Cassini Significant Events 07/01/15 – 07/07/15

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 8 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 has good neighbors in space; neighbors who sometimes help one another in a friendly manner. Although there are many millions of kilometers between spacecraft, Cassini shares the same quadrant of sky, as seen from Earth, with Voyager 1, Voyager 2, Dawn the asteroid mission, and New Horizons, which is fast approaching the Pluto-Charon system. The latter is 3,900,000,000 kilometers away from Cassini, but close enough in Earth's two-dimensional sky that we often use the same complex of Deep Space Network (DSN) antennas at the same time. A few weeks ago New Horizons helped their Saturnian neighbor by giving Cassini several hours on "their" DSN station, while "our" station had to undergo urgent maintenance. On Tuesday this week (see below), Cassini's flight team reciprocated and approved commands that will have the spacecraft image Pluto one final time for the New Horizons mission.

Wednesday, July 1 (DOY 182)

Cassini's Imaging Science Subsystem (ISS) took control of spacecraft pointing for nearly 20 hours today to track and observe the small, dark, irregular moon of Saturn called Kiviuq (described here on May 10: http://go.nasa.gov/1LDtVGC ).

Thursday, July 2 (DOY 183)

During today's DSN tracking and communications period, the flight team began uplinking "instrument-expanded block" commands to Cassini that will support science instrument operations during the 10-week period starting July 13, when the S90 command sequence will take effect. After the DSN support, ISS turned and watched Kiviuq for another 13 hours.

Friday, July 3 (DOY 184)

ISS turned to monitor Titan with a 90-minute observation; the Visible and Infrared Mapping Spectrometer (VIMS) rode along. Next, the Ultraviolet Imaging Spectrograph (UVIS) turned towards Saturn and observed its aurorae, with ISS, VIMS, and the Composite Infrared Spectrometer (CIRS) observing as riders.

Saturday, July 4 (DOY 185)

Every six months or so, the Magnetospheric and Plasma Science (MAPS) instruments dedicate a period to collecting uninterrupted magnetospheric science data. The Magnetometer (MAG) participated in the high priority in-situ observations while inbound to periapsis today, and then again while outbound on the following day, studying Saturn's inner magnetosphere in the equatorial region where most of the dust and plasma are confined. The Magnetospheric Imaging Instrument (MIMI) took part by having the spacecraft roll about its longitudinal axis on both days totaling 16.5 hours, so that the instrument's in-situ, direct-sensing components could measure the distribution of energetic particles around the magnetic field direction. These observations provide important information for understanding the radiation environment in the inner magnetosphere.

Sunday, July 5 (DOY 186)

Cassini passed through the periapsis of its Saturn orbit #218 today. It had reached 60,048 kilometers per hour relative to the planet -- fully 10 times its speed when it was at apoapsis 10 days earlier. This closest approach to Saturn came within 188,000 kilometers of the edge of Saturn's atmosphere.

Both before and after periapsis, the spacecraft passed slowly through Saturn's ring plane. The Cosmic Dust Analyzer (CDA) took full advantage of these passages, and performed direct-sensing observations of the particles populating the equatorial plane. CDA's observations totaled 16.5 hours in duration.

Monday, July 6 (DOY 187)

Around mid-day today Titan loomed closer to Cassini than Earth's Moon is to us. Titan is half again as large as our Moon is, so it would have appeared huge. Earlier in the day, Cassini's telescopes were all trained on the atmosphere-enshrouded giant as the optical remote-sensing instruments ISS, VIMS, VIRS, and UVIS began making a series of observations that would continue throughout the T-112 Titan encounter.

An image featured today captures Saturn's little moon Prometheus, which orbits Saturn every 14-and-one-half hours interior to the F ring, which it often perturbs with its gravitation. The image is at: /resources/16206 .

Tuesday, July 7 (DOY 188)

Today Cassini coasted by Saturn's largest moon Titan for a closest approach of 10,953 kilometers above its haze-covered surface, at which time CIRS had the helm for making observations. During the flyby, the spacecraft made an exchange of orbital momentum with the 5,152-kilometer-diameter body, which resulted in a slight increase (0.1 degree) in Cassini's orbital inclination, and an increase of its orbital period about Saturn from 18.9 days to 21.8 days. As part of the momentum tradeoff, Titan's own motion in orbit changed, though far too little to measure. Details of the spacecraft's activities during this T-112 Titan encounter may be seen here: http://saturn.jpl.nasa.gov/mission/flybys/titan20150707 .

While Cassini was encountering Titan, members of the flight team approved recently built commands for the ISS that will turn the spacecraft to track Pluto next week, and take a long-exposure image. This has been done several times in the past to assist New Horizons with optical navigation images. Given the speed of light and the immense distance to Pluto, the image will capture the Pluto-Charon system within several minutes of New Horizon's closest approach as it speeds past those distant bodies, and continues on its high-velocity journey deeper into the Kuiper Belt.

NASA's Astronomy Picture of the Day for today is as unusual as it is beautiful, with Saturn gracing the starry sky as the brightest object in the upper right: http://apod.nasa.gov/apod/ap150707.html .

During the past week, the DSN communicated with and tracked Cassini on nine routine occasions, using deep space stations in California and Australia. A total of 6,699 individual commands were uplinked, and about 1,084 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 7: https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=-82&vbody=1001&month=7&day=07&year=2015&hour=23&minute=55&fovmul=1&rfov=45&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/ .