Cassini Significant Events 05/16/07 - 05/22/07

May 25, 2007

(Source: Cassini Project)

The most recent spacecraft telemetry was acquired on Tuesday, May 22, 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

Wednesday, May 16 (DOY 136):

The Cassini Deputy Project Scientist gave an in-reach talk today to members of the flight team. Every quarter - this time on May 7 - Cassini gives a presentation on project status to NASA personnel. One aspect of that presentation includes the most significant science results from the previous three months. Over the last year, the flight team has requested that this presentation be given internally to project members. The team always looks forward to it and is never disappointed.

A delivery coordination meeting was held today for Version 5 of the Cassini Archive Tracking Software. This version focused on porting the software from Sybase to MySQL, so that responsibility for software could be transferred from the Multi-Mission Image Processing Laboratory to Cassini Instrument Operations, and to fix some confusing display information.

Thursday, May 17 (DOY 137):

A kick off meeting was held today for a live update for Tethys/Saturn/Mimas/Rhea observations to occur on May 26, and a Radio Science (RSS) Live Update Block to execute on May 28. The Titan 31 flyby will also occur on May 28.

Friday, May 18 (DOY 138):

The Aftermarket Process for the S35 sequence, orbits 51-54, began today. All proposed science and engineering changes were submitted to the Cassini Information Management System by participating teams. The process runs for five weeks and addresses changes that require re-integration of the science segments contained in S35. If all of the requested changes do not fit within scope, an assessment meeting will be held on May 22 with the Project Scientist to discuss the proposed changes. If there are still conflicts, a final decision meeting will be held on June 5 to select what changes will be made to S35.

Today Cassini took an image of the rings, Mimas, Enceladus, Telesto, and Epimetheus. The team fondly refers to such images as Kodak Moments (KM). About once per sequence there is an opportunity for an aesthetically pleasing image to be taken. Some of the most beautiful and iconic images to come out of Prime Mission have been KM images. There will be about 32 images in this collection at the end of Prime Mission.

Sunday, May 20 (DOY 140):

Orbit Trim Maneuver (OTM) #111 was performed today. This was the apoapsis maneuver targeting to the Titan 31 encounter on May 28. The main engine (ME) burn began at 2:45 AM PST. Telemetry immediately after the maneuver showed the burn duration was 34.26 seconds, giving a delta-V of 5.53 m/s. All subsystems reported nominal performance after the maneuver.

OTM-111 was the first attempt at a "hydrazine efficient" yaw turn rate. Analysis showed that if the yaw turn rate was reduced, hydrazine usage would decrease. Science Planning bookkeeps a playback gap of 1 hr 22 minutes for each prime OTM pass, so that was the time constraint. The usual turn rate is 4.36 mrad/sec. This time the turn was slower, at 1.1 mrad/sec.

OTM-108, on May 4, was a comparable ME burn with a similar yaw turn of about 116 degrees. Compared to hydrazine usage of 94.8 g for that OTM, 62.2 g were used in OTM-111, giving about a 30% savings. Even though the off-Earth time was obviously greater, 1 hour 11 minutes for OTM-111 vs. 25 minutes for OTM-108, contributing to increased navigation uncertainty, Spacecraft Operations plans to continue with this new strategy in the future.

Monday, May 21 (DOY 141):

Science this week was dominated by Magnetospheric and Plasma Science observations of Saturn at apoapsis. The Ultraviolet Imaging Spectrograph (UVIS) also made observations of Enceladus and Rhea, while ISS continued a series of observations of the smaller satellites.

Various Cassini outreach and flight team members collapsed with exhaustion and not a little pleasure after over 32,000 people came to visit the Cassini booth over the weekend at the annual JPL open house. See this report from last week for a description of the Cassini display.

Tuesday, May 22 (DOY 142):

At a Go/No Go meeting, the RSS Live Update Block and a live update for Tethys/Saturn/Mimas/Rhea were approved. Commands for these events will be sent to the spacecraft on May 24.

The B ring, the largest and most densely packed ring orbiting Saturn, is composed of tightly packed clumps of particles separated by nearly empty gaps, according to new findings from UVIS. These clumps are neatly organized and constantly colliding. Because previous interpretations assumed the ring particles were distributed uniformly, scientists underestimated the total mass of Saturn's rings. The mass may actually be two or more times previous estimates. For the full details of this release, link to:

An encounter strategy meeting was held today to cover the period between May 28 and June 13, Titan flybys T31 and T32, and maneuvers 113-115.