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We are now just one year from Jupiter arrival on December 7, 1995. All our interplanetary targets of opportunity are well behind us and each was observed with grand success. Ida data return was completed as planned in June. Galileo's unique direct observations of Comet Shoemaker-Levy 9 fragment impacts in July are providing invaluable additions to the Earth-based observations' data set. The exact impact time and evolution of several of the major events have been determined by Galileo data. Data return is now suspended for three weeks around our December 1 solar conjunction. The balance of the planned return will be between mid-December and the end of January. The Deep Space Network (DSN) has captured over 98 percent of the Galileo SL9 data downlinked to date!
SL9 data return was also suspended as planned from mid-August to mid-September to perform a check of the functionality of every memory cell in Galileo's Command and Data Subsystem (CDS) extended memories and the Attitude and Articulation Control Subsystem (AACS) spare memory before loading new Flight Software (FSW) in these memories early next year. Every cell was found functional. Ironically, just weeks later on September 13, a cell failure caused the data return sequence to be aborted; it took two weeks to fully diagnose what had happened and resume playback. It is encouraging that this is the first Galileo memory cell failure; the prelaunch prediction was that quite a number of cells would have failed by now and, accordingly, we have always had workarounds in our plans. Now, based upon the flight experience of Galileo and Magellan, we should see no more than a few cells fail, which should be quite tractable.
We are delighted that NASA and Australia's Commonwealth Scientific Industrial Research Organization (CSIRO) are now proceeding to modify the Parkes 64-m Radio Astronomy Antenna in Australia in order to include it in the DSN/Galileo S-band antenna array for the orbital tour data return. Parkes will improve our data return by nearly 20 percent for the orbits that most need improvement and will contribute very substantially to the overall mission, just as it did for Voyager.
Calendar year 1995 is the crucial year for Galileo. Beginning in February and through mid-March, we will be uplinking the new FSW that provides backup capture of Probe data in the CDS and vital new autonomous fault-protection algorithms. The final checkout of the Probe will be performed next using the new software to buffer and return checkout data.
The Probe Release is scheduled for July 13 following a week of painstaking operations. Final prerelease Trajectory Correction Maneuvers (TCMs) for refining the Probe trajectory will be April 12 and June 23, 1995.
On July 20, the Galileo Orbiter 400-N main rocket engine will be used for the first time to perform the Orbiter Deflection Maneuver (ODM) that aims the Orbiter to its required Io flyby point, which properly establishes the Orbiter's trajectory for Relay and the Jupiter Orbit Insertion (JOI) maneuver.
In 1995, virtually all spacecraft activity will involve preparations for Jupiter arrival. And the large majority of arrival preparation effort on the ground will be in preparing for contingencies. If we could count on everything going as planned, we would be nearly ready right now. The big job is to determine what problems to prepare for and program the spacecraft to detect and correct such problems or, if time permits, safe itself and wait for corrective commands from the ground.
When performing the Probe Relay and Jupiter Orbit Insertion, all fault protection must be autonomous since each of these events occurs in less than the nearly 2-hour round-trip light time making ground interaction out of the question without even considering think-time and commanding reliability. Our goal is to require no ground commanding during the last 21 days before arrival except for TCMs and setting the command loss timer. Throughout the life of the Project, arrival contingency planning has been a continuing process. Now in the home stretch, with five years of flight experience and some new insights to potential vulnerabilities, we will be doing everything we reasonably can to maximize the reliability of Relay and JOI.
In parallel with our arrival preparations, work on the orbital mission will continue in full swing. The new Orbital Phase FSW must be completed and thoroughly tested and detailed orbital sequences for many of the orbits generated. We are currently facing a substantial schedule challenge to be ready for the first orbital tour satellite encounter--Ganymede 1 (G1)--on July 4, 1996. Our Spacecraft System Testbed planning is being streamlined and the planning staff increased to ensure our G1 readiness.
Happy holidays to the friends of Galileo everywhere and let us all look forward to 1995 culminating in the successful arrival of Galileo at Jupiter!!!