Cassini Significant Events 12/12/07 - 12/18/07

December 20, 2007

(Source: Cassini Project)

The most recent spacecraft telemetry was acquired on Tuesday, Dec. 18, from the Madrid 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, Dec. 12 (DOY 346):

Data from the Radio and Plasma Wave Science instrument is helping to provide a clue to the interior period of rotation for Saturn. The article is available from the European Space Agency at

New observations by Cassini indicate the rings of Saturn, once thought to have formed during the age of the dinosaurs, instead may have been created roughly 4.5 billion years ago, when the solar system was still forming. For more details link to:

A delivery coordination meeting was held this week for Mission Sequence Subsystem (MSS) version D13.0.1, along with a Software Requirements and Certification Review for AACS flight software (FSW) version A8.7.6 and Cosmic Dust Analyzer (CDA) instrument FSW Version 12.0. The AACS parameter patch updates the default thruster performance parameters and the secondary vector used by the safing response. The CDA delivery is to deploy a special version of flight software specifically meant for close Enceladus flybys. The MSS delivery is driven by the need to update slew margin policy files in the Pointing Design Tool software for the proposed extended mission, and implement support of these files in the Sequence Phase List of Ancillary Files tool.

Thursday, Dec. 13 (DOY 347):

Orbit Trim Maneuver (OTM) #138 was performed today. This is the apoapsis maneuver setting up for the Titan 39 encounter on Dec. 20. The main engine burn began at 12:24 AM PST. Telemetry immediately after the maneuver showed the burn duration was 59.07 seconds, giving the planned delta-V of 9.64 m/sec. All subsystems reported nominal performance after the maneuver.

When changes occur in the Spacecraft Clock/Spacecraft Event Time (SCLK/SCET) file used by the flight team, a new file is created. Members of the Spacecraft Operations Office (SCO) have noticed an interesting pattern with the last 40 days of SCLK/SCET drift. The pattern showed a high drift followed by relative quiet. These high drift times were found to correlate exactly with temperature increases at the times Radio Science (RSS) turned on S-Band or Ka-Band transmitters. The RSS hardware is located in Bay 7 and CDS is next door in Bay 8. SCO swapped strings from CDS-B to CDS-A last October as part of the V10 flight software upload. It appears that the CDS-A clock is more sensitive than CDS-B's was to this change in temperature. This is not an issue for either CDS or RSS. SCO has asked that RSS supply the times when they expect to power up the S or Ka-Band transmitters so that the flight team may be more proactive about updates to the SCLK/SCET file.

An encounter strategy meeting was held today to cover the period between Dec. 20, and Jan. 5, Titan flybys T39 and T40, and maneuvers 140 - 142.

Friday, Dec. 14 (DOY 348):

The S35 sequence concluded and S36 began execution today at 2007-348T16:00 SCET. The sequence will run for 38 days and conclude on Jan. 22 at 2008-022T13:35 SCET. During that time there will be two targeted encounters of Titan and eight non-targeted flybys, one each of Dione, Pallene, Janus, Daphnis, Prometheus, and Methone, and two of Pandora. Five OTMs are scheduled, numbered 139 through 143.

Science at the end of S35 consisted of the continuation of the Imaging Science Subsystem (ISS) satellite orbit determination campaign, Cassini Plasma Spectrometer (CAPS) observations of dusk-side magnetospheric boundaries at a variety of latitudes, and Magnetospheric and Plasma Science (MAPS) instruments monitoring of Saturn's aurora and the solar wind while upstream of Saturn's bowshock. S36 began with a Composite Infrared Spectrometer (CIRS) mid-infrared observation for the determination of the troposphere and tropopause temperature with spatial resolution of about two degrees of latitude and longitude. 

Another sequence integration milestone was achieved today for the development of the proposed Extended Mission (XM). The third set of Cassini Information Management System inputs covering the period from Orbit 103 through Orbit 122 was delivered. These inputs consist of all science instrument team, SCO, Instrument Operations, and Optical Navigation observation requests for the period listed. This delivery date was required to meet the challenging integration milestones needed to support the just-in-time XM Science Operations Plan implementation process. 

Sunday, Dec. 16 (DOY 350)

Uplink Operations sent commands to the spacecraft today for the Radio Science Live Moveable Block due to execute on DOY-353.

Monday, Dec. 17 (DOY 351)

Orbit Trim Maneuver (OTM) #139 was performed today. This is the approach maneuver setting up for the Titan 39 encounter on Dec. 20. The reaction control subsystem burn began at 10:30 PM PST. Telemetry immediately after the maneuver showed the burn duration was 7.13 seconds, giving a delta-V of 0.013 m/sec. All subsystems reported nominal performance after the maneuver.

A kickoff meeting was held today for the start of the Science Operations Plan Update process for S40.

A beautiful picture of the rings of Saturn is Astronomy Picture of the Day today. Go to:

Tuesday, Dec. 18 (DOY 352)

The Navigation Team has released the official memorandum documenting the release of the 070918 Cassini Reference Trajectory database which includes the time period of the proposed extended mission. The reference trajectory database is a PDF document of 776 plots and the tabular data used to generate these plots. The plots are Cassini spacecraft parameters with respect to the following bodies: Dione, Enceladus, Hyperion, Iapetus, Mimas, Phoebe, Rhea, Tethys, Titan, Saturn, Earth, and the Sun. Plots of orbital elements in both Earth Mean Ecliptic of J2000 and Saturn Equator and Equinox of Date are also included in the document. The parameters are: altitude, range, range rate, velocity, declination, right ascension, latitude, longitude, and the angles between Cassini, the Saturnian satellites, Saturn, Earth, and the Sun.