Cassini Titan-3 Mission Description

http://saturn.jpl.nasa.gov/multimedi...by20050207.pdf

Note: A detailed timeline and additional graphics are available in the
PDF file.

Cassini Titan-3 Mission Description

OVERVIEW

The third targeted flyby of Titan occurs on Tuesday, February
15, 2005 at 6:58 SCET (Ground: 8:06 UTC - 12:06 AM Pacific time).
Cassini's closest approach to Saturn's largest satellite is at an
altitude of 1577 km (980 miles) above the surface at a speed of
6.1 kilometers per second (14,000 mph). Titan has a diameter of
5150 km (3200 miles), so the spacecraft passes within 1.6 Titan
radii.

This encounter is set up with two maneuvers: an apoapsis maneuver
scheduled for February 1st, and a Titan approach maneuver,
scheduled for February 11th. Titan-3 is an inbound flyby, with
Saturn periapsis occurring about two days after closest-approach,
on February 17th. The Navigation team expects to deliver the
orbiter to within 30 km of the target altitude at a confidence
of 99% (three sigma).

Titan-3 is Cassini's fourth targeted satellite encounter. The first
was Phoebe, on June 11 th, at an altitude of 2000 km. The second
was Titan A, on October 26th, at an altitude of 1200 km and the
third was Titan-B, on December 13th at an altitude of 1200 km.

ABOUT TITAN

Titan is one of the primary scientific interests of the
Cassini-Huygens mission. Through observations by Earth based
telescopes and the Voyager spacecraft, Titan has been revealed
to be an intriguing world both similar in nature to Earth and
unique among both satellites and terrestrial planets. The largest
of Saturn's satellites, Titan is larger than the planets Mercury
or Pluto. Titan is the only satellite in the solar system with an
appreciable atmosphere. Like Earth's atmosphere, Titan's atmosphere
is composed mostly of Nitrogen, yet appears to have few clouds.
However, it also contains significant quantities of aerosols and
organic compounds (hydrocarbons), including methane and ethane.
Although Titan's thick smoggy atmosphere masks its surface,
scientists have speculated Titan's surface could contain solid,
liquid and muddy material creating features such as lakes,
seas, or rivers. Additionally liquid reservoirs may exist beneath
the surface forming geysers or volcanoes that feed flowing liquid
onto the surface.

Titan's peak surface temperature is about 95 Kelvins, too
cold for liquid water, and due to its thick atmosphere, the pressure
at the surface is 1.6 times greater than Earth's atmosphere. At
this temperature and pressure, chemicals such as methane, ethane,
propane, ammonia, water-ice and acetylene may be involved in
complex interior-surface-atmosphere chemical cycles resulting in
eruptions, condensation and precipitation (or rain). Initial
observations obtained by Cassini during the first two passes of
Titan provided our first close up views of Titan in wavelengths ranging

from visible light to infrared to radar. The Huygens probe successfully

returned atmosphereic data and images of the surface, providing groud
truth for the Cassini Orbiter measurements. The results show a
mysterious
world even more complex than previously thought. The and the diversity
of surface composition and its connection to Titan's geologic features
remains a fundamental question. Huygens results indicate the methane
sits
as a liquid just below the surface and may rain from the atmosphere
periodically. Clouds in Titan's atmosphere were observed in the
southern
hemisphere, yet no clear explanation has emerged on what the clouds are

composed of, or why more clouds do not exist. Observations of Titan's
interaction with Saturn's magnetosphere indicates the presence of
complex
processes complicated by Titan's occasional emergence out of Saturn's
magnetosphere into the solar wind.

Observations by the Cassini orbiter during T3 will provide critical
information to our understanding of Titan. New infrared and visible
measurements will help to understand the relationship
between features seen in the visible and radar wavelength images and
surface
composition. RADAR Synthetic Aperature Imaging will provide detailed
swaths
across Titan's surface features and imaging from the ISS and VIMS
instruments
will provide joint imaging of RADAR observations. ISS and UVIS will
also
examine particle distributions in the atmosphere as well as cloud
formation
and atmospheric variations and together, these new observations will
continue
the detailed investigation of the variability on Titan. Are there
volcanoes
or geysers? Is there evidence for flowing liquids on the surface? What
is the extent of weather on Titan? How often does methane fall as rain?

How does Titan's upper atmosphere react to the variability of Saturn's
magnetosphere? The variations of Titan's surface, atmosphere and
magnetosphere
are clues to the active processes dictating its evolution and the
origin
of its intriguing complexity.


TITAN-3 SCIENCE ACTIVITIES

The Cassini/Huygens project is interested in four broad science themes
concerning Titan: its interior stucture, surface characteristics,
atmospheric properties, and interaction with Saturn's magnetosphere.

At an altitude of 1577 km, Titan-3 will not provide direct measurements

of the density of Titan's atmosphere.

CAPS will make measurements of Titan's upper ionosphere and gather
science from Cassini's crossing through Titan's plasma
wake. They will make both ion and electron measurements during the
flyby.
CAPS will also closely examine the interaction between Titan and
Saturn's Magnetosphere.

CIRS will perform two 4-hr limb integrations using their
mid-IR detectors to search for new molecules in the stratosphere. They
will also continue their campaign of far-IR integrations (begun on T0)
to search for species at longer wavelengths, and obtain a thermal map
of the stratosphere, lending insight into the dynamics of Titan's
atmosphere.

ISS plans to do a full-disk mosaic, during T03, that covers much of the

leading and anti-saturnian hemispheres (including Xanadu) at multiple
wavelengths to observe the surface and atmosphere, a 5x5 mosaic that
covers
western Xanadu and the dark area to the west, and two footprints
designed
to coincide with points along the T03 RADAR altimetry and SAR
observations.
It will be the first joint coverage of the same site by ISS, and VIMS,
who will be riding along, and RADAR-altimetry/SAR. ISS also has a
number
of ride-along observations, including outbound observations of Titan's
night side.

RPWS will study the interaction of the magnetosphere with
Titan at intermediate distances for evidence of ion pickup, radio
emissions,
density profiles, and the general wave environment. Given the
approximate
similarity of the T3 flyby geometry to that of Ta and Tb, RPWS will
concentrate
on variations between the three flybys. Already, a significant
difference
has been observed in the inbound vs. outbound asysmmetry of the plasma
density when comparing the Ta and Tb results. RPWS will use a somewhat
modified instrument configuration to concentrate on lower-frequency
plasma
waves associated with the magnetosphere-Titan interaction and to
fine-tune
the Langmuir Probe thermal plasma measurements.

RADAR will control spacecraft attitude for the two hours around closest

approach, beginning 046T06:19. During that time, RADAR will perform SAR

Imaging including the first real "bright terrain', which includes part
of
Xanadu to be the subject of joint ORS/RADAR investigation. RADAR
Altimetry measurements taken during T3 will establish whether the lack
of topography identified during the Titan-A flyby was atypical.

MAG will investigate the large-scale and
distant aspects of the Titan interaction by observing during the entire

period around an encounter from 10 to 25 RS. (03TI (T3)). T3 will
complete
the triad of close flybys at almost the same Saturnian local time just
before local noon in the magnetospheric wake region of Titan. This will

provide a data set Ta,Tb,T3 to describe and understand the formation of

Titan's induced magnetic tail in three dimensions.

MIMI will investigate
micro-scale and near aspects of the Titan interaction by observing
during
~one hour period around the encounter. With -Y pointed toward Titan,
within
30 minutes of the targeted flyby, the secondary axis is optimized for
corotation flow as close to the S/C -X, +/- Z plane as works with the
other constraints on pointing. Also, Titan's exosphere/magnetosphere
interaction is measured by imaging in ENA with INCA.

UVIS will perform several slow scans across Titan's visible
hemisphere to form spectral images of Titan's upper atmosphere.
VIMS will image the surface of Titan at small solar phase angles, and
investigate the formation and evolution of clouds on Titan. They will
also search for lightning and hot spots and will attempt airglow
characterization.