From: Jet Propulsion Laboratory
Posted: Tuesday, August 7, 2001
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 region.
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 Received Time.
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:
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