Cassini Significant Events 05/13/2015 – 05/19/2015

Cassini is currently orbiting Saturn with a 18.9-day period in a plane inclined 0.3 degree from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on May 20 using the newest of the 34-meter diameter Deep Space Network stations 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 .

Many attractions compete for Cassini's observing time in the Saturn system. Enceladus has its plumes and snowy surface; Titan has its cloudy atmosphere, lakes, and rivers; there are rings galore, and all the diverse icy satellites. Not to mention the magnetosphere, particles of dust, charged atomic particles, and radio and plasma waves to be investigated. But the study of Saturn's own deep atmosphere remains a high-priority objective. This week, the gas giant found itself in the "spotlight" of Cassini's telescopes and optical remote-sensing (ORS) instruments for most of the spacecraft's observing time. Scientists used this week, in part, as another opportunity to investigate the aftermath of the most powerful storm ever seen on Saturn, which occurred in 2010 through 2011. The week's observations spanned the spectrum from extreme ultraviolet to the far infrared, but in the visible part of the spectrum alone, the Imaging Science Subsystem (ISS) acquired and returned a total of 1,252 images.

Wednesday, May 13 (DOY 133)

The Ultraviolet Imaging Spectrograph (UVIS) completed a 14-hour observation of Saturn in the extreme ultraviolet part of the spectrum, which it had begun the day before. Following this, the Composite Infrared Spectrometer (CIRS) took control of pointing to make a 22-hour observation of Saturn, mapping it in the far-infrared. The Visible and Infrared Mapping Spectrometer (VIMS) also made observations while riding along.

Thursday, May 14 (DOY 134)

VIMS assumed pointing control to observe Saturn's aurorae for six hours, while CIRS, UVIS, and ISS rode along.

Friday, May 15 (DOY 135)

Still pointing at Saturn's aurorae when VIMS finished up, UVIS took over prime pointing control to examine the aurorae in a different part of the spectrum. CIRS and VIMS rode along. Finally, CIRS took over again to stare at Saturn for 12.25 hours to observe the signatures of its chemical composition. ISS, VIMS, and UVIS rode along.

Saturday, May 16 (DOY 136)

After some intervening engineering activities and a session communicating with Earth, UVIS took back the reins to examine Saturn in the extreme- and far-ultraviolet parts of the spectrum. ISS, CIRS, and VIMS rode along, making their own observations during the 14-hour period.

Sunday, May 17 (DOY 137)

CIRS mapped Saturn in the mid-infrared, with ISS and VIMS also participating. The observation lasted 22 hours.

Monday, May 18 (DOY 138)

ISS took control for 24 hours to track and observe Saturn's irregular moon Paaliaq. Named for a giant in Inuit mythology, this small object occupies a highly inclined, highly eccentric orbit that reaches as far as 15.2 million kilometers from the planet. It has a very dark surface and is about 20 kilometers in diameter.

Diminutive Janus, one of a curiously co-orbital pair of icy moons, showed one of its faces lit by the Sun in an image featured today. Part of the narrow F ring, and a small but bright portion of the A ring, are also visible:
/resources/16191 .

Tuesday, May 19 (DOY 139)

While ISS was watching Paaliaq, the spacecraft coasted through apoapsis, marking the start of its Orbit #216. Cassini had slowed all down to 6,000 kilometers per hour relative to Saturn, and reached 2,485,000 kilometers out from the planet. It will be accelerating towards its orbital periapsis for the next 9.5 days.

After ISS finished its day-long watch of Paaliaq, VIMS turned back to Saturn's aurorae, which it watched for the next six hours. The other ORS instruments, ISS, CIRS, and UVIS, participated as riders.

During the past week, the DSN communicated with and tracked Cassini on five occasions, all using antennas at the Canberra complex in Australia. A total of 10 individual commands were uplinked, and about 1,306 megabytes of telemetry data were downlinked and captured at rates as high as 142,201 bits per second.

This illustration shows Cassini's position on May 19: https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=-82&vbody=1001&month=5&day=19&year=2015&hour=23&minute=55&fovmul=1&rfov=30&bfov=30&brite=1&showsc=1&showac=1 .

Milestones spanning the whole orbital tour are listed here: http://saturn.jpl.nasa.gov/mission/saturntourdates .

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/ .