Cassini Significant Events 6/10/15 – 6/16/15

Cassini is currently orbiting Saturn with a period of 18.9 days in a plane inclined 0.4 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on June 16 using one of the 34-meter diameter Deep Space Network stations in Madrid. 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 .

This week Cassini's Imaging Science Subsystem (ISS) produced 842 images, and the Visible and Infrared Mapping Spectrometer (VIMS) generated 101 data "cubes." Since January 10, 2004, when Cassini’s approach science began, 342,343 images from ISS and 230,832 cubes from VIMS have been returned and processed. The S89 command sequence continued to orchestrate all of Cassini’s activities this week. Meanwhile on the ground, the Sequence Implementation Process teams worked on creating the 10-week sequences S90, S91 and S92.

Wednesday, June 10 (DOY 161)

Science activities began with the Composite Infrared Spectrometer (CIRS) completing an observation to determine Saturn’s atmospheric composition. ISS then performed a 13.5-hour observation of the irregular moon, Hyrrokkin. Named after a giantess in Norse mythology, Hyrrokkin is about 8 kilometers in diameter, and orbits Saturn with a period of 914 days in an inclined and eccentric retrograde orbit.

Thursday, June 11 (DOY 162)

The Cosmic Dust Analyzer (CDA) performed a 13.25-hour observation in their retrograde dust campaign today.

Attitude and Articulation Control Subsystem (AACS) engineers read out and then reset the spacecraft's Reaction Wheel Assembly revolution counter. This is done about every six months to maintain an accurate accounting of wheel usage and avoid rollover of the counter.

Friday, June 12 (DOY 163)

ISS performed a brief 30-minute observation in their satellite orbit campaign, followed by an Optical Navigation image. CIRS performed a compositional study to examine Saturn’s atmosphere.

Saturday, June 13 (DOY 164)

Orbit Trim Maneuver (OTM) #412, the approach maneuver for the upcoming Dione flyby on June 16, was scheduled to execute today but was cancelled. The Cassini Navigation Team determined that the correction the flight team would have to execute was too small to be effectively performed by the spacecraft. Additionally, the expected target miss was in a favorable direction to slightly lessen downstream propellant costs. The miss had negligible impact on science activities.

CIRS continued observations of Saturn’s atmosphere for 12-hours in an effort to better determine upper troposphere and tropopause temperature.

Sunday, June 14 (DOY 165)

ISS performed another observation in their satellite orbit campaign and then took observations of the transit of Enceladus across Mimas. The day concluded with the Ultraviolet Imaging Spectrograph (UVIS) capturing a 12.75-hour observation of Saturn’s aurora.

Monday, June 15 (DOY 166)

A project-wide Mission Planning Forum was held today to discuss the results of dispersion analysis for the Proximal Orbit OTM study. The talk focused on how the Proximal OTMs affect the dispersions in periapsis timing and along track position.

Today started with the first observation in a series of three ISS observations with UVIS and VIMS riding along of the irregular moon Tarvos to obtain a light curve. The activities -- two on Monday, one on Tuesday -- covered one full rotation of this moon. These observations will help Cassini scientists determine Tarvos’ object shape and pole-axis determination. With an estimated diameter of 15 km, Tarvos is one of the larger irregular moons of Saturn. Its distance to the ring planet varies between ~8.4 and 28 million kilometers. During the observation, the Cassini spacecraft and Tarvos were separated by 21.5 million kilometers.

The day also included observations of Rhea with CIRS as the prime instrument. The observations (with the other ORS instruments riding along) allowed global multi-color observations of the leading side. At a range of 214,000 km, Rhea appeared slightly larger than the ISS narrow angle camera field of view.

Orbiting Saturn in nearly the same plane as the rings and its larger moons, Cassini captured an image of one of the icy satellites, which is featured today. Tethys' diameter is 1,060 kilometers; the ringed planet in the background is 120,660 kilometers across at its equator:
/resources/16199 .

Tuesday, June 16 (DOY 167)

Cassini Radio Science (RSS) successfully completed their activities during the Dione (D4) gravity observation this morning, with all data acquired as planned. The D4 observation consisted of one segment (3.5 hours in duration), centered on Dione’s closest approach at an altitude of 516 km. Closest approach was over the Deep Space Network’s (DSN) Madrid complex. The goal of gravity science at Dione is the improvement of the determination of Dione’s interior structure.

The analysis of previously acquired Doppler data suggests that Dione’s interior is not compatible with hydrostatic equilibrium. However, a reliable determination of this requires at least two flybys with suitable geometries. Data from D4 are expected to reduce significantly the current uncertainties. The final Dione (D5) flyby in the mission is in two months (August 17, 2015), where again RSS will be prime.

While observations focused on gravity field determination during closest approach, Cassini’s cameras, spectrometers, and fields and particles instruments also participated in the science activities. For more information on the flyby, visit:
http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20150615/ .

During the past week, the DSN communicated with and tracked Cassini on eight routine occasions, all from Canberra, Australia Deep Space Stations (DSS). A total of 13 individual commands were uplinked. This week’s tracking concluded with a successful Radio Science (RS) Gravity Science Enhancement (GSE).

This illustration shows Cassini's position on June 16:
https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=-82&vbody=1001&month=6&day=16&year=2015&hour=23&minute=55&fovmul=1&rfov=80&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/ .