Fundamental Technologies

Galileo Spacecraft Pages

Galileo Energetic Particles Detector

Space Science Reviews Article: Schematic View of EPD

Schematic showing the EPD telescope heads, the overall EPD configuration, the EPD stepper motor rotation axis, and the Galileo spin axis direction.

The detector heads are mounted on a platform and rotated by a stepper motor contained in the main electronics box. The stepper motor positions as seen looking down onto the top of the EPD along the motor rotation axis can be seen in the figure below

View looking down EPD along stepper motor rotation axis showing EPD viewing positions. Galileo spin axis direction is parallel to plane of figure and from right to left. Up to 60 samples per spin for the nominal spin period of 20s are obtained, giving good angular resolution over the full 4pi steradian of the unit sphere.

The combination of the satellite spin and the stepper motor rotation (nominally stepping to the next position after each spacecraft spin) provides 4pi steradian coverage of the unit sphere. The zero degree ends of the two telescopes have a clear field of view over the unit sphere and also can be positioned behind a foreground shield/source holder for background measurements and in-flight calibrations. The 180 degree ends experience obscuration effects in motor positions 4, 5 and 6 caused by the magnetometer boom and foreground shield.

The primary elements of the system are the LEMMS/CMS detector heads with their analog electronics, the motorized scanning system, the digital support electronics, and the data system. The following figure shows a functional block diagram of the EPD.

EPD functional block diagram.

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Updated 10/18/02, T. Hunt-Ward