News | December 14, 2006
Cassini Significant Events 12/07/06 - 12/13/06
Cassini Significant Events 12/07/06 - 12/13/06
December 15, 2006
(Source: Cassini Project)
The most recent spacecraft telemetry was acquired on Wednesday, December 13, from the Goldstone 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" web page at http://saturn.jpl.nasa.gov/operations/present-position.cfm .
Thursday, December 7 (DOY 341):
On November 2, Cassini used its 4000th DSN tracking pass since the spacecraft was launched in October of 1997. The first 2837 passes were used during the cruise phase prior to arrival at Saturn.
The last Cassini Monthly Management Review for 2006 was held today. At these reviews, Program Management is informed of ongoing status through a series of presentations by Resource Management, Scheduling, Outreach, Mission Planning, Spacecraft Operations, Mission Assurance, Navigation, Mission Support and Services, Telecommunications and Mission Services, and Science and Uplink.
Two competing candidate plans were developed for the scientific observations to be carried out on the T32 Titan flyby in June of 2007. One plan features the collection of Ion and Neutral Mass Spectrometer (INMS) data, and the other emphasizes Optical Remote Sensing (ORS) observations, in particular a solar occultation egress measurement by the Ultraviolet Imaging Spectrograph (UVIS) and the Visual and Infrared Mapping Spectrometer (VIMS). Members of the Titan Orbiter Science Team (TOST) were unable to form a consensus as to which plan to choose, and attempts to "merge" the plans in some way have not been successful. The decision was handed over to the Project Scientist. What made the decision difficult was the fact that both plans offer excellent science at Titan. Also, with respect to Titan's surface and sensible atmosphere, it is difficult to find a scientific criterion for choosing one over the other. As a result, the Project Scientist fell back to the basics of considering the project and the established science goals as a whole. The following is extracted from the scientific objectives of the mission in the NASA Announcement of Opportunity for Cassini:
-- Determine abundances of atmospheric constituents (including any noble gases);
establish isotope ratios for abundant elements; constrain scenarios of formation and evolution of Titan and its atmosphere
-- Observe vertical and horizontal distributions of trace gases; search for more complex organic molecules; investigate energy sources for atmospheric chemistry; model the photochemistry of the stratosphere; study formation and composition of aerosols;
-- Measure winds and global temperatures; investigate cloud physics, general circulation and seasonal effects in Titan's atmosphere; search for lightning discharges;
-- Determine the physical state, topography and the composition of the surface; infer the internal structure of the satellite;
-- Investigate the upper atmosphere, its ionization, and its role as a source of neutral and ionized material for the magnetosphere of Saturn
-- Determine the configuration of the nearly axially symmetric magnetic field and its relation to the modulation of Saturn Kilometric Radiation (SKR).
-- Determine current systems, composition, sources, and sinks of magnetosphere charged particles;
-- Investigate wave-particle interactions and dynamics of the dayside magnetosphere, and the magnetotail of Saturn and their interactions with the solar wind, the satellites, and the rings;
-- Study the effect of Titan's interaction with the solar wind and magnetospheric plasma
-- Investigate interactions of Titan's atmosphere and exosphere with the surrounding plasma
Review of these objectives provided a clear way to resolve the "tie". Both plans address, to some degree, the 1st, 2nd, and 5th Titan objectives. With respect to the magnetospheric objectives, the INMS plan addresses the 4th and 5th objectives. The ORS plan does not significantly address any of the these objectives. The INMS plan was selected as it addresses more of the mission's objectives.
Friday, December 8 (DOY 342):
A Dione, Pan, Saturn live update is now being planned to execute from DOY 348-350. This update was not officially scheduled at the time that S26 was approved but has been carried on the books as a "possible" by Science Planning. The observations during this time were just under the threshold of the update limit when initial analysis of pointing variations in the reference trajectory was performed. However, the variations have become large enough to be over the live update threshold, hence the need for the update. The kick-off meeting was held yesterday and the Go/No Go meeting for today was cancelled, as all driving instruments wanted the update. The mini-sequence will be uplinked next Tuesday, and the update will begin execution on Thursday, December 14.
Monday, December 11 (DOY 345):
The Spacecraft Operations Office began a week-long final end-to-end test of AACS flight software version A8.7.5. today in the Integrated Test Laboratory. The software will be uplinked to the spacecraft in late January or early February of 2007.
Tuesday, December 12 (DOY 346):
Cassini flew by Titan for the T21 encounter at an altitude of 1000 kilometers. Traveling at a Titan-relative speed of 5.9 kilometers per second, Cassini could travel from Los Angeles, CA to New York, NY in just over 11 minutes.
T21 is an upstream encounter with appreciable inclination with respect to the equatorial plane. It is thus the first very close upstream pass and may enable the Magnetospheric and Plasma Science (MAPS) instruments, especially the Magnetometer (MAG), to study the magnetized ionosphere down to below the ionopause on the upstream side. Additionally for MAG, this flyby has considerable potential for internal magnetic field studies.
For this flyby the Synthetic Aperture RADAR (SAR) took a swath covering a wide range of latitudes from just below the equator overlapping with the T8 swath and moving up to about 50 deg N. This image will be the only SAR image in this region making it extremely valuable coverage. RADAR scatterometry covered a wide range of incidence angles including the very valuable low incidence angle range around the nadir point. It also extended down to the south pole providing valuable south polar coverage, which is in short supply. RADAR radiometry provided more coverage and polarization diversity to help resolve the properties of Titan's surface materials.
Meanwhile, the Composite Infrared Spectrometer (CIRS) obtained a combination of composition integrations in nadir mode and limb integrations in the mid-infrared, and the entire suite of Magnetospheric and Plasma Science (MAPS) instruments performed observations to study the interaction between Titan and Saturn's magnetosphere.
Wednesday, December 13 (DOY 347):
The Spacecraft Operations Office held an AACS Flight Computer Reset tabletop walk-through today. Walk-throughs are part of on-going training. This was the latest in a series designed to acquaint, or re-acquaint, team members with the behavior of System Fault Protection algorithms.
Official port 1 products were due today as part of the Science Operations Plan Update process for S29. The joint Project Briefing and final sequence development process kickoff meeting for S29 will be held on January 17.
JPL Media Relations supported a Titan news briefing for two dozen reporters at the American Geophysical Union (AGU) meeting held this week in San Francisco, CA. In conjunction with this briefing, a news release was issued on the tallest mountains ever seen on Titan by the Cassini spacecraft. These mountains appear to be coated with layers of organic material and blanketed by clouds. To find out more link to: http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=709
At the Tuesday Ops Status and Coordination Meeting, Radio and Plasma Wave Science (RPWS) team members reported that they had received science data from the future, May of 2007 to be exact. Although amused by the report, the flight team recognized that this could be a serious problem. In fact, it is just the latest in a string of reports from the instrument teams regarding recent problems with the data from DOY 336 -343. Command & Data Subsystem (CDS) personnel have been reviewing the raw telemetry data and have determined that the data corruption is due to double bit error hits in the SSR memory after the data was recorded.
CDS monitors the hourly rate of Single Bit Errors (SBE) and Double Bit Errors (DBE) on each SSR. A significant rise in the rates started on DOY 336, with a new high peak of 3820 SBEs per hour. This is coincident with a strong increase in solar flare activity recently reported in the news. CDS believes that the DBEs are a result of the solar activity, and there are no indications of any CDS flight software problems or SSR memory degradation. Double bit errors are temporary, being removed the next time the affected memory is overwritten. SSR memory is not radiation hardened and some SBE and DBE errors are expected. SBEs are corrected automatically by the SSR hardware using Error Detection And Correction (EDAC) logic, but the DBEs cannot be corrected and will result in some data corruption. CDS expects the SBE and DBE rates to return to normal levels once the solar activity subsides.