The spacecraft is due to touchdown at 15:04 local time (2004 GMT).

NEAR Shoemaker fired its thrusters for 20 seconds to ease the spacecraft down toward an altitude of 25 kilometers (15.5 miles).

"The de-orbit burn ... has worked quite well," said Robert Farquhar, NEAR mission director at the University's Applied Physics Laboratory (APL) in Laurel, Maryland, outside Washington.

"We are within one percent of our targeted accuracy. We're quite happy about that," he said.

With the first of five thrusters firing, the spacecraft was to slow to a speed of eight kilometers (five miles) per hour from 32 kilometers (20 miles) per hour.

Touchdown procedures, expected to last four and a half hours, began at 10:31 local time (1531 GMT). The spacecraft had been orbiting Eros at 35 kilometers (22 miles) altitude.

Asteroid 433 Eros, named after the Greek god of love, is 33 kilometers (21 miles) long and 13 kilometers (8 miles) in diameter, and lies 316 million kilometers (196 million miles) from earth.

It takes just more than 17 minutes for a command from Earth to reach the NEAR spacecraft.

The orbital plot shown left is NEAR Shoemaker's projected path from orbit to the surface of Eros on Feb. 12. Viewed from the sun, Eros is moving in a clockwise direction as it spins on its axis, while the spacecraft moves counterclockwise in a circular orbit 35 kilometers (22 miles) from the asteroid's center.

If the touchdown is successful -- there is no guarantee NEAR will survive the landing -- it will be the first time in the history of space exploration that a spacecraft has landed on an asteroid.

NEAR Shoemaker has been orbiting Eros for a year and during that time collected 10 times more data than originally expected during its five-year, two billion-mile, 223-million-dollar mission.

Now the craft is almost out of fuel, its final approach toward the asteroid it has long gazed at -- not originally planned as part of the mission -- is "bonus science," according 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 had said earlier.

During its year-long orbit of the asteroid, NEAR transmitted some 160,000 images of the rocky surface. NEAR is to touch down in an area of particular interest to scientists: largely-crater free but marked by large rocks and furrows.

Asteroids -- material left over from the formation of the solar system -- are rocky and metallic objects that orbit the Sun but are too small to be considered planets.

Because asteroids are material from the very early solar system, scientists are interested in their composition.

Eros, for example, is believed to contain magnesium, silicate and aluminum.

Before 1991 the only information obtained on asteroids was that which could be observed from Earth. In October 1991, the Galileo spacecraft whizzed by 951 Gaspra, taking the first high-resolution images of an asteroid.

In August 1993 Galileo made a close encounter with asteroid 243 Ida. Both Gaspra and Ida, like Eros, are classified as S-type asteroids composed of metal-rich silicates (stone).

On June 27, 1997, NEAR, although not designed for flyby encounters, made a high-speed close encounter with asteroid 253 Mathilde, granting scientists the first close-up look of a carbon-rich C-type asteroid.

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