soft touchdown. The unknown nature of the surface makes it hard to predict what will happen to the spacecraft, especially since it wasn`t designed to land," Farquhar said.

The controlled descent, set to start at 1631 GMT, will enable NASA to practice landing maneuvers ahead of future missions to other small celestial bodies, space officials said.

NEAR is currently orbiting Eros at 35 kilometers (22 miles) altitude. On touchdown day, it will fire its thrusters six times during a four-hour descent to slow to one-to-three meters per second, Farquhar explained.

Asteroid 433 Eros is 33 kilometers (21 miles) long and 13 kilometers (8 miles) in diameter, and lies 196 million miles from earth.

During its year-long orbit of the asteroid, NEAR transmitted some 160,000 images of the rocky surface.