Cassini Significant Events 04/22/09 – 04/28/09

The most recent spacecraft telemetry was acquired on Apr. 28 from the Deep Space Network tracking complex at Canberra, Australia. 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, April 22 (DOY 112)

Thanks to the very accurate delivery to the Titan 53 flyby on April 20, and the upcoming OTM-192, which is a reasonable size deterministic targeting maneuver, there is no delta V penalty for cancellation of OTM-191. As a result, OTM-191, due to execute later today, has been cancelled.

Thursday, April 23 (DOY 113)

The Composite Infrared Spectrometer (CIRS) performed a high priority observation today when it collected nine hours of data for a vertical temperature map of the rings at 60 deg phase angle.

Uplink Operations sent commands to the spacecraft for telemetry mode changes to execute on DOY-115 through 117. These commands were required because of the loss of coverage from DSS-14 on DOY-114 and 115. In addition, commands were sent to power the Ka-band hardware on and off in support of DSN testing on DOY-116.

Friday, April 24 (DOY 114):

Today Imaging Science (ISS) acquired high priority science data for an 11-hour movie of the streamer-channel feature raised in the F-ring by the apoapsis passage of Prometheus.

The S49 DOY-116 Rhea live Inertial Vector Propagator update was uplinked to the spacecraft on Saturday along with a main engine parameter patch.

An AACS friction test of the prime wheels - numbers 1, 2, and 4 - was executed on Saturday, Apr. 25. Performed every three months, the wheels are spun up to 900 rpm in both directions and timed as they are allowed to spin down to 0 rpm. In this particular test the spin down time for wheel-2 improved substantially relative to what has been seen in recent prior tests.

Sunday, April 26 (DOY 116):

A non-targeted flyby of Titan occurred today.

In a sixth and final planned attempt, ISS acquired images at Rhea today to try to confirm the report of possible rings around that satellite by the Magnetospheric and Plasma Science instruments. If confirmed, Rhea would become the first moon in the solar system to have rings. The camera was pointed off the edge of the moon – which was out of the field of view, but still scattered a significant amount of light into the camera - while looking edge-on at Rhea's equatorial plane. To avoid saturating the camera, multiple exposures were taken and will later be combined to enhance any faint signatures detected. Because the viewing geometry is low-phase with the Sun approximately behind the camera, this observation will be sensitive mostly to macroscopic or sand-size and larger particles.

Monday, April 27 (DOY 117):

A very nice image of Prometheus in Saturn's F ring was Astronomy Picture of the Day today. Check it out at: http://antwrp.gsfc.nasa.gov/apod/ap090427.html

As part of the Science Operations Plan process, files were delivered for the third and final port for S52, and for the second port for S53. The files for each sequence have been merged and the results released to the participants.

Seven Instrument Expanded Block files for ISS, CIRS, the Visual and Infrared Mapping Spectrometer, Ion and Neutral Mass Spectrometer, Optical Navigation, and Cassini Plasma Spectrometer were uplinked to the spacecraft in support of S50 late Sunday and early Monday morning. S50 will begin execution on May 5.

Tuesday, April 28 (DOY 118):

The Cassini-Huygens Analysis and Results of the Mission (CHARM) teleconference for April was entitled: "That's Why We Carry Backup Hardware," and described the behind-the-scenes story of the recent swap from the RCS A-branch thrusters to the B-branch thrusters. It was presented by the manager of the Cassini Spacecraft Operations Office.

Orbit Trim Maneuver (OTM) #192 was performed today. This is the apoapsis maneuver setting up for the Titan 54 encounter on May 5. The main engine burn began at 5:14 AM PDT. Telemetry immediately after the maneuver showed the burn duration was 14.8 seconds, giving a delta-V of 2.49 m/s, as designed. All subsystems reported nominal performance after the maneuver. OTM-192 included the first use of new main engine parameters to reduce small fixed magnitude and proportional magnitude error statistics. Along with OTM-192, the spacecraft office uplinked an Immediate/Delayed Action Program containing commands to turn on the Main-Engine-A heater B-line Solid State Power Switch (SSPS), and the Main-Engine-B B-line SSPS. This will power on the main engine heaters using both lines. The file will execute over the DSN pass reserved as a backup for OTM-192. This switch configuration will eliminate the need for Autonomous Thermal Control to track the temperature of the main engine using the potentially unreliable temperature transducers.