Cassini Significant Events for 03/31/05 - 04/06/05

April 8, 2005

(Source: JPL)

The most recent spacecraft telemetry was acquired Wednesday from the Goldstone tracking station. The Cassini spacecraft is in an excellent state of health and is operating normally. Information on the present position and
speed of the Cassini spacecraft may be found on the "Present Position" web page located at .

Activities this week:

Science activities this week included the Titan-4 targeted flyby and associated observations, several magnetospheric boundary and solar wind campaigns performed by the Magnetospheric and Plasma Science (MAPS) instruments, and a 14-hour post-probe release Radio and Plasma Wave Science (RPWS) antenna calibration on April 6.

Thursday, March 31:

The Titan-4 targeted flyby occurred today with closest approach at 2,400 km. This was a first time event as the spacecraft was under reaction wheel control (RWA) during the encounter. Members of the Spacecraft Operations Office (SCO) studied the time histories of the per-axis attitude control errors and attitude rate control errors, and found them to be nominal. The
spin rate, drag torque, and total motor torque of the three prime wheels were also nominal. Finally the high water marks of various ACS attitude estimation and control functions were well below their respective thresholds. As a quick look, this RWA-based flyby of Titan is completely nominal.

During the flyby, the Ultraviolet Imaging Spectrograph (UVIS) EUV/FUV conducted observations to map airglow emission lines from nitrogen and carbon and measure reflected sunlight from Titan's haze, which carries information about particle size and properties. RADAR continued fulfilling one of the Cassini primary mission objectives by taking more detailed images of the moon's surface. Radiometry observations for this event will provide
complementary coverage to the Ta flyby and will be combined with those collected during flybys last October, and in February of this year. Visual and Infrared Mapping Spectrometer (VIMS) observed the evolution of clouds and other transient features on Titan, and obtained high-resolution compositional mapping of the northern hemisphere. General RPWS objectives
near all Titan closest approaches are to determine thermal plasma parameters of electron temperature and density, investigate the interaction between the magnetosphere and Titan's ionosphere, search for lightning on Titan, and
look for new phenomena, such as radio emissions from the Titan-magnetosphere interaction. Cassini is scheduled to return to Titan on April 16 for a pass at 1, 025 kilometers.

Friday, April 1:

The Titan Orbiter Science Team (TOST) hosted a Titan-5 preview meeting. This meeting was for Cassini-Huygens Project personnel, and those interested in a preview of T5 science objectives and activities. The agenda included presentations given by all the instrument teams, an overview of the geometry
of the flyby, and the data return schedule.

Cassini Outreach participated in the National Science Teachers Association (NSTA) annual conference April 1-4, 2005. The conference was held in Dallas, Texas. A workshop on "Reading, Writing, and Rings" was held with over 80 educators attending. "Reading, Writing, and Rings" was also presented in conjunction with a Sun-Earth workshop with 55 additional educators

Sunday, April 3:

Orbit trim maneuver #20 (OTM-20) was successfully completed on the spacecraft this evening. This T4 flyby cleanup maneuver, together with upcoming OTM-21, places the spacecraft on the proper trajectory for the April 16 flyby of Titan (T5).

The main engine burn began at 8:36 p.m. PDT. A "quick look" immediately after the maneuver showed the burn duration was 5.9 sec long, giving a delta-V of 0.91 m/s. All subsystems reported nominal performance after the burn.

Here is some follow up information on the decision to update the reference trajectory to accommodate a closer flyby of Tethys. On Tuesday, March 29, the project decided to spend about 8 m/sec to tweak the spacecraft trajectory for orbits 14-17 to accommodate a close, targeted-class flyby of
Saturn's satellite Tethys. Tethys was the only medium-sized satellite of Saturn that did not have a close flyby scheduled in the nominal mission.

Nearly a dozen high level scientific objectives from the AO are
significantly addressed by this tweak. The new baseline trajectory will now include three close icy satellite flybys within 17 days - with no Titan encounters between them - a feat that is extremely fortuitous, and on a par with the alignment of the planets for Voyager's Grand Tour. The icy satellite flybys in order are Tethys, Hyperion, and Dione. These are the
only close flybys of these bodies in the nominal mission.

Monday, April 4:

Program Science gave a Cassini talk to over 250 individuals at the Stanford Linear Accelerator Center.

ULO began uplink of the first files in support of S10. The Cassini Plasma Spectrometer (CAPS) Instrument Expanded Blocks (IEB) were the first to be sent. At the time of this writing the team was awaiting CAPS confirmation
that the file has been received and is executing as expected. Additional IEB uplinks will continue over the next two days.

Tuesday, April 5:

The final sequence approval meeting for S10 was held today. The sequence has been approved and is awaiting uplink to the spacecraft.

Imaging Science Subsystem (ISS) conducted an Integrated Test Lab (ITL) regression test of the latest version of the upgraded flight software. In addition, special tests of camera timing and a new method of flight software loading were run.

VIMS continues the process of reprocessing early Cruise data with the modern telemetry processor. This is to provide products more consistent with those generated in Tour for the science data archiving process. Products for C21
were delivered to the VIMS science team for evaluation.

Wednesday April 6:

The S10 background sequence was sent up to the spacecraft today. The sequence leads are ready for a change over from S09 to S10 this coming weekend.

Science Planning hosted a Project Briefing for S12. The products are in the process of being handed off to the sequence leads for the start of the Science and Sequence Update Process on April 7.

Given the approximate work-load of the discretionary and must-do changes proposed for S14 coupled with the Tethys tweak impact, it was determined that there was no need to hold the S14 Aftermarket Decision meeting scheduled for today. All changes have been "approved" and are now at the
discretion of the Target Working Teams and Orbiter Science Teams.

Next week Cassini will hit an all time activity high as the program executes three OTMs in 10 days! OTM #21 executes on April 9, and OTM #22 and #23 on April 13, and April 19.

Wrap up:

Check out the Cassini web site at for the latest press releases and images.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington,
D.C. JPL designed, developed and assembled the Cassini orbiter.