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NEAR EARTH ASTEROID RENDEZVOUS (NEAR)
Mathilde Encounter: June 27, 1997
The NEAR flyby of Mainbelt Asteroid 253 Mathilde:
Science Objectives and Encounter Strategy
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A. Harch, J. Veverka, J.F. Bell, C. Chapman, M. Malin, L.A.
McFadden, S. Murchie, M. Robinson, P.C. Thomas, D.K. Yeomans, B.G.
Williams, S. Squyres, R.W. Farquhar, A. Cheng, D.W. Dunham
On June 27, 1997 the NEAR spacecraft will pass within about 1200
km of main belt asteroid 253 Mathilde. Complementing the Galileo
flyby's of S-asteroids Gaspra and Ida, this will be the first ever
close observation of a C-asteroid. Mathilde has attracted recent
attention due to its extremely slow rotation period of 17.5 days.
Primary science objectives during this 10 km/sec flyby include
high- resolution imaging, as well as albedo and spectral mapping
of the illuminated surface of the large (50x50x70 km) asteroid.
The best monochrome images will achieve resolutions of 200
meters/pixel. Global imaging in seven colors between 0.4 and 1.1
micron will be carried out at resolutions of 400-500 m/pixel. On
departure a satellite search will be made in which bodies as small
as 100 meters across could be detected. A determination of the
mass of Mathilde to about ±10% will be carried out by the Radio
Science experiment.
Due to the encounter geometry (approach phase angle 139°,
departure at 39°) the best imaging of Mathilde will occur around
and just after closest approach. Locating Mathilde with sufficient
accuracy to insure the the highest resolution observations are
obtained near closest approach requires optical navigation updates
of Mathilde's position as late as 12 hours before encounter. This
will be the first ever fast flyby of an asteroid with a
spacecraft, which unlike Galileo, does not have a scan platform.