Today on Galileo
Tuesday through Thursday, August 7-9, 2001
The Conclusion of the Io 31 Encounter
The pace has truly slowed down, now, as the Flight Team heaves a sigh of
relief at the successful encounter. But there are still a few choice
science observation opportunities to take advantage of. On Tuesday, at 6:43
a.m. PDT [See Note 1], the Solid State Imaging camera (SSI) takes a 3-color
picture of the face of Io which perpetually faces Jupiter, looking for
recent volcanic activity.
Then at 7:39 a.m. PDT, SSI looks at Jupiter for over two hours, taking 13
pictures, mostly through a green filter, of an area just north of the
equator. By watching the same area of clouds over time, scientists can
measure the propagation speed of mesoscale, or medium-scale, waves in the
visible clouds. The motions of these clouds provides a probe into what is
occurring in the underlying layers of the atmosphere. The wavelength and
speed of these waves give information about the thermal stratification of
the atmosphere, and about wind shear at depth, which affect the meteorology
at the cloud-top levels.
At 10:17 a.m. PDT the instruments that measure the electromagnetic fields
and particles of the Jovian environment end their period of continuous data
collection, which began 59 hours ago, on Saturday.
At 1:50 p.m. PDT, a routine test of the on-board gyroscopes is performed.
These gyros have shown a great sensitivity to the high radiation
environment through which we fly. This test will determine if the software
scale factors that are used to interpret the signals provided to the
spacecraft's attitude control software will need to be updated prior to our
next required use of the gyros.
Wednesday morning, at 2:20 a.m. PDT, the Near Infrared Mapping Spectrometer
(NIMS) again looks at the area trailing the Great Red Spot in Jupiter's
atmosphere, looking at cloud dynamics and compositional variation in the
At 3:26 a.m. PDT, SSI takes one last look at Io, a 3-color picture of the
face of the satellite which forever faces away from Jupiter. This picture
will also capture the Tvashtar volcano, arguably our most exciting target
for this flyby. This is our last recorded observation for this orbit,
because at 1:48 p.m. PDT, we begin playing back all of the data that we
have stored on the tape recorder over the last 4 days.
As we begin playing the data back, we are also using the large 70-meter
(230 foot) diameter communications antenna near Canberra in Australia to
send up the next series of commands that will govern the Galileo
spacecraft's activities for the next two months of cruise. On Friday at
2:55 p.m. PDT, the scepter of control is passed to this new set of
commands, and we bid a fond (and tired!) farewell to the Io encounter.
Note 1. Pacific Daylight Time (PDT) is 7 hours behind Greenwich Mean Time
(GMT). The time when an event occurs at the spacecraft is known as
Spacecraft Event Time (SCET). The time at which radio signals reach Earth
indicating that an event has occurred is known as Earth Received Time
(ERT). Currently, it takes Galileo's radio signals 49 minutes to travel
between the spacecraft and Earth. All times quoted above are in Earth