A NEW SYNCHRONIZATION CONCEPT FOR SOLAR ARRAY DEPLOYMENTS Yannick Baudasse (1), Laurent D'Abrigeon (2), Nicolas Pingault (3) (1) ALCATEL SPACE, 100 Bd du Midi BP99 06156 Cannes La Bocca cedex France, Email: yannick.baudasse@space.alcatel.fr (2) ALCATEL SPACE, 100 Bd du Midi BP99 06156 Cannes La Bocca cedex France, Email: laurent.d-abrigeon@space.alcatel.fr (3) ALCATEL SPACE, 100 Bd du Midi BP99 06156 Cannes La Bocca cedex France, Email: nicolas.pingault@space.alcatel.fr ABSTRACT/RESUME Cosmo SkyMed is an Italian scientific space project involving three satellites, each of them equipped with a two-wing solar array. ALCATEL SPACE is in charge of the development, qualification and delivery of these solar arrays, one particularity of which is the deployment kinematics : each wing is deployed on a 180 angular stroke, but the four-panel stack must unfold during the second half only (i.e. from 90 to 180 ). The deployment concept is based on a cable synchronization device providing several key advantages and allowing a size similar to usual ALCATEL SPACE solar array deployment mechanisms. 1. OVERALL DESCRIPTION With the exception of the synchronization device, the parts and components of the root hinge are derived from the mechanisms used on ALCATEL SPACE Spacebus telecom satellites, and adapted to fit the specific Cosmo SkyMed interface requirements. These include : - the structural brackets, - the electrical motor gear, - the latching device, - the ball joints (for rotation guidance). Synchro Brush Motor Latching The mechanism used to link the Solar Array Wing (SAW) to the spacecraft and perform its deployment is called the Root Hinge. Power harness Interface Connectors VUE DA Solar Array Drive Mechanism ROOTH HINGE Fig.2. Root Hinge Overview Fig.1. Solar Array Overview The root hinge ensures : - the deployment of the whole solar array from the stowed position to the deployed configuration (0 to 180 ), - the locking in deployed configuration, - the wing interface with the solar array drive mechanism.
2. THE NEW SYNCHRONIZATION CONCEPT 2.1 The Synchronization Need In stowed position, all the panels of a wing are stacked. Kinematically, they are linked by means of synchronization cables and pulleys. Fig.3. Stowed SAW Along the first 90 of the deployment, the whole stack of panels shall be rotated. Relative positions of all the synchro cables remain unchanged. Note that the 90 position (see Fig.4) is just an intermediate one, it is not required to keep the SAW in this position. 2.2 The Chosen Concept The selected concept involves a synchronization by cables and specific pulley quarters. Two synchronization cables are installed between the root hinge and the first hinge line of the wing. The driven hinge (on the wing) is equipped with standard pulleys. The driving root hinge features a specific profile which enables cable winding between 90 and 180 deployment. So, while the electrical motor gear rotates continuously, the two-phase deployment sequence is ensured by the cable being clutched in the static specific profile. At the same time, a rotating rod provides a variable lever arm in order to unwind the cable at one end, so that the length of the cable remains constant and the clutching induces no major increase of the cable tension. As a result, cables are respectively wound and unwound with specific lengths calculated to manage : - a null synchronization ratio during the first 90 of the deployment; the wing panels are held in stacked position by the cables, - a 2:1 ratio in the last 90 of deployment, with the synchronization device releasing the springactuated hinges located between the panels of the SAW. See the functional diagram on Fig.7 and the stowed and deployed configurations on Fig.8. 2.3 Key Assets of the Concept Fig.4. SAW after 90 Deployment From 90 to 180, the panels shall be deployed following a 2:1 ratio with respect to the root hinge rotation (total relative angular stroke between two adjacent panels : 180 ). α First, the chosen concept allows a continuous control of the deployment, with reversibility at any point (no specific latch). It avoids mechanical shock at the switching point (i.e. at 90 ) and is compatible with deployments involving alternate motion directions for instance uncontrolled movement of the wing in the case it is not fully damped. In addition, no specific operation is requested for either deployment or folding, making for easy wing deployment tests. Most of all, the design is simple and reliable. It involves no additional motor or mechanical part such as cam or latch of clutch. Consequently, potential problems linked to mobile parts and tribological aspects are minimized. Fig.5. SAW during Deployment 2 nd phase This simplicity also results in lightweightness and compacity : the Cosmo SkyMed root hinge is not significantly bulkier than the standard root hinge used on ALCATEL SPACE Spacebus satellites.
3. THE ROOT HINGE DEVELOPMENT PLAN The first manufactured root hinge was submitted to a Proto-Flight Model test sequence. No Qualification Model was needed. Locking motorization Synchro bracket static test test at 40 C/+75 C (thermal nitrogen) Locking motorization Static test in deployed configuration Locking motorization Fig.6. Proto-Flight Model Root Hinge Test Sequence* * The test sequence presented in Fig.6 is performed at root hinge level. This sequence is completed by vibration tests and SAW deployments at SAW level. This development philosophy is in line with the fact that most of the parts and components of the root hinge are derived from the standard mechanisms used by ALCATEL SPACE on the Spacebus telecom satellites. Compliance with the thermal and mechanical environments specified for the Cosmo SkyMed mission is checked through detailed analyses before submitting the first model to the test sequence. As regards the specific Cosmo SkyMed synchronization device, given the simplicity of the concept the development was essentially based on kinematics analyses and mechanical design optimization. Functional test on the synchro device cannot be performed at root hinge level, since it involves pulleys located on the SAW. Hence a functional mock-up was used to demonstrate the capabilities of the synchronization design at an early stage of the project. See photograph of the synchro mock-up on Fig.9, along with a graph of its potentiometers giving angular values of SAW panels versus root hinge deployment. 4. LESSONS LEARNT Most of the difficulties during the design phase came from the numerous interfaces, some of which were not frozen before we had to work on them. A cautious development philosophy was planning a lot of verifications, but with a simple concept and technologies already mastered by the ALCATEL SPACE teams, the validation stage was reached with no major obstacle. 5. CONCLUSION The six Cosmo SkyMed root hinges are currently in the final stages of manufacturing and testing. The Proto- Flight Model test sequence was performed successfully on the first root hinge, as well as the full test sequence at SAW level. The synchronization principle proved efficient and easy to operate. This concept could be adapted to other multiple deployment with non-linear ratios.
1. Stowed Configuration (0 ) 3. Half turn - The cables are clutched in pulleys quarters (90 ) 180 90 Phase 1 Phase 2 2. First step opening intermediate angle 0 4. Second step intermediate angle α 5. Deployed Configuration (180 ) Fig.7. Synchronization Principle
Stowed Configuration Unwinder arm Arm Stop Winding SAW panel Deployed Configuration Fig.8. Root Hinge Main Configurations
Root Hinge Mock-up 225 Theoretical Measured 180 SAW Panels Relative Angle 135 90 45 0 0 45 90 135 180 225 Root Hinge Deployment Angle Fig.9. Synchronization Device Mock-up