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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:

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:

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: