Cassini Significant Events 04/21/10 - 04/27/10
The most recent spacecraft telemetry was acquired on April 27th 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 21 (DOY 111)
An image of Dione with Titan in the background was astronomy picture
of the day on April 20. To view the image and caption link to:
http://antwrp.gsfc.nasa.gov/apod/ap100420.html
An encounter strategy meeting was held today to cover the period between
April 28 and May 20, Enceladus flybys E9 and E10, Titan flyby T68, and
maneuvers 245-247.
Thursday, April 22 (DOY 112)
Thanks to two very accurate maneuvers, the predicted delivery to
Enceladus on April 28 was within 500 meters of the target. Science
planning evaluated the predicted flyby and did not require the usual
final approach maneuver to achieve their objectives. The uncertainty in
this prediction was much less than the uncertainty in the Enceladus
ephemeris, which does not improve with additional tracking time prior to
the encounter. Since the solutions for the spacecraft orbit have
converged, there was no need to wait for additional tracking data.
Therefore Orbit Trim Maneuver (OTM) #244 has been cancelled.
Friday, April 23 (DOY 113)
Science activities this week included Imaging Science (ISS),
Composite Infrared Spectrometer (CIRS) and Ultraviolet Imaging
Spectrograph (UVIS) observations as part of the Titan cloud monitoring
campaign. The Cassini Plasma Spectrometer (CAPS) led the pointing for
several Magnetosphere and Plasma Science (MAPS) observations. Data was
taken by the instruments in order to study the acceleration region of the
magnetosphere and the Saturn kilometric radiation source regions, for
dawn-side magnetospheric boundary campaign observations, for the Dusk
Magnetosphere MAPS Campaign, and a MAPS survey. ISS led the pointing for
a Titan Monitoring Campaign observation at a phase angle of 80.5 degrees
and a range of 1.7 million kilometers, and performed a medium resolution
plume observation of Enceladus at high phase. UVIS mapped volatiles in
the immediate neighborhood of Enceladus to test connection of volatile
changes to plume eruptions. The Visual and Infrared Mapping Spectrometer
(VIMS) performed an E and G ring observation at 130-degree phase angle.
CIRS made helium abundance measurements at the Radio Science (RSS)
occultation egress point. RSS performed two Saturn occultation
operational readiness tests in preparation for observations beginning on
April 26.
Monday, April 26 (DOY 116)
Target Working Team and Orbiter Science Team integrated products for
S64 were delivered today. S64 is the first sequence of the Extended
Extended Solstice Mission, covering orbits 139 through 141 in October and
November 2010. The integrated products are in their final form and no
re-integration is planned. The next step in sequence development, SIP
implementation -- a new process developed for XXM where the old Science
Operations Plan and Science and Sequence Update processes have been
streamlined and combined -- will kick off on May 18. A Science Planning
Attitude Strategy Spreadsheet will be delivered to the instrument teams
today so that they can begin working on the pointing designs for this
sequence. The final Cassini DSN station requests will also be delivered
to the DSN schedulers today.
Tuesday, April 27 (DOY 117)
Traveling at 6.5 km/sec, Cassini flew past Enceladus for a targeted
flyby today (April 28 GMT). Closest approach occurred at an altitude of
100 kilometers. Spacecraft Operations powered on the backup Sun Sensor
Assembly for the flyby.
E9 was a high-priority Radio Science (RSS) gravity experiment to look for
mass anomalies associated with the Enceladus plume. The flyby segment
began with an RSS observation of a Saturn-solar occultation, both ingress
and egress, which was followed by gravity observations that continued as
Cassini traveled under the south pole through the plume. These
back-to-back observations required almost 30 hours of continuous DSN
support provided sequentially by all three complexes. These observations
will be used to look for anomalies indicating the presence or absence of
mass concentrations at the south polar region of Enceladus, which may in
turn provide insight into the source material for the plume.
This Saturn atmospheric occultation was one of only a few in the mission
able to probe Saturn's low northern latitudes. Capturing this latitude
range is only possible when the rings do not obstruct the radio signal to
Earth. This means that the observation must be performed at a time when
Earth lies in or fairly close to the plane of the rings.
The gravity measurement was a key test for two different hypotheses about
the interior of Enceladus. One theory is that a global ocean exists
beneath a thin ice crust. Another argues that there's a diapir -- upward
intrusion of a rock mass into overlying rock -- underneath the active
south polar terrain that is the source of the moon's plume. After passing
Enceladus, RSS continued to monitor the spacecraft trajectory as a
baseline for comparison with the flyby results.
The MAPS instruments collected data as the spacecraft passed through the
plume, the Magnetospheric Imaging Instrument and the other fields and
particles instruments investigated the electron environment around
Enceladus, and sought to measure local gradients in the magnetic and
electric fields, and in electron beams moving towards Enceladus. The
Radio and Plasma Wave Science (RPWS) instrument searched for evidence of
local ionization in the plumes, and measured plasma waves and other
interactions of Enceladus with its magnetic environment. RPWS also
determined the amount and size of dust particles from vents contributing
to the plume. For additional information on this flyby link to:
http://saturn.jpl.nasa.gov/mission/flybys/enceladus20100428/ and
http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20100426/
Non-targeted flybys of Prometheus, Telesto, Titan, Daphnis, Pandora,
Pallene, and Pan occurred today.
Mission Planning and Navigation presented an update on consumables at the
Mission Planning Forum today. Topic: Hydrazine and Delta-V budget update,
review of predicted and actual usage for Equinox mission.
At the Cassini-Huygens Analysis and Results of the Mission (CHARM)
teleconference for April, the topic was Titan: The moon that would be a
planet - Carbon cycle, geology and dynamics. The presentation is
available on line and may be downloaded from:
http://saturn.jpl.nasa.gov/video/products/MultimediaProductsCharm/
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