July 15 - August 11, 2002
The Next Four Weeks on Galileo
As the Galileo spacecraft continues its long trek back in towards Jupiter
for its final planned science pass in November, the first two weeks of this
reporting period are occupied by an event called solar conjunction. This
occurs roughly every 13 months as the paths of Jupiter and the spacecraft
have them appear to pass behind the Sun as seen from Earth. Solar
conjunction itself is an instantaneous event, and occurs on Thursday, July
18, at 1:51 p.m. PDT, when the line of sight from Earth to Galileo will
skim a mere 20th of a degree over the visible surface of the Sun. However,
for a period of about 3 weeks centered around that event, the spacecraft is
less than 7 degrees from the Sun and radio interference from the turbulent
solar atmosphere makes communication unreliable. This period will end on
Sunday, July 28, and normal spacecraft activities can resume.
Normally, the spacecraft is placed in a quiescent state during conjunction,
with no activities planned. Recent problems with our on-board tape recorder
have prompted engineers to suggest an alternate strategy. To prevent the
tape from sticking to the record heads, we now have the recorder
continuously moving slowly up and down the entire length of the tape in
small steps, traversing all four tracks of tape about every 36 hours. This
action should condition the tape, making it less likely to stick when we
start to move longer distances and at higher speeds. The current motion
will continue until early Tuesday morning, July 30, clearing the way for a
more aggressive series of tests of the recorder.
On Friday, August 2, the next series of tape recorder tests will begin.
During the conjunction test, it took 29 small steps to move from one end of
the tape to the other. These new tests will increase our stride so that it
only takes six steps to move the length of the tape. Five days later, on
Tuesday, August 6, we pick up the pace again, and will span the tape in
only two steps, a pace we will maintain until Monday, August 12. Subsequent
tests are being planned that will increase the speed with which we traverse
the tape, to gain confidence that we can again use the recorder freely, as
we have planned for the Amalthea flyby in November.
On Tuesday, July 30, routine maintenance of the propulsion system is
performed. On Thursday, August 1, the spacecraft is turned in place by 4
degrees to keep the communications antenna pointed towards Earth.
The spacecraft is still well outside the magnetosphere of Jupiter on the
sunward side of the planet, and continuous data collection by the
Magnetometer, the Dust Detector, and the Extreme Ultraviolet Spectrometer
instruments provides scientists with information about the interplanetary