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Cassini Significant Events 07/27/16 – 08/02/16

Cassini is orbiting Saturn with a period of 16 days in a plane inclined 49.2 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Aug. 3, using one of the 34-meter diameter Deep Space Network 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 reached apoapsis this week, marking the start of its orbit #239 of Saturn. With the exception of two Orbit Trim Maneuvers (OTMs) commanded in real time, all of the spacecraft's activities were controlled by the on-board command sequence S95. Meanwhile, members of the flight team on two continents continued working on the S96 sequence, which goes active on Sept. 8, and S97 which starts in November. Activities for S98 development are already on the calendar; it begins in February 2017.

Wednesday, July 27 (DOY 209)

Cassini started the day with its high-gain antenna trained on Earth, continuing to play back telemetry (the digital data) from scientific observations carried out during the July-25 Titan encounter, via the Deep Space Network (DSN); this data went to the appropriate science teams. Meanwhile, engineers on the flight team monitored realtime and playback telemetry detailing the spacecraft's health. The Navigation team obtained more radiometric tracking data (Doppler shift and range signals) at the same time, to update orbit-determination solutions. The Realtime Ops team sent a routine command to the spacecraft as well. Thanks to advanced forward-error-correction algorithms in common use by spacecraft and DSN, virtually all telemetry and command communications work as flawlessly as trading email, despite the enormous distances.

Thursday, July 28 (DOY 210)

During today's DSN support, the flight team sent commands to Cassini that were based on the latest navigation solutions. Cassini turned and fired its small rocket thrusters for 188 seconds, executing Orbit Trim Maneuver (OTM)-455. This post-Titan trajectory clean-up maneuver provided the required change in Cassini's velocity (delta-V) of 184 millimeters per second. Once the OTM was completed, Cassini's Composite Infrared Spectrometer (CIRS) led the pointing for 12 hours to study Saturn's atmospheric composition. The Visible and Infrared Mapping Spectrometer (VIMS) participated.

Friday, July 29 (DOY 211)

Cassini's Navigation team controlled spacecraft pointing for 90 minutes, using the Imaging Science Subsystem (ISS) to take exposures of Saturn's moon Tethys against the background stars for optical navigation purposes. While Cassini no longer needs to include "opnav" data in its orbit-determination process, these images are being used to maintain accurate natural-satellite ephemerides for possible future missions.

Next, ISS, CIRS and VIMS performed a 90-minute observation in the Titan monitoring campaign while Saturn's planet-like moon was at a range of 1.8 million km. VIMS and CIRS rode along. ISS then took control to make an hour-long observation as part of the satellite orbit campaign, intended to recover and discover small objects near the planet. VIMS rode along with this. Finally, VIMS undertook an eight-hour study of the sunlit side of Saturn's rings to make a mosaic, with ISS, CIRS, and the Ultraviolet Imaging Spectrograph riding along.

News features released today examines some details of Titan's surface as revealed by Cassini's Synthetic-Aperture Radar close-up imaging: /resources/17397 and /resources/17398.

In 300 days from now it will be the summer solstice on Saturn's northern hemisphere, the epoch for which the current Solstice Mission phase is named. Saturn's year is equivalent to 29.5 Earth years.

Saturday, July 30 (DOY 212)

The Cosmic Dust Analyzer (CDA) spent 13 hours observing exogenous dust, sensing and analyzing particles coming into the Saturn system. Cassini passed through apoapsis at the time, having climbed to 1,866,000 km out from Saturn and slowing to 10,949 km per hour relative to the planet. This marked the start of Cassini's Saturn orbit #239.

Sunday, July 31 (DOY 213)

Planetary scientists, including some from Cassini, plus other icy-satellite scientists, met during the past several days at the “Enceladus and Icy Moons of Saturn” workshop in Boulder, Colorado. Discussions included the origin, evolution, geology, ages, and cratering of these icy worlds, as well as Enceladus's astrobiological potential.

Today, the Asia Oceania Geosciences Society (AOGS) meeting began in Beijing, China with participation by a number of Cassini scientists.

Monday, Aug. 1 (DOY 214)

ISS began a 14.5-hour observation of Saturn's irregular moon, Tarqeq, with VIMS participating. This object is about 6 km in diameter and occupies an inclined orbit that reaches as far as 20.9 million kilometers from Saturn; it is named after the Inuit "Moon god."

If ever an image were qualified to be selected as NASA's Astronomy Picture of the Day, it is this stunning view of Saturn, taken by the wide-angle camera in Cassini's ISS, through a near-infrared filter: http://apod.nasa.gov/apod/ap160801.html .

So many of the objects in Saturn's retinue have extraordinary features. The bright icy moon Rhea, featured on the Cassini website this week, seems more ordinary by comparison: /resources/17396 .

Tuesday, Aug. 2 (DOY 215)

Having used Titan last week for a gravity assist that reduced the spacecraft's orbit period to only 16 days, opportunities for OTMs, typically three per orbit, are coming more frequently. Based on the past few days' worth of DSN radiometric tracking data, the Navigation team determined that OTM-456 needed to provide Cassini a delta-V of 794 mm/s, to target for the upcoming Titan T-122 fly-by on Aug. 10. Commands for it were prepared and uplinked, and today Cassini's bi-propellent-fed 400-newton main engine provided the push. It was a quick burn, at 4.5 seconds duration.

Following the successful OTM, ISS, CIRS and VIMS observed Saturn's narrow, twisted, F ring for 15 hours. The images will be stitched together on the ground. Today's view from Cassini is remarkable, looking "down" on Saturn's north pole from its location near apoapsis in a high-inclination orbit.

On three occasions during the week, while Cassini's optical instruments were pointing at or near Saturn, ISS carried out two-minute Saturn storm-watch observations.

The DSN communicated with and tracked Cassini on eight occasions this week, using stations in California and Australia. A total of 6,836 individual commands were uplinked, and about 1,616 megabytes of telemetry data were downlinked and captured at rates as high as 142,201 bits per second.

Milestones spanning the whole orbital tour are listed here: https://saturn.jpl.nasa.gov/mission/saturn-tour/tour-dates .

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.