Cassini Significant Events 07/17/2013 – 07/23/2013

Cassini is orbiting Saturn with a 16-day period in a plane inclined 56.7 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on July 25 using the 70-meter diameter Deep Space Network stations at Canberra, Australia. Except for some science instrument issues described in previous reports (for more information search the Cassini website for CAPS and USO), the spacecraft continues to be in an excellent state of health with all of its subsystems operating normally. Information on the present position of the Cassini spacecraft may be found on the "Present Position" page at: http://saturn.jpl.nasa.gov/mission/presentposition/.

This week's highlight was a high-priority observation from behind Saturn on July 19 while the Sun was eclipsed by the planet. It included a set of images of the Earth, something we can only do when Cassini is in eclipse. A 30-minute video mission report, with interviews and clips regarding the unique observation and the public's participation, may be seen on USTREAM: http://go.nasa.gov/12LNNy2.

Wednesday, July 17 (DOY 198)

The Imaging Science Subsystem (ISS) led spacecraft pointing for a Titan cloud monitoring observation from a distance of 1.3 million kilometers, while the Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) were also allocated enough data volume on the solid-state recorder to make observations. The Ultraviolet Imaging Spectrograph (UVIS) then executed a long-duration observation of Saturn in the extreme-ultraviolet (EUV) and the far-ultraviolet (FUV) parts of the spectrum, making a slow scan across Saturn's illuminated hemisphere to form spectral images. VIMS and ISS rode along during the UVIS observation, which was repeated on Thursday to complete a series of six of these since last Saturday.

Thursday, July 18 (DOY 199)

Orbit Trim Maneuver (OTM) 354 fired the main engine for 13.2 seconds to provide Cassini a change in velocity of 2.26 meters per second, putting us on target for the Titan T-93 flyby coming up on July 26. This occurred three days after apoapsis passage. The T-93 flyby information page has been set up here: http://saturn.jpl.nasa.gov/mission/flybys/titan20130726

Friday, July 19 (DOY 200)

Today, VIMS led the highest-priority observation of the rings in the S79 command sequence, while the other optical remote-sensing instruments (CIRS, UVIS, and ISS) rode along taking data. For more than three hours, the spacecraft was in Saturn's shadow. For 15 minutes of this time, people back on this pale-blue dot waved and smiled for Cassini while the imaging cameras captured pictures of the Earth and Moon. With the burning Sun eclipsed, forward-scattered light made the finest particles in the ring system shine most brightly in this unique high-phase observing geometry. A primary science goal is to address questions raised by the previous distant eclipse in 2006, which revealed unexpectedly large longitudinal asymmetries in the brightness and color of the E ring, the largest and most diffuse of the rings. The eerie 2006 image, which also caught the Earth and Moon (though without public participation), may be seen here: /resources/13314

Today's observations should help clarify the processes sculpting the E ring, which in turn might have implications for the surfaces of icy satellites and the inner magnetosphere. VIMS obtained spectral data at multiple E-ring longitudes, to see how its particle size distribution varies with longitude. VIMS also obtained spectral measurements of the other faint rings, including the innermost D ring and the thin F ring just outside the main rings. This will provide further constraints on the knowledge of particle size distributions and look for any large-scale changes in their distribution.

Saturday, July 20 (DOY 201)

Today and on subsequent days, telemetry from Friday's high-priority observations was transmitted back in two copies to DSN stations on two continents, guarding against possible data loss from any errant rainstorm near an Earth antenna or technical issues with a station. As the observations were being received, raw images were quickly made available on the Cassini Mission web pages.

The Magnetosphere and Plasma Science teams continued their dust and outer-magnetosphere survey campaigns to monitor the plasma environment in the Saturnian system. UVIS began another series of high-priority EUV and FUV slow-scan examinations of Saturn's upper atmosphere as a function of phase, with ISS and VIMS riding along. The observation was repeated each remaining day this week.

The Radio Science team turned on Cassini's Ka-band radio transmitter and conducted an operations readiness test with a 34-meter diameter DSN station in Spain, preparing for an occultation experiment coming up on Aug. 8.

Sunday, July 21 (DOY 202)

UVIS scanned the interplanetary medium to search for hydrogen, measuring its Lyman Alpha emissions. The Radio and Plasma Wave Science instrument then observed the auroral magnetosphere as part of an auroral and Saturn magnetosphere campaign. UVIS continued its campaign to observe Saturn's upper atmosphere. Last, VIMS observed Saturn's north pole to make auroral maps while CIRS and ISS rode along.

Monday, July 22 (DOY 203)

UVIS continued its interplanetary hydrogen search campaign, after which it continued to carry out its high priority campaign to view the EUV and FUV emission from Saturn, with ISS, VIMS and CIRS riding along. The latter observation was repeated on Tuesday. Finishing out the day, VIMS looked again to Saturn's north pole to make a mosaic movie of atmospheric dynamics.

A processed image from Friday's high-phase observation was released today, and it was featured as NASA's "Astronomy Picture of the Day." The brightest ring in the image is the F ring, and Earth is visible just below the faint G ring. High-altitude haze in Saturn's atmosphere is brightly lit from behind as sunlight is refracted by the atmosphere, but darkened here and there by shadows cast onto the atmosphere by the rings on the other side. The image may be seen here: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20130722/

An image showing Saturn's satellites Mimas and Pandora, brightly lighted beyond the dark rings, was featured today: /resources/15853

Tuesday, July 23 (DOY 204)

The Titan T-93 approach maneuver OTM 355 executed early today using Cassini's small thrusters. The 66.9-second burn provided a change in velocity of 70 millimeters per second. A few hours later, the spacecraft flew through periapsis going 25,652 kilometers per hour relative to the planet. This time it came only as close as 863,000 kilometers above Saturn's atmosphere, which is more than twice the distance to the E ring.

UVIS continued its interplanetary hydrogen search campaign. The instrument also continued its campaign to observe Saturn's upper atmosphere for hazes as a function of phase. Finally, VIMS observed Saturn's northern hemisphere to make mosaics of the latitudes where storms are typically seen.