300 Lessons  

During development of the deployment and latch mechanism , many key challenges were solved. The  following is a list of useful lessons . 

Don’t forget about spring hysteresis   Spring hysteresis is always a concern . Spring manufacturers typically  only provide maximum force and  spring rate. They are unable to provide accurate hysteresis values,  since h ysteresis is highly dependent on  design and resultant friction . Development testing confirmed spring force dropped 10% -  20% after cycling.  Moog planned for spring force hysteresis losses and performed cyclic spring force testing . Moog’s new  latch system compensates for all environmental conditions providing repeatable performance.  

Initial design development needs  to include spring force hysteresis losses in the design. All springs have  hysteresis , so quantification of the hysteresis should be completed before finalization of fabrication of parts .  Early development testing should be performed in flight configuration to determine actual force at final  position.  

Iterate until optimal design is reached   Complex systems like the deployment and latch mechanism need to balance all the requirements . It would  be easy to design a latch with 4 times the force required. There would be no concern of the latch moving   when loaded, but  torque margin requirements could not be met without increasing all other components .  Problem s arise from increased loads, friction  (requires higher motor torque), and weight . Since this is a  space mechanism , the latch is required to have a safety factor greater than three. To address this problem ,  the most critical requirement was determined to be the resultant force on the latch. The latch force was  sized to be only slightly higher  than the worst case resultant force on the latch. This established t he baseline  concept that was the n optimized with the mathematical model . Through the optimization process , we  balanced the latch capabilities to the motor capabilities, creating a more robust design while still maintaining a safety factor in excess of three. Moog’s optimization of the deployment and latching system resulted in a  system that exceeded program requirements.     Determine key requirements and balance the design around these requirements . Iterate until  an optimal  design solution is found.  

Design improvements could change operating scenarios   The NICER mechanism requires  each actuator to have provisions to be overridden by a robot or astronaut’s  tool to return it to a stowed position in case of loss of power, motor failure, etc . Additional requirement s  were flowed down after completion of initial design requir ing incorporation of range limit ing features  to  prevent impact with space station structures . A limit bar and guardrail were incorporated into the design,  this caus ed an issue with the EVA/EVR  implementation . Moog designed a completely new compact clutch  designed t o slip before the actuator limits  were  reached , utilizing Moog extensive space heritage  technology . This also protected the deployment and latch mechanism if the latching actuator was  mistakenly left in the latched position and the deployment actuator EVA/EVR was engaged or the latch  actuator was attempting to latch without the deployment actuator in either the stowed or latched position.    Laying out of all possible s cenarios beyond the typical operating envelope can directly influence the design  requirements . These can include the addition of safety features not only to limit unanticipated problems but  also add to the robustness of the design.  

Manage your requirements   Torque margin is always the basis of design for electromechanical space mechanisms . Inertias, harness  losses, internal losses of the mechanisms, etc. as well as the temperature extrem es that these mechanisms  must  perform in,  all have an effect on torque margins . In the cas e of the NICER program, factors of safety  requirements were higher  at the beginning of the program and dropped at different milestones as the design  moved to finalization. During the Preliminary  Design R eview , the factors were greater than used during the