Cassini Significant Events 04/24/2013 - 04/30/2013 Cassini is orbiting Saturn with a 9.6-day period in a plane inclined 61.7 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on April 30 by the 70-meter Deep Space Network station at Madrid, Spain. Except for some science instrument issues described in previous reports, 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/. Sequence Implementation Process teams continued working on the ten-week command sequences S79 and S80, which will go active on the flight system in June and August respectively, and planning continued for the 2016 start of Cassini's F-ring and Proximal Orbits phase. Under control of the S78 sequence, the spacecraft turned frequently to point its telescopic instruments and its direct-sensing instruments for their various observations. As usual, the turns were carried out using Cassini's electrically driven reaction wheels (also called "momentum wheels" on other spacecraft, see http://go.usa.gov/TmDR). Every few days, the sequence performs routine maneuvers to adjust wheel speeds while thrusters stabilize the spacecraft. The Navigation team uses either realtime Doppler data, or telemetry played back later, to model the thrusters' effects on the spacecraft's trajectory. Wednesday, April 24 (DOY 114) The Ultraviolet Imaging Spectrograph (UVIS) studied the rings as they occulted the bright blue star Beta Libra. Following this, and again on Sunday, the Imaging Science Subsystem (ISS) performed observations in the Satellite Orbit Campaign, looking at small known satellites near Saturn and searching for new ones. The Cosmic Dust Analyzer (CDA) then carried out an observation of dust particles orbiting Saturn in the retrograde direction. CDA repeated this observation on Saturday and again on Sunday. Thursday, April 25 (DOY 115) ISS began a 37-hour observation of the irregular moon, Tarvos. This dark-surfaced object is about 14 kilometers in diameter and orbits almost 18 million kilometers away from Saturn. Meteors have been caught impacting Saturn's rings over the past few years! This news feature describes and illustrates the phenomenon: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20130425/ In Earth's sky, that bright, non-twinkling object right above the full Moon was Saturn, ready to have its rings examined with a telescope of any size. Friday, April 26 (DOY 116) Cassini passed through apoapsis, having coasted 1.4 million kilometers from the planet -- a little farther than the orbit of Titan -- and slowing to 12,509 kilometers per hour relative to Saturn. This marked the beginning of Cassini's orbit #188. Saturday, April 27 (DOY 117) The Deep Space Network carried out tracking and communications sessions with Cassini on seven occasions totaling 48 hours this week, employing its large parabolic antenna facilities in Spain, Australia, and California. Sunday, April 28 (DOY 118) UVIS, ISS, VIMS, and the Composite Infrared Spectrometer (CIRS) trained their telescopes on Vega, not to learn about this very bright star, but to watch while Saturn's moon Dione passed before it due to the spacecraft's motion in orbit. This fortunate observation will help look for volatiles near Dione as part of the Icy Satellite Exosphere study. ISS then reacquired and tracked the orbits of known propellers (http://go.usa.gov/YyGR) in Saturn’s rings. VIMS squeezed in a two-minute Saturn storm-watch observation before and again after the other observations. Saturn was at opposition tonight, as seen from Earth. It rose at sunset, reached its highest elevation at midnight, and set at sunrise. At opposition the planet is closest to Earth and therefore brighter. The rings, easily seen in any small telescope, appear inclined at 18 degrees this month. Saturn's largest moons, Titan, Dione, Iapetus, Rhea and Tethys are easily seen in a modest amateur telescope. Some tips for viewing Saturn may be found here: http://saturn.jpl.nasa.gov/education/saturnobservation/viewingsaturn/ The storm that raged on Saturn for most of 2011 is the subject of today's Astronomy Picture of the Day: http://apod.nasa.gov/apod/ap130428.html Monday, April 29 (DOY 119) The Visible and Infrared Mapping Spectrometer (VIMS) stared at Saturn's southern pole, observing the aurora while all the other optical remote-sensing instruments rode along, taking data. UVIS then conducted Saturn auroral observations by slewing its field of view across the south pole, with CIRS and VIMS also taking data. Magnetospheric and Plasma Science (MAPS) instruments continued their survey of the magnetosphere, with the Radio and Plasma Wave Science subsystem specifically observing the auroral and Saturn Kilometric Radiation (SKR) source regions. As described last week, telescopes on and orbiting Earth participated in these auroral studies. More information about the SKR may be found here: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20110322/ The hurricane that has been centered on Saturn's north pole at least since Cassini's arrival in 2004 was the subject of images and movies released today. It appeared on national newscasts the next day. In the false color renderings, red indicates lower-altitude clouds in the giant atmospheric vortex, which spans 2,000 kilometers: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20130429/ The face of Saturn's small moon Enceladus is seen illuminated in Saturn-shine, with the plume from its icy jets backlit by the Sun, in an image featured today: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4803 Tuesday, April 30 (DOY 120) Cassini fired its main rocket engine for 2.8 seconds for Orbit Trim Maneuver 348, providing half a meter per second velocity change, targeting the T91 encounter coming up on May 23. VIMS carried out mapping of Saturn's south pole, creating a movie while CIRS again took data. 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