News | December 3, 2014
Cassini Significant Events 11/19/2014 - 12/02/2014
Cassini is currently orbiting Saturn with a 47.8-day period in a plane inclined 33.1 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on December 3 using one of the 34-meter diameter Deep Space Network antennas in California. The spacecraft continues to be in an excellent state of health with all of its subsystems operating normally except for the instrument issues described at http://saturn.jpl.nasa.gov/news/significantevents/anomalies. Information on the present position of the Cassini spacecraft may be found on "Eyes on the Solar System".
Cassini spent the past two weeks gathering speed inbound along its orbit toward its next periapsis on Dec. 8. From our point of view back on Earth, Cassini, along with Saturn, is proceeding further west of the Sun in the sky (due to Earth’s heliocentric motion), so the communications interference from our star’s plasma envelope is diminishing. Even so, the Radio Science team continued using Cassini's three-frequency downlink to probe the solar corona until Dec. 1.
Wednesday, Nov. 19 (DOY 323)
The ten-week-long sequence of onboard commands known as S86 kept the spacecraft Earth-pointed today and Thursday while the direct-sensing Magnetospheric and Plasma Science (MAPS) instruments acquired data about Saturn's magnetosphere.
Thursday, Nov. 20 (DOY 324)
As seen from Earth, Saturn's apparent distance from the Sun increased past three degrees today; communications should be relatively free of solar interference until the next conjunction in late November 2015.
Friday, Nov. 21 (DOY 325)
Cassini's Attitude and Articulation Control Subsystem transitioned from using the small hydrazine-fed rocket thrusters for three-axis stabilization, and began using the electrically driven reaction wheels instead. The spacecraft continued pointing its high-gain antenna dish toward Earth through the day for communications, radio science, and tracking by the Deep Space Network (DSN).
During today's DSN pass, the flight team sent up freshly created commands to execute an Orbit Trim Maneuver (OTM) while the spacecraft was not far past apoapsis in its orbit about Saturn. OTM-396 turned the spacecraft and fired the small thrusters for 201 seconds. This thrust provided a change in velocity of 198 millimeters per second, targeting Cassini to fly by Titan for the T-107 encounter on December 10 at 980 kilometers above its surface. This altitude will allow the spacecraft to dip into the huge moon's thin upper atmosphere enough to obtain data on its density.
The December 10 Titan flyby, which is 48 days since the prior flyby T-106, breaks the pattern of a Titan encounter every 32 days which Cassini has been following since May. The orbit designers added an extra 16 days between encounters to “hop” over the solar conjunction period.
Saturday, Nov. 22 (DOY 326)
The Imaging Science Subsystem (ISS), the Composite Infrared Spectrometer (CIRS), and the Visible and Infrared Mapping Spectrometer (VIMS) carried out an observation in the Titan monitoring campaign. This 90-minute observation was repeated again on Sunday, Tuesday, and Thursday of this week, and then again on Sunday, November 30. For today's observation the target was at a distance of 5.2 million kilometers, and by the 30th the distance had gradually decreased to 2.1 million kilometers. When today's Titan viewing was finished, S86 had the spacecraft turn, and CIRS observed Saturn for 12 hours, obtaining infrared spectra to better understand the atmosphere's composition. VIMS took advantage of the pointing and rode along to make its own observations.
Sunday, Nov. 23 (DOY 327)
ISS made a one-hour observation in the satellite orbit campaign, looking for small objects near Saturn. This was repeated on Tuesday and again on the following Sunday. As soon as ISS was finished today, Cassini turned so that UVIS, CIRS, and VIMS could spend nine hours watching Saturn’s northern aurora.
Monday, Nov. 24 (DOY 328)
ISS trained its telescopes on the irregular moon Albiorix, and tracked it for 13.5 hours; UVIS rode along. This dark-surfaced, icy object orbits as far as 16.2 million kilometers out from Saturn, in a highly elliptical, inclined orbital path. Named for a giant king in Gallic mythology, its diameter of about 26 kilometers makes it the largest of Saturn's Gallic group of satellites. How many satellites does Saturn have in total? The count is currently 62 with confirmed orbits, 53 of which have been named. Only 13 of them have diameters greater than 50 kilometers.
NASA's Astronomy Picture of the Day website featured a video simulating an extraordinary flight above Titan's northern lakes, using data returned from Cassini's synthetic-aperture radar investigation: http://apod.nasa.gov/apod/ap141124.html
Tuesday, Nov. 25 (DOY 329)
CIRS began a 23-hour observation of Saturn’s atmosphere to determine temperatures in the upper troposphere and tropopause. VIMS rode along.
Wednesday, Nov. 26 (DOY 330)
ISS spent another four hours observing Albiorix again, with UVIS again riding along.
Thursday, Nov. 27 (DOY 331)
MIMI, UVIS, CIRS and VIMS began a 34-hour observation of Saturn’s northern aurora.
Friday, Nov. 28 (DOY 332)
Cassini turned to point the Cosmic Dust Analyzer (CDA) to the attitude needed for studying dust that orbits Saturn in the retrograde direction. This observation lasted nearly twenty hours.
Saturday, Nov. 29 (DOY 333)
Saturn is inching past the Sun as viewed from Earth, but is still too close for observing with a telescope. In the first weeks of January, though, early risers will be able to catch sight of the beautiful ringed planet in the East just before dawn.
Sunday, Nov. 30 (DOY 334)
ISS observed the arc of Saturn's G ring for 18 hours.
Monday, Dec. 1 (DOY 335)
MIMI, UVIS, CIRS and VIMS monitored Saturn’s northern aurora for 15.5 hours. During today's DSN communications, the Radio Science team carried out their final observation of the solar corona, wrapping up this year's superior conjunction experiment.
Saturn's moon Enceladus can be found in front of the majestic gas giant in an image featured today:
Tuesday, Dec. 2 (DOY 336)
The spacecraft remained Earth-pointed, with the MAPS instruments collecting data again today.
During the past two weeks, the DSN communicated with and tracked Cassini on 13 occasions, using stations in Australia and California. Each also participated in Cassini's Radio Science superior conjunction experiment. A total of 166 individual commands were uplinked, and about 1,790 megabytes of telemetry data were downlinked and captured at rates as high as 110,601 bits per second.