This Week on Galileo June 4 – 24, 2001
Galileo, the spacecraft, is now settling into a 3-week-long period of
extreme rest, even while Galileo, the flight team, is gearing up in
planning for the next flyby in early August. On Monday, June 4, the
spacecraft enters a period called solar conjunction. Each year there comes
a time when Jupiter, with Galileo in orbit around it, appears to pass
behind the Sun. On Monday, the angle between the Sun and Galileo with Earth
at the apex shrinks to less than 7 degrees. At this point, even in the best
of circumstances, the noise from the solar atmosphere interferes with the
radio signal from Galileo, making reception of the science and engineering
data doubtful. This year in particular, with the Sun reaching the time in
its activity cycle called solar maximum, the interference is particularly
bad, and some of our planned data return has already been lost in the
noise. On Wednesday, June 13, the apparent separation between Galileo and
the Sun as seen from Earth reaches its minimum of a third of a degree.
So for now, the spacecraft systems have been battened down and prepared for
the long dry spell. The routine maintenance activities are complete, the
playback of data from the on-board tape recorder is paused, and the
computer routines that look for regular communications from Earth have been
told not to expect any messages for the duration. There is no increased
risk to the spacecraft during this time, but our inability to see what’s
going on makes us wary of performing any activities.
The sole exceptions to this enforced quiet are for the Extreme Ultraviolet
Spectrometer (EUV) instrument, and passive support of a radio science
experiment. EUV is continuing to look for variations in the Sun’s output by
looking for light reflected off of interplanetary hydrogen gas. This is a
simple task, however, which only involves storing the science data in
buffer areas of computer memory. Radio science investigators in Germany
take this opportunity to study the way the radio signal is affected by its
journey through the Sun’s atmosphere. This provides information about the
structure, content, and dynamics of the gases streaming out from the Sun.
This study relies on the primary radio signal itself, not on the correct
reception of the ones and zeros which are the meat and potatoes of the
remaining science telemetry.
Join us again in late June, when we revive Galileo from its artificial
hibernation, and resume our normal cruise activities.
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: