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Earth Swingby Puts NEAR Spacecraft On Final Approach To Eros

Donald Savage
Headquarters, Washington, DC                      January 20, 1998
(Phone:  202/358-1547)

Helen Worth
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD
(Phone:  301/953-5113)

RELEASE:  98-9

EARTH SWINGBY PUTS NEAR SPACECRAFT ON FINAL APPROACH TO EROS

       NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft, 
built by The Johns Hopkins University Applied Physics Laboratory 
(APL) in Laurel, MD, will become the first interplanetary 
spacecraft that can possibly be seen with the naked eye when it 
swings by Earth Jan. 22-23.  The spacecraft's solar panels will 
reflect the Sun's rays onto the Earth in a greeting as it flies by 
for an adjustment of its trajectory to correctly align the 
spacecraft for a rendezvous with asteroid 433 Eros, its mission target.  

       Launched Feb. 17, 1996, NEAR completed a flyby of the 
asteroid Mathilde in June 1997 and is now on its way back to 
Earth.  Late Thursday, Jan. 22, the spacecraft will approach Earth 
over the Pacific Ocean traveling at about 20,000 mph.  Because the 
United States will be in darkness as NEAR approaches, if there is 
no cloud cover, several geographic areas will be able to see the 
Sun reflecting off the spacecraft's solar panels, which will act 
as large mirrors.  These sunglints will be visible on the East 
Coast, Friday, Jan. 23, at about 1:30 a.m. EST and the West Coast 
at about 1:45 a.m. EST (Thursday, 10:45 p.m. PST). 

       The spacecraft then swings around the Aleutian Islands and 
over Siberia before reaching its closest point to Earth, about 336 
miles above Ahvaz in southwest Iran, Friday, Jan. 23, at 11:23 
a.m. local time (2:23 a.m. EST), traveling at about 29,000 mph, 
its fastest speed for the swingby.  Although NEAR will be close to 
Earth at this time, daylight may obscure its image.  

         The spacecraft then swings over Africa and on to 
Antarctica before pulling away from the Earth at a speed of about 
15,000 mph.  The swingby will have changed NEAR's trajectory to 
approximately 11 degrees south of the Earth's ecliptic plane, the 
orbital path the Earth takes as it circles the Sun, and put the 
spacecraft on target for its Jan. 10, 1999, rendezvous with Eros. 

       NEAR scientists and engineers are using the swingby as an 
opportunity to test performance and calibration of the 
spacecraft's six instruments and to practice coordinated multi-
instrument observations of the type that will be used at Eros. 

       The Multispectral Imager, a visible light camera that will 
help determine the physical characteristics of Eros, and the NEAR-
Infrared Spectrograph, used to study surface minerals, will be 
calibrated by comparing their readings of geological features with 
proven measurements of the same areas.  These instruments will 
also be used to take images of the Earth along the spacecraft's 
path.  NEAR's Magnetometer will be calibrated by comparing swingby 
data with known measurements of the Earth's magnetic field. 

       Other activities during the swingby will include using the 
X-Ray/Gamma-Ray Spectrometer to observe celestial gamma ray bursts 
and to collect data on gamma ray and X-ray backgrounds.  These 
data are needed so scientists can better remove background 
impurities from the measurements to be made at Eros.  

       NEAR is expected to capture its first images of Eros, a 25-
mile-long near-Earth asteroid, a few months prior to the 100th 
anniversary of the asteroid's discovery on 
Aug. 13, 1898.  After reaching Eros, the spacecraft will start its 
orbit about 600 miles above the asteroid's surface, descending to 
200 miles by February and coming as close as 10 miles during its 
yearlong study. Scientists will thoroughly map Eros and will 
examine its surface composition and physical properties.  On Feb. 
6, 2000, the mission is expected to end with a controlled descent 
onto the asteroid, sending dozens of high-resolution pictures as 
the spacecraft closes in on Eros.  

       The NEAR mission will be the first close-up study of an 
asteroid.  APL, the first non-NASA center to conduct a NASA 
planetary mission, is managing the mission for NASA's Office of 
Space Science, Washington, DC.   

       Information on the NEAR mission, including a list of areas 
most likely to see NEAR's sunglint and how to find NEAR as it 
swings by Earth, is available on the Internet at:
http://sd-www.jhuapl.edu/NEAR/

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