A Sun gate for Galileo spacecraft attitude control

The combination of a Sun sensor called a Sun gate (SG) and a digital programmable signal processor on the Galileo spacecraft attitude and articulation control subsystem (AACS) will orient the rotation axis of the spacecraft toward the Sun to satisfy a new requirement imposed by the new spacecraft trajectory. The combination will continuously monitor the pointing direction of the rotation axis, and any off-Sun excursions of more than a preset threshold will be detected, triggering appropriate actions by the flight software to prevent off-Sun cone angles of more than 14 degrees . The design of the SG is described in detail, its principle of operation is given, and the flight software processing of the SG output is discussed.<
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