33 Therefore, it was necessary to sacrifice deter minacy in the load path by adding redundant nonconforming contacts for some degrees of restraint (DOR) to meet our minimum stiffness requirements.  

Having a hinge as part of the deployed load path of a precision deployment mechanism adds complexity  and uncertainty. Using a loose hinge pin that contro ls deployment but takes the hinge out of the latched  load path can alleviate the uncertainty while minimizing  complexity. We found this to be the case for the  PM wing latches. However, we found the benefits of this  approach to be application specific and felt that  the SMSS mid-hinge design was better with the hi nge designed as part of the deployed load path. 

In other instances it was difficult to have semi-kin ematic or non-conforming interfaces and the loads  needed to be taken by friction joints. This was the case for the SMSS end-hinges. To compensate, the load capacity (i.e., stick-slip load) of the interface was designed per the recommendation of [1], to be  much greater (e.g., a factor of 10 greater) than t he maximum expected operating load of the mechanism.   In all applications the deployment mechanisms were  located in-line with the primary load carrying  members of the structure and the footprint of the latc hes was maximized to minimize the sensitivity to  instabilities at the latch interfaces. In addition, the stiffness of the latches was maximized by minimizing  their effective length and maximizing the elastic stiff ness with high-modulus materials (e.g., titanium). This  also proved to be beneficial for thermal stability since it  minimized the length of the higher CTE materials.    Distributed preload sy stems were used in  most applications since it was not practical  from a mass and cost standpoint to have an  independent preload device for each latch interface. However, the preload mechanisms  were designed to be much more compliant  than the interface fittings which transfer the operational loads. Providing this compliance  keeps the preload device out of the primary  stiffness path and maintains a relatively constant preload across the interfaces.  

Primary Mirror

The primary mirror deployment and latch mechanisms consist of a pair of hinges and four latches for each wing. The deployment hinges and  wing latches act as independent systems.    Wing Deployment Hinges 

The hinges have a dual function. First, the hinges, along with two launch restraint mechanisms, carry the wing launch loads. Second, they rotate the wings  103 degrees into the capture range of the deployed  wing latches. The wing deployment sequence is shown in Figure 5. Each hinge has a pair of lug and  clevis fittings joined by a loose hinge pin providing  redundant rotating surfaces. The hinge pin has sufficient clearance to the lug and clevis fittings to  preclude it from being in the load path after the  latches have been secured. This guarantees the hinges will not affect deployment repeatability or  generate loads during operation that could cause  micro-dynamic inst abilities at the critical latch  interface.    A stepper gear-motor mounted to the lug of one of  103°  DeployedClevis Fitting  (Titanium)  Lug Fitting (Titanium) Pin   (Nitronic 60)  PinionDriven Gear  (Cut into Lug) StowedStowed hinges carry  launch loads Wing Fold  Angle  200 In-lb stepper   gear-motor  Figure 6. Deployment Hinge Design DetailsLoose pin removes hinge from  deployed stiffness path  Figure 5.  Primary Mirror Wing Deployment  Deploy –Y  Wing Deploy +Y  Wing  Launch  Restraints