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Cassini Significant Events 10/26/16 - 11/01/16
Forty-five weeks and 46 orbits of Saturn remain in the Cassini mission. During this week's orbit, the spacecraft continued executing commands from its on-board S96 sequence, rotating and pointing its instruments to make observations,
and turning again to play them back to Earth. Meanwhile, at several locations on Earth, work proceeded on the ten-week command sequences S97, S98 and S99, which will control Cassini up through mid-May of next year, four months before the Grand Finale plunge
into Saturn's atmosphere.
Wednesday, Oct. 26 (DOY 300)
As soon as Cassini's Imaging Science Subsystem (ISS) finished a 31-hour observation of Saturn's irregular moon Erriapus, which was described in last week's report, one of the Deep Space Network (DSN) stations at Goldstone, California,
participated in one of a series of Operational Readiness Tests, preparing for a Radio Science experiment coming up on Nov. 2. During that Saturn Ring Occultation experiment, the spacecraft will actively probe Saturn's outer A ring and F ring for a total of
five hours, obtaining high quality data for ring studies. Cassini transmits three continuous, pure, radio frequency signals to do this, based on a continuous frequency-reference signal sent from Earth. A total of five DSN stations will be participating, spanning
two continents.
This image from Cassini's 2009 equinox observations, which shows vertical disruptions in Saturn's rings, was selected as NASA's Astronomy Picture of the Day today: http://apod.nasa.gov/apod/ap161026.html .
Thursday, Oct. 27 (DOY 301)
ISS and the Visible and Infrared Mapping Spectrometer (VIMS) performed a 90-minute observation in the Titan monitoring campaign, while the planet-like moon was at a distance of 1.2 million km. (This also happens to be the distance
from Saturn to Titan's orbit.)
Next up today was a 10-hour Composite Infrared Spectrometer (CIRS) study of the sunlit side of Saturn's rings, to obtain thermal-infrared spectra for studying ring-particle composition. Finally, ISS began an 18-hour series of images
of Saturn's narrow F ring; this was more than enough time to see one complete revolution of the high-speed ring material around the planet. CIRS rode along.
During its observations of the F ring, Cassini coasted through apoapsis, marking the start of Saturn Orbit #247. The spacecraft's speed and distance were similar to those reported for Oct. 18.
Friday, Oct. 28 (DOY 302)
ISS devoted seven hours to making high-resolution, full color observations of Saturn's main rings, with CIRS riding along.
Saturday, Oct. 29 (DOY 303)
ISS spent one hour on a satellite-orbit campaign observation, looking for small objects near Saturn. When this was done, CIRS, VIMS, and the Ultraviolet Imaging Spectrometer (UVIS) jointly observed Saturn’s aurora for nearly 16.5
hours. The view from Cassini at this point is illustrated here: http://go.nasa.gov/2eVbUdF . The last activity of the day was the start of a 12-hour long-range Titan monitoring observation. This observation had a great view of high northern latitudes, allowing
ISS to observe cloud dynamics, if Titan’s weather cooperates.
Sunday, Oct. 30 (DOY 304)
VIMS created a mosaic of the sunlit side of Saturn's rings, mapping out variations of their brightness with respect to elevation and phase angle. CIRS and UVIS rode along with this 7.3-hour long activity.
Monday, Oct. 31 (DOY 305)
CIRS stared at one selected longitude on Saturn for six hours today, a little more than half of a planet-rotation period. Observations such as these, at mid-infrared wavelengths, measure longitudinal variations in the temperature
of the planet's tropopause.
Next, VIMS tracked the star Alpha Centauri for 4.25 hours as it passed behind Saturn's main rings. In particular, this stellar occultation allowed VIMS to obtain high-resolution measurements of the F ring. CIRS rode along.
After this event, ISS pointed toward Saturn's A ring, to image "propeller" features for two hours, with CIRS and UVIS riding along (this page discusses "propellers": http://go.nasa.gov/17oqTWF) .
Finally today, CIRS began a four-hour observation of the outermost region of Saturn's A ring, between the Encke Gap and the ring's outer edge, which is called the trans-Encke region. VIMS and UVIS rode along. Spectra obtained will
help scientists understand the composition and structure of this unique region the ring.
Pumpkins always make great feature stories this time of year: https://saturn.jpl.nasa.gov/news/2957/the-last-great-pumpkin .
The image that was highlighted on the Cassini website today, however, had nothing to do with pumpkins but everything to do with the view of Saturn from high in the north: https://saturn.jpl.nasa.gov/resources/7545 .
Tuesday, Nov. 1 (DOY 306)
UVIS recorded two stellar ring occultations today, with CIRS riding along. For the first one, the blue-white star Kappa Scorpii made a turn-around behind Saturn's nearly opaque B ring, offering measurements of small-scale azimuthal
variations in the rings near this point. UVIS then turned to track the bright blue star Epsilon Sagitarii, as it passed behind the trans-Encke region and into the mid-A ring before moving outward again, all thanks to Cassini's orbital motion.
Next, VIMS led CIRS and UVIS in generating a radial mosaic across the sunlit side of Saturn's rings, to derive compositional information about the ring particles. It repeated the observation a little later, but from the rings' dark
side; each observation took about three hours. In between the two VIMS observations, the Cosmic Dust Analyzer (CDA) sampled grains of material as Cassini coasted through Saturn's tenuous E ring.
Finally, ISS began a 2.3-hour examination of the A ring, looking for propellers with UVIS and CIRS riding along. During this activity Cassini glided through periapsis in its Orbit #247.
On three occasions this week while the optical instruments were already pointing at or near Saturn, ISS turned the spacecraft and made a two-minute storm-watch observation of the planet. VIMS rode along with two of them.
The distance to Cassini was increasing this week, as Earth circles the Sun; on Wednesday the robot was 1,613,000,000 kilometers away from Earth, and by the end of today it had slipped another 10 million km away. The Deep Space Network
(DSN) took the increase in stride, as if the added distance (about 28 times the distance from Earth to our own Moon) didn't matter, and provided two-way digital communications and navigational tracking without a hitch.
The Deep Space Network (DSN) communicated with and tracked Cassini six times this week, using stations in Spain, Australia and California. A total of 10 individual commands were uplinked, and about 1,800 megabytes of telemetry data
were downlinked and captured at rates as high as 110,601 bits per second.
Wrap up:
Cassini is orbiting Saturn with a period of 9.6 days in a plane inclined 57.9 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Nov. 2, using one of the 34-meter diameter
DSN 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/anomalies .
Cassini's path up to mid-day Nov. 1 is illustrated here: http://go.nasa.gov/2cEs3ld . At that time, the countdown clock in Mission Control was showing 317 days until the end of the mission.
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Milestones spanning the whole orbital tour are listed here:
<https://saturn.jpl.nasa.gov/mission/saturn-tour/tour-dates/>
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Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at:
<https://saturn.jpl.nasa.gov/mission/saturn-tour/where-is-cassini-now/>
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