Fundamental Technologies

Galileo Spacecraft Pages

Stepping Motor Subsystem

Stepping Motor Subsystem

Source: The Galileo Energetic Particles Detector, D. J. Williams et al., Space Science Reviews, 60, 385, 1992 (excerpts).

The EPD LEMMS and CMS telescopes are mounted on a platform and rotated by a stepper motor contained in the main electronics box. Figure 1-86 shows the stepper motor positions as seen looking down on the top of the EPD along the motor rotation axis.  The combination of the satellite spin and the stepper motor rotation (nominally stepping to the next position after each spacecraft spin) provides 4p steradian coverage of the unit sphere. The 0 deg. 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 deg. ends experience obscuration effects in motor positions 4, 5, and 6 caused by the magnetometer boom and foreground shield.

Figure 1-86. View looking down on EPD along stepper motor rotation axis showing EPD viewing positions. Galileo spin axis direction is parallel to plane of the figure and from right to left. Up to 60 samples per spin for the nominal spin period of 20 s are obtained, giving good angular resolution over the full 4p steradian of the unit sphere.

Next: The Galileo Energetic Particles Detector Scanning System, by D. E. Fort

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Updated 5/4/04, T. Hunt-Ward