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During this update period (January 1-June 15, 1994), the spacecraft performed operational activities associated with health and attitude maintenance, telecommunications link characterization, trajectory correction maneuvers, routine science memory readouts, data return from the Ida encounter, and the gravity wave experiment.
Four Reserved Box Sequences were uplinked to the spacecraft for the playback of Ida science data. Playback has continued throughout the spring, revealing much more from Galileo's flyby of the asteroid late last summer. An innovative procedure was developed in February and March to process data through the Mission Telemetry System (MTS). The procedure was developed in response to an MTS problem in which lockup occurred on compressed imaging frames sent in jailbox search memory readouts (MROs). The problem occurred because not enough frame headers were included in the sequence design of the MROs.
Data from the Ida encounter have been successfully received from all instruments (except the Heavy Ion Counter, which was not taking data), including almost 30 minutes of fields and particles data acquired just after closest approach. To date, over 98 percent of the data have been successfully received with only minor outages due to weather and short-term ground equipment problems.
With the successful completion of Trajectory Correction Maneuver 22A on February 15, which imparted a 0.1-meter/second change to the spacecraft velocity, Galileo is now aimed at a point inside of Jupiter's atmosphere. To be precise, Galileo is targeted inside the atmospheric entry Probe's required entry corridor, which is defined by time of arrival, latitude, and flight-path angle. This is the desired situation, since the Orbiter is responsible for the precise delivery of the Probe, which is scheduled for release on July 13, 1995.
The gravity wave experiment ran from April 28 through June 11. Both closed-loop (Doppler tracking) and open-loop (radio science receiver) data were processed.
Six routine Retropropulsion Module 10-N maintenance flushing activities were completed. Regular science data acquisition from the Extreme Ultraviolet Spectrometer, Dust Detector, and Magnetometer has continued successfully in parallel with the Ida data return, using the Command and Data Subsystem (CDS) MRO technique. CDS MROs were also performed between January 15 and 20 to play back selected low-rate science data from the Ida encounter. Preliminary analysis has shown that the data were properly received.
Seven Ultrastable Oscillator (USO) tests were performed between January 4 and April 25 to verify the instrument's health and to collect gravitational red-shift experimental data. Long-term trend analysis is continuing.
Six Block V receiver fast-acquisition tests were performed; all six were unsuccessful in demonstrating the Performance Verification Model receiver operation in the suppressed carrier mode. Troubleshooting on the receiver is now highly focused and successful operation is expected this fall.
Between January 22 and 25, Ida engineering data were played back using CDS MROs. Scientists used these data to study the anomalous attitude-control flight fault-protection trip that occurred hours before the Ida encounter on August 28, 1993. Using those data as a guide, an anomaly test sequence was designed to provide insight into the Attitude and Articulation Control Subsystem fault indications by rerunning key parts of the Ida encounter sequence. The test sequence ran from May 9 through 13 without any fault indication.
The alternating current (AC) bus imbalance measurement has remained fairly stable since March 1992 and currently reads 4.3 V.
The direct current (DC) bus imbalance measurement has shown significant change. On May 19, the measurement exhibited a gradual drop from ~17 V to near 12.5 V over a 36-hour period. On May 21, it abruptly increased from 12.5 V to near 22.5 V and has since remained stable. Other telemetry measurements also changed during the time period of the bus imbalance change, which included the DC bus current, AC bus current, system DC shunt current, CDS 10-VDC power supply current, SBA temperature, and USO oven current.
The AC/DC anomaly team was convened to verify that these telemetry changes are consistent with the slipping-brush debris model. Preliminary analysis indicates that all telemetry changes seem consistent with clearing a debris path in the SBA. The Project will be briefed on July 12, 1994.
The Project has approved the EJ-7 Cruise Plan, which will be executed by the spacecraft starting July 11. This sequence will include the Shoemaker-Levy 9 observations and some early data return.
Transition from the MTS-based telemetry support to the new Multimission Ground Data System (MGDS)-based support is nearly complete. The MGDS telemetry capabilities, supplied by the Multimission Operations Systems Office, provide workstations for telemetry display and analysis to supplement digital television and printer telemetry display devices. A period of parallel operations started March 31, during which both MTS and MGDS telemetry displays were provided in the Mission Support Area for comparison. In May, MGDS data were declared prime for real-time mission support.
As of this writing, July 1 was the date for the real-time MSA to relocate from one building to another at the Laboratory. At that time, MTS support of real-time operations was to be decommitted. Some problems are continuing with the MGDS non-realtime product support, particularly with the support of imaging data products provided to the Multimission Image Processing System (MIPS). This is the interface used for processing imaging data after Data Memory subsystem MRO from the spacecraft (i.e., Ida images). Decommitment of the MTS-MIPS interface support will be deferred until problems with the MGDS interface are resolved.
GDS integration of the E2.0 software deliveries was completed. In addition to the MGDS telemetry capabilities, the E2.0 build provided Galileo Phase-1 GDS support capabilities. The software associated with the E3.0 mission build was delivered. As part of the mission build, 12 program sets and two command databases were redelivered. The most significant new capability provided in the E3.0 software was support of the new SSI "on-chip mosaic" capability that will be first used during the Shoemaker-Levy 9 sequencing in July.
-- Matt Landano, Deputy Mission Director
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