To Galileo Mission Summary
The following activity occurred over the last four months (November 25, 1994, to April 7, 1995).
The Command and Data Subsystem (CDS) 9.5 software inflight load (IFL) and the Attitude and Articulation Control Subsystem (AACS) 13.1 software IFL completed nominally on February 12, 1995, and February 24, 1995, respectively (see story, Reloading the Operating System on Galileo's PC).
The Shoemaker-Levy 9 (SL9) science data return was completed on January 29, 1995 (see story, A Comet's Fiery Dance at Jupiter). Overall, 98.84 percent of the SL9 science data transmitted by the spacecraft were successfully received and processed through the ground data system during the 1994-95 SL9 data playback campaign.
The synthesis of results from the radio propagation measurements conducted during the Galileo superior conjunctions and other similar measurements is providing the first global picture of the charged-particle environment near the Sun. The emerging picture is one in which the solar corona is permeated by a wide variety of ray-like structures that are organized by the large-scale solar magnetic field. During the current phase of the solar cycle, coronal streamers with dense filamentary structure dominate the ecliptic plane, while large-scale coronal plumes pervade the low-density polar regions of the Sun.
Routine operations maintenance continued, including Data Management Subsystem (DMS) conditioning, Ultrastable Oscillator tests, an Energetic Particle Detector motor maintenance exercise, Retropropulsion Module 10-N flushing activities, and a Solid State Imaging instrument checkout. Regular science data acquisition from the Extreme Ultraviolet Spectrometer, Dust Detector, and Magnetometer has continued successfully.
Conjunction command tests were successfully performed at Sun-Earth-Spacecraft (SEC) angles ranging from 10.5 to 3.3 deg. Solar conjunction occurred on December 1, 1994.
Seven Block V Receiver (BVR) tests were performed over DSS-14, the last of a series. The tests successfully demonstrated Block V receiver suppressed carrier acquisition and tracking. A test result briefing covering this series of tests was presented to the Project on January 31, 1995. Full Spectrum Recorder (FSR) tests were also performed over DSS 14/DSS-43.
BVR operations are critical to the continued success of the Galileo mission because of the major improvement in telecommunication performance they offer. By putting all the downlink power in the data channel and eliminating use of a carrier signal, the BVR provides more than twice the otherwise supportable data return at Jupiter. Even with BVR performance below that predicted by lab testing and theoretical models, Galileo will be able to transmit more data at higher rates than those the Block IV receivers could support. As Galileo approaches round the net use of the BVR receivers, we look forward to saying good-bye to our worst telecommunication performance.
A variety of routine telemetry tests (Command Detector Unit Signal-to-Noise Ratio tests, Command Threshold tests, Radio Frequency Subsystem Automatic Gain Control tests, and Radio Frequency Subsystem Tracking Loop Capacitor tests) were successfully performed, providing detailed information relative to telecommunication hardware functionality and performance.
On March 16, the Probe Abbreviated System Functional Test (ASFT) was performed on the spacecraft (see story, Ready to Go--The Probe Checkout Results). Playback of Probe ASFT data, including Probe and Relay Radio Hardware (RRH) data, from the tape recorder began on March 18, and completed on April 5, 1995, as planned.
The AC/DC bus imbalance measurements have not exhibited significant change throughout this period.
The Project approved Orbit Profiles for the G1 and G2 orbits, the C3 Orbit Activity Plan, and Trajectory Correction Maneuver 23 (which was subsequently executed successfully).
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