Cassini Significant Events 04/09/08 - 04/15/08
April 17, 2008

The most recent spacecraft telemetry was acquired on Tuesday, April 15, from the Goldstone, California tracking complex. The Cassini spacecraft is in an excellent state of health and all subsystems are operating normally.

Wednesday, April 9 (DOY 100)

Based on analysis performed by members of the Science Planning Team, the live update for Saturn and Tethys due to execute DOY 111-113 has been cancelled. Comparison of the reference trajectory with the maneuver #152 orbit determination solution showed that the Tethys observation had a pointing difference of only 0.53 mrad, not enough to warrant an update.

Announced within the last few weeks both here in the weekly event report and on the Cassini web site, the Cassini Scientist for a Day essay contest has now received international media coverage. NASA Headquarters has added support by sending out an announcement on the Scientist for a Day contest to all of the educators on the NASA Education e-mail distribution list, and proposing an interview about Cassini Scientist for a Day in its "This Week @ NASA" broadcast on NASA TV. In the past week, 24 e-mail requests for additional information have come from students in Canada, Vietnam, Singapore, India, Iran, and Africa, as well as from Americans who are out of the participant age range, but would like to participate anyway.

Thursday, April 10 (DOY 101):

Cassini has two targeted encounters of Enceladus scheduled to occur towards the latter part of this year. E4 is planned for Aug. 11, and E5 on Oct. 9. Today the project held a meeting to determine if the altitudes planned for these flybys should remain as they are in the current trajectory design or if they should be altered. There were pretty strong cases made for leaving E4 as-is, and leaving the E5 altitude as-is but changing the aim point to fly more deeply into the plume. There are a couple of open engineering issues that need to be worked before the final decision is made. These require study by attitude control with atmospheric profiles from the Ion and Neutral Mass Spectrometer (INMS), as well as some follow-up communications with navigation. A wrap-up meeting will be held in the next week or so to discuss the findings and announce the decisions.

Orbit Trim Maneuver (OTM) #152 was performed today. This is the cleanup maneuver following the Titan 42 encounter on March 25. The main engine burn began at 7:15 PM PDT. Telemetry immediately after the maneuver showed the burn duration was 20.16 seconds, giving a delta-V of 3.31 m/sec, as designed. All subsystems reported nominal performance after the maneuver.

Members of the Spacecraft Office Integrated Test Laboratory (ITL) presented a paper at the IEEE Aerospace Conference last month on "System Testbed Use on a Mature Deep Space Mission: Cassini" as well as providing a tour of the ITL facility to members of the Cassini Extended Mission Review Board when they were at JPL.

Friday, April 11 (DOY 102):

A non-targeted flyby of Mimas occurred today.

Today was the first time a Radio Science Receiver (RSR) acquired Cassini Ka-band data over DSS-47, the Narrabri six 22-m antenna array. The proficiency track occurred during a Cassini Radio Science (RSS) rings and ionospheric occultation. Canberra's DSS-34 and Goldstone's DSS-25 were tracking Cassini Ka-band at the same time. The DSS-47 signal power was 2-3 dB higher than observed at the other two 34-m stations. Narrabri's array seemed to track the signal dynamics well throughout the ring occultation period. Although the data still needs to be processed and its quality assessed, especially that of the phase observation which is not monitored in real-time, indications are that once any problems are worked out, Narrabri will have the potential to provide valuable Ka-band support for upcoming Cassini Radio Science observations when needed.

Monday, April 14 (DOY 105):

Seven instrument expanded block (IEB) files in support of the S40 sequence were uplinked by the sequence leads and Mission Support and Services Office personnel today. During the Goldstone pass on DOY-106, an additional six IEBs will be sent with the last file going up on DOY-107. A final sequence approval meeting is scheduled for Tuesday. After that, the background sequence will be uplinked on Wednesday.

Science today began with a continuation of the study of Saturn with a methane fluorescence map taken by the Visual and Infrared Mapping Spectrometer (VIMS) with the Ultraviolet Imaging Spectrograph (UVIS) participating. The next target was Tethys with observations at various wavelengths including Imaging Science (ISS) color photometry, UVIS albedo measurements, and Composite Infrared Spectrometer (CIRS) infrared measurements. As part of the ongoing campaign to better determine the orbits of minor satellites, images were taken of Atlas, Janus, Polydeuces, Prometheus, and Calypso.

Tuesday, April 15 (DOY 106):

NASA Extends Cassini's Grand Tour of Saturn

NASA has approved extending the Cassini-Huygens mission by two years. The mission was originally scheduled to end in July 2008. The newly announced two-year extension will include 60 additional orbits of Saturn, 26 flybys of Titan, seven of Enceladus, and one each of Dione, Rhea and Helene. The extension also includes studies of Saturn's rings, its complex magnetosphere, and the planet itself. Other activities will include monitoring seasons on Titan and Saturn, observing unique ring events such as the 2009 equinox crossing when the sun will pass through the plane of the rings, and exploring new places within Saturn's magnetosphere. Sequence development for the mission extension began last year to enable the S42 sequence to be completed in time for start of execution on July 1, 2008, once approval was received.

The spacecraft will have enough propellant left after the extended mission to potentially allow a third phase of operations. In order to determine if a further mission extension will be feasible, preliminary work on such a mission has begun. The determination of science objectives and opportunities, possible trajectories and supporting analysis take time to develop so the team must begin now to be able to have something - if approved - in place by 2010.

But until then, data from the first mission extension could help lay the groundwork for possible new missions to Titan and Enceladus. For the full release link to: http://www.sflorg.com/cassini/missionnews/casmn041508_01.html

Source / Credit: NASA / The Cassini Project

Jan. 5, 2008: Titan flyby (T40) -- the Visual and Infrared Mapping Spectrometer (VIMS) maps the Huygens landing site with a highly illuminated surface. This flyby features two separate stellar occultations to study the structure of Titan's atmosphere. VIMS watches the star Alpha Bootes, and the Ultraviolet Imaging Spectrograph (UVIS) watches Alpha Lyra.

Feb. 22, 2008: Titan flyby (T41) -- features a RADAR Synthetic Aperture Radar Imager (SAR) swath of Titan's southeast quadrant and the Huygens landing site. This flyby also has the mission's "longest" stellar occultation of Titan's atmosphere, occurring about a day after closest approach.

March 12, 2008: Enceladus flyby -- This is the third and final targeted flyby of Enceladus in the prime mission. It is an inclined flyby with a closest approach distance near the equator of about 50 kilometers, enabling the first good views of the northern hemisphere. The trajectory will take Cassini through the plume at a grazing angle (deeper into the plume than during the July 2005 flyby), allowing for fields-and-particles measurements within the plume. Enceladus will enter eclipse (Saturn's shadow) shortly after closest approach, allowing for thermal measurements of the south pole at high resolution.

March 25, 2008: Titan flyby (T42) -- it is "High Noon" for Cassini during this encounter, with the Sun high in Titan's sky. Just prior to closest approach, the Ion and Neutral Mass Spectrometer (INMS) examines Titan's upper atmosphere. Immediately after closest approach, VIMS captures high resolution imaging of the probe landing site.

May 12, 2008: Titan flyby (T43) -- RADAR captures SAR imaging of Titan's bright region known as Xanadu. The only other RADAR coverage of this area was back in April 2006 (T13).

May 28, 2008: Titan flyby (T44) -- this unique and highly important flyby features a RADAR pass across Xanadu, making T44 and T41 [should this be T43?] coverage of the area the only RADAR pass other than the T13 flyby (in April 2006).

June through August 2008: The Cassini spacecraft enters the highest inclination orbits of the tour. In these high inclined orbits scientists will have their best opportunities to use Stellar Occultations to penetrate the B ring. And the spacecraft will be able to show views of Saturn as no one has seen it before! The rings will be spread out like a giant halo around Saturn.

These high inclined orbits also present the Magnetosphere and Plasma Science (MAPS) scientists with many science opportunities that have been long awaited.

June 30, 2008: End of Prime Mission.

The events listed below are proposed pending official approval of an extended mission.

July 31, 2008: Titan flyby (T45) -- Radio Science Subsystem (RSS) uses this pass to measure Titan's gravity field, allowing us to explore the moon's interior. This is the fourth of four fly-bys needed to determine if Titan has an internal ocean.

Aug. 11, 2008: Enceladus flyby -- This is the first targeted flyby of Enceladus in the Extended Mission. The flyby geometry is very similar to that of the March 2008 flyby, however the spacecraft will be oriented to optimize the flyby for viewing by cameras and spectrometers, to obtain the highest resolution views of the active south pole region.

Oct. 9, 2008: Enceladus flyby -- This is the second of seven targeted Enceladus fly-bys in the Extended Mission. The flyby geometry is very similar to that of the March 2008 flyby: an inclined trajectory allowing Cassini to pass through the plumes for fields-and-particles measurements near closest approach.

Oct. 31, 2008: Enceladus flyby -- This is the final inclined flyby of Enceladus, and at about 200 kilometers, is more distant than the earlier fly-bys in the year. This flyby will be dedicated to remote sensing measurements by cameras and spectrometers, to obtain images as well as compositional and thermal information on the north and south pole regions.

Nov. 3, 2008: Titan flyby (T46) -- Radio Science watches as the Earth slips behind Titan, using the spacecraft's signal to probe Titan's atmosphere in the north mid latitude, with the occultation at 26 degrees North. In another RSS experiment, a signal is bounced off of Titan's surface and then returned to Earth.

Nov. 19, 2008: Titan flyby (T47) -- VIMS observes the Huygens probe landing site, and UVIS observes a star (Beta Cma) through Titan's atmosphere, using the star as a "flashlight" to study Titan's atmospheric structure and composition. This is one of the best "low phase" fly-bys for the VIMS instrument in the extended mission.

Dec. 5, 2008: Titan flyby (T48) -- Cassini swoops down to 960 kilometers (about 580 miles) over Titan's surface. The Ion and Neutral Mass Spectrometer (INMS) takes advantage of this low altitude, sampling Titan's ionosphere on the dayside. In fact, this is the best dayside pass for INMS during the extended mission. RADAR gets to capture a SAR swath over the Tui Regio area of Xanadu, a very bright feature in VIMS observations.

Dec. 21, 2008: Titan flyby (T49) -- Closing out the year, RADAR will carry out altimetry observations over the area known as Ontario Lacus, in Titan's Southern hemisphere.

Dec. 26, 2008: 100th orbit periapsis.

Source: NASA / JPL