UPDATE: NEAR Shoemaker is now on the outbound leg of its low-altitude flyover, having dipped to about three miles over Eros' surface at just before 3 a.m. EDT.

Early Thursday, after more than eight months in orbit around asteroid Eros, the NEAR Shoemaker spacecraft will swoop to within three miles (5.3 kilometers) of the asteroid, taking images and collecting data from a distance closer than any spacecraft has ever come to an asteroid.

Illustration of flyover. Photo: JHU/APL

"Our proximity to Eros will be equivalent to the cruising altitude of a commuter airplane on Earth," says Dr. Robert W. Farquhar, NEAR mission director at The Johns Hopkins University Applied Physics Laboratory (APL) Laurel, Md., which manages the Near Earth Asteroid Rendezvous (NEAR) mission for NASA. "When you consider that the asteroid is tumbling end to end in its orbit, getting this close is a little tricky, but we're very well-prepared." The low-altitude flyover will begin with a maneuver on Oct. 25 that will drop the spacecraft from a circular, 31-mile (50-kilometer) orbit. The NEAR Shoemaker spacecraft will be closest to the asteroid at about 3 a.m. (Eastern Daylight Time) on Oct. 26 as it approaches Eros at approximately three miles (5.3 kilometers) above its surface and traveling at about 14 miles per hour (6 meters per second).

The spacecraft will take images and collect data for more than five hours during its descent. It will remain at its lowest altitude for approximately 30 minutes before the distance increases due to the asteroid's rotation and its irregular shape.

"We expect to get clear images of boulders as small as two feet across and see ridges and craters in exquisite detail," says APL's Dr. Andrew F. Cheng, who serves as the NEAR project scientist. "The laser rangefinder and x-ray spectrometer will also obtain their highest resolution data to date," he says. Although the closest approach is targeted near one end of Eros in the southern hemisphere, the precise location is uncertain. "But that wouldn't be a problem," Cheng says. "A close look at almost any area of Eros' surface will give us detailed information that we don't have now."

At approximately 1:40 p.m. (EDT) on Oct. 26, an engine burn will push the spacecraft away from Eros toward a 125-mile (200-kilometer) orbit, where it will stay for the next month. In December, the spacecraft will begin descending to lower and lower orbits as it completes its science objectives. The mission is scheduled to end in February 2001-one year after NEAR Shoemaker began orbiting the asteroid.

Images from the low altitude flyby will be available starting about 11 a.m., (EDT) Oct. 26, on the NEAR Web site (near.jhuapl.edu).