From Newsgroup: sci.space.news


Cassini Significant Events 
for 04/20/11 - 04/26/11

The most recent spacecraft telemetry was acquired on April 26 from the Deep
Space Network tracking complex at Goldstone, California. 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/mission/presentposition/ .

Wednesday, April 20 (DOY 110)

A news release called "Cassini Sees Saturn Electric Link with Enceladus" is
available on the Cassini web site. NASA is releasing the first images and
sounds of an electrical connection between Saturn and one of its moons,
Enceladus. The data collected by the Cassini spacecraft enable scientists to
improve their understanding of the complex web of interactions between the
planet and its numerous moons. The results of the data analysis are
published in the journals Nature and Geophysical Research Letters. For more
information on this subject and images link to:

http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20110420/ .

The S68 background sequence was uplinked today at 2011-111T02:46:00 over
Goldstone's DSS-14 station. S68 has been registered on-board the spacecraft
and will start executing on Monday, April 25.

Thursday, April 21 (DOY 111)

This week in science the Optical Remote Sensing (ORS) instruments made two
5-hour Titan observations to track clouds and study seasonal changes in the
methane-hydrocarbon hydrological cycle of lakes, clouds, aerosols, and their
seasonal transport. These observations provide the best views to date of the
region where significant surface changes were seen during the last quarter
of 2010. The Radar instrument obtained distant Titan radiometer science and
calibration data, and performed an engineering test of the diagnostic modes
on the flight unit. The Composite Infrared Spectrometer (CIRS) performed an
8 hour stray light calibration measurement. Imaging Science (ISS) performed
a pair of observations in its Satellite Orbit Campaign, observing the small
moons Polydeuces, Pallene, Prometheus, Helene, Telesto, Methone, and
Pandora. UVIS made an 11 hour observation of Saturn's aurora to monitor
variability and the footprint of Enceladus. The Cosmic Dust Analyzer
completed a 44 hour interstellar dust observation.

Friday, April 22 (DOY 112)

Orbit Trim Maneuver (OTM) #281 was performed today. This was the cleanup
maneuver following Titan 75 and setting up for the Titan 76 encounter on May
8. The Reaction Control Subsystem (RCS) burn began at 1:00 AM PDT. Telemetry
immediately after the maneuver showed a burn duration of 35.5 seconds,
giving a delta-V of 0.042 m/s. All subsystems reported nominal performance
after the maneuver. The Navigation Team is in the process of re-converging
the spacecraft orbit solution to determine if Orbit Trim Maneuver 282,
scheduled for April 29, and/or OTM 283, scheduled for May 5, will be needed.

Saturday, April 23 (DOY 113)

Sixty-five campers braved 50 mile per hour wind gusts to attend a Saturn
viewing party at the Mojave National Preserve on April 22 and 23. Cassini
Outreach and friends of the National Preserve provided stunning views of the
planet, its rings, and several moons for local desert residents, park
interpreters, and friends from all over southern California.

Monday, April 25 (DOY 115)

The S68 sequence began execution today at 2011-115T16:03:00. The sequence
will run for 69 days and conclude on July 3. During that time there will be
two targeted encounters of Titan - T-76 and T-77, and two non-targeted
flybys - Helene and Telesto. Six OTMs are scheduled, numbered 282 through
287. At the beginning of the S68 sequence, ISS observed the transit of Rhea
across Dione and monitored Saturn for one and a half hours to monitor the
giant storm. CIRS completed its 23 hour mapping of Saturn in the
mid-infrared in order to determine upper troposphere and tropopause
temperatures.

Reaction wheel #3 was taken off-line and wheel #4 brought back on today.
Wheel #3 had been brought into use for the duration of the S67 sequence to
provide an assessment of its suitability for long term use in the event of a
failure of one of the other wheels. Wheel #3's performance was flawless in
its support of the attitude control function, but some of the increased
friction levels that led to the decision to take it off-line earlier were
still evident. Analysis of the telemetry data acquired on the wheel's
performance will continue.

Tuesday, April 26 (DOY 116)

At the Mission Planning forum today, the Navigation team presented a
preliminary analysis of trajectory dispersions and uncertainties for the
proximal orbits. The analysis showed the timing and position errors which
may occur during these orbits. The science and engineering teams will use
this information in doing their planning for the proximal orbits.

The most recent Cassini-Huygens Analysis and Results of the Mission (CHARM)
teleconference was held today. The topic: "Titan: Dead or Alive", was
presented by a NASA Ames Research Center Scientist. A PDF of the
presentation package may be obtained at:

http://saturn.jpl.nasa.gov/video/products/MultimediaProductsCharm/ .

An audio recording of the presentation was made and will be linked to the
same location within a few days.

Visit the JPL Cassini home page for more information about the Cassini
Project: 

http://saturn.jpl.nasa.gov/

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