This Week On Galileo - June 29- July 5, 1998
This week Galileo's processing and transmission of pictures and science information to Earth continues, but is interrupted to perform important engineering tasks.
On Tuesday, the spacecraft will perform a gyroscope performance test. The test will provide information that will allow engineers here on Earth to determine whether performance of the gyroscope continues to degrade. The gyroscope, one of two on the spacecraft, has been producing anomalous data since December 1997. Since March 1998, a modification to the software used by the attitude control computer has allowed correct interpretation of the gyroscope data. If the data from this test shows that the gyroscope performance has changed, engineers may decide to make minor adjustments to parameters in the modified attitude control software.
The other engineering activities for this week are performed on Wednesday. Data processing is interrupted to perform regular maintenance on the spacecraft's propulsion system, and to turn the spacecraft to keep the radio antenna pointed toward Earth.
This week's data return activity begins with the retrieval of data from a section of the onboard tape recorder that has already been accessed once during this orbit. This second processing and transmission opportunity allows the Galileo project team to fill in data gaps, select entirely new data, or re-process data with different parameters.
On this week's data return schedule, the near infrared spectrometer returns two observations. Both of the observations cover the Pele, Marduk and Reiden regions of Jupiter's fiery moon Io. Observations of these regions are also planned for late 1999 when the spacecraft is scheduled, if healthy, for two close flybys of Io.
The spacecraft's camera returns the other three observations scheduled this week. One is another moderate-resolution image taken near Europa's terminator. The other is a photometry observation of a region observed in April 1997 during Galileo's primary mission. The photometric data will provide information about how intensely light is reflected from Europa's surface. This will provide scientists with clues for identifying the surface materials found in the region. Finally, the camera returns an image of the Cilix region of Europa. In low resolution Voyager images, Cilix appeared to be an impact crater. Images obtained during Galileo's first orbit caused scientists to think that the feature was instead a large mound. The data recently returned during the first pass through the data stored on the tape recorder have settled the issue: Cilix is, in fact, an impact crater. The last of this observation will be returned in this second pass.