Up to Date
The following activities occurred during the last 6 months, September 1, 1995, through February 29, 1996. For in-depth reporting concerning Jupiter arrival, the probe mission, OTM-1, and the tape recorder, please see other articles in this issue. Overall the spacecraft is healthy and operating normally.
Special Relay Preparations
The Probe relay symbol storage, which could initially hold
39 minutes of data in the Command and Data Subsystem (CDS) memory, was increased to 73 minutes to provide additional backup to the tape recorder. The Critical Engineering Sequence for probe relay and JOI was updated to be consistent.
Additional preparations for Relay/JOI, including turn-on of the Relay Radio Hardware, proceeded smoothly.
Post-Arrival Day Engineering Cleanup
On December 8, the spacecraft spun down from high to low spin as planned. After the spin down, real-time commands were sent to restore attitude control subsystem fault protection and spin parameters to their pre-JOI states. Additionally, System Fault
Protection (SFP) updates were made via real-time commands to change the Helium Loss monitor trip limit and make modifications to the Helium Loss response algorithm.
Navigation
On December 9, the spacecraft entered the solar conjunction period, which is when the solar separation angle is less than
7 degrees. The solar conjunction period ended on December 28. Spacecraft telemetry could not be received from December 15 (when the solar separation angle was at approximately 3 degrees) until December 26 (when the solar separation angle was at approximately 6 degrees).
Probe Data
Memory Readouts (MROs) of the Probe symbol data started earlier than originally planned, on December 9, 1995. These additional MROs, starting at approximately 40 minutes into the Probe relay data and including over
57 minutes of Doppler Wind Experiment data, were possible because the Orbit Trim Maneuver OTM-1 was not performed.
Science Data Return and Instrument Turn-On
The Near-Infrared Mapping Spectrometer (NIMS) and Energetic Particle Detector instrument turn-ons proceeded nominally and all instrument telemetry indications were as expected. The plan to turn on NIMS was in place long before the tape recorder anomaly and the consequent decision to forego the remote sensing observations on arrival day.
Cruise science and Jupiter Approach Memory Readouts were performed throughout this period for the Extreme Ultraviolet Spectrometer (EUV), Magnetometer (MAG), and Dust Detector (DDS) instruments. The EUV measurements provided detailed maps of the Io Plasma Torus emissions. The MAG detected that the spacecraft finally crossed into the Jovian magnetosphere on November 26, 1995, after having initially detected the magnetosphere's bow-shock as early as November 16, 1995.
Solar Wind Scintillation Experiment
A solar wind scintillation experiment using the spacecraft's radio frequency equipment ran from November 24, 1995, through January 13, 1996.
Telecommunications/Ground System
A telecommunications test on February 11 tested various modulation index values along with three Block V receiver carrier bandwidths at DSS-63. The test's purpose was to determine the telecom configuration that provides the best prospects for supporting 8-bits/s telemetry at the Perijove Raise (PJR) off-Earth (46°) attitude. Analysis of the test results are ongoing.
Anomaly Status
On September 18, "B" string telemetry from the spacecraft indicated that the CDS "B" string Power on Reset (POR) detector in the CDS power converter had tripped. It is believed that the event was transient and has no future implications.
On December 12 at approximately 12:30 am PST Earth Received Time (ERT), telemetry readings indicated an unexpected increase of about 7 W on the DC bus because the Relay Radio Hardware (RRH)-1 receiver went from the standby to the wideband mode. The power margin was sufficient to accommodate the change.
On January 5, the spacecraft entered safing due to a command constraint violation bit that had not yet been reset to its appropriate post-JOI value. The J0C-A sequence was terminated and the sequence-controlled Probe symbol data return interrupted. The sequence and Probe symbol data return were successfully restarted.
Key Uplink Planning Activities
The project approved the final updates to the sequences that cover spacecraft activity from November 6, 1995, to March 12, 1996. These sequences included the Probe Symbol Memory Readouts, return of the Probe science data recorded on the tape recorder, the Perijove Raise maneuver, scan platform performance update, and the HGA's Dual Drive Actuator (DDA) Hammer. The project also approved the orbit profile for the G7A sequence (March 30 through April 6, 1997), which includes a targeted encounter with Ganymede on April 5, 1997. Other major work has been the replanning of the G1 encounter sequence to account for the new flyby date and the new tape recorder operational rules.
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