endurance and analysis. The most important factor that we are communicating here is that the torque and  velocity that is transmitted through stepper motor actuators are typically significantly higher than the load  friction and step-rate velocity requirements. Increasing torque motorization margin will necessarily increase  the torque transmitted through the gearbox, regardless of the magnitude of the load frictional components.  Another key take-away, the Loaded Lifetime can be orders of magnitude less than the operational time,  since stepper motor actuators are not transmitting torque during idle and settled times between steps.  Additionally, if you run through the numbers, you will see that lower gear ratios will reduce T αL at the actuator  output. Doing this will increase your inertia factor and increase the probability of unstable step performance,  as described in Ref. [1].  Reliability Analysis  There are many statistical approaches to calculate the failure rates of components and systems. Many of  which do not adequately assess the failure rates of electro-mechanical systems such as a mechanical. It is  also impractical to manufacture a statistically significant number of units to determine failure rates and  probabilities. The authors believe the approach presented herein is much more appropriate and statistically  valid for mechanisms and components manufactured for the space industry.   Reliability Block Diagram The example in Fig. 1 breaks down the components of an actuator in a Reliability Block Diagram. The motor  may be driven through either the primary or redundant motor winding. Single-string gearbox components  are typical for the industry, as differential gearing adds significant cost, mass and complexity. The output  position may be measured by either the primary or redundant sensor windings. Reliability Block Diagrams  may seem trivial, but it provides a graphic representation of the system configuration and aides in the  determination of potential failure modes and their effects. Also of note in the example that the mechanism  is still functional even with the loss of both resolvers. Step counting or optical performance data may be  used to determine load position.   Figure 1. Reliability Block Diagram  Reliability Analysis of Each Component  The methodologies of the reliability of the components are presented in the 3.3.1 of this paper. The detail  summaries are shown in Appendix A herein. This methodology uses a combination of estimated L 2 life  analysis, combined with classical Weibull reliability statistical analysis. We must first determine the L 2 of the  Mechanical and Electrical components of the actuator. Note: Avior uses L 2 for most space flight hardware  analysis, although mathematically, you will achieve the similar reliability figures for Characteristic Life and  MTBF if you use L 10 values.   Gears and Bearings Structural bending fatigue analysis is conducted on all gears, per AGMA 2001. The analysis is conducted  to determine how many cycles and hours of operation at the mean torque and velocities described in section  3 herein may be achieved. We calculate the L 2 life each of the mechanical gearing elements in the gearbox,  NASA/CP—2018-219887 225