QUESTION:
During the C18 sequence, the weekly logs claim "This will enable the 
targeting of the asteroid Masursky in January as part of the C18 
sequence." What will take place during this event?

ANSWER from Brian Rush on January 4, 2000:
Cassini will flyby the asteroid 2685 Masursky, with a closest
approach of about 1.50 million km occurring at 9:58 UTC on January 23.

Three of Cassiniís Optical Remote Sensing (ORS) instruments will
make observations of Masursky a few hours before closest approach,
from 03:00-04:40 UTC.  The Imaging Science Subsystem (ISS), the
Visible and Infrared Mapping Spectrometer (VIMS), and the Ultraviolet
Imaging Spectrograph (UVIS) instruments will obtain about 120, 250,
and 2.2 Megabits of data, respectively. The image scale of the NAC
at the distance of Masursky will be about 10 km/pixel, which requires
that the asteroid be several times larger than 10 km for its size
and dimensions to be determined. At the very least, an upper limit
to its size can be determined, and the three instruments will be
able to make albedo, photometric, and spectral measurements of
Masursky. The rarity of data like these taken from beyond
the effects of the near-earth environment makes them particularly
valuable. VIMS, for example, will provide the first high-resolution
spectrum of an asteroid in the 2.5-5.0 micron region.

The data will be downlinked on 1 Feb 2000, and will then be sent to
the instrument teams who will reduce and analyze them: The ISS
and VIMS teams centered at the Lunar and Planetary Laboratory at
the University of Arizona at Tucson, and the UVIS team, centered a
at the Laboratory for Atmospheric and Space Physics at the University
of Colorado at Bolder.

The sparsity of observations of 2685 Masursky (discovered only in 1981)
make its trajectory difficult to determine, so there is no guarantee
that Cassini can target the asteroid successfully. However, this activity
was not part of the original mission plan for Cassini and is considered
bonus if successful.