304 History  

Original design   The hinge design was originally built to deploy a large membrane supported by a light weight frame. This  hinge was developed using engineering units to understand the operation of the hinge, and after  development, the prototype or qualification unit was built to demonstrate design margin. The qualification  test program included Torque O utput testing, Thermal Vacuum testing, Thermal Cycle testing, Vibration  testing, Acoustic testing, as well as Life Cyc le testing  The lessons learned from the qualification unit were  used to improve the  processing of the flight units, which resulted in significant savings because multiple  units were built for each shipset . Several shipsets  have been flown and successfully deployed on- orbit.  

Second- Generation Design   When a new application was identified on a different spacecraft, the hinges were redesigned to deploy a  panel -mounted membrane rather than the frame- mounted membrane. The hinge  design was revised to be  more modular and the test program was designed to minimize the manufacturing and test costs while  maintaining the technical integrity of the hinge. While this iteration on the design was later determined to  not be required for the mission, the proposed design changes are discussed,  based on the lessons learned  and the proposed benefits.  

Design  

Original design   The hi nge design is a carpenters tape or lenticular strut hinge. To increase the torque output without  increasing the maximum strain there are a total of four tape spring elements, two in each orie ntation . The  orientation of the tape springs was chosen to be in the convex orientation. The convex configuration allows for good control when flattening the hinge during stowin g, as shown in Figure 2, as the two edges can easily  be pinched during the stow  operation . The material selected was chosen for the stiffness and strain rate.  The hinges shown are painted black for thermal control.    The radius  of the spring cross section in the free state is  R 1. The stowed radius R 2 is 80% of R 1 on the  inside of hinge. Our investigation into the design suggest s that these two radii sho uld be the same, however  the installation required a smaller stowed radius  than the spring cross section radius . 

One effect this has is  that the hinge,  with a stow ed radius smaller than the cross section radius , will not just  rotate when released. When released, the hinge will rotate, but the stowed radius will expand until it is  approximately the cross section radius . This effectively causes some unintended translation motion at the  release point.  

Sliding interfaces were examined at the attachment of the tape spring to the fitting, but the final design  clamps all four tape spring elements  and prevents any sliding at the ends of tape springs . While sliding  interfaces were examined, these tended to move around more than desirable. Additionally, keeping the  ends clamped means the ends are electrically bonded, which is ideal for ESD and other electrical grounding  requirements . Structurally joining all four spring ends does create some non- linearity in the deployment  torque as the outside tape spring constrains the interior elements and causes a secondary buckle shown  in Figure 3. The secondary buckle wasn't detrimental  to the hinge torque output , but is probably the source  of some small nonlinearities in the torque output, discussed later and shown in Figure 10.   The stowed radius , R 2, is formed by the p lacement of the hinge support  and the end fittings in the assembly .  The support controls the stowed radius of the hinge and also prevents "rolling" of the stowed hinge . This  "rolling" is  where the center of the radius moves without any rotation , and because there is no net change  in the total curvature of the spring elements, there is almost no resistance to this motion without the support .  Without this  support,  the stowed hinge would hav e almost no structural stability . The hinge support and  rolling direction are shown in Figure 3.