Operational reliability criteria are required to define the probability of successful completion of sequential mission functions, the probability of crew safety, the probability of launch-on-time, the abort and recall capabilities, and the space system availability and operation. Since reliability is a function of complexity, mission usage cycle, mission environmental profiles, equipment operation, and system element integration, reliability is dynamic in nature.
This paper discusses a method for application of reliability criteria to space station operational availability optimization. Operational availability is defined as the percent of the time the space station is available to perform its primary mission function.
The method encompasses sequential mission time phase (prelaunch, booster flight, orbit, reentry, recovery) and space system modules (booster, re-entry vehicle, space station, ground equipment). These time phases and modules are referred to as “building blocks” that use parametric reliability data as a function of time. This technique readily lends itself to evaluation of existing “off-the-shelf” space system modules. When applied to conceptual space station subsystem analysis and integration, the approach provides reliability criteria for space station availability as a function of size, weight, cost, and development-time constraints.
A functional model relating the system reliability building blocks to space station operational availability determination is presented including subroutines for maintainability, space station recycle requirements, logistics support plans, crew safety and cost consideration. The reliability building block method is a simplified solution for using reliability criteria for space system synthesis.