Cassini Significant Events 07/22/15

Cassini is currently orbiting Saturn with a period of 21.8 days in a plane inclined 0.5 degree from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on July 28 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 .

Cassini carried out a wide variety of observations this week, ranging from remote observations of Saturn's atmosphere and its aurorae, to studying several of its natural satellites, various rings, and the interaction they have with the planet's vast, dynamic, magnetic field.

Wednesday, July 22 (DOY 203)

The Imaging Science Subsystem (ISS) had the spacecraft turn to point its telescopes to Saturn's largest moon Titan, and monitored its atmosphere for 90 minutes at a distance of 2.3 million kilometers. The Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) made observations while riding along. When this was over, ISS turned to Saturn for a two-minute storm-watch observation, and then spent 60 minutes making a satellite orbit campaign observation, looking at, and for, objects near the planet. Next, the Ultraviolet Imaging Spectrograph (UVIS) spent 6.25 hours observing Saturn’s thermosphere and atmosphere, after which came another quick ISS storm watch; VIMS participated in this one.

Thursday, July 23 (DOY 204)

CIRS made two observations of Titan's atmosphere to measure its composition, one today and one the following day. Today's lasted 13.3 hours, and Friday's was 13.5 hours long.

Friday, July 24 (DOY 205)

A member of the Cassini flight team showed views of Saturn tonight from a brightly lit and busy Colorado Boulevard in Pasadena, a sidewalk exercise in "guerrilla astronomy.” More than 300 surprised passers-by had a view through the telescope; many of them reported that it was their first-ever sighting of the beautiful ringed planet and its moons.

Saturday, July 25 (DOY 206)

Ordinarily, the direct-sensing Magnetospheric and Plasma Science (MAPS) instruments collect data nearly continuously, largely independent of the spacecraft's orientation, reporting on conditions in the spacecraft's immediate environment. Today, however, began three days of high-priority MAPS observations, coordinating with the UVIS-led remote-sensing investigations of the electromagnetic footprint that is made by the moon Enceladus on Saturn's polar aurora. Also of interest were Saturn's equatorial magnetotail and its own influence on the aurora.

Next, Cassini turned to align the Cosmic Dust Analyzer (CDA) for a 10-hour, top-priority scan while passing through Titan's orbit. The goal was to characterize Titan's interaction with particles in the wide, diffuse E ring; particles that originally came from Enceladus's icy geysers. Finally, ISS began a two-hour observation in the Titan monitoring campaign, with CIRS riding along. The hazy moon was in the neighborhood of 735,000 km from Cassini's telescopes.

Sunday, July 26 (DOY 207)

ISS made another hour-long observation in the satellite orbit campaign. Then, after a session with the Deep Space Network (DSN) for communications and tracking, CIRS took the reins to make a two-hour observation of Saturn's 1,528-km diameter icy moon Rhea. The rest of the optical remote-sensing (ORS) instruments -- ISS, UVIS and VIMS -- rode along with CIRS. The "Voyager-class" distance to Rhea was within 270,000 km, and the scientific goals included understanding the body's thermal properties and surface texture, mapping its composition, and viewing geologic features that have only been poorly imaged until now.

As Cassini proceeded slowly northward through Saturn's ring plane, CDA turned to measure dust impacting the instrument for 7.75 hours.

Following CDA's activity, ISS turned and examined Saturn's moon Dione, which is somewhat smaller than Rhea. The other ORS instruments rode along, making similar types of observations as the ones they did of Rhea; ISS concentrated on mapping the long ice cliffs that lie across Dione's surface. For a total of seven hours, ISS and CIRS alternated in the lead role in observing Dione, while the others took turns riding along.

Monday, July 27 (DOY 208)

Over the weekend, the ISS Wide Angle Camera experienced a single event upset in its detector temperature control circuitry that caused a slight increase in the detector temperature. The flight team quickly prepared and radiated commands to power-cycle the instrument. This action reset the temperature control logic and restored the ISS to its normal state.

With the Dione observations complete, CIRS turned to examine Saturn's moon Enceladus for two hours while the other ORS instruments rode along. Cassini came within 114,000 km of the 504-km-diameter, geologically active moon.

The spacecraft glided through periapsis in its Saturn orbit #219 while observing Enceladus. It came within about 223,000 km of Saturn's visible limb, having reached a speed of 56,069 km per hour relative to the planet -- more than nine times its speed at apoapsis last week.

At the end of the Enceladus observation, UVIS rotated Cassini to slew its field of view slowly across Saturn’s auroral zone for six hours, searching for Enceladus-related footprints in collaboration with VIMS; CIRS rode along.

UVIS, still partnering with VIMS, turned to concentrate on Saturn’s polar region, staring at the auroral oval for 4.5 hours. CDA then took over for two hours, while Cassini was crossing the ring plane going southward. CDA's objectives included measuring the equatorial dust flux as a function of radial distance and obtaining high-resolution information on plasma waves at the magnetic equator.

Near the end of the day, the Magnetospheric Imaging Instrument (MIMI) had the spacecraft roll for 6.75 hours, observing the inner magnetosphere.

A picture of Saturn's 450-km-wide moon Tethys featured today helps show that there is great diversity among Saturn's moons:
/resources/16214 .

Tuesday, July 28 (DOY 209)

After making another two-minute storm-watch on Saturn, ISS spent nearly 13 hours tracking the planet's shadow as it was cast into the very distant Phoebe ring. The dusty ring is so named because it engulfs the retrograde, inclined orbit of Saturn's moon Phoebe, more than 12 million km from the planet. An external website describes the ring here: https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=-82&vbody=1001&month=7&day=28&year=2015&hour=23&minute=55&fovmul=1&rfov=45&bfov=30&brite=1&showsc=1&showac=1 .

During the past week, the DSN communicated with and tracked Cassini on eight routine occasions, using deep space stations in Australia. A total of 34 individual commands were uplinked, and about 1,669 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 July 28: http://go.nasa.gov/1D3H62g .

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/ .