Cassini Significant Events 04/28/05 - 05/04/05

May 6, 2005

(Source: Jet Propulsion Laboratory)

The most recent spacecraft telemetry was acquired Wednesday from the Madrid
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:

The main event this week is the first Radio Science Subsystem (RSS)
occultation observation during the solar and Earth occultation at the Rev 7
periapse. At this time RSS will perform inbound and outbound ring and
Saturn occultation experiments. The occultation season runs from now until
September. During that time RSS will have 8 opportunities for collecting
this unique science data. The Optical Remote Sensing (ORS) instruments will
also participate by making a hi-phase observation of Saturn and its rings
while they are occulting the sun.

Additional ORS activities include brief observations of Titan, Dione, and
the mutual interaction of Telesto and Tethys, the Imaging Science Subsystem
(ISS) will perform an azimuthal scan of the rings at low phase catching
Atlas at the same time, ISS and VIMS will focus on imaging Saturn's
atmosphere at phase angles of 100-120 degrees during the outbound segment
after periapse, and the Ultraviolet Imaging Spectrograph (UVIS) and
Composite InfraRed Spectrometer (CIRS) will conduct slow scans across the
visible hemisphere to provide ultraviolet and infrared spectra of the same

During this time the Magnetospheric and Plasma Science (MAPS) instruments
will be conducting observations in survey mode. Survey mode is a generic
statement that means a MAPS instrument is on and collecting data
continuously at a low rate. The rate is different for each instrument. Not
overfilling the SSR is one reason to be in survey mode versus a higher data
collection rate mode.

Thursday, April 28 (DOY 118):

Orbit trim maneuver #24 (OTM) was successfully completed on the spacecraft
tonight. This maneuver, performed near apoapsis, targets to the moon
Enceladus for the 175 km "Enceladus-2" flyby on July 14. The main engine
burn began at 7:15 p.m. PDT. A "quick look" immediately after the maneuver
showed the burn duration was 131.6 seconds long, giving a delta-V of 20.5
m/s. All subsystems reported nominal performance after the maneuver.

Between OTM-24 and OTM-25 the primary focus of science investigations is on
Saturn and ring occultations. There will be 5 revolutions of Cassini around
Saturn during this time where RSS will perform unique observations.

The last targeted encounter, Titan 5 occurred on April 16. The next targeted
encounter doesn't occur until Enceladus 2 on July 14. The first two OTMs of
the three maneuver set between T5 and E2 occurred on April 20, April 29, and
the last will occur July 8 just before the Enceladus flyby.

This over two-month break in OTMs was specifically built into the T18-5 Tour
that Cassini is currently flying. The way it usually works is that
Navigation schedules three maneuvers between targeted flybys so the
spacecraft can get close enough to the target to assure that requirements
for pointing, and delta-v cost are met. There are no targeted encounters
between the end of April and the middle of July to allow for occultation

Today JPL held the annual Take your Child to Work Day. To support this
event, Cassini outreach prepared packets of material for the children of
Cassini program members. In addition, a model of the Cassini spacecraft was
on display alongside the "Cassini -Huygens Spacecraft" and "Spacecraft
Components" lithographs, which are available for download at

Friday, April 29 (DOY 119):

Beginning tomorrow and running through the weekend, JPL will be hosting a
Saturn Educators Conference. Cassini/Huygens scientists, engineers, managers
and educators will tell what they know about Saturn, Titan, and the rings,
icy moons, fields and particles, and what's planned over the next several
years. Thirty-three educators will participate in the event.

A picture of Saturn's moon Epimetheus is Astronomy Picture of the Day today.

As part of sequence development for S11, all nine Preliminary Sequence
Integration and Validation-2 SSR instrument expanded block (IEB) and
instrument direct IEB files required for uplink before the start of the S11
sequence have been moved out to the Program file repository. A command
approval meeting for these files will be held on May 5, and the files will
be uplinked to the spacecraft on May 9 and 10.

A Software Review/Certification Requirements meeting was held today for
Version 1.4 of ISS flight software. The software was approved and is
currently planned to be uplinked to the spacecraft in mid-June.

Uplink Operations sent a number of commands to the spacecraft today. Among
them were Live Movable Block files that will execute on DOY 123 in support
of the RSS occultation observations, an update to the Tethys vector based on
the OTM-24 Orbit Determination Solution, CIRS trigger commands, and a
Cassini Plasma Spectrometer housekeeping memory readout address update.

Monday, May 2 (DOY 122):

Non-targeted flybys of Tethys and Epimetheus occurred today. By the way, if
you are interested in more information on Saturn's moons, don't forget to
checkout the Cassini Web site, specifically the new moons page

The first of 8 RSS occultation experiments began today at 9:13 pm and will
continue until about 3:00 am tomorrow morning. Event times are as follows:

Entry (May 2nd)
Start Rings Ingress Occultation 09:13 pm
End Rings Ingress Occultation 10:43 pm
Start Saturn Ingress Occultation 10:47 pm
End Saturn Ingress Occultation 11:33 pm

Exit (May 3rd)
Start Saturn Egress Occultation 12:52 am
Start Rings Egress Occultation 01:33 am
End Saturn Egress Occultation 01:34 am
End Rings Egress Occultation 02:57 am

More details will be available next week on how the observations went.

The Radio and Plasma Wave Experiment (RPWS) observed a Type II solar burst,
indicative of a coronal mass ejection (CME) shock, on May 2 at 23:45 UTC.
Given one way light time from the Sun to Saturn this would correspond
roughly to a launch time of the ejection from the Sun at 22:25 UTC, one hour
and 20 minutes earlier.

The shock front from the CME propagates through the solar system at about
700 to 800 km/sec, and is projected to arrive at Saturn, after traveling
more than 1 billion km, on or about May 23.

So how did RPWS see something from Cassini when the event doesn't get there
until May 23? What was observed on May 2 was the radio signal from the CME
shock which travels at the speed of light. The particles that make up the
CME shock front are only traveling at 700 -800 km/sec. That's pretty fast
but nothing like the speed of light. So the particles, which will interact
strongly with Saturn's magnetosphere and cause all sorts of interesting
effects, take 21 days to get out to Saturn's orbit from the sun.

When it arrives, if it hasn't dissipated, the CME shock will compress
Saturn's magnetosphere, trigger auroral emission and kilometer-wave radio
emission, and other effects detectable by RPWS and other MAPS instruments.

This particular event is related to the X-ray flare of 21:13 from solar
active region AR0758 observed on the eastern limb (77 degrees East) given
the timing and the Saturn-Sun-Earth geometry.

Tuesday, May 3 (DOY 123):

Navigation released an update to the reference trajectory today. This
update reflects the lowering of altitudes at Tethys in Rev 15, Hyperion in
Rev 15, and Enceladus in Rev 11.

The new reference trajectory was discussed in detail at today's Mission
Planning Forum. RADAR playback options to avoid coherency change induced
data gaps were also discussed.

Wednesday, May 4 (DOY 124):

A non-targeted flyby of Titan occurred today.

An image of Saturn with the rings edge-on is Astronomy Picture of the Day
today. This kind of image is only possible when the observer - in this case
the Cassini spacecraft -is crossing the ring plane.

As part of sequence development for S11, the final merged sequence products
have been published to the Program file repository and are available for
review by the sequence development team. The final sequence approval
meeting will be held on Monday of next week.

A delivery coordination meeting for the Cassini Information Management
System was held today. This delivery was focused on new functionality for
Science Planners to aid in automated resource checking of sequence planning

Wrap up:

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.