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Cassini Significant Events 09/16/15 – 09/22/15

Cassini is currently orbiting Saturn with a period of 21.8 days in a plane inclined 0.4 degree from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Sept. 23 using one of the 34-meter diameter DSN stations 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 .

After rounding apoapsis this week, Cassini began executing the first part of the 10-week-long command sequence known as S91. Back on the home planet, Sequence Implementation Process teams continued working on the 10-week sequences S92 and S93. Plans proceeded as well for Cassini's F-ring and Grand Finale orbits in 2016 and 2017.

Wednesday, Sept. 16 (DOY 259)

Cassini spent the first seven hours of today finishing up a 37-hour observation in which the Composite Infrared Spectrometer (CIRS) mapped temperatures in Saturn's upper troposphere and lower stratosphere. The Magnetospheric and Plasma Science (MAPS) instruments took data all the while.

With the science activities completed, the spacecraft turned to face its parabolic high-gain antenna to Earth. After propagating for 76 minutes across space at the speed of light, commands arrived at Cassini, riding on the radio signal from Earth. These were the 7,264 individual, time-tagged commands comprising the first part of the S91 sequence, which will control the robot's activities for 32 days; the second part will be uplinked later on. After the telemetry data returned on Cassini's radio signal back to Earth, the flight team confirmed that all the commands had been properly received and stored in memory.

Thursday, Sept. 17 (DOY 260)

The bright blue-white star Vega, also known as Alpha Lyre, is familiar to many; it can be found high in the east these evenings and is the second brightest in the northern hemisphere. Today, the Imaging Science Subsystem (ISS) spent 13.4 hours with its telescopes trained on the star, using it to perform a photometric calibration of the instrument.

Friday, Sept. 18 (DOY 261)

The Cosmic Dust Analyzer (CDA) began collecting data for 24 hours while its detector was positioned to measure and characterize tiny dust grains coming in from interstellar space.

Saturday, Sept. 19 (DOY 262)

CIRS studied Saturn’s atmosphere for 12 hours, gathering high-quality infrared spectra to analyze its composition. ISS and the Visible and Infrared Mapping Spectrometer (VIMS) rode along making their own observations of the planet. Before and after this observation, ISS carried out two-minute Saturn storm-watch observations. Next, the Ultraviolet Imaging Spectrograph (UVIS) spent 75 minutes determining the structure of Saturn’s extended atmosphere, with the instrument's slit-shaped aperture aligned radially from Saturn's center.

At the completion of the UVIS observations, CDA began another 24-hour interstellar dust observation. While it was in progress, Cassini passed through apoapsis, marking the start of its orbit #222 about Saturn. It had reached 2.7 million kilometers from the giant planet and slowed to 5,820 km per hour relative to it.

This illustration shows today’s viewing geometry and illumination; the rings are edge-on to Cassini: https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=699&vbody=-82&month=9&day=19&year=2015&hour=00&minute=00&fovmul=1&rfov=10&bfov=30&showsc=1&showac=1 .

Sunday, Sept. 20 (DOY 263)

NASA's Astronomy Picture of the Day featured Cassini's view of the southern hemisphere of Enceladus and its deep south polar crevasses, following last week's news confirming the little moon's global, salty, subsurface ocean: http://apod.nasa.gov/apod/ap150920.html .

Monday, Sept. 21 (DOY 264)

The first part of the S91 Sequence, which was transmitted to Cassini on Wednesday, began clocking out today. For its first science activity, CDA performed a 12-hour interstellar dust observation. These observations allow scientists to characterize tiny dust grains coming in from interstellar space and how they differ from other sources of dust within the Saturn system.

An image featured today captures Prometheus and Pandora, Saturn's moons that orbit outside the main rings, and straddle the narrow F ring: /resources/16244 .

Tuesday, Sept. 22 (DOY 265)

ISS and VIMS tracked Saturn's six-km diameter irregular moon Bestla for 13.75 hours today. Named after a frost giantess from Norse mythology and mother of Odin, Bestla moves in a retrograde, highly inclined and highly eccentric orbit that takes it as far as 30 million km from the planet. UVIS collected ultraviolet data while the imaging cameras were conducting their observations.

During the past week, the Deep Space Network communicated with and tracked Cassini on five occasions, using DSN stations in California. A total of 7,294 individual commands were uplinked, and about 1,300 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 Sept. 22: http://go.nasa.gov/1flNJkS . 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.