NASA Cassini Significant Events for 05/29/2013 – 06/04/2013
Cassini is orbiting Saturn with a 12-day period in a plane inclined 59.4 degrees from the planet’s equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on June 4 using the 70-meter diameter Deep Space Network (DSN) station at Goldstone, California. 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.
Cassini enjoys essentially flawless interplanetary communications. Science planners and engineers formulate commands and send them to Cassini using the DSN’s 18 kilowatt X-band (8 GHz) radio transmitters. Cassini stores and executes the commands, then sends the resulting data as telemetry on an X-band downlink to the DSN, and on to the Cassini flight team. Doppler shifts and ranging tones that the DSN measures and calibrates provide velocity and distance data to the Cassini navigators. Radio scientists use subtle variations in the radio signal during satellite flybys to determine their internal structure and probe the rings and atmospheres during occultations. The immensity of the colossal steel and concrete structures of the DSN belie their cutting-edge levels of precision. Complete details about this extraordinary facility, including its history, its technical publications, and how to arrange a public tour, may be found here:
http://deepspace.jpl.nasa.gov.
Wednesday, May 29 (DOY 149)
Instrument-Expanded Block commands were uplinked and stored on the spacecraft. They will support the ten-week command sequence S79, which will begin controlling the spacecraft on June 7. After the round-trip light time of two and a half hours, telemetry showed that all 10,900 individual commands were properly received.
The Imaging Science Subsystem (ISS) reacquired and tracked propellers (http://go.usa.gov/YyGR) in the ring system for an hour, then led the Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) on an observation in the Titan Monitoring Campaign from a distance of 1.2 million kilometers. Next, VIMS observed the occultation of R Cassiopeia, as Cassini’s motion caused the red star to cross behind the entire ring system and disappear behind Saturn.
ISS, with CIRS riding along, made a five-hour observation of the F ring and the Roche Division near the boundary of Saturn’s shadow. The Roche Division is the space that spans the 3,400 kilometers from the narrow F ring inward to the outer edge of the A ring.
Does Saturn’s moon Dione have liquid water below its icy surface? Hints of geologic activity on this otherwise bland body are the subject of today’s news release:
http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20130529/
Thursday, May 30 (DOY 150)
Today, and again on Friday after a Radio Science experiment, ISS led an observation in the Titan Long Range Monitoring campaign, watching Saturn’s largest satellite. Today’s observation was nearly fifteen hours; Friday’s was about two and a half hours.
Friday, May 31 (DOY 151)
The Radio Science team carried out another Saturn atmosphere and ring occultation experiment using the spacecraft’s S-band, X-band, and Ka-band transmitters. The page http://go.usa.gov/bKBQ provides a good illustration of today’s experiment, except that Cassini’s path behind Saturn (represented by the horizontal blue line) was further toward the bottom of the page (southeast in Earth’s sky) this time, so that the radio beams barely grazed the planet’s atmosphere. DSN stations in California and Australia participated.
Saturday, June 1 (DOY 152)
ISS led a medium-resolution observation of the F ring for 12 hours 50 minutes. An F-ring particle takes just under fifteen hours to revolve about Saturn, going nearly 60,000 kilometers per hour relative to the planet. At the very end of this observation, Cassini turned slightly allowing the ISS to catch Daphnis, the icy body less than ten kilometers in diameter, in its orbit within the Keeler gap in the outer A ring. (A previous image of Daphnis is visible here in the full-resolution version: http://go.usa.gov/bk4h) Today’s view will supply data for astrometry and orbit determination.
During the F ring observation, Cassini passed through periapsis going 33,232 kilometers per hour relative to Saturn, at about 557,000 kilometers above the cloud tops. This the highest-altitude periapse Cassini has had in over four years, and periapse altitudes will continue to increase; Cassini will not come closer than this to Saturn again until early 2015.
CIRS made a “temperature difference” observation of the rings, watching the sunlit side for three hours. Paired with similar observations of the unlit side, the CIRS team is working to determine how the rings’ optical depth controls the differences between lit and unlit temperatures, and to constrain models of the degree to which thermal energy is exchanged between the sides as a function of optical depth. Next, VIMS watched the red star R Carinae as it was occulted by Saturn’s rings for almost four hours.
Sunday, June 2 (DOY 153)
The Ultraviolet Imaging Spectrograph (UVIS) mapped the rings for about an hour and a half, and then watched the blue-white star Delta Centauri as Cassini’s motion made it pass behind the rings for more than three hours. Next, CIRS scanned Saturn’s north polar region, making temperature measurements. ISS then retargeted some propellers and finally, VIMS scanned the sunlit rings near Saturn’s shadow, a viewing geometry that minimizes the effect of scattered light from Saturn’s atmosphere.
Monday, June 3 (DOY 154)
CIRS led a mapping observation, scanning Saturn’s north polar region to measure temperatures in the hurricane-like vortex. VIMS then started observing the northern hemisphere to map the after-effects of the planet-circling storm from 2011, and determine whether the String of Pearls (http://go.usa.gov/bkZR) has re-emerged. CIRS and ISS also rode along to make thermal measurements and take images in the visible spectrum.
Part-1 of the S79 command sequence was uplinked, and all 6,376 individual commands were confirmed as properly received and stored, ready to begin executing on June 7.
Dark fields of dunes are visible on an image of Titan featured today, thanks to Cassini’s ability to take images in near-infrared light, which penetrates the dense, smoggy atmosphere:
http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4824
Tuesday, June 4 (DOY 155)
ISS imaged selected Saturn latitudes at a range of emission angles as the planet rotated. CIRS and VIMS also rode along, taking data while CIRS controlled the spacecraft’s pointing.
Visit the JPL Cassini home page for more information about the Cassini Project:
