Today on Galileo - December 20, 1996
Today on Galileo, we find the spacecraft still pointed such that high solar phase angle observations of the selected hot spot on Jupiter are possible. This morning's observations, the last of the hot spot observations for this orbit, include UVS, NIMS, PPR and SSI. Also during the morning, SSI performs the last Io monitoring observation of this encounter.
Closest approach to Callisto occurs today at about 6 a.m. PST. At a distance of close to 1.5 million kilometers, only the NIMS instrument takes the opportunity to observe Callisto. In a single global observation, the NIMS observation is expected to provide data required at specific latitudes to help answer some questions raised during observations of Callisto from Earth. In addition, the observation will provide NIMS with information that will allow them to select which wavelengths are of interest for future observations.
Around mid-day, just prior to turning the spacecraft so that it will be pointing back at the Earth, NIMS performs the only ring observation of this encounter. This observation is performed at a distance of 100,000 kilometers and is designed to determine how big individual particles in the ring are and what they are made of. A resolution of 800 km per nimsel (NIMS pixel) is expected.
After the spacecraft turn, Galileo turns its attention toward trying to solve the anomaly with the PPR instrument. In an attempt free PPR's filter wheel, the instrument will be left to cool to very low temperatures and then warmed back up to normal operating temperature over the course of the next day. It is hoped that this thermal cycle will cause the different parts in the PPR instrument to shrink and expand enough to free the filter wheel.
Toward the end of the day, flight team members will send the first part of the cruise sequence of commands to the spacecraft. This set of commands will begin to execute at the end of the encounter sequence on Sunday morning and will take the spacecraft through the first few days of February.
The last activity of the day is an observation of the minor moon Himalia performed by the UVS instrument. This observation will be used to supplement and complement NIMS surface property measurements.