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Cassini Significant Events 05/12/10 – 05/18/10

The most recent spacecraft telemetry was acquired on May 18th from the Deep Space Network tracking complex at Madrid, Spain. 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, May 12 (DOY 132)

Final science observations in S59 included Cassini Plasma Spectrometer magnetospheric observations and solar wind auroral observations. The solar wind is a stream of particles emitted from the Sun which interact with the magnetosphere of Saturn to produce aurora. Imaging Science (ISS) took images of Iapetus. The Composite Infrared Spectrometer (CIRS) performed Saturn atmospheric composition measurements and a scattered light calibration. This calibration measured the amount of possible degradation of the primary mirror of the instrument after years of operation. The Visual and Infrared Mapping Spectrometer (VIMS) took data for a mosaic covering an entire hemisphere of Saturn. Centered on the equator, this 3 x 3 global dynamics mosaic will allow scientists to measure the global atmospheric changes that take place during one Saturn rotation. Scanning across Saturn, the Ultraviolet Imaging Spectrograph (UVIS) obtained ultraviolet spectral images which will help scientists understand Saturn's atmosphere.

Thursday, May 13 (DOY 133)

Uplink Operations and the Spacecraft Office uplinked the S60 background sequence today along with an end of sequence bias for S59, and an AACS memory readout to dump selected sections of AACS restart data from CDS XBA memory that would be used in the event of an AACS restart.

Friday, May 14 (DOY 134)

AACS Periodic Engineering Maintenance was performed today along with an exercise of the backup reaction wheel performed while under reaction wheel control.

Thanks to a very accurate orbit determination solution and the accurate execution of Orbit Trim Maneuver (OTM) 246, the double flyby of Enceladus and Titan does not require a trajectory correction from either a science or delta V perspective. As a result, OTM-247, the Titan 68 approach maneuver due to execute tomorrow, has been cancelled.

Monday, May 17 (DOY 137)

JPL's Open House on May 15 and 16 was once again a very successful event.

More than 36,000 members of the public came through the Laboratory's gates over the weekend, providing them with an opportunity to learn about Cassini and all of JPL's other programs in space exploration and research. Another 14,400 experienced the Open House virtually by Internet-delivered video.

The S59 sequence concluded and S60 began execution today at 2010-137T14:45 SCET. S60 will run for 34 days and conclude on June 25, 2010. During that time there will be three targeted encounters, one with Enceladus and two with Titan, and ten non-targeted flybys - two of Rhea and one each of Methone, Titan, Helene, Calypso, Pandora, Tethys, Pan, and Polydeuces. Seven OTMs are scheduled, numbered 248 through 254. The Titan 70 flyby is being considered a "first time event." The flyby altitude will be 880 km ­ the lowest so far - and the pointing at closest approach (C/A) was chosen by AACS to be the attitude giving the least atmospheric torque. AACS is designing the turns for the Magnetometer observation at C/A.

Planet-C, the Japanese Venus Orbiter mission, scrubbed its launch scheduled for today. The next planned launch window is on May 20. There is no impact to Cassini DSN tracks for that day. If the launch moves to the 21st, the DOY 141 contingency plan reported in the Cassini Significant Events Report last week will be active. The change involves the loss of an entire DSS-15 track but DSS-26 will be swapped in for that time and a real-time TLM mode overlay file will be built. After that, the situation will be examined on a day-by-day basis until a successful launch is achieved.

The Enceladus 10 flyby segment began with the start of the S60 sequence. UVIS began the segment with a 5-hour icy atmosphere observation to map volatiles in the immediate neighborhood of Enceladus. Observations will test the connection of volatile changes to plume eruptions. ISS then performed a high-resolution plume observation at high phase, and CIRS a Dione observation.

A feature was published on the Cassini Web site today on the double flyby of Enceladus and Titan. About a month and a half after its last double flyby, another will occur. The alignment of the moons means that Cassini can make observations of both of these two contrasting worlds within less than 48 hours, with no maneuver in between. The main scientific goal at Enceladus will be a solar occultation by the plume emanating from the moon's south polar region. Radio Science is prime for the Titan encounter, observing subtle variations in the gravitational tug on the spacecraft in the hopes of learning whether Titan has a liquid ocean under its surface and get a better picture of its internal structure.

Tuesday, May 18 (DOY 138)

Today Cassini flew by Enceladus at an altitude of 435 kilometers and a speed of 6.5 km/sec. At closest approach UVIS had pointing control of the spacecraft for an ingress/egress solar occultation by the plume. The observation was made in the Extreme Ultraviolet (EUV). Nitrogen (N2) has a strong absorption feature in the EUV, which will be apparent if N2 is a constituent of the plume at the 3 - 4 percent level.

The Ion and Neutral Mass Spectrometer had previously detected a constituent with an atomic mass of 28. This could be N2, Carbon monoxide (CO), or Ethylene (C2H4), so this observation by UVIS will differentiate among these possibilities. The EUV solar occultation port will be centered on the sun.

Ammonia has already been detected in the plume and scientists know heat can decompose ammonia into nitrogen molecules. Determining the amount of molecular nitrogen in the plume will give scientists clues about thermal processing in the moon's interior.

After closest approach, ISS and VIMS with Optical Remote Sensing and Magnetospheric and Plasma Science riders each performed post-flyby imaging of Enceladus, providing mosaic coverage of the Saturn-facing hemisphere with spatial resolution as fine as 70 m/pixel. The mosaic will provide coverage of a currently poorly resolved region in the western hemisphere. Combined with images from the E8 flyby, it should also provide stereo coverage of surface geological features.

During the flyby, ISS obtained the highest resolution images of the jets at high phase to date. Very fine variations in the structure of the plume near the surface will be discernible. VIMS rode along during the solar occultation to make the first ever near-infrared transmission measurements of the plumes. These measurements will allow very sensitive tests for other compounds, including carbon monoxide, various organics, water gas versus water ice, hydrogen sulfide and other compounds. The slow relative orbital velocity will enable a detailed profile of compounds to be constructed, perhaps showing compositional differences among the various plume source regions. For more information link to:

The S64 Sequence Implementation Process (SIP) kickoff meeting was held today. SIP is the new sequence development process implemented for Extended Extended Mission (XXM) and combines the old Science Operations Plan Process (SOP) and Science and Sequence Update Process (SSUP) used since the start of prime mission. The meeting was well attended. In addition to providing information pertaining to the sequence, leads reviewed changes to the process.

Although sequence development for XXM has now begun, development for Extended Mission is still ongoing. The handoff meeting for S62 SOP to SSUP was held today. S61 is still in development with execution beginning on June 25, and S63, the final sequence in XM, hands off to SSUP on June 22.

A non-targeted flyby of Methone occurred today.