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NASA Cassini Significant Events for 03/19/08 - 03/25/08

Status Report From: Jet Propulsion Laboratory
Posted: Monday, March 31, 2008

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The most recent spacecraft telemetry was acquired on Monday, March 24, from the Madrid, Spain 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, March 19 (DOY 079):

An encounter strategy meeting was held today to cover the period between Mar. 25 and May 12, Titan flybys T42 and T43, and maneuvers 152-154.

Thursday, March 20 (DOY 080):

During the day today the Solid State Power Switch (SSPS) for Traveling Wave Tube Amplifier (TWTA) B Line A tripped off. The trip was detected once Cassini began receiving telemetry from a scheduled overnight DSN pass. The last safing event on the spacecraft, on September 11, 2007, was triggered by a trip of this same switch. This time, however, safing was avoided. In the new V10 CDS flight software, the SSPS / System Fault Protection (SFP) interaction had been changed to allow the SSPS FP to take action before safing would be invoked. The software responded as designed by commanding the switch OFF to clear the trip, and then back ON. The TWTA and spacecraft are performing nominally following this activity. The CDS team will send real-time commands to the spacecraft on Saturday to clear the response counter for TWTA-B line A.

This is trip #24, and the second one on this particular switch. Two other SSPSs have also tripped twice. These trips were predicted to occur at a rate of about two per year. Being in the Saturnian system has accelerated the SSPS trip rate for Cassini. Starting in April of 2004 until the present, the trip rate has more than doubled compared to the cruise period.

Cassini has discovered evidence that points to the existence of an underground ocean of water and ammonia on Saturn's moon Titan. The findings made using RADAR measurements of Titan's rotation will appear in the Mar. 21 issue of the journal Science. For the full news release link to: http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=826

Friday, March 21 (DOY 081):

Today the Composite Infrared Spectrometer (CIRS) will target the rings for a longitudinal scan on the unlit face, outside shadow area, and at mid phase angle. Imaging Science (ISS) will target satellites in their continuing satellite orbit determination campaign.

Saturday, March 22 (DOY 082):

At the preliminary Orbit Trim Maneuver (OTM)-151 Navigation review, the required B-plane correction at Titan 42 was about 400 meters, requiring a correction of about 3.7 mm/sec (That's about 0.01 km/hr!), which is well below the minimum delta V capability. A quick look at the tracking data from Friday night's pass indicated a further shift of about 100 meters in the trajectory solution. This change was insufficient to increase the delta V to an acceptable level, about 14 mm/s. Science has reviewed the trajectory without the OTM and has not found any negative impact to science acquisition. Therefore OTM-151, scheduled to execute today, has been cancelled.

Sunday, March 23 (DOY 083):

Non-targeted flybys of Pallene, Epimetheus, and Methone occurred today.

The main engine cover was closed today at the end of the OTM-151 prime pass for dust hazard avoidance. It will be reopened tomorrow at the start of the OTM-151 backup pass. This is the 38th cycling of the cover. A cycle consists of deployment or closing of the cover, then stow or opening of the cover to a retracted position. The next cover closure is scheduled for June 1, 2008.

The S38 sequence concluded and S39 began execution today. The sequence will run for 27 days and conclude on April 19. During that time there will be one targeted encounter of Titan and seven non-targeted flybys - two of Pallene, and one each of Epimetheus, Methone, Titan, Janus, and Mimas. OTM-152 is the only OTM scheduled to execute during this 4-week period.

Today was a busy day for science, commencing with a CIRS radial scan to obtain ring temperature measurements over varying solar elevation and phase angles on both the lit and unlit sides of rings. CIRS also obtained a longitudinal scan on the lit face of ring, in and around the shadows, at low phase angle. The Visual and Infrared Mapping Spectrometer (VIMS) performed a complete high resolution radial scan of the unlit face of the A, B and C rings at high phase angle, and observed the sun continuously as it crossed behind the east ansa, with coverage mostly of the A and B rings. ISS captured a retargeted observation of specific gap edges and narrow ringlet structures. Some time was given to satellite observations, with VIMS observing the lit surface of Dione and Mimas, and CIRS observing Dione's solar eclipse entry and Mimas's solar eclipse exit.

Monday, March 24 (DOY 084):

A beautiful picture of Saturn and Titan is Astronomy Picture of the Day today. Check it out at http://antwrp.gsfc.nasa.gov/apod/ap080324.html

A presentation was given today at JPL on "The Role of Tides on Enceladus."

Science Operations Plan implementation for S44 began today. The Science Planning Attitude Spread Sheet (SPASS) will be delivered to the instrument teams on Mar. 26 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 that day.

Tuesday, March 25 (DOY 085):

Today Cassini flew by Titan at an altitude of 1000 km, and a speed of 6.3 km/sec. Closest approach (CA) occurred at 2008-085T14:28:48 SCET. Just prior to CA of this T42 flyby, the Ion and Neutral Mass Spectrometer (INMS) examined the upper atmosphere. Immediately after, VIMS captured images of Titan near the Huygens landing site using the so-called "noodle" mode, where VIMS captures a long noodle-shaped swatch of Titan's surface. CIRS spent eight hours looking at several positions on Titan's limb, measuring stratospheric temperatures around one quarter of the visible disk, and also searching for new trace species. Additionally, CIRS rode along with ISS to obtain imagery of the landing site. Link to the following for more information on this flyby: http://saturn.jpl.nasa.gov/news/events/titan20080325/index.cfm

The Cassini-Huygens Analysis and Results of the Mission (CHARM) teleconference for March addressed the topic of: Organics on Titan, Water on Enceladus: Worlds of Possibilities for Life.

The final sequence development process for S41 kicked off today. The process will run approximately ten weeks and conclude just before the start of sequence execution on May 31. S41 is the final sequence in the Prime Mission.

Today a two-day NASA review began at JPL to assess Cassini operations preparedness to support Extended Mission. The review will conclude tomorrow. Update: At the end of the review on Mar. 26, the board had found no negative aspects to the Cassini operations plan. An official report of the board's findings will be released shortly.

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.

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