This Week On Galileo - April 27 - May 3, 1998
Many different activities are on Galileo's to-do list this week as the spacecraft passes through apojove (the furthest distance from Jupiter for each orbit) and starts heading back toward Jupiter again. Processing and transmission to Earth of science information, also known as playback, continues throughout the week. Included on this week's schedule is data from Europa, Ganymede, Io and Callisto. Playback of data stored on the onboard tape recorder is interrupted several times this week to perform important navigation and engineering activities.
On this week's playback schedule, we find information collected by the spacecraft's camera, or solid-state imaging subsystem (SSI), the near infrared mapping spectrometer (NIMS) and the photopolarimeter radiometer (PPR). Europa information that is retrieved this week includes data on the materials, obtained by NIMS, and temperatures, obtained by PPR, that are found on its surface. Global views of Europa, by SSI and NIMS, are also processed and transmitted to Earth.
A global view of Ganymede obtained by SSI is returned to Earth this week. The image is expected to provide more information on the radius, shape, color and photometry of the satellite. Remember that photometry is the measurement of light intensity and it helps to identify different materials. The image is also expected to tell scientists whether frost on the surface of Ganymede is mobile enough to be noticed at a global scale. SSI also returns an image of Io obtained while in eclipse. Due to the lack of sunlight, these types of images have proven to be the best way to discover and monitor lava temperatures and interactions of plumes from Io with Io's atmosphere and Jupiter's magnetic and electric field environment. Finally, NIMS returns a global map of Callisto. Together with an observation planned for May 1999, the information gathered from this observation is expected to shed some light on open questions regarding differences in materials found in different regions of Callisto.
Engineering and navigation activities are initiated this week when the spacecraft performs regular maintenance on its onboard tape recorder. On Thursday, the spacecraft will perform a flight path correction in preparation for its next encounters with Europa and Jupiter in late May. Regular maintenance of the spacecraft's propulsion system is performed on Friday. And on Sunday, the flight team will transmit commands to the spacecraft to change onboard attitude control software. The changes to the software will allow the attitude control computer to, on its own, interpret the anomalous behavior of the gyroscopes. Back here on Earth, the behavior of the gyroscopes will continue to be monitored and updates to the onboard software will be made as required.