Cassini Significant Events 05/09/07 - 05/15/07
May 17, 2007
(Source: Cassini Project)
The most recent spacecraft telemetry was acquired on Tuesday, May 15, from the Goldstone tracking complex. 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" web page located at http://saturn.jpl.nasa.gov/operations/present-position.cfm.
Wednesday, May 9 (DOY 129):
An article on Cassini was included in the April publication of "National Geographic Explorer." This version of National Geographic is distributed to over one million school children ages 6 to 12, grades 2 through 6. The 24-page magazine contains only three features each month and is accompanied by a teacher's guide.
Uplink Operations sent commands to the spacecraft today for a live update to modify the pointing vectors for the Titan 30 flyby to occur on Saturday, May 12.
Thursday, May 10 (DOY 130):
On May 10th, the Radio Science (RSS) team performed ingress and egress ionospheric/atmospheric Saturn occultations, and an egress only ring occultation. The ingress occultation covered Saturn northern latitudes around 71 degrees, the highest latitude to be probed by radio signal in both the Cassini prime and proposed extended missions. The egress ring occultation is one of two occultations that were especially designed to view the rings at an intermediate opening angle of about 15 degrees. The next opportunity will occur during orbit 46. Collectively, the occultations provide important information about the atmosphere's thermal structure, the microwave absorbing species, the hydrogen-to-helium ratio, and the winds of Saturn. Composite Infrared Spectrometer (CIRS) and Ultraviolet Imaging Spectrograph (UVIS) Saturn limb observations, and Visual and Infrared Mapping Spectrometer (VIMS) cylindrical mapping followed the RSS occultations.
Mission Planning (MP) hosted a Titan Atmosphere Model Working Group (TAMWG) meeting today to review Titan atmospheric density results from the Ion and Neutral Mass Spectrometer (INMS), AACS, and Navigation teams for the Titan 23 through 29 flybys. It was noted that the T29 density was unusually high compared to T19, which was at a similar altitude and latitude at closest approach. The T29 results are being reviewed for more data pertinent to the atmosphere model. Including T29, all the recent flybys appear to be consistent with the current model.
A discussion of flyby altitudes for the proposed extended mission was included in the meeting agenda. In general a case was made for being somewhat aggressive in lowering flyby altitudes in order to increase science value. The TAMWG accepted the MP proposal of new extended mission flyby altitudes, although some specific passes may still be adjusted after meeting with the Project Manager. The next TAMWG meeting is scheduled for 15 October to review in particular the T36 pass, which will be the first low altitude pass so far in the southern hemisphere.
Friday, May 11 (DOY 131):
The spacecraft transitioned from reaction wheel to thruster attitude control today in order to support the third RPWS Whistler activity. In this observation, performed over a downlink pass, the wheels are turned off to eliminate interference during the observation, then turned back on before the next activity begins.
Scientists have long known that the lower atmosphere of Saturn's moon Titan contains organic aerosols, or tholins, formed from simple organic molecules, such as methane and nitrogen. Researchers had thought these tholins formed at altitudes of several hundred kilometers, but new information gathered by three particle spectrometers aboard the Cassini spacecraft shows tholin formation happens in Titan's atmosphere at altitudes greater than 1,000 kilometers. The results also show tholins form differently than previously thought. Understanding how tholins form could provide valuable insight into the origin of life in the solar system. For more information on this subject, see a news release at: http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=746
Saturday, May 12 (DOY 132):
Cassini flew past Titan today for the 31st targeted encounter of the prime mission. [Recall that the number assigned to a Titan encounter, e.g., T30, is always one less than the number of encounters that have occurred at that point due to the extra orbit and Titan flyby that were inserted in the tour as part of the solution to the Huygens receiver problem.] Closest approach occurred at 2007-132T20:05:28 Spacecraft Event Time, at an altitude of 960 km, and a speed of 6.2 km/sec. The latitude at closest approach was 68.9° N. SCO reported 345 g of hydrazine were used, and a peak thruster duty cycle of 53.8 percent.
Science for this flyby included RADAR high latitude Synthetic Aperture RADAR observations of a large, expansive dark area dubbed the "Caspian Sea" in the Fensal/Aaru region of Titan. This north polar feature stretches over 1,000 kilometers and is only slightly smaller than Earth's Caspian Sea. The Ion and Neutral Mass Spectrometer (INMS) 'rode-along' with RADAR to make in-situ observations of Titan's upper atmosphere, measuring neutral particles and ions, UVIS measured Titan's stratospheric temperatures, VIMS obtained surface observations at small solar angles of the northern hemisphere, and ISS performed imaging between 620 m/pixel and 1 km/pixel at phase angles less than 30 degrees. For the complete mission description of the T30 flyby link to: http://saturn.jpl.nasa.gov/news/events/titan20070512/index.cfm
Monday, May 14 (DOY 134):
The final sequence development process for S31 is about half way through and negotiations for DSN allocations for this sequence are complete. As a result, Science Planning was able to initiate the Science Allocation Panel (SAP) process and allocate additional available SSR data volume for six periods in S31 to the instrument teams. More SSR data volume means more science data. This is only the second time since the Stereo Launch slips in October of 2006 that the SAP process could be performed during the background sequence development time frame. Kudos to the DSN schedulers who are still working very hard to return to their original schedule of deliverables.
Tuesday, May 15 (DOY 135):
AACS Periodic Engineering Maintenance was completed today. This activity, performed every 90 days, exercises the Engine Gimbal Actuators, the backup reaction wheel assembly - or RWA-3 - and scrubs the Backdoor Assisted Load Format Injection Loader memory.
On the extended mission front (XM), having completed the Senior Review in February of this year, the flight team now awaits the final approval from NASA, expected after an Operations Review is completed later this year. In the mean time, XM planning activities must continue in order to be ready by the time the Prime Mission concludes on June 30, 2008. The Segmentation Working Group met today to complete negotiations for the periapsis allocations. This determines which of the Orbiter Science Teams or Target Working Teams will be primary for science occurring at periapsis for each of the extended mission orbits. For trajectory design development, tumble densities and minimum Titan altitudes have been finalized, and tweaks to the proposed extended mission trajectory have been released for review. Everything is on track.
The official and final port for the S33 Science Operations Plan Update process occurred today. All science teams, SCO, and Navigation delivered their files. These have now been merged and the concatenated file posted to the data repository for the teams to review. This process will conclude on June 1. The final development process for this sequence will then begin on the following Monday.
Orbit Trim Maneuver (OTM) #110, the T30 cleanup maneuver scheduled for May 15, 2007, has been cancelled. This was a benefit realized from the T30 aim point adjustment performed by OTM-109, and the relatively large size of the next OTM, #111. The estimate for OTM-110 was 0.125 m/s. The following maneuver #111 is a deterministic maneuver of about 5.6 m/s. Due primarily to the relatively large size of OTM-111, the cost of OTM-110 cancellation was only 0.112 m/s.
FYI - Deterministic maneuvers must be performed, as they are part of the original trajectory design and are required to change the trajectory to keep the spacecraft on its designed path. Other maneuvers are "statistical" and are used to compensate for the statistical variations that are a normal part of the navigation process. Many maneuvers are a combination of both. The statistical maneuvers are the ones that are candidates for cancellation.
Two news releases were posted on the Cassini Web site on May 16 concerning Enceladus. The first article postulates that frictional heating may be what powers the geysers jetting out from the surface of Saturn's moon Enceladus. For the details link to: http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=747.
The second article from Goddard Space Flight Center concerns the opening and closing of the cracks or "Tiger Stripes" on the surface of Enceladus. Tides generated by the gravitational effects of Saturn could control the occurrence of the eruptions. For the full article link to: http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=748
Saturday and Sunday, May 19 and 20, JPL will open its doors for the annual open house event. The Cassini display will be on the mall as you enter the campus from the main gate. A full-scale model of the Huygens probe and a quarter scale model of the Cassini spacecraft will be at our booth this year. Some of the most recent images will be on display along with the themed exhibits Titan-The Most Earth-Like Body in the Solar System, and Enceladus-The Multi-Discipline Nature of Discovery. Trading cards are back this year along with bookmarks and other outreach handouts. The Moon Walk- a walk among the moons of Saturn, hugely popular last year, is back for a return engagement. Drop by and say hi to the Outreach Folks and other Cassini Flight Team members who will be staffing the booth.