The NESTEM code is a combination of a heat transfer analysis program (CSTEM), a constiuent-level ceramic material composite code (CEMCAN), and a NASA-sponsored probabilistic structural analysis code called NESSUS (Numerical Evaluation of Stochastic Structures Under Stress). NESTEM can be used to analyze complex ceramic composite combustors and other high-temperature/high-stress aerospace components subject to modeling uncertainties. It can handle heat transfer uncertainties and composite material uncertainties as well as loading, material, and boundary condition uncertainties. It can generate a geometric model of simple structures or, alternatively, accept the geometric models generated by ANSYS or NASTRAN. In addition to enabling probabilistic heat-transfer analysis, NESTEM makes it possible to generate mathematical models of components by use of selected modules from the NASA Composite Blade Structural Analyzer (COBSTRAN) computer code. N&R also interfaced NESSUS with NASA's Quantitative Risk Assessment System code (QRAS).