The team also wanted to characterize the damage tolerance of the design. The CCM was also pressurized to design limits while critical interfaces, like the landing system main parachute, were pulled to simulate the combined loads a future crew module might experience during launch and a return to earth.“We then impacted parts that might get damaged, and then subjected it through four times the design life. In that test, we learned that none of the damage grew, demonstrating composites structural integrity and an ability to tolerate damage,” he says.
Yet the experience was not all positive. “Composites generally shine in applications where the design is driven by stiffness, fatigue or thermal stability. For example, on the new Boeing 787, they wanted composites because they have high fatigue life, meaning cracks don’t grow, which enables them to double the life of a part and inspect half as much. Or on a satellite, composites keep the shape of the satellite as it passes between drastic temperature differences,” explains Kirsch. “However, one of the criticisms of composites is that they look really promising on screen, but by the time you look at the finished product, the weight savings have dwindled in order to make up for different problems created by using the material.”
So will NASA adopt an all-composite crew module in the future? Probably not. “Unfortunately none of the usual composite benefits are seen on a CCM. It won’t experience thermal extremes, people are in it. And it will only ever be used once, so fatigue is not an issue. “But we learned invaluable lessons for future NASA applications; primarily, how to make, inspect and repair composite materials. Running parallel to the Orion program also allowed us to make mistakes where they couldn’t. And although the Orion pressure shell is not composites, other parts of the Orion, 40 percent by weight, are composites. Now, NASA and other team partners can benefit from the CCM lessons.”