From The Project Manager

We have had a wonderfully successful and productive summer.

The Probe was flawlessly released from the Orbiter as scheduled the evening of July 12th. The Probe is in perfect condition and on a trajectory and attitude well within specification. The Orbiter control of the spacecraft pointing and wobble at release was so good that the Orbiter made essentially no contribution to the Probe entry angle-of-attack (AOA) error. This is particularly satisfying because AOA turned out to be the hardest parameter to control and it demonstrated conclusively the high-spin spacecraft dynamic model corrections made after the 1993 spin-up demo. Navigation performance for the probe targeting was so good that the final pre-release TCM (24) scheduled for June 23rd was cancelled; the trajectory following the April 12th TCM-23 was already essentially perfect.

It was delightful to see a packed house ("standing room only" would be an understatement) of family and friends in von Kármán Auditorium on Release night to share in the excitement of this truly historic event.

The orbiter deflection maneuver (ODM) was executed exactly as planned on July 27th. Because this was the first inflight firing of the 400-N main engine, the ODM sequence was one of the most critical and demanding we have executed to date. The sequence was two weeks long in order to accommodate several propulsion component tests (including the engine itself) before committing to the 5-minute ODM burn. The 400-N engine worked beautifully. The steady-state thrust is estimated to be 3 percent below the pre-flight predict- -well within the 6 percent spec. Interestingly, this does not mean JOI will take 3 percent more propellant. The lower thrust could simply be due to a lower propellant flow rate. The amount of propellant required is determined by the specific impulse (Isp)--the impulse (force x time) per kg of propellant. Only the large propellant consumption of JOI gives us an opportunity to estimate the actual Isp. However, the observed lower thrust has been used to update our estimate of the nominal JOI burn time. The onboard fault protection will terminate the JOI burn at this time if certain faults have been detected; e.g., accelerometer failure or Attitude and Articulation Control Subsystem (AACS) power-on reset (POR). This nominal burn time is also used in setting the minimum and maximum burn time limits in the fault protection.

Detailed analysis of the telemetry data following ODM shows that one of the two helium pressurant check valves is not closed. The purpose of these valves--one on the fuel side and one on the oxidizer side of the propellant system--is to limit the amount of propellant vapor that can flow upstream and potentially mingle in the pressurization system. The Galileo propulsion system design makes the potential for any harmful interaction of these vapors extremely low even with an open checkvalve. Nonetheless, we are now holding the propellant temperature constant to minimize any vapor transport.

The Probe Release and ODM are very publicly visible events. What is not visible is the tremendous amount of careful planning--especially the contingency planning--that goes into these events. We re-visited all aspects of Probe Release this past year. And for well over a year, we have been working intensely with our colleagues at DARA and DASA (designers and builders of Galileo's propulsion system), studying every possible contingency and performing further testing at DASA on flight identical hardware in order to have the very best plan for ODM and JOI for all plausible contingencies. Our contingency plans for the Release and ODM were outstanding. They were the product of the utmost careful thought and dedication.

It has been suggested that "John Casani's intergalactic ghoul" monitors our activities closely and will not visit upon us any contingency that we are prepared for. In any case, we must do our best to be prepared for those reasonably plausible contingencies that could threaten our major objectives.

The Project Galileo and Deep Space Network teams continue to do a truly outstanding job operating the Galileo mission.

Preparations for Jupiter are also not publicly visible and these have made tremendous progress over the summer. The Project has been absolutely relentless in making the Relay/JOI Critical Engineering Sequence (CES) as reliable and robust as possible. The CES is now finalized and entering a rigorous final testing program on the Spacecraft Testbed. We are satisfied that we now have the best possible CES!

Completion of the Orbital Operations Flight Software (Phase 2) continued to be a great challenge. In spite of Herculean efforts we didn't complete "flyable" Command and Data Subsystem (CDS) flight software (FSW) in July. Fortunately, those continuing efforts did deliver the intended final CDS FSW to the Project for System Testing this month. The final testing of this FSW is now proceeding in parallel with the design of the Phase 2 Inflight Loading process with little, but adequate, schedule margin to begin the uplink to the spacecraft on schedule in March 1996. It is crucial that Phase 2 be installed then so that the arrival Orbiter science observations can be played back from the tape recorder before the July 4, 1996, Ganymede 1 encounter.

Five of the ten orbital tour encounter sequences are now completed and ready for translation to uplink command files, pending only some final updates shortly before transmission to the spacecraft.

In August, the Orbiter's Relay Radio Antenna (RRA) was slewed to its initial Relay cone angle where it will remain for the first 32 minutes of the Probe Relay Link. The four stepping slews that will be done in the remaining 43 minutes of the Link were nicely incorporated in this deployment to verify their performance. Cone angle is analogous to elevation angle. The azimuth or clock angle of the RRA is controlled by positioning the stator (despun section). This month a test is being run on the spacecraft to demonstrate the new capability to control the stator using only the star Canopus as a roll reference, which is part of the autonomous fault protection to be invoked if a gyro problem occurs during relay.

Galileo's Jupiter approach observation sequences begin October 9th. On October 11th Galileo will take a color image of Jupiter, containing the Galilean satellites Io and Ganymede. Since the Phase 2 capabilities won't be onboard yet, it will take nearly a month to return this color image. We hope to present it early in November. It will be the only image returned until the Phase 2 software is running on the spacecraft in May 1996.

Are we there yet? Almost!