Eros Orbital Countdown Begins

The NEAR (Near Earth Asteroid Rendezvous) spacecraft is about to make interplanetary history. On Jan. 10, 1999, after traveling more than a billion and a half miles it will reach asteroid 433 Eros and embark on the first close-up and comprehensive study of an asteroid. The NEAR mission, the first launch in NASA’s Discovery program, is being managed by The Johns Hopkins University Applied Physics Laboratory (APL), in Laurel, Md., which also built the spacecraft.

“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 yearlong 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      Jan. 10, 1999     Jan. 14, 1999

           1 p.m.             noon              1 p.m.

           NASA Headquarters  JHU/APL           JHU/APL

           Washington, D.C.   Laurel, Maryland  Laurel, Maryland

           Live over NASA TV  Live over NASA TV Live over NASA TV

For directions to the APL campus and information on hotel accommodations,
visit Web site.