This Week on Galileo
May 14 - 20, 2001
The Galileo Spacecraft is Preparing for the Callisto Flyby
As Galileo closes in on Callisto, preparations heat up. On Monday, a
standard test of the on-board gyroscopes is performed. These gyroscopes
seem to show the most sensitivity of any of the spacecraft systems to the
accumulated radiation dose that the spacecraft has received over the years.
The test will determine if software parameters related to this sensitivity
need to be updated prior to the flyby.
Following this test a new sequence of commands begins operating the
spacecraft. This sequence updates already planned activities to account for
changes in the availability of ground communication antennas, and to change
telecommunications parameters to account for the effects of solar
conjunction. Solar conjunction is when the spacecraft appears to pass
behind the Sun as seen from Earth. Since the Sun is now near the maximum in
its activity cycle, the noisy and highly dynamic solar atmosphere can wreak
havoc on the radio signal trying to reach Earth. Changing the way the
spacecraft modulates the signal that it transmits improves the chance of
properly receiving and decoding that signal when it finally reaches the ground.
On Thursday, the spacecraft closes to within a distance of 60 Jupiter radii
(4.3 million kilometers, 2.7 million miles) of the giant planet. At this
point the Magnetometer instrument is reconfigured to provide better
sensitivity to measure this portion of the magnetosphere which lies closer
to the planet.
And while all this is going on, playback of previously recorded data
continues. This week we expect to see the conclusion of the calibration
data that was recorded three weeks ago. The last of these data are from the
Solid State Imaging camera, and were pictures taken of the Photometric
Calibration Target plate mounted on the spacecraft. Following the
calibration data, we will pass one final time completely through the tape,
collecting bits and pieces of data that were not properly received the
first time we tried to play them back.