Today on Galileo
August 9-11, 1999
Prior to the start of the encounter, the spacecraft completes playback of data stored on its onboard tape recorder during its July encounter with the Jupiter system. Two observations are on the playback schedule. The first contains measurements of plasma and magnetic and electric fields within the Io torus obtained by the Fields and Particles instruments. The second is an observation of Io performed by the Solid-State Imaging camera. In it the camera captures a view of Io at a resolution of 2.6 kilometers (1.6 miles) per picture element. After playback has been completed, the spacecraft performs standard maintenance on its onboard tape recorder. Finally, on Wednesday, just prior to the start of the encounter, the spacecraft executes a flight path correction to ensure a successful close flyby of Callisto.
Encounter commands begin to execute on Wednesday at 7:00 am PDT [see Note 1], and span the next 3-1/2 days, ending Saturday afternoon, August 14. During this time, the spacecraft is approximately 688 million kilometers (428 million miles) from Earth. It will take radio signals just over 38 minutes to travel between the spacecraft and Earth.
The close flyby of Callisto occurs on Saturday, August 14, at about 1:31 am PDT at a distance of 2296 kilometers (1427 miles) above Callisto's surface. As a result of the flyby, the spacecraft's Perijove distance, or closest distance to Jupiter for a given orbit, will be changed from 7.3 Jupiter radii (523,000 kilometers, 325,000 miles) during this encounter to 6.5 Jupiter radii (465,000 kilometers, 289,000 miles) at Galileo's next encounter in mid-September. The change in Perijove distance is not seen until Galileo's next encounter because the Callisto flyby occurs after this encounter's Perijove passage. On Wednesday, the spacecraft flies through closest approach to Io. The distant flyby occurs at 7:42 am PDT at a distance of 730,000 kilometers (454,000 miles).
With the start of the encounter comes the resumption of the magnetospheric survey performed by the Fields and Particles Instruments. The Fields and Particles Instruments are comprised of the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Detector, and Plasma Wave Instrument. During the survey, the instruments take measurements of plasma, dust, and electric and magnetic fields. These measurements have been repeated from encounter to encounter and will allow scientists to study the long term variations within the inner portions of Jupiter's magnetosphere.
The Near-Infrared Mapping Spectrometer makes six observations on Wednesday. Five observations are directed towards Jupiter's atmosphere, while one focuses on Io. The observation of Io will allow scientists to track volcanic activity on Io's surface. Two of the Jupiter observations are designed to allow scientists to study changes in atmosphere composition and temperature over time. The remaining three observations are for the study of similar changes near one of Jupiter's hot spots. These data will allow scientists to continue their work on Jupiter's atmospheric structure, such as cloud heights and densities, and particle sizes and distributions.
The Photopolarimeter Radiometer is the remaining participant in Wednesday's observing. Three observations, all of Jupiter's atmosphere, are designed to provide measurements of small temperature variations within small regions of Jupiter's atmosphere.
More encounter news tomorrow with the return of Today on Galileo!
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 38 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.
Return to Project Galileo Homepage
| Comments and suggestions about this website may be directed to gllbug@jplpio.jpl.nasa.gov Last updated: August 9, 1999 |
 |