Cassini Significant Events 11/28/07 - 12/04/07
December 6, 2007
(Source: Cassini Project)
The most recent spacecraft telemetry was acquired on Tuesday, Dec. 4, from the Madrid tracking complex. 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.
Wednesday, Nov. 28 (DOY 332):
Mission Assurance hosted part two of the periodic Cassini Risk Review today. Long before a spacecraft leaves the ground, project management identifies and tracks what possible risks are associated with all aspects of the mission, as well as what mitigation can be put in place to minimize these risks. Periodically the list is reviewed to determine what can be retired, if there are any new risks to be added, or if the mitigation can be augmented. Part one of this review was held on Sept. 19. Part two completed the review of existing risks and documented what risks should be added to the database for the proposed extended mission.
An encounter strategy meeting was held today to cover the period between Dec. 5 and Dec. 20, Titan flybys T38 and T39, and maneuvers 137-139.
Outreach gave Cassini presentations to three 9th grade classes with a total of 87 students at Gladstone High School in Covina, CA. One of the three classes was comprised of kids with Spanish as their first language, and was assisted by a bilingual aide.
"Reading, Writing and Rings: The Cassini Mission Literacy Program" has been nominated for peer review by the Multimedia Educational Resource for Learning and Online Teaching (MERLOT), consisting of online members throughout the US education community. MERLOT is used by the California State University system for training the next generation of teachers.
Thursday, Nov. 29 (DOY 333):
Uplink Operations sent commands to the spacecraft this morning for the DOY 336-337 Mimas/Epimetheus Live Update, and a RADAR DOY 337 Mimas mini-sequence.
The latter part of the science day today was spent observing the small recently discovered outer Saturnian satellites Kiviuq, Siarnaq and Paaliaq.
The Titan Atmosphere Model Working Group (TAMWG) met today to review results from the T37 flyby that occurred on Nov. 18. Because spacecraft telemetry containing thruster data at closest approach was lost during playback over Madrid due to a heavy rainstorm, there was no AACS input to the atmospheric density estimation discussion. However, the Ion and Neutral Mass Spectrometer (INMS) and Navigation (NAV) were able to obtain data and presented their analyses. The INMS and NAV solutions for density fit within results from previous flybys. This is encouraging since there are only two other passes with closest approach in the southern hemisphere of Titan and the T36 data hinted at the possibly of a lower density in that hemisphere. The T38 pass at 970 km and -70 deg latitude is expected to stay near the predicted thruster duty cycle of around 50%.
The last item on the agenda was the Saturn Target Working Team presentation of the Cassini model for the Saturn atmosphere, based on Voyager and Cassini observations.
The next TAMWG is planned for 16 January 2008, after the T38 and T39 flybys, in order to avoid the end of year holiday period. Exact time and location are being negotiated and will be announced before the end of the year.
Friday, Nov. 30 (DOY 334):
The next scheduled science data archive delivery is planned for Jan. 1, 2008, and will include data obtained from January 1, 2007 through April 1, 2007. All reporting instrument teams plan to deliver early or on time for this milestone. In January the Radar team will be reprocessing all of its Titan data to reflect the new estimate of pole position. This update is scheduled for the April 1 archive delivery. Two new products will also be officially delivered at that time: a new altimetry product, and a Synthetic Aperture RADAR (SAR) topographic map. More will be reported on these products in January.
As part of the "Scientist for a Day" essay contest, schoolchildren in the United States were invited to select from among four targets for Cassini to image, defending their choices in an essay. The contest received nearly 200 essays from 400 students either as groups or individuals in grades 5-12, from 24 U.S. states. Volunteers in the United Kingdom, India, and other countries ran parallel contests. Students wrote 500-word essays on the scientific justification for selecting one of four possible targets for Cassini to image on Nov. 30, 2007. NOTE: The winners were notified on Monday, Dec. 3, and will be invited to discuss their choice with Cassini scientists via videoconference on Dec. 5.
Sunday, Dec. 2 (DOY 336):
Cassini passed by Telesto, Mimas, and Epimetheus for a set of non-targeted flybys today.
Orbit Trim Maneuver (OTM) #136 was performed today. This is the approach maneuver setting up for the Titan 38 encounter on Dec. 5. The reaction control subsystem burn began at 5:30 AM PST. Telemetry immediately after the maneuver showed the burn duration was 10.6 seconds, giving a delta-V of 0.019 m/sec. All subsystems reported nominal performance after the maneuver.
Monday, Dec. 3 (DOY 337)
Science observations today began with RADAR obtaining simultaneous scatterometry and radiometry of the satellite Mimas. Following this, Cassini prepared to watch first Earth, then the Sun, pass behind Saturn and its rings.
As Earth passed behind the rings, Radio Science (RSS) probed the F ring, A ring, Cassini Division, and the outer portion of the B ring at three different wavelengths. The experiment was covered by Madrid using DSS-63 for S- and X-band support, and DSS-55 with X- and Ka-band support.
This orbit 53 RSS ring occultation was the first in a sequence of eight occultations to be implemented during the last seven months of the Cassini prime mission during the Cassini high-inclination sequence. The occultations capture the rings when the angle between the Cassini-to-Earth line-of-sight and the ring plane is relatively small. A more elongated path of the radio signal through the rings allows enhanced sensitivity to tenuous ring features at the expense of more attenuation by dense ring features. As a result, early and late occultation sets obtained at different points in the mission provide complementary information about ring structure and physical properties
Following RSS, the Cosmic Dust Analyzer (CDA) performed a study of the orbital elements of dust in the vicinity of the inner rim of the E ring. Then the Ultraviolet Imaging Spectrograph (UVIS) turned towards Saturn to watch the Sun emerge from behind the limb of the planet. These occultations are used by UVIS to measure the transmission of energetic ultraviolet photons through the Saturn atmosphere, to obtain atmospheric vertical temperature distribution and composition, and to identify atmospheric haze layers.
During the downlink that followed the observations today, the Radio and Plasma Wave Science (RPWS) instrument searched for wideband evidence of lightning whistlers. These would verify the existence of lightning already suspected from Saturn Electrostatic Discharges (SED) and would provide information on the electron density along the field line to the source.
Tuesday, Dec. 4 (DOY 338)
Cassini flew by the southern hemisphere of Titan today for the T38 encounter. Closest approach occurred at 2007-338T22:55:50 Spacecraft Event Time (SCET) with Cassini passing by at an altitude of 1300 km, and a speed of 6.3 km/sec.
Science activities began with a downlink to Earth as Radio Science (RSS) took data to measure Titan's gravity field. After the downlink, the Optical Remote Sensing (ORS) instruments took over. The Composite Infrared Spectrometer (CIRS) took measurements during this flyby to carry out vertical temperature sounding of Titan's tropopause and stratosphere, and to learn about the distribution of various components of Titan's atmosphere, such as methane, water, carbon monoxide and aerosols. ISS monitored the atmosphere for lightning and aurorae. UVIS performed several slow scans across Titan's visible hemisphere to form spectral images of that moon. An infrared camera on board performed high-resolution imaging of a dark region called Ontario Lacus, which may be a large lake, first spotted by the imaging cameras in 2005. Images were also taken of the Huygens probe-landing site. For more information link to:
The AACS Flight Software A8.7.6 Uplink Readiness Review was held today. This software delivery will update the default thruster force magnitudes and the secondary safing vector pair for the time period from Jan. 8, 2008, through mid-June 2009.
The S41 Aftermarket process began today, and is the last process of its kind for the Cassini Program. S41 is the last sequence in the Prime mission, and there will be no Aftermarket process as part of sequence development in the proposed extended mission. Aftermarket is a 5-week process that addresses proposed changes that require re-integration of the segments contained in a sequence.
Members of the Target Working Teams (TWT) met with Mission Planning to discuss the impact of the Phoenix Entry, Descent, and Landing (EDL) period on DSN support for Cassini. Unfortunately, the Saturn TWT orbits 64/65, or 2008-138T04:20:00 to 2008-148T04:43:00, along with the other TWTs and Orbiter Science Teams (OST) had planned extensive observations for that time frame and will be losing a good deal of planned 70m station coverage. In particular, EDL is on the day of periapse, closest approach to Saturn. Since the Aftermarket process for S40 is over on Dec. 6, a discussion of science priorities and data volume cuts - probably about 50% - for that time frame will be the main topic of conversation at upcoming TWT/OST meetings.