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Eros First Light:
During the approach to Eros, repeated images were used to pinpoint the asteroid in the sky to refine spacecraft navigation. This technique is called "optical navigation." The first of these images on 5 November, 1998 showed Eros as a tiny point against the star background.
This first image of the asteroid Eros from NEAR was acquired on November 5, 1998, from a range of 2.5 million miles (4 million kilometers). Eros appears against the star background in a single illuminated pixel. NEAR was 200 million miles (321 million kilometers) from Earth when this image was taken,
By mid-December, NEAR has approached Eros closely enough to make accurate measurments of the asteroid's brightness. As seen from the spacecraft, its brightness varied by a factor of three, because of the asteroid's tumbling end over end as it rotates.
Brightness variations of Eros were measured on December 14-15, 1998, when NEAR was at
a distance of 460,000 miles (740,000 kilometers). The period of the measurements covers
just over one rotation of the asteroid. At this time, Eros still appeared smaller than one
pixel in size, so its shape was not resolvable. The two inset images, acquired as NEAR
passed the asteroid on December 23, show the approximate orientation of the asteroid
at the points of maximum brightness (top) and minimum brightness (bottom).
This movie is the time sequence of images taken
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December 14-15, 1998, which show brightness
variations of Eros during its rotation.
- Attempt to Orbit
- At 5 PM EST on December 20, NEAR's main engine was commanded to fire, to match the speed of the spacecraft with the speed of Eros for insertion into orbit around the asteroid on January 10, 1999. However the burn was aborted by the spacecraft after less than two seconds. Contact with ground controllers was temporarily lost, but it was regained at 8 PM EST December 21 when autonomous spacecraft safety mechanisms regained control and transmitted a signal to the ground. All spacecraft systems were determined to be healthy, but orbit insertion, originally scheduled for January 10 was now out of the question.
- Emergency Orders
- Within hours, an "emergency" flyby observation sequence was sent to the spacecraft. As NEAR flew by Eros on December 23 at nearly one kilometer per second, the "emergency sequence" was executed flawlessly! 1026 images were acquired during repeated scans over the region containing the asteroid. These would determine the size, shape, morphology, rotational state, and color properties of Eros, and determine whether there were small moons. The infrared spectrometer measured spectral properties of the asteroid to determine what minerals are present, and the magnetometer searched for a natural magnetic field.
- Successful Fly By
- In the early morning of December 24, the flyby data began coming down to the ground. Expectant, exhausted mission engineers, controllers, and scientists waited in anticipation of a close-up look at the asteroid. The first image (upper left in the montage below) was christened by one of the scientists as "Christmas dinner," for its turkey-drumstick shape. All the images were received by the end of Christmas Eve, and it was clear that the flyby had been a success!
This montage of the 17 best views of Eros was acquired between 10:44 AM and 2:05 PM EST December 23 as the spacecraft range closed from 7300 miles (11,100) km to 2320 miles (3830 kilometers). From upper left to lower right, progressively less of the day side of Eros is visible as the NEAR's view shifted from the day side to the night side.
This movie, acquired by NEAR's camera as the spacecraft flew by Eros
MPEG Video
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on December 23, shows about two-thirds of a rotation of the asteroid.The first view, taken at 10:44 AM EST from a range of 7150 miles (11,890 km), shows about half of the dayside of Eros. The movie ends at 2:05 PM EST, just after closest approach, when only a tiny portion of the dayside of Eros is seen (phase angle 119°). During the movie, the spacecraft's view of the asteroid changed dramatically. As is the case with most asteroids, Eros is rotating uniformly about a fixed axis, and is not tumbling randomly through space.
For the remainder of December, 1998 and early January, 1999, mission planners and engineers analyzed data from the aborted engine firing of December 20, and designed a new burn (schedule) to reach the asteroid. The pressure was on, because each day's delay meant a month's delay in reaching the asteroid. Despite all worries, however, the main engine was fired successfully on January 3, 1999, placing NEAR on course for a February 2000 rendezvous with the elusive and still mysterious asteroid, 433 Eros.
-- END OF PICTORIAL VOYAGE --
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Created: 20 Dec, 1998
Revised: 21 Jan, 1998
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