Applying fuzzy bi-dimensional scenario-based model to the assessment of Mars mission architecture scenarios

Sending man to Mars has been a long-held dream of humankind. NASA plans human planetary explorations using approaches that are technically feasible, have reasonable risks and have relatively low costs. This study presents a novel Multi-Attribute Decision Making (MADM) model for evaluating a range of potential mission scenarios for the human exploration of Mars. The three alternatives identified by the Mission Operations Directorate (MOD) at the Johnson Space Center (JSC) include split mission, combo lander and dual scenarios. The proposed framework subsumes the following key methods: first, the conjunction method is used to minimize the number of alternative mission scenarios; second, the Fuzzy Risk Failure Mode and Effects Analysis (RFMEA) is used to analyze the potential failure of the alternative scenarios; third, the fuzzy group Real Option Analysis (ROA) is used to estimate the expected costs and benefits of the alternative scenarios; and fourth, the fuzzy group permutation approach is used to select the optimal mission scenario. We present the results of a case study at NASA’s Johnson Space center to demonstrate: (1) the complexity of mission scenario selection involving subjective and objective judgments provided by multiple space exploration experts; and (2) a systematic and structured method for aggregating quantitative and qualitative data concerning a large number of competing and conflicting mission events.     

Analysis of the effect of stiffener profile on buckling strength in composite isogrid stiffened shell under axial loading

In this paper, the buckling behavior of thin-walled GFRP cylindrical shells with triangular lattice patterned reinforcements formed by helical and circumferential ribs under axial force is analyzed. In this analysis, various models of composite isogrid stiffened cylindrical shells with outer diameter of 150 millimeters, shell thickness of 0.5 millimeters and height of 280 millimeters, stiffened with 6 helical and 2 circumferential ribs and all with the same material properties of shell and ribs are used. Ribs have constant section areas but different shapes and cross section profiles. The effects of these differences on buckling strengths of structures under axial load are studied. For analysis and modeling of structures, Finite Element Analysis method and ANSYS software were used. The results (elastic buckling load) for each model were derived and based on these results, ratio of buckling strengths to weight parameters were calculated for each model and were compared to results obtained from other models. The effect of profile of the ribs on the buckling of shells under axial loading can be concluded from the results. Results showed that stiffening the shells increased the buckling load from 10% up to 36% while decreased the buckling load to weight ratio to 42% up to 52% of an unstiffened shell.