News | April 25, 2012
Cassini Significant Events 04/18/2012 - 04/24/2012
The most recent spacecraft tracking and telemetry data were collected April 26 using the Deep Space Network's 34 meter high-efficiency Station 15 at Goldstone, California. Aside from the issues in work with the Ultrastable Oscillator (see the January 5, 2012 Significant Events) and the Cosmic Dust Analyzer, which is powered off until next week, the Cassini spacecraft is in an excellent state of health. Its subsystems are operating normally as the spacecraft orbits, nearly in Saturn's equatorial plane, once every 17.8 days. 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/.
There were no targeted encounters this week, but routine activities included three observations in the Titan monitoring campaign looking for cloud activity over a long time baseline. Cassini also made three observations in the Satellite Orbit Campaign this week, measuring positions of small satellites and improving knowledge of their orbits (discussions about why this is important appear in the March 30 and April 20 reports).
Wednesday, April 18 (DOY 109)
Orbit Trim Maneuver (OTM) 317, the clean-up maneuver scheduled for today following the Enceladus E-17 flyby, was canceled.
JPL Division 33 (Communications, Tracking, and Radar) held follow-up meetings today and on April 23 regarding the previous review of Cassini's Deep Space Transponder/Ultra Stable Oscillator (USO) test proposal. They are continuing to look at possible USO failure scenarios.
Thursday, April 19 (DOY 110)
ISS observed the transit of Dione across Rhea for orbit determination purposes. The Cassini Plasma Spectrometer (CAPS) performed a 9 hour observation of the plasma that co-rotates with Saturn's magnetic field near the equatorial plane. This was followed by a four-hour calibration of the instrument's ion beam spectrometer and ion mass spectrometer. The Visible and Infrared Mapping Spectrometer (VIMS) performed a Saturn storm watch observation.
The feature "Cassini Finds Titan Lake is Like a Namibia Mudflat" was published today. It suggests that one Titan lake previously thought to be completely filled with liquid could actually be a depression that drains and refills from below:
Friday, April 20 (DOY 111)
ISS searched for satellites around the Titan L5 Lagrange point, the stable orbital point 60 degrees behind the large satellite, and then observed a transit of the moon Rhea in front of Tethys.
The Deep Space Network (DSN) tracks Cassini nearly every day, though it's not always mentioned in these reports. About 99% of the time, the DSN has no problem capturing every bit of incoming telemetry while transmitting command data and navigation tones routinely across interplanetary space. Today, though, when the Goldstone 70 meter diameter antenna was scheduled to rotate its six-million pound dish to point to Saturn in the east, it would not move. An emergency-stop circuit had been tripped in the antenna's safety interlock system, and station personnel were unable to clear the problem. Telemetry playing back from the spacecraft's solid-state recorders included many of the observations mentioned above; unfortunately they were lost. Before Cassini pointed away from Earth, though, the DSN provided a means to send commands by pointing a smaller station toward Saturn: the 34 meter Station 55 in Madrid, Spain, which enabled the Cassini Realtime Operations team to command a reset of the spacecraft's command-loss timer.
Saturday, April 21 (DOY 112)
The Goldstone 70 meter station's emergency-stop problem was resolved, and it successfully captured the latest data from the spacecraft today (the capability to re-play previously lost data is not available during Cassini's extended mission for cost reduction purposes).
DSN tracking allocations have been completed for the first four weeks of command sequence S74, a ten-week sequence that is scheduled to go active mid June.
Sunday, April 22 (DOY 113)
The Magnetometer performed a seven-hour calibration while rotating the spacecraft about its X-axis. An animation of this pitching maneuver may be seen here: http://1.usa.gov/lEJIc1
Monday, April 23 (DOY 114)
Two 34 meter DSN stations, one at Madrid, Spain, and one at Goldstone, California, participated today in an Operations Readiness Test in preparation for a Radio Science experiment that will measure Enceladus's gravity field during the E-19 encounter on May 2.
The Optical Remote Sensing instruments performed an 11 hour observation of Saturn's E and G rings.
Cassini began its 165th orbit of Saturn today as it passed apoapsis, having slowed to 5,491 kilometers per hour relative to Saturn.
The feature "Cassini Sees Objects Blazing Trails in Saturn Ring" was published. It illustrates and explains how snowballs, formed in the F ring by gravitational interaction with the small moon Prometheus, sometimes can come back around in their orbits to punch through the narrow ring and perturb it:
Tuesday, April 24 (DOY 115)
Commands for Orbit Trim Maneuver (OTM) 318 were created, reviewed and approved, uplinked, and executed tonight. This was a targeting maneuver for the upcoming Enceladus E-19 fly-by. It fired Cassini's 440 newton bipropellant main engine for 1.3 seconds, providing a delta V of 0.234 meter per second.
ISS then performed a 15 hour observation of the tiny irregular moon Erriapus in its orbit more than 17 million kilometers from Saturn.
The feature "Cassini Investigates Titan's Chemical Factory" went online today, describing Titan, with its cold atmosphere and surface liquids, as one of the most complex chemical environments in the solar system.: