Probabilistic Structural Analysis of Ares Upper Stage
Ares I-X launch vehicle USS - The N&R staff applies a variety of commercial and in-house structural analysis codes to perform both deterministic and probabilistic structural analyses. High-temperature/high-stress composite material structures are a specialty that we have handled for both NASA and the aerospace industry. A recent example involves the next generation launch vehicles that NASA is developing. The first test launch is scheduled for the spring of 2009 and involves an upper stage of the first Ares 1 launch vehicle that is a simulation of the real upper stage. That is, it has no active propulsion system and its structure is not the operational flight version. But the Upper Stage Simulation (USS) does have the same dimensions and overall mass properties to simulate the behavior of the real upper stage. Designated Ares I-X this test vehicle will verify the performance and flight dynamics of the active first stage.
The USS primary structure consists of a series of stacked steel “tuna cans” welded and bolted together from mild plate steel. Because concerns were raised regarding the structural integrity of the welded joints of this structure, N&R was contracted to perform a probabilistic analysis of this primary structure to identify the critical stress locations and, more importantly, to determine the catastrophic failure risk of un-detected welding flaws. This required detailed modeling of the welding joints, and the application of crack-growth modeling tools, as well as our probabilistic code to determine failure probabilities.
The final results demonstrated that the failure probability from un-detected welding flaws is not very large, thus giving NASA program managers confidence that the Ares USS is structurally sound given the estimated loads. NASA was grateful to N&R for their contribution to resolve this major uncertainty.