Cassini Significant Events
for 07/29/08 - 08/05/08
The most recent spacecraft telemetry was acquired on Aug. 5 from the
DSN tracking complex at Madrid, Spain. The Cassini spacecraft is in
an excellent state of health and all subsystems are operating
normally. Information on the present position and speed of the
Cassini spacecraft may be found on the “Present Position” page at:
http://saturn.jpl.nasa.gov/operations/present-position.cfm.
Tuesday, July 29 (Day of Year (DOY) 211):
A review was held today of all the spacecraft engineering activities
to be executed during S48.
Optical Remote Sensing instrument observations today focused on
azimuthal variations in Saturn’s B ring, such as its well known spoke
features. An hour was dedicated to studying Rhea and obtaining a
global color image. Following the Rhea imaging, the Magnetometer
Subsystem executed a five hour instrument calibration activity, and
an optical navigation image was obtained.
The Cassini-Huygens Analysis and Results of the Mission (CHARM)
teleconference was held today. The topic: Cassini’s Fourth
Anniversary, part 2 (of 3). Included in the presentation were
magnetosphere results by the end of the prime mission, and
observations of Titan in the final year of the mission.
Wednesday, July 30 (DOY 212):
Scientists have now confirmed that a lake-like feature in the south
polar region of Saturn’s moon Titan is truly “wet.” The lake is about
235 kilometers long. When the Visual and Infrared Mapping
Spectrometer (VIMS) observed the lake, named Ontario Lacus, it
detected ethane, a simple hydrocarbon that Titan experts have long
been searching for. The ethane is in liquid solution with methane,
nitrogen and other low-molecular weight hydrocarbons. Ethane is a
simple hydrocarbon produced when ultraviolet light from the sun
breaks up its parent molecule, methane, in Titan’s methane-rich,
mostly nitrogen atmosphere. The VIMS measurements rule out the
presence of water ice, ammonia, ammonia hydrate and carbon dioxide in
Ontario Lacus. Titan, which is one-and-a-half times the size of
Earth’s moon in diameter, and bigger than either Mercury or Pluto, is
one of the most fascinating bodies in the solar system when it comes
to exploring environments that may give rise to life. For a link to
the full news release go to:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=858
Thursday, July 31 (DOY 213):
A Cosmic Dust Analyzer (CDA) DOY 217 ring plane crossing activity was
uplinked to the spacecraft at 21:45 UTC today. The observation will
execute next Monday, and the data will be downlinked the next day.
The schedule has been released for the last Live Inertial Vector
Propagator (IVP) Update in S42. It is extremely compressed with the
kickoff meeting to be held today, and the bulk of the work being
performed Friday and Saturday. If the update is a “go”, the command
approval meeting will be held on Saturday with uplink of the files
shortly thereafter. Composite Infrared Spectrometer (CIRS), Imaging
Science (ISS), Radio Science (RSS), and VIMS are the prime
instruments along with the Spacecraft Office and Science Planning
(SP) for this update of Saturn and Mimas vectors.
On July 31, Cassini flew by Titan at an altitude of 1613 km, and a
speed of 6.2 km/sec for the T45 targeted encounter. Closest approach
occurred at 2:13 SCET and latitude of 43.3 degrees S. ISS, CIRS, and
RSS science observations were the focus for this event. ISS
monitored cloud movement and acquired a full-disk mosaic of Titan’s
leading hemisphere, including coverage of Hotei Arcus. CIRS
continued the search for trace atmospheric molecular species in
Titan’s winter polar - northern - hemisphere by limb sounding of the
stratosphere. CIRS also continued a mapping campaign in the mid and
far- infrared to obtain the spatial and temporal variations of
temperature and hydrocarbon/nitrile molecules, providing information
on observable seasonal changes in weather, climate and chemistry that
may be occurring.
For RSS, the prime instrument at closest approach for this flyby,
observations focused on gravity field determination. An instrument
might be given a couple of hours near closest approach for a typical
Titan flyby, but in this special case, RSS was given over 16 hours
straddling closest approach. This was the first RSS gravity
observation in the Cassini extended mission, and the fourth Titan
flyby allocated to radio science for the determination of Titan’s
gravity field and the Love number, k2. The observation consisted of
two segments: an inbound, which included Titan closest approach, and
an outbound. A Gravity Science Enhancement (GSE) pass immediately
followed the outbound segment. Almost 40 hours of continuous
coverage were provided by a combination of all three DSS complexes at
Spain, Madrid, and Goldstone. In addition, the DSS-47 6-antenna
array at Narrabri provided Ka-band support during part of the first
segment.
RSS observations of Titan’s gravity field should allow us to
determine the internal structure of Titan, with the exciting
possibility that Titan may have an interior ocean below its frozen
surface. Complicating matters is Titan’s shifting shape: the moon
deforms as it rotates and as it orbits around Saturn. That means that
Titan’s gravity field changes as well. If Titan has a subsurface
interior ocean, gravity field measurements from this flyby as well as
T11, T22 and T33 may be able to confirm its presence.
Saturday, Aug. 2 (DOY 215):
The sequence leads for S43 were busy indeed this weekend. Instrument
Expanded Block (IEB) files for VIMS, ISS, CIRS, the Ultraviolet
Imaging Spectrograph (UVIS), and Cassini Plasma Spectrometer (CAPS)
were uplinked and verified. In addition, Orbit Trim Maneuver (OTM)
#162, a reaction wheel bias for the end of the S42 sequence, and the
DOY 217-218 Saturn/Mimas Live Update also went up.
Sunday, Aug. 3 (DOY 216):
Cycle #42 occurred today when the Main Engine cover was closed at the
end of the OTM-162 prime maneuver window for a dust hazard tomorrow.
It will be opened Aug. 5 at the start of the OTM-162 backup window.
OTM-162 was performed today. This is the Titan 45 clean up and
periapsis maneuver setting up for the Enceladus 4 encounter on Aug.
11. The main engine burn began at 6:40pm AM PDT. Telemetry
immediately after the maneuver showed the burn duration was 15.4
seconds, giving a delta-V of 2.53 m/s. All subsystems reported
nominal performance after the maneuver.
If you are wondering what happened to OTM-161, the number 161, not
the actual maneuver, was deleted to maintain a numbering convention.
All apoapsis maneuver numbers up to this point have been divisible by
three. It made sense to keep this convention for simplicity, data
query, and other reasons.
Monday, Aug. 4 (DOY 217):
Non-targeted flybys of Mimas and Epimetheus occurred today.
S46 port 2 products were delivered today as part of the Science
Operations Plan (SOP) process. The files have been merged and an
analysis from Science Planning will be coming out later today.
The Cassini Radio Science (RSS) S42 orbit 79 rings chord occultation
was completed today. The experiment was supported by Madrid stations
DSS-63 providing X- and S-band support, and DSS-55 providing X- and
Ka-band. This was the first RSS rings occultation of the Cassini
extended mission. A quick summary provided by RSS indicated that the
experiment executed nominally and very good data sets were acquired.
This observation is the first in a family of four fast chord
occultations that probe the rings when the opening angle B is small,
about 4 to 7 degrees. For orbit 79, B = 6.8 deg. The long path of the
radio signals through the rings when B is small makes these
occultations especially sensitive to ring features of small optical
depth, like Ring C and the Cassini Division. More optically thick
ring regions, like Ring B, become mostly noise-limited. The
observation geometry complements in nature earlier occultations
conducted at larger B angles, providing valuable information about
the variability of ring structure and scattering properties with
viewing geometry.
Tuesday, Aug. 5 (DOY 218):
At the S43 final approval meeting today, all participating
instruments and engineering teams gave their confirmation that S43
was good to go for uplink. The background sequence will be sent to
the spacecraft later today and begin execution on Sunday, Aug. 10.
S45 began its final sequence development process when it completed
the SOP process last Friday and was handed off from Science Planning
to Uplink Operations at the S45 kick-off meeting today.
Coming up
Back in March, a NASA blog was set up to cover the Enceladus 3 flyby.
The blog allowed the general public to post comments in real time and
follow along as the flyby unfolded. We received very positive
feedback and so we are going to do it again for the Enceladus 4 flyby
on Monday, Aug. 11!
The Blog should be active by Friday morning. To follow along see:
http://blogs.nasa.gov/cm/blog/cassini-aug08/
Visit the JPL Cassini home page for more information about the
Cassini Project: http://saturn.jpl.nasa.gov/