Today on Galileo - September 26-27, 1998
Galileo's latest encounter with Europa continues at much lower activity level this weekend, coming to a close Sunday evening at 7 pm PDT [See Note 1]. Saturday's activities include two observations of Europa and a standard attitude control gyroscope checkout. The checkout is being performed in the encounter to obtain information on time-varying radiation effects on the gyroscopes.
Here on Earth, flight team members are in the process of analyzing a minor anomaly that occurred late Thursday night just after the start of the first observation. The anomaly turned the gyroscopes off, which are needed, among other things, for precision instrument pointing. However, the anomaly is only expected to cause a small degradation of the near-infrared mapping spectrometer data acquired during the encounter. Saturday's gyroscope checkout should also provide engineers with more data to analyze.
Playback of the data stored on the spacecraft's onboard tape recorder during the last couple days is also initiated on Saturday morning, after the final Europa observations have been completed. A remote observation of the Io torus, performed by the ultraviolet and extreme ultraviolet spectrometers, interrupts the transmission of playback data on Sunday. The fields and particles instruments survey of Jupiter's magnetosphere ends on Saturday at 7:00 pm PDT. Dust Detector measurements of small dust particles moving outward from Jupiter will continue until early in the morning on October 1st.
The spacecraft's closest approaches to Jupiter and Callisto for this orbit both occur on Saturday. Jupiter closest approach occurs just prior to 1:30 a.m. PDT at a distance of 8.9 Jupiter Radii (636,000 kilometers, 395,000 miles). Callisto closest approach occurs just prior to 8:30 a.m. PDT at a distance of 1.2 million kilometers (753,000 miles).
Saturday's observing is performed by the photopolarimeter radiometer with an observation looking at Europa's dark side designed to obtain data on the thermal variations across Europa's surface. The near-infrared mapping spectrometer and ultraviolet spectrometer jointly conduct the last Europa observation of the encounter consisting of a global scale observation of the icy moon.
This weekend's playback schedule contains two observations of Europa and three of Jupiter. One Europa observation is returned by the near-infrared mapping spectrometer and will provide data on Europa's surface with a special emphasis on detecting non-ice components. The other Europa observation is returned by the spacecraft camera and captures a global scale image of the moon. All three Jupiter observations capture Jupiter's newly formed white oval. Two observations were taken by the near-infrared mapping spectrometer and one by the spacecraft camera. The white oval in question was formed in Spring 1998, when two other while ovals merged.
Don't forget to come back tomorrow for the return of "This Week on Galileo"!
Note 1. All times listed correspond to the Pacific Time zone (currently daylight saving) and spacecraft event time. Radio signals indicating that an event has occurred on the spacecraft reach the Earth 33 to 50 minutes later, depending on the time of year (currently 33 minutes).