NASA Cassini Significant Events for 04/02/08 - 04/08/08

Status Report From: Jet Propulsion Laboratory
Posted: Wednesday, April 16, 2008


The most recent spacecraft telemetry was acquired on Tuesday, April 8, from the Goldstone, California tracking complex. 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" web page located at

Wednesday, April 2 (DOY 093)

The AACS team has been performing analysis on the recent Enceladus flyby data in order to reconstruct the density of the Enceladus plume as a function of altitude based on the torques imparted to the spacecraft by the plumes. AACS density estimates made using two different approaches deviate from each other by less than 10%. It is calculated that the peak density encountered is 6.05 +/- 0.25 x10-12 kg/m3. The latest calculations for the time and altitude of peak density are approximately Enceladus closest approach + 45 seconds and 450 km, respectively.

Thursday, April 3 (DOY 094):

The first of the principal science activities of the day was a calibration of the Magnetometer subsystem (MAG) sensors. Calibration rolls for this instrument are performed roughly once every three weeks.

The Instrument Operations Team (IO) here at JPL hosted an Instrument Operations Working Group meeting. The agenda included an overview of the new File Release Notification System, the process for how the software is to be used in support of sequence development, and a proposal for assisting the teams with a method of automatically filling out on-line forms.

Friday, April 4 (DOY 095):

Uplink Operations sent commands to the spacecraft today for a RADAR mini-sequence and the Mimas live update, both to execute on DOY-102. All files have been confirmed to be on-board.

First among the day's science activities was an Ultraviolet Imaging Spectrograph (UVIS) observation of a stellar ring occultation, followed by an observation in the Imaging Science (ISS) small satellite monitoring campaign. Then the Visual and Infrared Mapping Spectrometer (VIMS) turned towards Saturn to study the distribution of methane in the planet's atmosphere. After the subsequent Composite Infrared Spectrometer (CIRS) scan of the unlit rings, Cassini pointed its antenna back toward Earth to relay the day's data. Tomorrow, ISS will perform the first of two observations of Ymir designed to pin down the rotation rate of this small satellite and study any longitudinal variations across its surface.

Sunday, April 6 (DOY 097):

An AACS Reaction Wheel Assembly (RWA) friction test of the backup wheel, RWA-3, was completed today. In this test, performed every six months, the RWA is spun up to 600 rpm in both directions - clockwise and counterclockwise - and timed as it is allowed to run down to zero. Results, as compared to the last test performed October 28, 2007, show a slight improvement in both clockwise and counterclockwise directions. The rundown times are both above 40 minutes, much the same as for the test conducted a year ago, in April, 2007.

Monday, April 7 (DOY 098):

Back on Mar. 24, the Target Working Teams (TWT) and Orbiter Science Teams (OST) delivered integrated products for S44, the sequence Science Planning Attitude Spread Sheet (SPASS) and Sequence Phase List of Ancillary Files (SPLAF) files were delivered to the teams, and work began on pointing designs. Today, the official kick-off meeting was held for the S44 Science Operations Plan (SOP) process. The process will run for an additional 12 weeks and conclude on July 7. This sequence is of particular interest as it contains the Enceladus 5 flyby.

In addition to activities for S44, the third and final SOP delivery port for S42 occurred today. The handoff package will be transferred to Uplink Operations on Apr. 18 and final sequence development will begin on the 21st.

During the past couple of months, Radio Science (RSS) team members have been looking into utilizing the Australian Telescope Compact Array (ATCA) at Narrabri to provide Ka-band support for the RSS observations that occur over Canberra while DSS-34 is down for upgrades and maintenance. RSS would be using DSS-47, an array of six 22-m antennas.

All the relevant details have been worked out amongst the Project, the DSN and ATCA, and an initial request for tracking was submitted to ATCA. Due to cost, either withdrawing the request or keeping the activities to a minimum, including reduced amount of test time was under consideration. RSS determined that the science objectives enhanced by Ka-band are worth pursuing, and the facility and capability are worth demonstrating, so the team opted for minimized tracks of 24 hours total, with the understanding that the support will be on a best-efforts basis and the data quality is yet to be assessed.

An open loop Radio Science Receiver (RSR) was sent from Canberra to Narrabri, installed, and successfully accessed by Radio Science personnel at JPL. The plan is for the RSR to be shipped back to Canberra by the end of August, 2008. During the ATCA tracks, the RSR will be remotely controlled and operated from JPL by the RSS Group. This group will also be responsible for generating the RSR frequency predicts. The schedule for RSS use of DSS-47 is considered tentative until confirmed. The proposal is that it include six tracks occurring between DOY168-232 June 16 through Aug. 19. Independent of the Cassini requests, proficiency tracks using the Cassini signal are also scheduled, one of which is this Friday, DOY102 / April 11. Narrabri has tracked Cassini before, but not with an open- loop receiver. The track on DOY 102 will be the first opportunity to acquire open-loop Ka-band data during an actual occultation experiment, assess the data quality, and compare it to DSS-34 data.

Tuesday, April 8 (DOY 099):

Science observations began today with ISS performing a second observation in a campaign to study the satellite Ymir.

The Spacecraft Operations Office held a review for engineering activities to execute during the S45 background sequence.

25,000 copies of the new Reading, Writing & Rings CD have been received at JPL. These CDs include the entire contents of the K-4 language arts program, "Reading Writing & Rings", as well as the "Saturn in your Kitchen and Backyard" activities for grades 5-8, the "Ring World" planetarium show in English and Spanish, and some Cassini lithographs, images, and web links for teachers, students, and the public.

Reading Writing and Rings was presented at the following workshops at the National Science Teachers Association (NSTA):

1) What's New for the Cassini Spacecraft at Saturn: Updates for the K-5 Classroom

2) Read-to-go Space Science Activities for the K-5 Classroom

3) Balancing Accessibility and Complexity: Strategies for Developing Science Materials for the Primary Classroom

4) Reading, Writing and Rings presented by the Center for Mathematics and Science Education, Arkansas NASA Educator Resource Center Northwest Partnership, Arkansas Discovery Network.

Wrap up:

Check out the Cassini web site at for the latest press releases and images.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter.

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