NASA Cassini Significant Events 03/16/11 – 03/22/11

The most recent spacecraft telemetry was acquired on March 21 from the Deep Space Network tracking complex at Madrid, Spain. The Cassini spacecraft is in an excellent state of health and all subsystems are operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the “Present Position” page at: http://saturn.jpl.nasa.gov/mission/presentposition/.

Wednesday, March 16 (DOY 075)

The Downlink Ground System team performed testing of the new Acelog software, the replacement tool for OLOG. Cassini ACEs have already tested the new Acelog, and users who simply view it can access and view it on the web. A tutorial will be offered for other users of the Acelog to familiarize them with this new tool.

Thursday, March 17 (DOY 076)

A news release called ‘Cassini Sees Seasonal Rains Transform Titan’s Surface’ is available on the Cassini web site. As spring continues to unfold at Saturn, April showers on the planet’s largest moon, Titan, have brought methane rain to its equatorial deserts, as revealed in images captured by the Cassini spacecraft. This is the first time scientists have obtained current evidence of rain soaking Titan’s surface at low latitudes. For more information on this subject link to: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20110317/

This week in science, Imaging Science (ISS) trained the cameras on Skathi, one of Saturn’s most distant satellites, to measure its rotational light curve. The Ultraviolet Imaging Spectrograph (UVIS) made two of its Extreme Ultraviolet/Far Ultraviolet scans of Saturn to map upper atmospheric constituents and variability, and the Composite Infrared Spectrometer (CIRS) performed two mid-infrared maps of the planet, probing deeper into the atmosphere. ISS then searched for lightning on Saturn with the Visual and Infrared Mapping Spectrometer (VIMS) observing in concert. VIMS and CIRS also made a series of global mosaics of Saturn – one inbound to periapsis and one outbound, bookending a RADAR high-resolution global map along the central meridian of Saturn during periapsis. This sequence of observations (VIMS/CIRS and RADAR) is designed to study dynamics deep within the planet’s atmosphere. The final day of last week’s science began a 26-day sequence of magnetospheric-focused observations that continues all the way until the next periapsis. This sequence of measurements gives the MAPS instruments an opportunity to acquire nearly complete and continuous measurements of Saturn’s outer magnetosphere and magnetosheath.

Friday, March 18 (DOY 077)

A number of Cassini scientists attended the Outer Planets Assessment Group (OPAG) meeting Mar. 17-18 in Alexandria, VA. The group’s discussion focused on the decadal survey results, first made public on March 7 at the Lunar and Planetary Science Conference (LPSC) meeting, from an outer planets perspective. The decadal survey was very positive about the Cassini Solstice mission. The OPAG was established by NASA in late 2004 to identify scientific priorities and pathways for exploration in the outer solar system. The group consists of a 15-person steering committee (see http://www.lpi.usra.edu/opag/committee.html) which actively solicits input from the scientific community and reports its findings to NASA Headquarters.

Saturday, March 19 (DOY 078)

The command loss timer (CLT) value was changed temporarily to 125 hours on Mar. 15, and restored back to its nominal default value of 115 hours today. A member of the Cassini Outreach team was nominated to the National Science Teachers Association (NSTA) National Board for their “Special Needs Advisory Board”. She is bi-lingual in English and American Sign Language, and has worked with the ‘Strides’ program for special needs children; therapeutic riding, the use of the horse and equine-oriented activities to achieve a variety of therapeutic goals.

Sunday, March 20 (DOY 079)

Last week, Cassini Outreach led workshops on Cassini’s Reading, Writing & Rings program, assisted in leading a day-long short course on NASA’s Year of the Solar System, and staffed the NASA exhibit at the National Science Teachers Association annual conference in San Francisco. A total of approximately 60 teachers attended the workshops and short course.

Tuesday, March 22 (DOY 081)

A feature story called “Cassini Finds Saturn Sends Mixed Signals’ is available on the Cassini web site. Like a petulant adolescent, Saturn is sending out mixed signals. Recent data from the Cassini spacecraft show that the variations in radio waves controlled by the planet’s rotation are different in the northern and southern hemispheres. Moreover, the northern and southern rotational variations also appear to change with the Saturnian seasons, and the hemispheres have actually swapped rates since the equinox crossing in August of 2009. For more information on this subject link to: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20110322/

Mission Planning is in discussions with the Satellite Orbiter Science Team (SOST) and Spacecraft Operations with respect to Orbit Trim Maneuver (OTM) #312, which occurs on 9 Mar 2012 on rev 162 in sequence S72. OTMs occur over downlink passes where the team can uplink files and monitor the maneuver. For OTM-312, there is a dust hazard that overlaps the downlink pass but the hazard ends before the maneuver executes. The dust fluence for this hazard is high enough that a main engine cover closure was recommended. However, because the maneuver is scheduled to occur ~2.5 hr after the hazard ends, there is not enough time to open the cover and verify that it is open before the maneuver executes. The possibility of waiving normal protections such as closing the cover or turning the High Gain Antenna (HGA) to the RAM direction for the hazard was raised, since the Earth-RAM angle is 26 deg and the nozzles would still be mostly shielded by the spacecraft, but Cassini upper management is not inclined to go this route. OTM-312 is estimated to be ~3.6 m/s which is sizable. Missing the prime opportunity and going to the backup would be a 6-7 m/s penalty, so the teams would like to ensure the maneuver is executed on the prime pass. Because of the maneuver size and potential penalties, the Navigation team would like to uplink the maneuver a pass early to make sure it is registered on board the spacecraft. Another option is to turn to HGA to the dust RAM direction during the dust hazard. This would take the spacecraft off Earth point and interrupt the downlink. This conflict occurs during a SOST segment, so SOST is looking at how to adjust the segment to take the dust hazard into account.