6 min read

Cassini Significant Events 10/07/15 – 10/13/15

Cassini is currently orbiting Saturn with a period of 13.9 days in a plane inclined 0.6 degree from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Oct. 14 using the 70-meter diameter Deep Space Network station in Australia. 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 .

Enceladus! Among Cassini's "business-as-usual" activities in Saturn orbit this week, the robot-observatory was precisely targeted for its Oct. 14 encounter with the strange, 500-kilometer wide world. Commands on-board, which the instruments will expand and use during the encounter, were updated from Earth this week to ensure the best results. The Enceladus E-20 flyby, at 1,845 km above the icy surface, will be the first one to occur since scientists' recent announcement of strong evidence for a global, sub-surface saltwater ocean there. The flyby page offers details, plus a beautiful two-minute animation of the encounter, in which the spacecraft's subtle attitude changes accurately portray science-instrument pointing: http://saturn.jpl.nasa.gov/mission/flybys/enceladus20151014 .

Wednesday, Oct. 7 (DOY 280)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) controlled spacecraft pointing for 13.5 hours today. During this time it made another in a series of mosaic scans of Saturn’s magnetosphere, examining the vicinity of Saturn to image the presence of oxygen.

During the UVIS observation, Cassini passed through apoapsis, marking the start of its orbit #223 about Saturn. It had reached 2.1 million km from the giant planet (almost twice the distance out to Titan's orbit) and slowed to 6,127 km per hour relative to Saturn.

Thursday, Oct. 8 (DOY 281)

The Imaging Science Subsystem (ISS), the Composite Infrared Spectrometer (CIRS), and the Visible and Infrared Mapping Spectrometer (VIMS) performed a 90-minute observation in the Titan monitoring campaign; the distance to the hazy moon from Cassini was 2.9 million km. With the Titan observation done, UVIS then embarked on a 10.75-hour mosaic scan for oxygen similar to the previous day's. The same set of observations was repeated on the following day.

Friday, Oct. 9 (DOY 282)

Members of Cassini's flight team met today to finalize and approve commands for Orbit Trim Maneuver (OTM)-424. Following approval, the commands were uplinked during the evening's session with the 70-meter diameter DSN station in Australia. They were timed to start executing on the following day.

Saturday, Oct. 10 (DOY 283)

Today and Sunday were busy days for many members of the Cassini flight team, as they joined JPL's other projects in engaging with thousands of visitors during the 2015 public Open House. Of special interest was a scale model of Enceladus on display, complete with working geysers. It graced many a snapshot.

Meanwhile, in Saturn orbit, Cassini's Cosmic Dust Analyzer (CDA) spent 15 hours observing interstellar dust. Near the end of the day, Cassini turned and fired its small rocket thrusters for 33 seconds as the OTM-424 commands took control. This provided the change in velocity of 33 millimeters per second, which the spacecraft needed for a fine adjustment in its trajectory for the Oct. 14 Enceladus E-20 encounter.

Sunday, Oct. 11 (DOY 284)

Today ISS, CIRS and VIMS performed another 90-minute Titan monitoring observation; the target distance had decreased to 1.7 million km. Next, ISS made an observation in the satellite orbit campaign, looking to recover sight of small objects known to orbit near the planet, or to discover new ones. These observations typically take an hour, but today's was planned to be a little shorter so that ISS and VIMS could turn and catch the transit of Saturn's 1,528-km diameter moon Rhea while it was passing in front of the smaller moon Tethys. This illustration shows the viewing geometry for the event: https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=603&vbody=-82&month=10&day=11&year=2015&hour=10&minute=48&fovmul=1&rfov=2&bfov=30&brite=1&showsc=1&showac=1 .

CDA finished out the day by performing an 11-hour retrograde dust observation.

Monday, Oct. 12 (DOY 285)

ISS carried out another satellite orbit observation today; this one lasted a full hour, and VIMS rode along. Following this, VIMS, ISS and CIRS began a 21-hour joint observation of Saturn's faint E ring and G ring. Halfway through this, though, VIMS made a planned interruption to train on the distant red star 56 Leo for 80 minutes while it entered occultation behind Saturn's atmosphere. With this completed, VIMS, ISS and CIRS returned to finish the faint ring observation.

Vast dark rings and small bright moons are captured in an image featured today: /resources/16253 .

Tuesday, Oct. 13 (DOY 286)

Hati is one of Saturn's 38 known irregular moons, and it is described in these pages for Aug. 26: http://go.nasa.gov/1GHtjdO . ISS observed the little object for 7.4 hours today from a distance of about 12 million km, as part of a campaign to refine knowledge of its shape and pole orientation. Due to its fast rotation, scientists suspect that this elongated body might be close to disruption, with almost zero effective gravity near its tips.

Enceladus will have only two more visits from Cassini after the E-20 encounter on Oct. 14; the E-21 encounter on Oct. 28 is being targeted for an altitude of 49.0 km, when Cassini will be crossing right through, and sampling, the plume of icy material spewing from its southern region. The final encounter, E-22 on Dec. 19, will be a relatively high-altitude flyby, at 10 times Enceladus's diameter. This page describes the encounter series: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20151013 .

On nine occasions this week, ISS conducted Saturn storm-watch observations; VIMS rode along with four of them. All were two minutes long, squeezed in while the optical instruments were already pointing on or near the planet. Throughout the week, and largely independent of which direction the spacecraft was turning to point its other instruments, the Magnetospheric and Plasma Science (MAPS) instruments continued collecting data in an ongoing survey of Saturn’s magnetosphere.

During the week, the Deep Space Network communicated with and tracked Cassini on six occasions, using DSN stations in Australia and Spain. A total of 298 individual commands were uplinked, and about 920 megabytes of telemetry data were downlinked and captured at rates as high as 110,601 bits per second.

This illustration shows Cassini's position on Oct. 13: http://go.nasa.gov/1jOtj6X . The format shows Cassini's path over most of its current orbit up to today; looking down from the north, all depicted objects revolve counter-clockwise, including Saturn along its orange-colored orbit of the Sun. Another illustration shows the spacecraft on the following day, a close-up snapped at 30 minutes prior to Enceladus closest approach (relative to Saturn, its speed at that point is 58,768 km/hr): http://go.nasa.gov/1G3rhtQ .