From: Jet Propulsion Laboratory
Posted: Sunday, November 8, 2009
The most recent spacecraft telemetry was acquired on Nov. 3 from the Deep Space Network 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.
Thursday, Oct. 29 (DOY 302):
Orbit Trim Maneuver (OTM) #220 was performed today. This was the approach maneuver setting up for the Enceladus 7 encounter on Nov. 2. The reaction control subsystem burn began at 6:00 PM PDT. Telemetry immediately after the maneuver showed the burn duration was 56.75 seconds, giving a delta-V of 66.96 mm/sec. All subsystems reported nominal performance after the maneuver.
In addition to the uplink of OTM-220, the S54 Radio Science (RSS) E7 Live Update Bloc was successfully uplinked at 19:57:00 UTC. The live update block begins execution at 305T15:36:59 SCET.
Sequence leads for S55 reported that since there were no change requests to the Preliminary Sequence Integration and Validation 2 (PSIV) phase products, the FSIV phase will be cancelled. The next meeting for S55 will be the final sequence approval and command approval meeting on Thursday, Nov. 5.
Today the Ultraviolet Imaging Spectrograph (UVIS) mapped volatiles in the immediate neighborhood of Enceladus to test for connection of volatile changes to plume eruptions. The Cassini Plasma Spectrometer (CAPS) performed a Magnetospheric and Plasma Science survey, and RADAR obtained distant Titan radiometer science and calibration data.
Friday, Oct. 30 (DOY 303):
The main engine cover was closed on Oct. 30, at the end of the OTM-220 backup pass. The cover will remain closed until Nov. 2. This will be the 52nd complete in-flight cycle of the cover.
In a JPL blog post, "Taking the Plunge: Cassini Soars by Enceladus," a Cassini science team member explains what makes scientists excited about the encounter planned for Nov. 2. It will be the deepest pass yet into the plumes spewing out from the moon's south polar region. Scientists want to learn more about the plumes' composition and density. The posting also pointed to a flyby animation and highlighted a new map of Enceladus. For the full posting link to: http://blogs.jpl.nasa.gov/?p=57
Saturday, Oct. 31 (DOY 304):
The backup sun sensor assembly onboard the spacecraft was powered up on Thursday for a checkout on Oct. 31. It will be powered off again on Monday.
Sunday, Nov. 1 (DOY 305):
A non-targeted flyby of Titan occurred today, and non-targeted flybys of Pallene, Epimetheus, and Calypso will occur tomorrow.
Today the Composite Infrared Spectrometer (CIRS) measured helium abundance at the location of a future RSS Saturn occultation. Later in the day, over the downlink to Earth, RSS performed gravity science to better determine the mass of Enceladus.
On DOY 305 Cassini Radio Science successfully completed the S54 Orbit 120 Saturn occultation experiment. The experiment included ingress and egress atmospheric occultations, and was covered by Goldstone's DSS-14 and DSS-25. Egress was also covered by Canberra's DSS-45 and DSS-34, as Goldstone was setting and reaching low elevation angles. This Radio Science atmospheric occultation was the first Saturn occultation in more than a year and was also the first after Saturn passed through equinox. The still nearly closed rings at this time with ~3 degrees ring opening angle frees the atmosphere from the rings allowing Cassini to probe a mid northern latitude range of angles that was sparsely sampled during the nominal mission. Overall, the experiment was a success, and the combined data from the two DSN complexes will provide a complete set of good observations.
Science activities today began with a UVIS high-phase Rhea observation to measure satellite albedo in ultraviolet light for a good sampling of longitude and phase space. Investigators will determine the phase function to investigate surface microstructure and frost properties as a function of location. Approaching Enceladus, ISS imaged the plume twice at very high phase while Cassini was in eclipse.
Monday, Nov. 2 (DOY 306):
Today Cassini flew by Enceladus at an altitude of 100 kilometers and a speed of 7.7 km/sec. Closest approach occurred at 89 degrees S latitude and at 306T07:42 SCET. To convert this to Pacific Time, subtract 8 hours and add one-way light time from Saturn to Earth. It was a little after midnight on Nov. 2.
Information provided by the AACS team after the flyby will be used to understand how much torque the plume exerted on the spacecraft. E9, an Enceladus flyby to occur in orbit 130, will have a trajectory similar to E7. The data from AACS will be used to determine whether thrusters or wheels will be used for E9 attitude.
The Visual and Infrared Mapping Spectrometer (VIMS) performed compositional and thermal mapping of Enceladus' surface and plumes. The data will be used to understand water ice grain size and ice crystal structure, and to map out the distribution of CO2 and organics on the surface, and to search for other compounds.
UVIS performed an experiment to measure the plume gas density by observing the plume in front of the disk of Saturn. In the past, UVIS has performed stellar occultations to measure plume gas density; in this experiment the disk of Saturn will be used in place of the star, and UVIS will investigate whether plume gas occults the Saturn signal.
With E7 being the first direct flyby through the Enceladus plume, and at a lower velocity than earlier inclined flybys, the Ion and Neutral Mass Spectrometer (INMS) was able to achieve very high signal-to-noise measurements of the gases in the plume, and looked for structure in the gases associated with the jets seen by ISS, UVIS and the Cosmic Dust Analyzer (CDA). Measurements should provide high enough signal-to-noise to allow INMS to discriminate between N2 and CO; distinguishing between these two species has been difficult in the past.
During the inbound leg RADAR took scatterometry measurements to determine cm-scale roughness and radiometry measurements to understand the energy balance. RADAR also targeted the instrument at Enceladus to execute a raster scan to obtain simultaneous scatterometry and radiometry data.
Magnetospheric and Plasma Science instruments took measurements to investigate interactions between Enceladus and its plume gases and the magnetospheric environment. The Magnetospheric Imaging Instrument in particular studied the field-aligned particles to explore connections to the Enceladus footprint in Saturn's auroral region. CAPS took measurements to map nanometer-sized charged particles and cold-water group ions. CDA explored the spatial alignment of the jets along Baghded and Alexandria sulci, and investigated the particle sizes of the ice grains in the jets.
A Science Forum was held today for S59. The agenda included an overview and context provided by the Science Planning lead, and science highlights/unique/highest priority observations provided by the Target Working Team and Orbiter Science Team leads, with comments from the Investigation Scientists and other instrument team representatives.
As reported in Circular No. 9091, Central Bureau for Astronomical Telegrams, INTERNATIONAL ASTRONOMICAL UNION, the Cassini Imaging Science Team reported the discovery of a satellite orbiting within the outer B ring. The satellite was detected through the presence of a 36-kilometer long shadow that it cast onto the rings during the equinox crossing period. The inferred diameter of the satellite, assuming an orbit co-planar with the ring material, is approximately 300 meters.
Tuesday, Nov. 3 (DOY 307): JPL posted a short feature highlighting two striking raw images from the Enceladus flyby that showed the plume spewing from the moon's south polar region. It also reported that the spacecraft weathered the passage in good health. See the post here: http://saturn.jpl.nasa.gov/news/cassinifeatures/newsfeature20091103/.
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