News | February 25, 2015
Cassini Significant Events 02/18/2015 - 02/24/2015
Cassini is currently orbiting Saturn with a 31.9-day period in a plane inclined 8.5 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Feb. 17 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/news/significantevents/anomalies . Milestones spanning the whole orbital tour are listed here:
Cassini's position on Feb. 24, two days before reaching apoapsis, is illustrated here:
Having dashed by Titan last week while coasting outbound from periapsis in its Saturn orbit, Cassini continued its "upward" arc, slowing naturally toward the high point of a Feb. 26 apoapsis. Activities on the spacecraft were orchestrated by on-board commands from the S87 background sequence through Saturday. Then the S88 sequence took command for its 10-week run.
Wednesday, Feb. 18 (DOY 049)
The Ultraviolet Imaging Spectrograph (UVIS) was in the "driver's seat" for 14 hours today, controlling Cassini's orientation so it could make a high-priority observation. The bright blue star Kappa Orionis, familiar by sight if not by name to anyone who can recognize Orion in the night sky, made a pass behind Saturn's rings, continued inward, and then passed behind the atmosphere near the equator. The Imaging Science Subsystem (ISS) and the Visible and Infrared Mapping Spectrometer (VIMS) made observations in "ride-along" mode. The reason this was a high priority activity is because it helped "feel out" the region of space between the rings and atmosphere where Cassini will be flying in 2017. This stellar occultation is expected to provide superb data about Saturn's tenuous atmosphere in that region. If you were riding along for this observation, here's a simulation of one view you'd have seen:
Thursday, Feb. 19 (DOY 050)
During a communications session with a Deep Space Network station in California today, the flight team uplinked the S88 command sequence, which the Sequence Implementation Process (SIP) team had been working on since last September. After a round-trip light-time of 2 hours 46 minutes, telemetry form the spacecraft confirmed that all 9,079 individual commands had been properly received and stored aboard.
Having passed completely behind the planet thanks to Cassini's motion in orbit, Kappa Orionis rose from behind Saturn’s atmosphere on the other side, and UVIS observed the stellar occultation egress for almost 2 hours 40 minutes, gaining additional data on Saturn's upper atmosphere. When this observation finished, ISS took two minutes to make a storm-watch observation on Saturn, with VIMS participating.
Friday, Feb. 20 (DOY 051)
The last science activity in the S87 sequence of commands turned ISS to Saturn for another two-minute storm watch. Back at JPL, the S87 SIP team began to wrap up and document the previous ten weeks of Cassini's activities.
Saturday, Feb. 21 (DOY 052)
The S88 command sequence began executing on board Cassini as planned, and the S88 SIP team stepped into the limelight of operations. For the sequence's first science observation, ISS turned to place Saturn's irregular moon Loge squarely in its telescope's field of view, and continued to track it for 36 hours. This distant object, named for a fire giant from Norse mythology, is estimated to be only about six kilometers in diameter; it occupies an inclined, retrograde orbit about Saturn that extends out to 23 million kilometers from the planet. This observation should help determine the object's rotation rate and characterize its surface.
Sunday, Feb. 22 (DOY 053)
Toward the end of the week, the Cassini Project Scientist and a few other Cassini scientists attended an Outer Planets Assessment Group meeting in northern California. The aim of this meeting was to help provide NASA with science input for planning and prioritizing outer planet exploration activities over the next several decades.
Monday, Feb. 23 (DOY 054)
After ISS made another quick storm-watch observation of Saturn, the Composite Infrared Spectrometer (CIRS), which has the largest-aperture telescope on Cassini -- about 19 inches -- began a nearly 23-hour long observation of Saturn’s atmosphere in the mid-infrared part of the spectrum to measure temperatures in the upper troposphere and the tropopause.
An image of rings and shadows of rings featured today might be as perplexing as it is beautiful. Hint: the uniformly wide bright streak in the upper left is where sunlight is falling onto Saturn through the A ring's Enke gap, which itself appears as a dark band nearer to the middle of the image:
Tuesday, Feb. 24 (DOY 055)
When CIRS completed its troposphere observation, ISS took control for a two-minute storm watch of Saturn, this time with VIMS also observing. CIRS then took over pointing control to perform a 12-hour observation of the planet to better determine the atmosphere's chemical composition, with VIMS riding along. With that observation done, ISS squeezed in one more storm watch.
During the past week, the Deep Space Network communicated with and tracked Cassini on 11 occasions, using stations in California, Australia and Spain. A total of 9,085 individual commands were uplinked, and about 1,173 megabytes of telemetry data were downlinked and captured at rates as high as 124,426 bits per second.