Cassini Significant Events for 04/26/06 - 05/03/06 The most recent spacecraft telemetry was acquired Wednesday, May 3, from the Goldstone tracking stations. The Cassini spacecraft is in an excellent state of health and is 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, April 26 (DOY 116): Unraveling the Twists and Turns of Saturn's Rings was the topic at the Cassini-Huygens Analysis and Results of the Mission (CHARM) teleconference on April 24. The presentation included a rings tutorial and recent Ultraviolet Imaging Spectrograph (UVIS) results. Orbit trim maneuver (OTM) # 58 was performed today. This is the approach maneuver setting up for the Titan 13 encounter on April 30. The reaction control subsystem burn began at 8:14 AM PDT. A "quick look" immediately after the maneuver showed the burn duration was 53.1 seconds, giving a delta-V of approximately 77.4 mm/s. Telecommunications reported a momentary 1dB drop in signal strength during the roll turn. They are currently investigating. All other subsystems reported nominal performance after the maneuver. Science activities today centered on the RADAR obtaining distant Titan radiometer science and calibration data over a range of phase angles. This observation is designed to reveal any phase variations that may be present in Titan radiometry and scatterometry data. The Science Planning leads for S22 briefed Program Management on the contents of the S22 sequence, and any issues that remain open that will be transferred into the next phase of sequence development. A Project Briefing is the final step in the Science Operations Plan update process. As was reported on Monday, April 24, the Program Scientist was to make a final decision on what data to protect from being overwritten in the event of a problem with the DSN after the Titan 13 (T13) flyby. He has asked Science Planning, the S20 sequence leads, and members of the Spacecraft Operations Office if it might be possible to preserve at least one block of the unique F ring data in the post T13 time period if such an anomaly were to occur. It was decided that the easiest strategy to implement was to save all of the Visual and Infrared Mapping Spectrometer (VIMS) data on the day after the T13 flyby, and to zero out all of the other instruments if a second playback is required. Since the total VIMS data volume is relatively small, the VIMS data, along with the Synthetic Aperture RADAR (SAR)/UVIS block, could all be played back over the next downlink. This strategy will preserve the key science data for both Titan and VIMS rings. In the event of a problem, a file will be uplinked that will 1) create a new data policing table so no science is recorded for remainder of the downlink on DOY 121, 2) enable this table immediately once the file reaches the spacecraft, and 3) modify Table 19 for the following observation period on DOY 121/21:14 - 122/19:43 SCET. Only VIMS packets will be recorded. A second file to be uplinked sometime around the start of track on DOY 122/21:10 UTC will move the pointers to recover the lost RADAR/UVIS data. The strategy behind this is not straightforward and does come with a risk. Anytime the pointers are moved there is a chance something can go wrong and data unintentionally lost. The CDS team met to discuss this and reduce the risk. Once the pointers are moved, all science data from then on will be played back as normal. Since all of this is a contingency plan, it would be nice if there were no problems after all, and the files not uplinked. Only time will tell, but the files will be approved and ready to go just in case. Thursday, April 27 (DOY 117): It was reported on Tuesday, April 18, that the S21 leads were planning to schedule a test in the Integrated Test Laboratory (ITL) in April to ensure that de-registration of S20 part 2, and the registration of the S21 background sequence occur as expected. It is desired to use the latest version of the S21 sequence for this "loading test". Based on the development schedule, the preliminary #2 merge will be available on May 22. If development continues on its present course, this will be the final merge in the sequence development process as a final phase will be unnecessary. ITL staff are currently reviewing the test schedule to determine if the week of May 22 is feasible for the test. Friday, April 28 (DOY 118): An ACS Reaction Wheel Assembly (RWA) exercise of the backup wheel was performed today. In this activity, RWA-3 is commanded to +100 rpm, -100 rpm, 0 rpm, then turned off. The Cosmic Dust Analyzer (CDA) instrument team has delivered their new flight software to the Project Software library. The Software Requirements and Certification Review (SRCR) is scheduled for Wednesday, May 3. Sunday, April 30, (DOY 120): At 2006-120T20:58 spacecraft event time, Cassini flew past Titan at an altitude of 1855 km for the 14th targeted Titan encounter of the tour. During this event, the Imaging Science Subsystem observed particle properties, vertical distributions, wind and cloud motions, and monitored lightning and aurora activity, the Composite Infrared Spectrometer (CIRS) obtained information on trace constituents in Titan's stratosphere by integrating on the limb at two positions, the Ultraviolet Imaging Spectrograph (UVIS) observed the star Beta Ori as it was occulted by Titan's atmosphere, and the Visible and Infrared Mapping Spectrometer (VIMS) obtained new high-resolution images that will help understand Titan's geology and the fate of CH4. The entire suite of Magnetospheric and Plasma Science (MAPS) instruments performed observations in the immediate vicinity of Titan studying magnetospheric and ionospheric interactions. Finally, RADAR collected altimetry, radiometry, and scatterometry data, and performed low and high resolution Synthetic Aperture RADAR (SAR) imaging of Titan's surface. The SAR swath cuts right across Xanadu, as well as some areas where there exists good ISS and VIMS coverage, enabling useful comparative studies between disciplines. Monday, May 1 (DOY 121): Remember those contingency plans discussed earlier in this report? Wellllllllll. Monday was a busy day. Cassini had a DSN pass over Goldstone on Saturday, nothing on Sunday as planned, and our next tracks were the Madrid array on Monday, May 1. What follows is a mini diary of a spacecraft anomaly. The following has been extracted from various e-mails jetting through the project today. Read on: DIARY START Sequence Lead: The planned downlink from the spacecraft (S/C) did not go as expected this morning. From the beginning of the track, we have been unable to see any signal from the orbiter. The uplink was swept multiple times, and a signal from the low-gain antenna has been looked for with no effect. I am callling an anomaly meeting for this morning at 9:00 PDT. Spacecraft Operations Office (SCO): A loss of downlink anomaly occurred on May 1, 2006. No one-way data was received at the beginning of track at around 6:30 a.m. PDT. We started the uplink drive on time at 6:40 a.m., but stopped after 50 minutes when the no-downlink anomaly continued. After looking for all combinations of spacecraft safing with DSS 63, DSS 55, and Radio Science Open Loop receivers, SCO decided to wait for nominal lockup at the two-way time. Sequence Lead: Good news! At the time we were scheduled to go 2-way with the S/C we regained downlink. Data is now coming in as expected. Telemetry indicates there was a Solid State Power Switch (SSPS) trip on the unit that powers the Ultra Stable Oscillator (USO), and the USO is currently powered off. This means that a 2-way light time after the transmitter was turned back off, during the recovery efforts, we will go back to 1-way, and thus will lose the downlink again, for approximately 2 hours. Since this will almost definitely impact the SAR data, we will be sending up the contingency command to zero out data policing during this pass, and zero out everything except VIMS during the following observation period. The SAR data will then be played back during tomorrow's pass. SCO is currently planning to investigate whether the SSPS trip was merely a cosmic ray hit or whether there is something actually wrong with the USO, and we should know that by the end of the current pass. I will forward that info as soon as I have it. We are trying to get our DSS-15 track tomorrow extended to our rise time, so that we can go 2-way as early as possible, in case the USO is damaged. Spacecraft Operations Office: It turns out that the SSPS for the USO was tripped, causing no one-way downlink carrier or data. This tripped switch condition is consistent with ones seen in the past. This is the sixteenth trip seen to date, the third trip of a switch that was ON at the time, and the second trip this year. The previous trip occurred very recently on March 2, 2006. They are predicted to occur at a rate of about two per year, and are most likely caused by Galactic Cosmic Rays. Commands were built and uplinked to cycle the SSPS OFF to clear the trip, then commanded it back ON. The S/C is operating nominally following this activity. Sequence Lead: The file to zero out data policing during the current pass and for all but VIMS on the next observation period has been sent with a bit-1 time of 121T17:34:55. We will confirm that this file reached the spacecraft at approximately 20:00. The DSN was able to extend tomorrow's track for Cassini, starting it at station rise at 19:15 rather than at our allocated time of 21:10. This will allow us to do an early uplink, and go 2-way sooner than we would otherwise, which will be a boon, if cycling the SSPS does not clear the issue up. Instrument teams have been reporting nominal operations for their instruments. All are awaiting playbacks to determine what data was overwritten. I will keep you posted on any further development. Tuesday, May 2 (DOY 122): DIARY CONTINUES Spacecraft Operations Office: Telemetry indicates that the command file to move the pointers to replay Titan data has executed. The pointers were moved to the appropriate locations discussed in yesterday's meeting with CDS, Science Planning, Mission Planning, Uplink Operations, and RADAR. Now we just wait for the data... RADAR Instrument Team: Just received the first RADAR packet on the ground. The time lines up at about -12 minutes from closest approach. So looks like the first ~90 Mbit got overwritten as predicted. Hopefully the end point is correct. Looks good and as expected so far!! UVIS Instrument Team: The UVIS T13 occultation data is on the ground. The data looks good except for an unfortunate 1-minute data gap just when the signal starts to decrease. It is assumed that this is due to the S/C going 2-way or to a telemetry rate change. In any case nice recovery work! Thanks to all involved in this data recovery. RADAR Instrument Team: Great pointer work!! The end point was also correct! We got all our data from about -12 minutes up to where we receive data yesterday. There was a small overlap, so there are no gaps in the data that we do have. The only missing data is the -20 to -12 minutes of SAR that was overwritten. So basically ~600 out of the expected 700 Mbit was recovered. Great work! Thanks is probably not enough.........but thanks! END DIARY The final sequence development process for S22 kicked off today. The process will run for approximately 11 weeks and will begin execution on July 17. Cassini Outreach has reported the release of the DVD "Ring World 2". The DVD includes both English and Spanish language versions, as well as closed captioning. Copies have been shipped out to members of the International Planetarium Society, the Navigator Program's Night Sky Network, NASA Solar System Ambassadors, Space Place's museum network, the USGS, and throughout the Cassini mission to flight team members who give Cassini outreach presentations. A RW2 version for video Ipod is now available and may be downloaded from: http://saturn.jpl.nasa.gov/multimedia/videos/video-details.cfm?videoID=114 Wednesday, May 3 (DOY 123): OTM #59 was performed today. This is the cleanup maneuver from the Titan13 encounter on April 30. The main engine burn began at 7:45 PM PDT. A "quick look" immediately after the maneuver showed the burn duration was 3 seconds, giving a delta-V of approximately 0.47 m/s. All subsystems reported nominal performance after the maneuver. At an SRCR held today, the new CDA flight software was approved for operations. The planned uplink date is June 5, with on-board checkout scheduled to occur on DOY 165, 9 days later. A beautiful color picture of Saturn is Astronomy Picture of the Day today. Upcoming Events: On May 6, over 70 Saturn Observation campaign members in 33 states and 10 countries are conducting daytime solar viewing activities and/or nighttime stargazing to celebrate International Astronomy Day. These events range from small neighborhood planet viewings to large events. Weather permitting, Saturn will be a primary viewing target. Contact Cassini Outreach for specifics, or contact your local astronomy club, science center, or college to see if there is an event in your community. JPL Open House - May 20-21, 2006: Expected Attendance: 50,000 Cassini will have a 30'x50' exhibit booth near the main entrance of JPL. The booth will highlight mission science results through graphic displays and multimedia presentations. The both will be staffed with project employees who will be available to answer questions. A kids' area will feature "temporary tattoos" of Saturn. Interactive features include "Take your photo on Titan" with a full scale Huygens probe model placed in a simulated landing environment as well as "spacecraft tours" using the 1/2-scale Cassini model. A "Moon Walk" will guide Open House visitors past highlights of Saturn's moons. The moonwalk will link the booth and the 167 conference room where Ring World will be shown. Wrap up: Check out the Cassini web site at http://saturn.jpl.nasa.gov for the latest press releases and images. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter.
