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Cassini Significant Events 03/23/16 – 03/29/16

Cassini is orbiting Saturn with a period of 23.9 days in a plane inclined 21.9 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on March 30, 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 .

On its way inbound towards Saturn from apoapsis this week, Cassini's activities were under control of the on-board S93 command sequence. Meanwhile, Sequence Implementation Process teams continued working on additional 10-week command sequences. S94 will start executing on April 18, and S95 will begin operating on June 26. The S96 sequence has begun taking shape, and will go active on the spacecraft on Sept. 8. Thereafter, only five command sequences remain to be developed before the mission ends with a plunge into Saturn on Sept. 15, 2017.

Wednesday, March 23 (DOY 083)

Cassini's Attitude and Articulation Control Subsystem switched from the spacecraft's reaction wheels to the hydrazine-fed rocket thrusters to stabilize the body attitude. It then set the three active wheels to rotational speeds that will be optimal for carrying out upcoming attitude changes; AACS then switched back to reaction-wheel control. These routine 90-minute maneuvers are not often reported here, but they are a normal part of managing the reaction wheels' store of angular momentum.

Next, AACS oriented the spacecraft to face its high-gain antenna dish towards Earth for a nine-hour tracking and communications session with one of the Deep Space Network's antennas at Goldstone, California. Among other activities, Cassini's Navigation team uses the tracking data to help estimate the effect the rocket thrusters imposed on the spacecraft's trajectory.

The Imaging Science Subsystem (ISS) had the spacecraft turn to aim its telescopes to Saturn's largest moon Titan. Along with the Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS), ISS monitored Titan's atmosphere for 90 minutes. This observation was repeated on March 29. When today's was completed, CIRS turned towards Saturn, and spent the remainder of the day mapping the gas giant at mid-infrared wavelengths. ISS and VIMS also participated. The viewing geometry, at about 2.8 million kilometers from Saturn, is illustrated here.

Thursday, March 24 (DOY 084)

ISS and CIRS took turns today and the following day, spending a total of 20 hours studying Saturn’s winds and the composition of its atmosphere. VIMS and the Ultraviolet Imaging Spectrograph (UVIS) rode along at times.

Prior to Cassini and Huygens, which is the Titan atmospheric probe that conducted its descent and survived landing in 2005, Saturn's planet-like moon was a well-veiled mystery. Today, its astounding surface, with great lakes and dune fields and bright highlands, has been scrutinized at many wavelengths, as illustrated in a pair of featured montages.

The tallest mountain peak on Titan is shown and discussed in a news feature released today: /news/10021/ .

Friday, March 25 (DOY 085)

Cassini fired its bi-propellant-fed main engine today, which glowed white-hot for about 45 seconds. This imparted a change in velocity for the spacecraft of 7.95 meters per second. That's a lot to ask of the propulsion system these days, and all eyes were on telemetry following the burn, to be sure we hadn't run out of propellant. All went fine with this Orbit Trim Maneuver (OTM)-444, and Cassini is right on track for a close flyby of Titan, the T-118 encounter at 990 km altitude, on April 4. In terms of velocity change, OTM-444 was the largest for the remainder of the mission. By the way, the small-thruster monopropellant-fed system is capable of fully taking over in case of bi-prop depletion before Cassini's end of mission.

Still some 25 million km from Saturn on the way "down" from apoapsis, UVIS started a 14 hours study of the gas giant in the extreme- and far-ultraviolet parts of the spectrum. ISS, CIRS and VIMS rode along.

Saturday, March 26 (DOY 086)

ISS and CIRS picked back up with their alternating studies of Saturn, beginning a total of 32 more hours, examining the winds and atmospheric composition. VIMS and UVIS rode along at selected times.

Towards the end of the day, the Magnetometer (MAG) and the Magnetospheric Imaging Instrument (MIMI) stepped up their data collection rates to record additional information on Saturn’s magnetic field and magnetosphere in the outer reaches of the Saturn system.

Sunday, March 27 (DOY 087)

The large tilt of Saturn's bright, icy rings makes for spectacular viewing by any morning person equipped with a small telescope. Rising soon after midnight and well south by dawn, the ringed giant can be found to the east (left) of two red objects: the star Antares, and the planet Mars.

Monday, March 28 (DOY 088)

CIRS began another 11.25-hour observation of Saturn at mid-infrared wavelengths.

An image featured today offers a look at some of Saturn's rings and moons, sunlit at high phase angles (that is, largely from behind): /resources/16292 .

Tuesday, March 29 (DOY 089)

On six occasions during the week, the Deep Space Network communicated with and tracked Cassini, using stations in Australia and California. A total of 207 individual commands were uplinked, and about 1,122 megabytes of telemetry data were downlinked and captured at rates as high as 142,201 bits per second.

Cassini position on March 29, 2016
This illustration shows Cassini's position mid-day on March 29: http://go.nasa.gov/1VGVGmP. The format shows Cassini's path over most of its current orbit up to today; looking down from the north, all depicted objects (except the background stars of course) revolve counter-clockwise, including Saturn along its orange-colored orbit of the Sun.

Significant Events Glossary

Deep Space Network


Cassini on March 29, 2016
This illustration shows Cassini's position mid-day on March 29. The format shows Cassini's path over most of its current orbit up to today.
Cassini on March 29, 2016
This illustration shows Cassini's position mid-day on March 29. The format shows Cassini's path over most of its current orbit up to today.