Today on Galileo
Sunday, May 2, 1999
Galileo starts the ninth encounter of the Galileo Europa Mission today, and with it, also starts a series of four close flybys of Callisto. These Callisto flybys are also called the Perijove Reduction Campaign, and are designed to incrementally change the spacecraft's orbit to allow for a close flyby of the innermost Galilean satellite, Io. In addition to the trajectory-altering objective, these four orbits also present extensive science opportunities. These opportunities include monitoring volcanic activity on Io, exploration of the Io plasma torus, observations of Callisto, and observations of Jupiter's atmosphere and magnetosphere.
During the Perijove Reduction Campaign, the spacecraft's Perijove distance, or closest distance to Jupiter for a given orbit, will be changed from its current distance at about the orbit of Europa (9 Jupiter radii, 643,000 kilometers, or 400,000 miles) to a distance that allows Galileo to fly within the orbit of Io (5.5 Jupiter radii, 393,000 kilometers, or 244,000 miles). With this reduction in the distance from Jupiter also comes an increase in the amount of radiation to which the spacecraft will be exposed. Flight team members will be closely monitoring spacecraft performance during the upcoming months to diagnose and mitigate any radiation effects the spacecraft might exhibit.
This week's encounter spans the next six days, ending on Friday, May 7. During this time, the spacecraft will be approximately 880 million kilometers (548 million miles) from Earth, and it will take Galileo's radio signals 49 minutes to travel between the spacecraft and Earth. This orbit's close flyby of Callisto occurs on Wednesday, May 5, just prior to 7 am PDT [see note 1], at a distance of 1315 kilometers (817 miles). Today's flyby schedule calls for a distant flyby of Io, at 12:52 PDT and a distance of 780,000 kilometers (485,000 miles).
With the start of the encounter comes the resumption of the magnetospheric survey performed every orbit by the Fields and Particles instruments. During this survey, the instruments sample the inner portions of Jupiter's magnetosphere, allowing scientists to study the long term variations in the plasma, dust, and electric and magnetic fields that comprise it. The survey is scheduled to continue through Wednesday.
The remote sensing observation schedule starts with an observation of Io performed by the Near-Infrared Mapping Spectrometer. The observation is designed to provide information on the surface composition of the Prometheus volcano region. Later in the day, the spacecraft camera, or Solid-State Imaging subsystem, the Near-Infrared Mapping Spectrometer, and Utraviolet Spectrometer take a look at Europa while it is in Jupiter's shadow. The observations are designed to detect atmospheric emissions, best seen in the dark, that could be an indication of geologic surface activity.
The observations then focus on Jupiter. In two observations, the Photopolarimeter Radiometer makes observations of Jupiter's clouds, looking for small temperature variations within cloud bands. Finally, the Near-Infrared Mapping Spectrometer performs a series of observations that have been repeated every orbit and are designed to detect long term, global variations in the composition and temperature of Jupiter's clouds.
Note 1. All times listed correspond to the Pacific Time zone (currently daylight time) and spacecraft event time. Radio signals indicating that an event has occurred on the spacecraft reach the Earth 33 to 50 minutes later, depending on the time of year. Currently, Pacific Daylight Time (PDT) is 7 hours behind Greenwich Meridian Time (GMT), and it takes radio signals 49 minutes to travel between the spacecraft and Earth.
For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page.
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