A time-dependent reliability model for spatial intermittent motion mechanisms via constant-amplitude alternating fatigue load equivalent method

Spatial intermittent motion mechanisms encompass non-continuously operating mechanisms in spacecraft, such as rotary tables, Solar Array Drive Assemblies (SADA), and spaceborne camera focusing mechanisms. Among these, failure assessment proves most complex for long-duration intermittent motion mechanisms due to their nonlinear polymorphic degradation characteristics. This paper proposes a probability-based time-dependent reliability analysis model to quantify the reliability of spaceborne optical detector focusing mechanisms, thereby establishin an analytical methodology for intermittent motion mechanisms subjected to long-term cyclic operations. Through profound deconstruction of reliability dependency chains and influence domain intersections among multiple kinematic pairs, the critical weak links contributing most significantly to system failure and their associated failure modes are identified. A dynamically equivalent approach is introduced, which transforms stochastic loading into equivalent constant-amplitude cyclic fatigue loading. This addresses the challenge in space mechanism reliability analysis where characterizing generalized loading is difficult due to complex operational profiles and the impracticality of acquiring sufficient sample data through extensive ground testing. Accounting for space system non-repairability and operational intervals/durations uncertainties, the model treats strength degradation as cumulative damage from multiple stochastically independent operational cycles. The analysis precision and efficiency are enhanced by implementing double-truncated probability distributions. The paper demonstrates the model’s application through case studies and validates its accuracy, providing benchmark references for engineering applications and revealing underlying mechanisms governing failure evolution.