NASA Cassini Significant Events 04/16/08 - 04/22/08

Status Report From: Astronomical Society of Australia
Posted: Tuesday, April 29, 2008


The most recent spacecraft telemetry was acquired on Tuesday, April 22, from the Goldstone, California,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" page at:

Wednesday, April 16 (DOY 107)

Uplink Operations sent part 1 of the S40 background sequence to the spacecraft today. S40 begins execution on Saturday, April 19.

Radio Science (RSS) team members have requested that the RSS Saturn atmospheric occultation observations occurring in S41 on DOYs 153, 168, 175 be exercised in the Integrated Test Laboratory. The tests are scheduled from April 22-23 with one test performed each day.

Friday, April 18 (DOY 109):

At the Enceladus 4 & 5 altitude decision follow-up meeting, it was decided to accept the E4 design as is with no change to the flyby altitude. More work remains to be done before the Program can come to a decision for E5. Since E5 does not occur until October, the decision date was moved out to May 15.

Study of the north polar region of Saturn continued today with a scan by the Ultraviolet Imaging Spectrograph (UVIS) extreme ultra-violet slit searching for auroral activity, with the Visual and Infrared Mapping Spectrometer (VIMS) riding along. Distant images of Mimas and Enceladus were taken for optical navigation, as were images of Epimetheus, Pan, Methone, and Pandora as part of the campaign to better determine the orbits of minor satellites. Finally, the Composite Infrared Spectrometer (CIRS) observed the C ring in a continuous azimuthal scan at a constant radial distance of 83,000 km.

Saturday, April 19 (DOY 109):

Non-targeted flybys of Mimas, Telesto, and Epimetheus occurred today.

An AACS Reaction Wheel (RWA) friction test of the prime wheels numbered 1, 2, and 4 was performed today. Results as compared to the last test performed Jan. 29, 2008 are:

RWA-1: Slightly worse in the clockwise direction, at least partially due to a drag torque spike during the spin-down, and better in the counterclockwise direction. The counterclockwise rundown time increased by about 11 minutes from the previous test, bringing it to almost 40 minutes.

RWA-2: Unchanged in either direction.

RWA-4: Better in both directions. In the clockwise direction, the rundown time increased by about 4 minutes, to about 34 minutes. In the counterclockwise direction, the rundown time increased by 13 minutes and is now the same as it was two friction tests ago, about 41 minutes. In spite of the recent increases in rundown times, the overall downward trend continues, and the viscous friction coefficients are increasing as expected.

The S39 sequence concluded and S40 began execution today at 2008-110T07:18:00. The sequence will run for 35 days and conclude on May 31, 2008. During that time there will be two targeted encounters of Titan and eleven non-targeted flybys - two each of Telesto, Methone, Epimetheus, and Janus, and one each of Titan, Pallene, and Atlas. Five Orbit Trim Maneuvers are scheduled, numbered 153 through 157. S40 is of a size that it will not fit in the sequencing memory in the CDS, so it has been split into two parts. Part 2 will uplinked on May 6, and will begin execution on May 13.

Sunday, April 20 (DOY 111):

Spacecraft Operations performed an AACS Periodic Engineering Maintenance (PEM) exercise over the weekend. Performed every 90 days, this activity exercises the Engine Gimbal Actuators and the backup RWA #3.

Monday, April 21 (DOY 112):

The Target Working Teams and Orbiter Science Teams delivered integrated products for the S45 background sequence today.

Tuesday, April 22 (DOY 113):

On Friday, April 18, Science Planning handed off to Uplink Operations the products necessary for the final sequence development process for S42. Today, the kickoff meeting for that process was held. S42 is the first sequence of the Cassini Extended Mission.

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