Cassini Significant Event Report
For Week Ending 07/09/04
The most recent spacecraft telemetry was acquired from the Goldstone tracking station on Wednesday, July 7. The Cassini spacecraft is in an excellent state of health and is operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" web page located at http://saturn.jpl.nasa.gov/operations/present-position.cfm .
On-board activities this week included the successful completion of the Saturn Orbit Insertion (SOI) Critical Sequence, playback of all SOI telemetry and science data, Cassini's first Titan flyby, and acquisition of temperature and composition data for validation of the Titan atmospheric model to be used by the Huygens probe when released in December 2004.
Solar Conjunction occurs when the Sun is between the spacecraft and Earth. This year it will last from July 5 through July 11, and is a time of reduced commanding and downlink capability. During this period the project will uplink a command file consisting of 10 no-op commands sent every 5 minutes, 10 to 20 times daily. The purpose of the test is to accumulate statistics for uplink reliability at decreased separation angles.
Just prior to the start of conjunction, a relative timed IDAP to modify the telemetry mode was uplinked to the spacecraft. This allowed the instrument teams to obtain real-time instrument "house keeping" data to confirm the state of their instruments. The spacecraft is in a normal state and will remain Earth pointed and quiescent throughout conjunction.
Preliminary port#2 of Science Operations Plan (SOP) Implementation of tour sequences S31/S32 occurred this week. The delivered products were merged and reports delivered to the implementation team.
The SOP Update process for S05 began this week, and the process for S04 completed. A handoff package was delivered to Uplink Operations. A kick-off meeting was then held as part of the S04 Science and Sequence Update Process, and the Sub-Sequence Generation integrated sequence products were released to the Sequence Team (ST).
The integrated sequence products and DSN keyword file for S03 were released to the ST for review, and the instrument teams delivered their instrument expanded block spacecraft activity sequence files to the file repository. The final sequence products for S03 will be available next week, and the sequence approval meeting held the week after. S03 will go active on board the spacecraft on July 30.
As reported last week, the Cassini Team successfully executed the SOI burn on June 30, 2004. This main engine burn slowed the spacecraft by 626.17 meters per second or about 2254.2 kilometers per hour and allowed the spacecraft to be captured by Saturn's gravity field.
Unlike delta-V burns executed by other JPL spacecraft, Cassini's SOI burn was the first and only burn designed to achieve a change in the specific energy of the spacecraft, instead of a change in the spacecraft velocity. The "energy" algorithm used was proposed, developed, coded, and flight-tested by the SCO and Navigation teams.
This maneuver was also unique in the history of JPL in that the burn direction was changed continuously with time. The SOI "steering" rate was about 0.008 degrees per second, for a total steering angle of about 46 deg. This is very close to the rotation rate of the hour hand of a clock. By "steering", the main engine thrust tracked approximately the Saturn-relative velocity of the spacecraft, and the efficiency of the SOI burn was improved. Less propellant was used as a result.
Following SOI, the decision was made to cancel both Orbital Trim Maneuver (OTM) 001, and 001a. It was determined that there was no significant propellant savings or mission benefits to be gained by performing these maneuvers.
Raytheon, Cassini Outreach, and the Instrument Operations (IO) Imaging Science Subsystem (ISS) team located at JPL were involved in the rapid development and deployment of the public web site for Cassini raw ISS images. The site was rolled out on SOI day. IO/ISS supplied design expertise, image data and metadata, testing, and site documentation.
Mission Assurance conducted a pair of Risk Team meetings to reassess risk to the probe mission. As a result, three new items were added to the Significant Risk List (SRL). There are no red risks in the SRL. All continue to be mitigated to either yellow or green. In addition, all risks related only to the Cruise portion of the mission and SOI were officially retired.
The flight team continues to be excited and energized by the number of articles appearing regarding Cassini, and the interest and enthusiasm of the public. During 64 hours surrounding the SOI period the total number of website hits were as follows:
261,216,092=Total for Cassini traffic
136,595,464=Mission website (saturn.jpl.nasa.gov)
124,620,628 = Portal (nasa.gov/cassini)
Additional information about Cassini-Huygens is online at http://saturn.jpl.nasa.gov.
Cassini will begin orbiting Saturn on July 1, 2004, and release its piggybacked Huygens probe about six months later for descent through the thick atmosphere of the moon Titan. Cassini-Huygens is a cooperative mission of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Office of Space Science, Washington, D.C.