Cassini Significant Events 09/28/11 – 10/04/11

The most recent spacecraft telemetry was acquired on Oct.4 from the Deep Space Network tracking complex at Canberra, Australia. The Cassini spacecraft is in an excellent state of health and with the exception of the CAPS instrument being powered off, 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/mission/presentposition/.

Wednesday, Sept. 28 (DOY 271)

Orbit Trim Maneuver (OTM) #292 was performed today. This was the approach maneuver setting up for the Enceladus 14 encounter on Oct. 1. The Reaction Control Subsystem (RCS) burn began at 7:30AM PDT. Telemetry immediately after the maneuver showed a burn duration of 26.75 seconds, giving a delta-V of 0.033 m/s. This OTM required two reaction wheel biases to avoid the low RPM region. All subsystems reported nominal performance after the maneuver.

The alternate timeline for the T-79 encounter was selected in time for the S71 Sequence Change Requests (SCRs) being submitted for the Preliminary Sequence Integration and Validation (PSIV) step, which were due today. The Project Scientist decided to recommend the alternate, non-Cassini Plasma Spectrometer (CAPS) option for the T-79 flyby, with careful consideration given to the one or two other Titan flybys existing in the remainder of the Solstice mission that provide similar geometries for CAPS Titan science. Titan's environment is temporally variable, however, and the loss of the T-79 flyby for CAPS will result in the loss of key Titan magnetospheric science. Until a final decision is made regarding future CAPS turn-ons, the plan is for CAPS to schedule observations and request data volume in all future sequences assuming that it will be on, with case-by-case dual options such as the T-79 flyby if schedule and workforce resources permit. It has also been recommended that, at the appropriate point in the sequencing process, if it is clear that CAPS will not be on for that sequence, the CAPS downlink bits are reallocated to other instruments as sponge bits.

A non-targeted flyby of Titan occurred today.

Thursday, Sept. 29 (DOY 272)

This week's science observations included a 10 hour observation of Saturn in order to measure oxygen compounds (H₂O, CO₂) in the stratosphere by the Composite Infrared Spectrometer (CIRS). The Ultraviolet Imaging Spectrograph (UVIS) later performed a 9 hour observation of Saturn’s aurora and the remote sensing instruments made measurements of Dione and its trailing hemisphere "wispy terrain." The E-14 Enceladus flyby followed with Enceladus observations during the encounter. This was then followed by further observations of Dione, this time of the leading hemisphere, and searches for objects in the L4 Lagrangian regions of Enceladus' and Titan's orbits. On the final day of the week, astrometric observations were made of some of Saturn's small inner moons, Rhea was observed passing in front of Titan, Titan itself was observed as part of the cloud monitoring campaign, and CIRS made an additional stratospheric compositional measurement of Saturn.

The Attitude and Articulation Control Subsystem (AACS) Safe Table value was updated to -30 degrees today.

Friday, Sept. 30 (DOY 273)

Cassini Real Time Operations (RTO) conducted the final Autorad demonstration and Ace procedure validation today. Autorad is now considered an operational command utility for Cassini. First use of the Autorad tool in operations will begin in S71. The S71 sequence team leads will use Autorad for the uplink of the S71 Instrument Expanded Block (IEB) files. Autorad is a tool used for the autonomous radiation of some of the command files being sent to the spacecraft.

A non-targeted flyby of Titan occurred today.

Saturday, Oct. 1 (DOY 274)

Today Cassini flew by Enceladus at an altitude of 99 kilometers and a speed of 7.4 km/sec. This close flyby of the south pole featured fields and particles instruments learning more about the nature and density of the particles in the plumes, with high-phase observations of the south polar plume and jets, and the Ion and Neutral Mass Spectrometer (INMS) measurements of plume & jet gas density, with measurements by other fields-and-particles instruments as well. On the outbound leg of the flyby, CIRS and the other remote sensing instruments made thermal and compositional measurements of Enceladus' equatorial and northern regions during and after eclipse. Remote sensing instruments also looked for changes in the level of activity on Enceladus. For more information and raw images, link to: http://saturn.jpl.nasa.gov/mission/flybys/enceladus20111001/.

Non-targeted flybys of Epimetheus and Calypso occurred today.

Sunday, Oct. 2 (DOY 275)

The main engine cover was closed on Thursday, Sept. 29, for dust hazard avoidance and was opened today. This was the 66th in-flight cycle of the cover.

IO/MIPL provided members of the Cassini Media Relations team file transfer software (FEI5) and access to the Imaging Science Subystem (ISS) web JPEG index file. This file provides the mapping between products the ISS team delivers to Media Relations and the metadata needed to describe those products. This file was successfully used to expedite posting flyby images from the E-14 flyby on the Cassini website (http://saturn.jpl.nasa.gov/).

Monday, Oct. 3 (DOY 276)

A feature story called “Saturn’s Geyser Moon Enceladus Shows Off for NASA’s Cassini” is available on the Cassini web site. It describes how the Cassini spacecraft successfully completed its Oct. 1 flyby of Saturn's moon Enceladus and its jets of water vapor and ice. For images and more information on this subject, link to: https://solarsystem.nasa.gov/news/12565/saturns-geyser-moon-enceladus-shows-off-for-nasas-cassini/.

The Division for Planetary Sciences (DPS) of the American Astronomical Society is holding its annual meeting this week in Nantes, France (Oct 3-7); many Cassini scientists are in attendance reporting on their most recent results. This meeting is to bring together the international community of specialists in the planetary sciences to present and discuss the latest results of research on the solar system.

AACS Periodic Engineering Maintenance was done today. This activity, performed approximately every 90 days, spins up the backup reaction wheel assembly to 100 rpm for lubrication purposes and exercises the back-up Engine Gimbal Actuator.

The S73 Engineering Activities Review was held today. At this review, Spacecraft Office personnel took a look at all spacecraft activities to be performed during the S73 sequence.

Tuesday, Oct. 4 (DOY 277)

OTM #294 was performed today. This was the clean up maneuver following Enceladus 14 and setting up for the Enceladus 15 encounter on Oct. 19. The Reaction Control Subsystem (RCS) burn began at 8:45PM PDT. Telemetry immediately after the maneuver showed a burn duration of 66.125 seconds, giving a delta-V of 0.074 m/s. All subsystems reported nominal performance after the maneuver.

OTM 295, the E15 approach maneuver, is scheduled to execute on Sunday, October 9. Afterwards, for four days beginning on Oct. 11, the spacecraft attitude control mode changes from a Reaction Wheel Assembly (RWA) mode to RCS mode as the spacecraft passes through solar conjunction with a minimum Sun Earth Probe (SEP) angle of 2.2 degrees.