Cassini Significant Events 08/29/07 - 09/04/07
September 6, 2007
(Source: Cassini Project)
The most recent spacecraft telemetry was acquired on Tuesday, Sept. 4, 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 located at http://saturn.jpl.nasa.gov/operations/present-position.cfm .
Wednesday, Aug. 29 (DOY 241):
Cassini passed Tethys today for a non-targeted flyby at a distance of 55,499 km. The Optical Remote Sensing (ORS) instruments performed imaging and mapping activities, and obtained measurements of the ultraviolet albedo across both longitude and phase space. Additional science activities included an F-Ring rotation movie and raster scans of the north and south regions of Saturn by the Composite Infrared Spectrometer (CIRS), and scatterometry and radiometry observations of Phoebe performed by RADAR.
Thursday, Aug. 30 (DOY 242.):
The day after Tethys, Cassini encountered Rhea during the outbound leg of orbit 49. Closest approach was 5,737 km at a phase angle of 46 deg. The Rhea science observations included Imaging Science Subsystem (ISS) mosaics, an Ultraviolet Imaging Spectrograph (UVIS) map of the surface albedo of Rhea in UV and limb drifts to determine atmospheric scattering, and CIRS high spatial resolution mapping. In addition to the ORS observations, the suite of Magnetospheric and Plasma Science (MAPS) instruments, which includes the Cassini Plasma Spectrometer (CAPS), Cosmic Dust Analyzer (CDA), Ion and Neutral Mass Spectrometer (INMS), Magnetometer Subsystem (MAG), Magnetospheric Imaging Instrument (MIMI), and Radio and Plasma Wave Science (RPWS), simultaneously performed low-rate magnetospheric surveys. The live update commands uplinked to the spacecraft on Aug. 28 were extremely successful. Very detailed images of a crater of interest have been returned and the scientists are quite excited.
Using the latest orbit determination (OD) solution, the maneuver team has been able to show that there is virtually no difference between the trajectory to Iapetus with or without OTM-126. Further, the current prediction is that OTM-126 would be very small and might have to be cancelled as a result of being below the minimum delta V. There was no mission delta V penalty associated with deleting OTM 126. The current OD solution has a relatively large uncertainty. The consensus of flight team members was that even if there were sizeable changes in the OD solutions, the conclusions relative to the deletion of OTM-126 would not change. Therefore OTM 126 is now deleted.
Near midnight, Cassini began observations for the Titan T35 targeted encounter. Closest approach was at an altitude of 3,326 km, a speed of 6.1 km/sec, outbound from Saturn at a phase angle of 87 degrees. The main engine cover was reopened just prior to the encounter. This flyby placed Cassini on a course to conduct the closest flyby of Iapetus that will be performed during the entire mission. On Sept. 10, Cassini will come within 1,650 kilometers from the surface of Iapetus. For more information on the Iapetus flyby link to: http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=771
You may see differences in the date reported for when the T35 flyby occurred. Was it the 30th or the 31st? The answer lies in Spacecraft Event Time (SCET), which is always stated in GMT at the spacecraft. Closest approach for Titan was at 2007-243T05:32:34 SCET. DOY 243 = Aug. 31. But, when you convert SCET to Pacific Daylight Time, the time moves earlier and lands on the 30th. FYI.
Friday, Aug. 31 (DOY 243):
Science for the Titan flyby included CIRS measurements of CH4 levels in the troposphere along with vertical profiles of temperatures in the stratosphere and on the surface, a UVIS observation of the Titan occultation of Sigma Sgr., a VIMS observation of the stellar occultation of alpha Sco and AlpCMa., Titan very high resolution imaging, and ISS observations including a regional map of Titan.
Sunday, Sept. 2 (DOY 245):
Science observations over the weekend included CIRS Saturn IR mapping, ISS Titan imaging, a UVIS mosaic of the Saturn inner magnetosphere, and a MAG calibration.
Orbit Trim Maneuver (OTM) #125 was performed today. This is the cleanup maneuver from the Titan 35 encounter on Aug. 31. The main engine burn began at 6:00 AM PDT. Telemetry immediately after the maneuver showed the burn duration was 2.98 seconds, giving a delta-V of 0.477 m/s. All subsystems reported nominal performance after the maneuver.
Tuesday, Sept. 4 (DOY 247)
A real-time command to perform a reaction wheel bias was sent up to the spacecraft today. The bias replaces the one that would have executed if OTM-126 had not been deleted.
The preliminary port for the S36 Science Operations Plan process occurred today. All teams have submitted the necessary files. The final port for this process occurs Sept. 12.
Final end-to-end testing for the Command Data Subsystem (CDS) Flight Software version 10 began today and will run through Sept. 11, 2007. CDS V10 uplink to the spacecraft is set for the end of September as part of the activities in S34.
Based on Spacecraft Office and Sequence Team recommendations, a real-time command is to be sent to the spacecraft as a result of changes to the Cassini DSN allocation file for the S33 background sequence now currently in execution. The command will pause playback for appropriate durations during shortened passes, and change the priority playback table. Three passes needed to be shorted to accommodate the needs of other missions:
DOY 256- shortened by 20 min. at the front end
DOY 260- shortened by 20 min. at the front end
DOY 263- shortened by 35 min. at the front end
A feature on how the studies of atmospheric turbulence on Earth and on Titan are each assisting the other is now available at: http://saturn.jpl.nasa.gov/news/features/feature20070828.cfm.