34 the two deployment hinges is used to rotate the wi ng from the stowed to the deployed position. The gearmotor drives the clevis fitting through spur gears that  provide a 4/1 gear ratio over the motors 22.5 Nm  (200 in-lb) output torque capability for roughly 90 Nm (800 in-lb) of available deployment torque. The  hinge fittings are machined out of titanium and the hi nge pins are Nitronic 60 to prevent galling. The bolt  hole pattern on the titanium fittings has a single pi nned hole along with oversized and slotted holes to  allow the fittings to shrink with respect to the near zero CTE composite backplane structure. MoS 2 dry film  lubricant is used on the hinge gears, hinge pins, and the spacers between the lug and clevis ears. The  details of the hinge design are shown in Figure 6. 

Wing Latches   The latches have a singular role and are not in the l oad path during launch. Their function is to align and  secure the deployed backplane wings to the backplane center section, thus cr eating the stable backplane  structure that supports the 36 primary mirror segments . The driving requirements for the wing latch design  were deployment repeatability, deployed stiffness (t o meet LOS and WFE jitter requirements), thermal  stability and micro dynamic stability.    We believed the best way to achieve good wing  deployment repeatability was to use a kinematic interface with fittings specific to the six degrees of restraint (DOR).  The six DOR are implemented at three locations across the  interface between each wing and the backplane center section.  At the first location a 3-DOR latch set provides a  sphere-in-cup interface that locates the wing in the two in-plane directions and provides one of the three points that defines the interface plane. The second location holds a 2DOR latch set that provides a sphere in groove interface  that fixes the rotation about the first fitting set and  establishes the second point of the interface plane. The  third location holds a 1-DOR latch set that is a sphere on a flat and is the final point needed to define the  latch interface plane. The latches are shown in Figure 7. They are lubricated with MoS 2 for low friction  between the mating pairs and to prevent cold welding, and a 2669-N (60-lb) preload is used to drive the  fittings into the same determinate position each time.  

Because the wing to center section is long and slender , it wasn’t possible to provide the deployed wing  natural frequency required for LOS and WFE jitter with just three fitting sets. Therefore, five adjustable  non-conforming 1-DOR (A1 Fittings) sets were added and c onfigured in pairs as shown in Figure 8 with a  cryogenic preload device centered between each pair. The pairs of fittings were located as far apart as  possible using the entire depth of the backplane to prov ide the largest footprint and most efficient stiffness  path. 

The latch sets, shown in Figure 7, are Ti 6Al-4V ELI. More exotic, lower coefficient of thermal expansion  (CTE) materials such as silicon carbide were considered for the latch materials. However, these materials  would have been very costly. By keeping the cross sect ions of the latches thin, this common, robust  metallic could be used while maintainin g overall thermal distortions to we ll within the allocation. The final  latch design was 12.7-mm (0.5”) thick (shown in Figure 9).   To eliminate loads at the latch interface due to thermal cool-down, cryogenic preload devices are  engaged and only lightly loaded during the initial deploy ment. Then, after the OTE has cooled to its final  operating temperature, the devices are backed off to remo ve any stresses in the system. Finally, the latch  sets are preloaded again to their flight operational levels.   To keep the Hertzian stresses low on the titanium latch sets with a 2669-N (600-lbf) preload, a 100-mm  (~4”) radius was required on the spherical half of the set. This was easy to accomplish with the 1-DOR  latch set that consisted of a spherical fitting interfacing with a flat. It was slightly more difficult for the 2DOR and 3-DOR latch sets since it was desirable for the spherical surfaces to interface with flats at a 45°

angle to provide similar stabilizing forces in the ax ial and transverse directions. The limits of 12.7 mm  Figure 7.  Latch Sets 3 DOR 2D O R 1 DOR