The Star Scanner is fully described by Fieseler, 2000, The Galileo Star Scanner as an Instrument For Measuring High Energy Electronsin the Jovian Environment, USC MS Thesis [FIESELER2000].
The Galileo spacecraft carries aboard it a photomultiplier tube based star scanner for the purpose of providing the spacecraft with an inertial attitude reference. This device has been subjected to the radiation environment within Jupiter's magnetosphere since 1995 and is providing measurements of the omnidirectional flux of 1.5 to 30 MeV electrons within about 12 Jupiter radii. The range of maximum sensitivity is roughly 4 to 15 MeV. The star scanner is measuring electrons in energy ranges similar to some channels of Galileo's Energetic Particles Detector (EPD) but the star scanner operates continuously thus providing a unique data set when EPD is not operating. The star scanner is generally not sensitive to pitch angle distribution. There is no data prior to the spacecraftreaching Jupiter.
The star scanner provides a single channel of data for measuring electrons termed 'background radiation count' (or sometimes 'raw background') along with other data on the health of the instrument,brightness of stars in the field of view and time.