NASA Cassini Significant Events for 06/18/08 – 06/23/08

The most recent spacecraft telemetry was acquired on June 23, 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” page at: http://saturn.jpl.nasa.gov/operations/present-position.cfm.

Wednesday, June 18 (Day of Year (DOY) 170)

AACS is continuing to investigate the significant change in RWA-2 friction test results. This has not affected any overall pointing or other spacecraft performance to date.

The third and final delivery port of the S44 Science Operations Plan process occurred today. All files have been received from teams participating in this sequence. The process will complete on July 7, when products will be handed over to Uplink Operations for the final development process. Tomorrow, files will be delivered for port 2 of the S45 process.

Thursday, June 19 (DOY 171)

Part 2 of the S41 background sequence began execution on board the spacecraft today at 9:47 p.m. PDT.

A kickoff meeting was held today for the fifth and final Live Update of S41. Science Planning analyzed current targeting based on the orbit determination solution that the Navigation Team released for Orbit Trim Manuever (OTM) 59. As a result, the vectors for Saturn, Enceladus, Janus, Mimas and Tethys on DOY 182 will be updated for six separate observations. Imaging Science (ISS), the Composite Infrared Spectrometer (CIRS) and Ultraviolet Imaging Spectrograph (UVIS) have concurred with the analysis and what will receive an update. The current plan is to approve the files at a Command Approval Meeting (CAM) on June 27, and uplink them that same day.

ISS begins observations on DOY 171 by conducting a photometric stellar calibration. As the spacecraft approaches apoapse, ISS images Saturn atmospheric dynamics using the narrow- and wide-angle cameras. Meanwhile, Magnetospheric and Plasma Science (MAPS) teams add more data to their ongoing campaign to image the dynamics of Saturn’s inner magnetosphere.

Uplink Operations sent commands to the spacecraft today for a Radio and Plasma Wave Science (RPWS) change from two-antenna to three-antenna direction finding in survey modes that will execute on Sunday, and the Radio Science (RSS) Live Movable Block Saturn Occultation Egress file for execution on Monday. Tomorrow, files will be sent for the DOY 173 Live Inertial Vector Propagator Update for Saturn/Tethys, and for OTM-159.

Monday, June 23 (DOY 175)

Non-targeted flybys of Methone and Pan occurred today.

DOY 175 was a very busy day on the spacecraft. It began with the MAPS instruments performing an auroral crossing experiment. In high-inclination orbits, such as Cassini’s current orbit, the spacecraft has an opportunity to sample the plasma environment near Saturn’s auroral regions near the poles. Furthermore, this auroral crossing took place during a spacecraft downlink over the Canberra’s 70-meter station. The convergence of a favorable geometry and a 70-meter downlink allowed MAPS instruments, such as RPWS and the Cassini Plasma Spectrometer, to collect and downlink data at a very high rate.

The auroral crossing and downlink was briefly interrupted by the execution of OTM-159. After the maneuver, the spacecraft slewed back to an Earth-pointed orientation and set up for an RSS Saturn Occultation. This was the last RSS observation the Cassini Prime Mission. A Saturn occultation occurs when Saturn blocks the Earth, as viewed from the spacecraft. This unique geometric configuration allows RSS to measure Saturn’s atmosphere and ionosphere by continuously sending a radio signal to Earth and measuring changes in the signal as it passes through Saturn’s atmosphere and ionosphere. While this was going on, the MAPS instruments continued their auroral-crossing investigation. This was possible because the spacecraft’s orientation allowed it to point the radio transmitter toward Earth and rotate around the transmitter axis to point the MAPS instruments at Saturn at the same time.

OTM-159 was performed today. This was the periapsis maneuver setting up the Titan- 45 encounter on July 29. The Main Engine burn began at 12:45 a.m. PDT. Telemetry immediately after the maneuver showed the burn duration was 73.5 seconds, giving a delta-V of 12.2 meters per second. All subsystems reported nominal performance after the maneuver. Due to the size of this maneuver, and the large costs of delta V if it were to be executed over the backup pass, the decision was made to uplink the files early to provide additional uplink windows should the need arise.

After the successful execution of OTM-159, the main engine cover was cycled for the 40th time since launch. It was closed to provide protection from dust hazards that would occur that day, and on June 30, July 7 and July 14. The cover will be opened again on July 21. At that point, it will have been closed for 25 days.

Visit the JPL Cassini home page for more information about the Cassini Project: http://saturn.jpl.nasa.gov/