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This Week on Galileo
May 7 - 13, 2001 This week sees a modest collection of engineering activities occupy Galileo's attention, in addition to the continuing playback of data from the tape recorder. On Thursday, the spacecraft performs an Orbit Trim Maneuver (OTM), a rocket engine burn used to fine-tune the path of the craft, and line it up for the next flyby of Callisto 15 days later. This is the 94th such maneuver planned for the orbital mission since Galileo first went into orbit around Jupiter in December 1995. Typically, three such engine burns are planned during each orbit. The first comes 3 to 4 days before the planned satellite flyby, and is used to fine tune the placement of the spacecraft at closest approach. The second is usually executed 3 to 4 days after the flyby and is used to clean up any errors seen in the flyby and to begin to shift the spacecraft towards the next encounter. The final maneuver occurs near apojove, the farthest point from Jupiter, when a relatively small expenditure of fuel can effect a relatively large change in postion at the next perijove, or closest point to Jupiter. On long orbits such as this one which has lasted nearly 5 months an additional maneuver is planned 10 to 15 days before the flyby to remove any residual errors in the trajectory. The Thursday OTM is one such additional maneuver. On Friday the spacecraft is turned about 4.5 degrees to keep the communications antenna pointed towards Earth. In addition, standard maintenance is performed on the propulsion system. Even though the propulsion system is used for both the OTM and the turn, any given activity does not necessarily exercise all of the different engine nozzles and valves. These periodic maintenance activities assure the engineers responsible for maintaining the health of the system that each of the parts works correctly, so that they are available when they are needed. The playback of science data consists of the calibration observations recorded two weeks ago. This week the Solid State Imaging (SSI) team expects to see the results of their flat-field calibration, a series of images which were taken of the Photometric Calibration Target (PCT). Its main purposes are to assess the overall response of the camera to a light source of known brightness and spectral properties, as well as to characterize any spatial variation (i.e., variation from one pixel to the next) in sensitivity over the entire area of the CCD. For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page at one of the following URL's: http://galileo.jpl.nasa.gov http://www.jpl.nasa.gov/galileo |
