Cassini Significant Events 10/17/2012 - 10/23/2012
Cassini Significant Events 10/17/2012 - 10/23/2012
Oct. 25, 2012
There's no sense in making observations if you're unable to downlink all the data from around behind the radio-noisy Sun. So during superior conjunction each year, science gathering activities are generally cut back on the spacecraft. This week, the Spacecraft Operations Office is taking advantage of the normally reduced-activity period by turning off science instruments to help cool down the spacecraft as a step in the Propellant Gauging Test (PGT). Analysis of the results of warming and then cooling should provide a more accurate estimate of the propellant mass remaining in Cassini's main tanks. There is no prospect of running out of propellant before the end of the mission in 2017, but information from the PGT could be useful to support decision making in the event of any anomaly that might require unplanned propellant usage.
Wednesday, Oct. 17 (DOY 291)
The Visible and Infrared Mapping Spectrometer (VIMS) did a 5.5-hour calibration through its solar port, obtaining spectra of the Sun in order to monitor variations in instrument sensitivity over time, as well as to look for subtle changes in the solar spectrum. These calibrations occur during high-phase periods when observations of the rings and Saturn are forbidden because sunlight entering the instruments' main apertures could damage the sensors.
The Imaging Science Subsystem (ISS), the Composite Infrared Spectrometer (CIRS), and VIMS jointly observed the E ring for 3.5 hours. ISS used its wide angle camera to scan the entire ring system, then used its narrow-angle camera for a 2.5-hour observation of Enceladus's plume.
Thursday, Oct. 18 (DOY 292)
Cassini shot through periapsis going 42,000 kilometers per hour relative to the planet, passing about 416,000 km above Saturn's atmosphere and just outside the diffuse E ring.
ISS, CIRS and VIMS observed the D ring close-up for four hours, then the Ultraviolet Imaging Spectrograph (UVIS) observed a full radial ring occultation of the bright star Epsilon Canis Majoris, providing an opportunity to study temporal changes in the C through F rings. UVIS also observed a nearly complete radial ring occultation of the bright blue star Gamma Columbae, which provided information on azimuthal variation in the rings that can be separated from temporal variations. Next, VIMS observed an occultation of Lambda Velorum as the star made a radial pass across the entire ring system. ISS, CIRS and VIMS then performed a high-resolution observation of the F ring in order to continue a study of small-scale structure variability in the narrow ring's core over time. CIRS then observed the rings for three hours in a campaign to catalog the variation of ring temperature with phase and latitude.
Friday, Oct. 19 (DOY 293)
ISS spent 1.5 hours reacquiring and tracking the orbits of known "propeller" features in the rings (see http://go.usa.gov/YyGR). UVIS made a 1-hour observation in the campaign to map the UV albedo of Enceladus as a function of longitude and phase angle. The instrument then observed a ring occultation of the star Spica. Since this is one of the brightest stars, it provided a high signal-to-noise ratio for the B ring, making it valuable for studying wakes in the B and A rings and for probing low optical-depth structure in the Cassini Division and F ring.
Outbound from periapsis, UVIS performed a 6-hour observation to obtain far ultraviolet spectra from the C ring through A ring at low phase angle.
The cooling phase of the PGT began today when the S75 sequence commanded the main engine cover to open, allowing internal heat to radiate away into space. Science instruments were powered down, and the reaction wheels were shut off, all to cool the spacecraft. Attitude control is being maintained using the thrusters.
Saturday, Oct. 20 (DOY 294)
Deep Space Network (DSN) antenna scheduling negotiations in support of the S77 command sequence were completed covering its first two weeks. The Sequence Implementation Process kickoff meeting was held for S78 sequence development. S77 will go active in January; S78 starts executing in March.
Sunday, Oct. 21 (DOY 295)
The first Instrument Expanded Block (IEB) commands to support the S76 sequence were uplinked today. All 6,008 commands were confirmed on-board after a round trip light time of two hours 58 minutes.
Monday, Oct. 22 (DOY 296)
The separation angle (SEP) between the Sun, Earth, and Cassini went below three degrees today. An image from the SOHO spacecraft that shows Saturn nearing the Sun, as viewed from Earth's vicinity, may be seen here: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20121024/
The Attitude and Articulation Control Subsystem version A8.9.0 flight software began its second ground based end-to-end dry run test today. This new software version goes on board in December.
An image called "Many Mini-Jets" shows off collisions in the F ring. It may be seen here:
Tuesday, Oct. 23 (DOY 297)The remaining S76 IEB commands were approved today for uplink. They will be transmitted to Cassini via the DSN on Sunday and Monday, once the SEP angle has increased beyond three degrees.