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This Week on Galileo?
October 2 - October 8, 2000
DOY 2000-276-282

Galileo's Maximum Transmission Rate This Week is 120 Bits Per Second

Galileo continues to return data stored on its onboard tape recorder this week. The spacecraft's maximum transmission rate this week is a whopping 120 bits per second! A data trickle by today's standards, but an impressive technological achievement considering that originally Galileo's low-gain antenna was designed to transmit a maximum of 16 bits per second at Jupiter distances. Enhancements to the Deep Space Network's (DSN) receiving antennas prior to the spacecraft's arrival at Jupiter allowed for an approximate factor of 10 improvement in the transmission rate. Another factor of 10 improvement in data content was accomplished by data compression algorithms designed and loaded into the spacecraft's operating system, also prior to arrival at Jupiter. Put together, these enhancements raised the low-gain antenna's effective data rate by a factor of 100!

This week's playback contains observations gathered during Galileo's May flyby of Ganymede, Jupiter's largest moon. The playback is from a second pass through the data stored on the tape recorder. This additional pass allows for the return of additional data, replay of data lost during the first transmission to Earth, and/or reprocessing of data using different parameters. Galileo's data return is interrupted once this week. On Thursday, the spacecraft performs standard maintenance on its propulsion systems.

First on the playback schedule is an observation by the Near-Infrared Mapping Spectrometer (NIMS). NIMS returns a spectral scan of Ganymede's limb, which is designed to provide scientists with a look at Ganymede's tenuous atmosphere. The Solid-State Imaging camera (SSI) is next on the schedule with the return of an image of enigmatic smooth dark terrain on Ganymede. NIMS returns to the playback schedule with three more observations. In the first, NIMS returns a spectral scan of the Perrine region on Ganymede. The next observation contains a high-resolution spectral map of Ganymede's entire disk. The third, however, moves away from Ganymede and captures a distant view of Europa while the icy moon is in Jupiter's shadow. With this last observation, NIMS scientists are looking for anomalously warm regions of the surface, due to either unusual surface materials, or the presence of recent low-temperature volcanic activity on Europa.

The Photopolarimeter Radiometer (PPR) joins the playback melee with the return of an observation of Jupiter's atmosphere. The observation is designed to capture polarimetry measurements, which will provide details on the structure and temperature of the atmosphere's upper levels. SSI continues the Jupiter theme with the return of three images of Jupiter's rings. The images will provide better determinations of the size distribution and light-scattering properties of the particles that make up Jupiter's main ring. The images may also allow detection of wave-like features, which could be important for understanding how the rings are maintained by Jupiter's small inner satellites.

NIMS returns to the schedule, returning eight out of a series of ten spectral scans of Jupiter's north polar region. The series consists of 10-minute samples taken at 60-minute intervals, and is designed to provide a unique view of auroral activity on Jupiter. NIMS continues with the return of one out of its three global observations of Jupiter. Once assembled, the observation set will provide a nearly complete spectral map of Jupiter. SSI then returns three observations of Jupiter's Great Red Spot. The observations will provide scientists with high spatial and time resolution of the Red Spot's activity. Similar observations of the Great Red Spot were taken at the beginning of Galileo's orbital tour in June 1996. Now scientists will be able to observe long-term changes in the characteristics of this long-lived storm.

Throughout the week, portions of a month-long, low-resolution survey of Jupiter's magnetosphere are also returned. The survey was performed by the Fields and Particles instruments. The lengthy survey not only provides context for the high-resolution recordings performed during the Ganymede flyby but also provides scientists with information on both the inner and outer regions of Jupiter's magnetosphere and the transition out into the solar wind.

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