are placed back-to-back and welded together at both the inside and outside edges. Custom 316L  stainless steel mounting flanges are then welded to each end of the bellows. The spring rate of the completed bellows is 670 N/m (3.8 lbf/in) and it has a rated cycle life of 100,000 cycles. Initially, there was a concern that the bellows might sag, buckle or squirm during the deploy/stow cycles and thereby  interfere with the ball screw. The buckling and squirming issues were eliminated by venting the bellows(the bellows does not need to hold a vacuum or pressure). The bellows has only minimal sag in the deployed state such that the inside of the bellows does not touch the shaft of the ball screw at any time during the deployment.  Stow Over-Travel Gage During the stow operation, the actuator must drive the mast down so that the 3X kinematic veespherolinder-cones are in flush contact with each other (see Figure 8). Only at that point can the restraint  bolts be torqued for launch configuration. An over-travel gage has been designed into the system to avoid over driving the ball nut once nominal kinematic engagement has been reached. This gage includes a stiff  linear spring [2,600 N/mm (15,000 lbf/in)] attached to the end of the ball screw shaft along with a simple  aluminum gage mounted to the top of the spring as shown in Figure 7. The nominal gap between the  aluminum gage and the yoke base is 1 mm (.04 in). If the ball nut is driven past nominal engagement, this  gap will decrease. Monitoring this gap during the stowing operation is essential to avoid over-driving the  ball nut. Hard Stop The deployed hard stop is used to avoid damaging the ball nut/screw in the unlikely event that both endof-travel position sensors fail during deployment. The hard stop uses a radial face-to-face design that is  non-jamming and minimizes stress on the ball screw. During the initial build of the Deployment Mechanism, the hard stop was positioned onto the ball screw such that it engaged with a stop tab on the ball nut at a position slightly beyond the nominal deployed position. In this nominal position the stop tower  compression spring is displaced by 2.54 mm (.100 in). The hard stop engages when the stop tower  compression spring is displaced by 3.18 mm (.125 in). During normal  operation, the end-of-travel will be  reached before the hard stop will engage. Figure 9 shows the hard  stop when it is engaged. After the hard stop was correctly positioned,  the ball screw was removed from the assembly and the hard stop was match drilled to it. During this  operation the threads of the ball screw were completely covered to  prevent contamination. A screw  and a dowel pin were used to fasten the two pieces together. The ball screw and hard stop werethen reassembled into the  mechanism after the match drilling operation. Yoke to Mast Interface The titanium yoke is attached to the aluminum mast via two radial ball bearings that fit into pockets machined into the side of the mast as shown in Figure 11. A titanium ring is placed around each 440C ball bearing to prevent damaging the ball bearings during cold survival due to the CTE mismatch between  the aluminum mast and 440C bearing rings. Each yoke arm has a single blade flexure machined into it to  allow for some compliance in the system. Figure 9. Deployed Hard Stop 443