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The term actuator refers to a control motor, and the term is commonly used for telescopes to refer to such devices that physically position the telescope or parts of it. A motor to keep the telescope pointed at an object (as Earth rotates) can go by that name. In large astronomical telescopes, smaller actuators may be used to align segmented mirrors to act as a single mirror or to position parts of an adaptive optics system. For a space telescope, the actuators may be positioning the attitude of the entire spacecraft.