Douglas Isbell
Headquarters, Washington, DC                December 30, 1998
(Phone:  202/358-1753)

Helen Worth
Johns Hopkins University Applied Physics Laboratory, Laurel, MD
(Phone:  240/228-5113)

RELEASE:  98-228

NEAR SPACECRAFT SET FOR JAN. 3 BURN

     A confident NEAR mission operations team is preparing to 
fire the main engine of the Near Earth Asteroid Rendezvous 
(NEAR) spacecraft at noon on Jan. 3 to put the mission on 
course for a rendezvous with its target, asteroid 433 Eros, in 
just over a year.  

     The upcoming burn will last 24 minutes and will increase 
the spacecraft's speed by 2,100 mph (939 meters per second), 
putting it at close to the same speed as Eros.  The burn will 
be divided into an initial three-minute "settling burn" with 
the spacecraft's small hydrazine thrusters that will change its 
velocity by only 11 mph (five meters per second), and a 21-
minute firing of the bipropellant main engine that will provide 
the rest of the velocity change.  

     The burn will lessen the distance between NEAR and Eros as 
they orbit the sun.  For the next year NEAR will travel behind 
Eros in a slightly closer orbit to the sun.  By mid-February 
2000, NEAR will catch up to Eros.  The spacecraft will then 
enter orbit around Eros and begin its planned yearlong study of 
the asteroid.

     The spacecraft's first attempted rendezvous burn was 
aborted on Dec. 20, 1998, just seconds after the settling burn 
was completed.  An investigation by mission personnel revealed 
that the brief engine burn exceeded certain safety limits 
associated with the onboard system that autonomously controls 
the spacecraft.  This resulted in the engine abort.  
Reprogramming of these values is now being completed and the 
spacecraft will be ready for the Jan. 3 burn.

     "We're very confident that we've found the problems 
associated with the Dec. 20 abort," says Thomas B. Coughlin, 
NEAR Project Manager at the Johns Hopkins University Applied 
Physics Laboratory (APL) in Laurel, MD, which manages the 
mission for NASA.  "The abort lost us time but the flyby gave 
us valuable information about Eros' shape and mass that we 
wouldn't have had -- information that will help us during our 
orbital phase a little more than a year from now." 

     Because the spacecraft did not complete the Dec. 20 burn, 
the opportunity to orbit Eros next month as originally planned 
was lost.  The setback presented mission planners with a huge 
challenge but also an unexpected opportunity.  Within days of 
the abort, the NEAR team developed a complicated command 
sequence for a Dec. 23 flyby of Eros to obtain multicolor 
images, near-infrared spectra, and magnetic field measurements.  
The commands were uploaded swiftly to the spacecraft and 
executed as planned, producing images of the asteroid and 
valuable data that is now being processed. 

     Despite the delay, NEAR is expected to complete all its 
science objectives.  To follow the NEAR mission as it unfolds, 
visit the project Web site at: http://near.jhuapl.edu   

     Updates on mission activities and science results are also 
available by phone on the NEAR Hot Line at (240) 228-5413.  Due 
to the rescheduling of mission events, the previously announced 
Jan. 10 and Jan. 14 press briefings have been canceled.