Development of a High Resolution Rotary Actuator for an   Antenna Trimming Mechanism  Jérôme Brossier*, Xavier Jeandot*, Yannick Baudasse*, David Grima* and Fabrice Champandard*  Abstract  The High Resolution Rotary Actuator (HR/g1A) product is one of the main components of the Antenna  Trimming System (ATS) developed for a commercial satellite. The mechanism needs to deploy and point  the reflector around two axes and is composed of two HR/g1A in a gimballed configuration. It operates in a  closed loop system using an RF beacon on the ground. This assembly is called MADPM, Multimedia Antenna Deployment and Pointing Mechanism. These mechanisms are located between the spacecraft  structure and the reflector. The positions and orientations of these mechanisms on the spacecraft result  from an architecture layout analysis, dealing with deployment and pointing objectives. The HR/g1A mechanism is developed to be able to steer a large reflector along a wide deployment angle (up to 180°  with steps of 0.02°), to point it with a small output resolution (0.002° each step) and to perform a large  number of micro cycles. The mechanism is qualified and 6 flight models have been built in parallel of the  qualification and are now assembled on the spacecraft.  Introduction  Initially, system engineers required that the mechanism shall be able to perform a high and not well  defined number and type of cycles. The first choices of technology were therefore based on this main  requirement. This requirement disqualifies automatically all the links with tribological contact. After more  work with system engineers and in order to be able to qualify this type of product, the number and types  of cycle were determined for the generic Thales Alenia Space platform. It appeared that the need still  required a technology and design with no risk with regard to the life time. Moreover, the mechanism will  have to be able to deploy the reflectors up to 180° of motion. Aiming at reducing the number of actuators,  we decided to use the same actuator for deployment and for pointing. The background of Thales Alenia  Space mechanism product line with very large number of cycles led us to use the heritage of the Scan  Drive Unit Actuator. The Scan Drive Unit actuator is a part of the SEVIRI instrument of METEOSAT  Second Generation spacecraft and has been fully developed by Thales Alenia Space. This mechanism is  a linear actuator constituted mainly by a stepper motor, a spindle, ball bearings and potentiometer. The  peculiarity of this mechanism is to be fully sealed and filled with oil. As a rotational movement is required  to deploy a reflector, it was necessary to have another mechanism able to transform a linear movement  into a rotational movement without risk with regards to life time. It is in this framework that the HR/g1A has  been successfully developed by Thales Alenia Space.  Mechanism Description  The High Resolution Rotary Actuators is made of different components based on several innovative  ideas.  /g2 A high life time capability linear drive unit.  /g2 A high life time capability reducer, that realizes, with the same linear kinematic input, a large  amplitude rotating movement (deployment), following by a small amplitude rotational movement,  with a high accuracy (fine pointing).   /g2 A specific guiding (and crossing) system, with flexible blades, that provides stiffness and loads  capabilities.                                                  * Thales Alenia Space, Cannes, France  Proceedings of the 39th Aerospace Mechanisms Symposium, NASA Marshall Space Flight Center, May 7-9, 2008  15