News | July 28, 2016
Cassini Significant Events 07/20/16 - 07/26/16
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 July 27, 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 .
Monday's close encounter with Titan, T-121, was the highlight this week. The spacecraft flew 976 kilometers off the surface of Saturn's planet-like moon, which itself is over 5,000 km wide. That was close enough to conduct Synthetic-Aperture Radar (SAR) imaging, which provides the highest-resolution views of that wild alien surface. Cassini's thrusters fired automatically to maintain its assigned attitude as it swept by, skimming the heights of Titan's thick atmosphere. Cassini reported this and many other engineering details of the encounter, along with the science data of course, via the Deep Space Network largest-aperture radio antennas. It was basically a flawless encounter.
Wednesday, July 20 (DOY 202)
Cassini's Imaging Science Instrument (ISS) watched Saturn for nearly eight hours today, observing the gas giant at low, medium, and high emission angles and mapping its features as it rotated. The Visible and Infrared Mapping Spectrometer (VIMS), the Ultraviolet Imaging Spectrograph (UVIS), and the Composite Infrared Spectrometer (CIRS) rode along.
Following this, UVIS called the shots for nearly eleven hours. First, it targeted Saturn's small moon Mimas while it was sunlit at low phase angles, with ISS, VIMS, and CIRS riding along. UVIS then turned and imaged Saturn's high-altitude thermosphere to refine knowledge of the density in that part of Saturn's atmosphere, which is important for the ongoing planning of Cassini's 2017 passages in between the rings and Saturn's upper atmosphere.
Thursday, July 21 (DOY 203)
ISS began a 13.4-hour observation, tracking features visible in Saturn's atmosphere while it rotated just over one full time, again observing at various emission angles. CIRS, UVIS, and VIMS rode along.
Friday, July 22 (DOY 204)
Orbit Trim Maneuver (OTM)-454, the T-121 approach maneuver, executed early today in response to realtime commanding. The monopropellant-fed thruster burn of 47.9 seconds provided the needed change in velocity of 50 mm/s.
With the OTM completed, UVIS and VIMS began a collaborative observation of Saturn's southern auroral oval for 14 hours, with CIRS and ISS riding along.
Today through Sunday, Cassini scientists supported the Dusty Vision Workshop at the University of Colorado, Boulder. Topics related to the Cassini mission were dust observations in Enceladus's plume and in the Saturn system in general.
Saturday, July 23 (DOY 205)
Early today, Cassini passed periapsis, the low point in its Saturn orbit #238, going 35,413 km per hour relative to the planet. It came within 586,000 km of Saturn's cloud tops.
VIMS controlled spacecraft pointing for 8.3 hours to map Saturn's southern hemisphere, from about 30 degrees south latitude, down to the south pole.
NASA's Astronomy Picture of the Day shows the Earth's sky as it appeared on July 6. Three planets are in nearly a straight line: Saturn, Mars, and Jupiter from left to right. Each is hosting one or more robot visitors from this planet. Saturn appears white in the sunlight, above and slightly left of the red-giant star Antares: http://apod.nasa.gov/apod/ap160723.html .
Sunday, July 24 (DOY 206)
As seen from Earth today, Cassini passed slowly behind Saturn and its rings. Executing elaborate plans that had been led by the Radio Science team, the spacecraft's radio signals, continuous pure tones at three frequencies, actively probed the rings and atmosphere, and were recorded on the ground using five DSN stations. Future study of this Radio Science occultation experiment data will tease out the imprint of rings and atmosphere at high resolution.
When the Radio Science experiment was done, ISS made a two-hour observation as part of the Titan monitoring campaign. This time, Titan was only half a million km away. ISS then spend 2.5 hours tracking the bright limb of Saturn while it was sunlit from behind the planet.
VIMS and CIRS then worked together, observing the occultation of the bright red star Alpha Orionis -- better known as Betelgeuse -- by Saturn’s southern atmosphere.
The extraordinary view of the backlit planet casting its shadow on the rings towards Cassini, and the stellar occultation, is simulated here.
Capping a busy day, CIRS kicked off the Titan encounter observations, as Saturn's largest moon took center stage.
Monday, July 25 (DOY 207)
During the close encounter with Titan today, Cassini's SAR took a close-up swath of surface imaging about 5,000 km long, and at its best part about 100 km wide. Cassini is the only interplanetary spacecraft currently using SAR (decades ago Magellan used that technique to map Venus). The "synthetic aperture" in SAR means that thanks to some fearsome computer code, some of the distance that the spacecraft travels can be used to sharpen target resolution as though the actual aperture were many times larger than its actual size (Cassini's high-gain antenna is only four meters wide). SAR uses distance and Doppler shift as the two spatial dimensions for its pixels.
Cassini borrowed some of that moon's own momentum in Saturn orbit. The spacecraft connected to that store of momentum using Titan's gravity field, while it bent Cassini's path. Precisely as planned, the spacecraft's orbital inclination was bumped up another 6.3 degrees to 49.2, measured from Saturn's equatorial (and ring) plane. The orbital period was decreased in this exchange too, meaning it will now take Cassini 16 days to orbit the gas giant instead of 24. Five more targeted Titan encounters remain in the mission.
This page describes the T-121 encounter: /news/12922/t-121-radar-switch-hitting-at-titan .
Saturn's F ring and A ring are visibly refracted by the planet's upper atmosphere in today's highlighted image: /resources/17394 .
Tuesday, July 26 (DOY 208)
The first order of business today was tracking Cassini with the 70-meter diameter DSN station in Australia. Two-way Doppler-shift and range data would enable the Navigation to determine precisely how the flyby affected the spacecraft's flight path. Telemetry data returned scientific observations, along with spacecraft health and safety information.
Following its allotted 7.5 hours of DSN time, Cassini turned to allow ISS to monitor Titan for 10 hours. VIMS rode along, looking for clouds at mid-northern latitudes, and it acquired global views of the seas and lakes near the north pole. CIRS and UVIS participated at times.
Many Cassini scientists met in Boulder, Colorado today for a week-long workshop on Enceladus and the Icy Moons of Saturn.
The DSN communicated with and tracked Cassini on seven days this week, using stations in California, Madrid, and Australia. A total of 140 individual commands were uplinked, and about 1,760 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:
Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at: