A Reliability Model for the Design and Optimization of Separated Spacecraft Interferometer Arrays

The concept of using identical spacecraft for space-based optical interferometry is introduced. The built in redundancy of such a separated spacecraft interferometer (SSI) design not only improves the reliability of the system, but also improves system performance by placing the redundant components where they can be used during nominal operations. Five metrics have been developed to compare SSI designs. These include 1) total system reliability, 2) specific system reliability, 3) cost per image, 4) time to produce an image, and 5) reduced mission effectiveness due to partial system failure. The reliability model incorporates both combinatorial analysis and Markov modeling to evaluate different SSI designs on the basis of these five metrics. The results indicate that the modular and multifunctional spacecraft (MAMS/C) design rates higher than the single function spacecraft design (SFD) for all five metrics under the assumed mission parameters. These parameters include the number of small satellites in the array, the failure rate of the three components within the array, and the mission design life. For small arrays with extremely reliable components and short mission design lives, the current NASA SFD array with only one combiner suffices. This is because the intended design life of the system is shorter than the mean-time-to failure of the system. For future larger arrays with more realistic component failure rates and longer mission design lives, designs that incorporate both collector and combiner functions on each small satellite bus rate higher. On the basis of these results, rules of thumb have been developed for the design and optimization of SSI small satellite arrays.