This Week on Galileo
October 22-28, 2001
The Conclusion of the Io 32 Encounter
The sequence of commands that governed the spacecraft activities during
last Monday's flyby of Io is still in control, winding down in its closing
days. Data are still being collected and added to the tape recorder.
Playback of this encounter's data does not begin until near the end of the
Most of Monday was set aside as a backup opportunity to execute the
post-encounter maneuver which occurred last Friday. However, the Navigation
Team did such a great job of delivering the Galileo spacecraft to the
desired location and time for the Io flyby that the need for a potentially
large maneuver was reduced to a mere shadow of its possible self, and the
Friday activity did the job quite well. We hit the mark on where and when
we wanted to be at Io to within 3.5 kilometers (2.1 miles) of the expected
181 kilometers (112 miles) from the surface of the volcanic satellite, and
got there only 0.7 seconds late!
From Monday through Thursday, the spacecraft is occupied with the
continuous collection of real-time data about the energetic particles and
electromagnetic fields that surround Jupiter. The instruments participating
in this data collection are the Dust Detector Subsystem, the Energetic
Particle Detector, the Heavy Ion Counter, the Magnetometer, the Plasma
Subsystem, and the Plasma Wave Subsystem. When complete, this data set will
span 12 days and cover the region from the Io torus to the bow shock
region, where the solar wind begins to win its constant struggle with
Jupiter's magnetic field. Whenever ground communications antennas are not
scheduled to listen to Galileo, the data are stored in on-board computer
memory and periodically dumped onto the tape recorder for later playback.
Two aspects of this continuous data collection are important to scientists.
First, the time continuity of the data provides the scientists with a good
look at how the environment is constantly changing and evolving. Second,
the spatial continuity gives the scientists a picture of the large-scale
structure of the environment, as Galileo passes from the distant reaches of
the Jupiter system down through the close-in, high-radiation environment,
and back out the other side.
But all good things must come to an end, and on Thursday, this data survey
ends for all but the Magnetometer and the Dust Detector, which continue to
collect data for another three days. When the bits are no longer devoted to
the real-time data, the spacecraft can look to the tape recorder and begin
sending its data to the eager flight team here on Earth.
The first priority in the playback data is to sample all of the images
captured by the Solid State Imaging camera (SSI) over the past week. During
recent orbits, radiation-induced problems in the camera have rendered many
of the pictures unusable. A recent change to the spacecraft's computer
software appears to have kept the problem from recurring during this flyby.
We won't be certain until the spacecraft completes a first pass through the
tape, returning some imaging data from each recorded frame. The second pass
through the recorded data should begin late Sunday or early Monday, and
will start returning the full set of data from all of the instruments.
On Friday, routine maintenance of the spacecraft propulsion system is