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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