NEAR Spacecraft Closing In On Eros Asteroid

"What we now know about asteroids is very limited," says NEAR Mission Manager Dr. Robert W. Farquhar of APL. "It's come from ground-based observations and quick flybys. But now, for the first time, we're going to go into orbit around an asteroid and study it intensely for a year. We expect to get astounding information."

During its year-long mission to unlock the secrets of asteroid Eros, NEAR will confront the challenge of orbiting a tumbling, irregularly shaped body from extremely close distances. Never before has any small body been orbited by a spacecraft, but the additional task of maneuvering a spacecraft within 9 miles (15 kilometers) of the asteroid's surface makes the engineering challenge even more complex.

A cluster of six instruments will take millions of measurements and images over the entire surface of Eros from various altitudes. From these data, scientists will determine the asteroid's physical and geological properties and its elemental and mineralogical composition.

NEAR's rendezvous with Eros requires that the spacecraft be sped up with a series of engine burns so that it can catch up with the faster-moving asteroid. At 5 p.m. (EST) on Dec. 20, 1998, when NEAR is nearly 150,000 miles (242,000 kilometers) from Eros, a bi-propellant rocket engine firing (or "burn") will increase the spacecraft's speed by 1,500 mph (650 meters per second).

On Dec. 28, a second burn will increase NEAR's speed by 680 mph (294 meters per second) while at a distance of 13,000 miles (21,000 kilometers) from Eros, reducing the spacecraft's speed relative to Eros to less than 70 mph (30 meters per second). On Jan. 3, 1999, a third burn will reduce the relative speed a further 50 mph (22 meters per second) at a distance of 3,000 miles (5,000 kilometers). At 10 a.m., on Jan. 10, 1999, NEAR is scheduled to lock into orbit around Eros with a final burn reducing relative speed to 19 mph (8 meters per second) at a distance of about 630 miles (1,000 kilometers).

For the next year NASA's Deep Space Network will transmit data from the spacecraft to NEAR's Science Data Center, at the Applied Physics Laboratory, and commands from the Laboratory's Mission Operations Center back to the spacecraft. Regular tweaking of the spacecraft's orbit will be needed to ensure that spacecraft instruments are used to their full advantage.

Dr. Joseph Veverka of Cornell University, Science Team Leader for the mission, says the challenges that face the NEAR mission are significant. "This will be the first characterization in detail, not only of the surface of an asteroid, but of the interior of the asteroid, and the history that this asteroid has gone through based on its surface characteristics and materials composition."

The NEAR spacecraft was launched Feb. 17, 1996. Its flyby of asteroid Mathilde on June 27, 1997, provided the program's first science return. By mission's end, Feb. 6, 2000, scientists expect to know much more about Eros and thus near-Earth asteroids in general. From this, they hope to gain insight into the Earth's origin and the formation of the solar system.

To follow the NEAR mission as it unfolds, visit the mission's Web site: http://near.jhuapl.edu

Updates of mission activities and science returns will be posted on the Web site and provided to media through press conferences and briefings. The following conferences and briefings are currently scheduled:

* Dec. 16, 1998, 1 p.m. EST, NASA headquarters, Washington, D.C., live over NASA TV.

* Jan. 10, 1999, noon EST, JHU/APL, Laurel, Md., live over NASA TV.

* Jan. 14, 1999, 1 p.m. EST, JHU/APL, Laurel, Md., live over NASA TV.

For directions to the APL campus and information on hotel accommodations, visit Web site: http://near.jhuapl.edu/public/visit/locat.htm

APL is located on Johns Hopkins Road, 0.5 mile west of the intersection of Johns Hopkins Road and U.S. Route 29, just south of Columbia, Md.