Cassini Significant Events 06/20/07 - 06/26/07

June 28, 2007

(Source: Cassini Project)


The most recent spacecraft telemetry was acquired on Tuesday, June 26, 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, June 20 (DOY 171):


Navigation has released an update to the Cassini Reference Trajectory. This update covers the period from April 11, 2008, the last part of the prime orbital mission, through July 1, 2010, the end date of the proposed mission extension. The start date was chosen to completely encompass S40, the first sequence affected by the merging of the prime and proposed extended missions.

Thursday, June 21 (DOY 172):


Orbit Trim Maneuver (OTM) #117 was performed today. This is the apoapsis maneuver setting up for the Titan 33 encounter on June 29. The main engine burn began at 5:44 PM PST. Telemetry immediately after the maneuver showed the burn duration was 49.0 seconds, giving a delta-V of 7.97 m/s. All subsystems reported nominal performance after the maneuver. Using the hydrazine efficient yaw rates, 60.3 grams of hydrazine were used.

Once a year, NASA honors individuals and groups for managerial and technical excellence and outstanding performance on demanding projects during the year. At a ceremony on the JPL mall today, awards for the Cassini/Huygens Project were given to the Huygens Atmospheric Structure Instrument Team (HASI), the Descent Imager/Spectral Radiometer Team (DISR), the Huygens Interdisciplinary Science Team (IDST), the Surface Science Package Team (SSP), the Descent Trajectory Working Group (DTWG), the Gas Chromatograph and Mass Spectrometer Team (GCMS), the Aerosol Collector and Pyrolyzer Team (ACP), the Doppler Wind Experiment Team (DWE), and the Cassini Spacecraft Operations Hydrazine Tank Recharge Team. An individual award was given to Aseel Anabtawi for her work on the Radio Science Team.


An encounter strategy meeting was held today to cover the period between June 29 and July 19, Titan flybys T33 and T34, and maneuvers 119-121.


All of the driving instrument teams and Science Planning have completed analysis based on the OTM-117 orbit determination (OD) solution for the S31 DOY 178-179 Live Update. All have given a no-go for the Tethys/Rhea Live Inertial Vector Propagator update. The Radio Science (RSS) team has also completed assessment of the Rev 47 Saturn atmosphere occultation based on the latest OD. The differences between this OD and the reference trajectory are very small, resulting in systematic pointing errors of only 0.05 mrad that are about 1/3 the size the predicted statistical pointing errors during the occultation. These are a relatively small fraction of the Ka-band beam width, and thus they will not materially affect the scientific return from the RSS observations. Based on these results, RSS recommended a no-go for the live update as well, and preferred to uplink the design currently on the shelf that has already been thoroughly tested through the Integrated Test Laboratory.


Friday, June 22 (DOY 173):

On Aug. 16, 2006, as the Cassini orbiter flew directly between the sun and Saturn, the Visual and Infrared Mapping Spectrometer captured a sequence of images that vividly show the "opposition effect." This effect occurs when the source of light is directly behind the observer. Terrestrial examples would be when the eyes of a cat seem to glow brightly when they are illuminated by a flashlight, or highway signs and reflectors that "light up" when they are caught in a car's headlights. For an image and description of this effect as it was observed at Saturn, link to: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=2652


The sequence leads for S32 have reported that the rescheduling of the DAWN launch to July 7 has created some conflicts with DSN allocations for that sequence. The start of the downlinks on DOY 214 and 219 will be delayed by 15 minutes. On DOY 218, the downlink will end 15 minutes early to resolve a conflict with the Cluster project. These changes have been documented in a sequence change request, and upon approval, a new SSR Management Tool report (SMT) and Spacecraft Activity Sequence File will be issued. The changes will then be implemented during the last portion of the final sequence development process. Fortunately, the team was able to absorb these changes from a data volume perspective and through the removal of Radio Science set-up time and monopulse on DOY 219.


Monday, June 25 (DOY 176):


Apoapsis science continues this week with the Composite Infrared Spectrometer making measurements to determine the upper trophosphere and tropopause temperature with spatial resolution of about two degrees of latitude and longitude. In addition, the Magnetospheric Imaging Instrument will execute a magnetospheric boundary campaign to image Saturn, and the Imaging Science Subsystem (ISS) will observe the transit of Tethys across Enceladus.


Tuesday, June 26 (DOY 177):

Two topics were presented at the Mission Planning forum today. First up was a discussion of the playback decision points for the Iapetus flyby in September of this year. This is a flyby with unique "high value" science, so the flight team is addressing a contingency downlink strategy now rather than trying to address a possible loss of DSN coverage in real-time. The purpose of the presentation was to give the instrument teams, Cross Discipline Working Group, and Satellite Orbiter Science Team a chance to fully digest the baseline plan. The second topic covered the guidelines Mission Planning will be using to lay down where DSN tracks and high-level activities should be located during the 2008 - 2010 time-frame of extended mission.


Orbit Trim Maneuver (OTM) #118 was performed today. This is the approach maneuver setting up for the Titan 33 encounter on June 29. The reaction control subsystem burn began at 5:30 PM PST. Telemetry immediately after the maneuver showed the burn duration was 6.88 seconds, giving a delta-V of 0.013 m/s. All subsystems reported nominal performance after the maneuver.


All teams delivered the necessary files as part of the official port for the S34 Science Operations Plan Update process.


A Cassini-Huygens Analysis and Results of the Mission (CHARM) teleconference occurred today. Speakers from Project Science, RADAR, ISS, Visual and Infrared Mapping Spectrometer, Magnetospheres, and Rings gave presentations in support of the upcoming third anniversary of Cassini Saturn Orbit Insertion on July 1, 2004. An audio recording of this teleconference will be made available on the Cassini website within a couple of days along with PDF and PowerPoint versions of the presentations.


Coming Up:

Quite a number of non-targeted flybys will be occurring June 27 along with the Titan 33 targeted encounter on June 29. Science details will be reported in the next Significant Events report. Advance information is available on the Cassini web site:
http://saturn.jpl.nasa.gov/news/events/t33-tethys/index.cfm