Assessment of Maintainability for Future Human Asteroid and Mars Missions

Abstract

Conducting future human exploration missions to destinations beyond low Earth orbit will present new challenges in repairing and maintaining the spacecraft. The durations of proposed missions can be relatively long and re-supply of logistics, including maintenance and repair items, will be limited or non-existent. In addition, mass and volume constraints in the transportation system will limit the total amount of logistics that can be flown along with the crew. These constraints will require that new strategies be developed with regards to how spacecraft systems are designed and maintained. Because the conditions under which these missions will operate are so different from previous human space missions, it is difficult to make accurate estimates of spacecraft reliability and safety, as well as estimates on requirements for spares, based only on historical analogs. In order to improve the analysis of spacecraft maintainability, NASA is developing a probabilistic simulation capability to evaluate the need for repair and maintenance activities during space missions and to estimate the logistics and crew requirements to support those activities. The Exploration Maintainability Analysis Tool (EMAT) employs a Monte Carlo approach to simulate potential failures in spacecraft systems, based on established component reliabilities. The model evaluates the capability of the crew to repair failures, given a defined inventory of spares and maintenance items. Statistical analysis of Monte Carlo runs provides probabilistic estimates of overall mission safety and reliability. The model is used as part of integrated design and analysis activities to evaluate the impacts of maintenance and repair on the overall mission. The tool is used to assess the potential contribution from spacecraft system failure to the overall probability of mission failure and to evaluate trade-offs in manifested spares and reliability. In addition, the model is used to support an assessment of the effectiveness of strategies intended to improve maintainability, such as improved component reliability, component level repair, commonality, and redundancy. This paper will briefly describe the operation of the Exploration Maintainability Analysis Tool. The paper will then present results from an EMAT model simulation of a