A D‐Optimal Design for Dual‐Stress Accelerated Degradation Testing of Space Traveling Wave Tube Cathodes

The reliability of space traveling wave tubes (TWTs) depends critically on the performance of their thermionic cathodes under combined temperature and current stress. Conventional accelerated test methods, which vary a single stress or use full‐factorial designs, are often inefficient or impractical for assessing the complex coupling between the two stresses. This study presents an optimized framework for dual‐stress accelerated degradation testing, integrating failure physics with the D‐optimal criterion under four engineering constraints, such as non‐axis point, anchor point, temperature coverage, and maximum current stress. The resulting L‐shaped four‐point design, consisting of (1100°C, 2.5 A/cm 2 ), (1100°C, 0.7 A/cm 2 ), (1020°C, 2.5 A/cm 2 ), and (1060°C, 1.5 A/cm 2 ), achieves a high intrinsic D‐efficiency of 0.945 with only four test runs, realizing clear separation of main effects and efficient coupling effect identification. Compared with full‐factorial designs, the design reduces the maximum test duration by over 75% while fully retaining the capability to quantify the temperature‐current coupling effect. It is rigorously validated from multiple dimensions: physical logic, statistical estimation precision, coupling detection power, robustness to model assumption deviations and prior parameter uncertainty, and engineering practicability. 0.945 four test runs. This work establishes a systematic design paradigm and a generalizable methodological framework for the reliability verification of high‐reliability, long‐life devices operating in multi‐stress environments.