Energen, Inc. has developed actuators based on cryogenic magnetostrictive materials. These actuators are designed to provide precision positioning and active control of adaptive optical surfaces such as those that are being considered for the Next Generation Space Telescope (NGST). The NGST is a large 8-mm diameter segmented reflecting telescope that uses a thin optical surface mounted on a rigid composite backstructure. The mounts consists of multiple actuators that are used to align the mirror segments and actively control the radius of curvature for optimum optical performance. Energen, Inc. has developed several types of actuators. A linear actuator consists of a rod of magnetostrictor surrounded by an electric coil that when energized causes the rod to elongate. These type of actuators are used for high speed active control. Energen also has developed a linear stepper motor that consists of an actuator mounted in two clamps. By operating the clamps and actuator in the proper sequence the actuator indexes forward and backward. Submicron positioning resolution along with strokes of 20 mm are possible. Furthermore, the stepper motor locks into position when powered off--ideal for applications where position must be held for long periods of time.