Galileo Heads Back Toward an Encounter with Ganymede in December 2000.
September 11 – September 17, 2000
DOY 2000-255-261
Having passed the farthest point from Jupiter in its current orbit, Galileo now heads back toward an encounter with Ganymede in December 2000. The spacecraft plays back data from two encounters this week.
The first part of the week sees data returned from an observation performed during Galileo’s May encounter with Jupiter. The second part of the week provides data from the spacecraft’s February flyby of Io. Data return is interrupted three times this week. On Monday, the spacecraft performs standard maintenance on its onboard tape recorder. On Wednesday, the Solid-State Imaging camera (SSI) takes a series of optical navigation (opnav) images. On Thursday, maintenance on the spacecraft’s propulsion systems is scheduled.
Wednesday’s opnav images are taken to replace similar images planned a couple of weeks ago. The spacecraft successfully took and transmitted those images, but they were not received here on Earth due to heavy rains in Goldstone, California. Goldstone is home to one of the three 70-m (230-foot) diameter radio antennas used by Galileo. The other two antennas, part of the Deep Space Network, are located in Madrid, Spain and Canberra, Australia. The optical navigation images will be used to determine the health of SSI, after a recent anomalous behavior from an internal light source.
Seven different observations are returned this week. One observation from May is returned by the Fields and Particles instruments (F&P). The F&P instruments are the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Detector, and Plasma Wave instrument. The remaining six observations are from the February flyby of Io and are returned by the Solid-State Imaging camera (SSI) and the Near-Infrared Mapping Spectrometer (NIMS). These latter observations are from a second pass through the observations stored on the tape recorder during the February encounter. This additional pass is scheduled for the return of additional data, replay of data lost in transmission to Earth, and/or reprocessing of data using different parameters.
The return of the F&P observation continues from previous weeks, and contains the recorded portions of a month-long low-resolution survey of Jupiter’s magnetosphere. The survey will provide scientists with measurements of the plasma, dust, and electric and magnetic fields in the inner and outer regions of Jupiter’s magnetosphere, and in the transition out into the solar wind. In addition, the low-resolution data provide contextual information for high-resolution recordings also made by the F&P instruments during the Ganymede flyby portion of the May encounter.
SSI returns portions of four observations of Io this week. The first captures the Prometheus plume source and active lava flow. The next observation is of Tohil Mons, one Io’s mountains, whose geological structure, origin and history are presently not well known. SSI’s next observation is a color mosaic of the Prometheus volcanic region. Finally, SSI returns portions of a 12-frame mosaic covering the Camaxtli Patera hot spot and nearby regions to the west, including the Chaac Patera region.
NIMS returns parts of two observations. The first is a mosaic of several different volcanic regions on Io. The second also captures different volcanic regions, but focuses on the Prometheus volcanic vent in particular.
