Because the team was working on an entirely new concept, they also needed new tools to work with. “We approached Janicki Industries, the same company that supplied tooling for the Boeing 787. They told us that they had a fairly new product that utilized chopped fiber impregnated with resin and then machined to the desired shape, but it hadn’t been tried on large parts yet,” says Kirsch. “Janicki is also known for their ability to machine large parts to very high tolerance, and it was because of Janicki’s precision that we were able to build both the upper and lower parts of the CCM to the same dimensions, with an accuracy of .010 in critical zones and .030 in non-critical zones. This is enabling, considering there is no autoclave for the larger heavy lift rocket-sized parts.”
Another unique design aspect that came from an all-composite crew module was the instrumentation system. Instead of using a large suite of traditional uniaxial, bi-axial, and rosette strain gauges, the CCM team used a fiber-optic strain gauge system containing 3,500 strain measurements spaced one centimeter apart. This allowed them to characterize the linear strain gradients, such as around each window, and made individual strain placement much less sensitive for location of peaks.
Despite the team’s impeccable communication and group effort, there were times that they had to prepare the manufacturing team for the next step, even though the design information had not been released, resulting in a just-in-time engineering release. At other times, the systems they put in place wouldn’t work. They would cure a part, but it would later warp or a disbond would occur. They would have to retrace their steps to figure out what happened; all while maintaining a fast track schedule.
Constructive Purpose and Criticism
The team’s main goal in building a CCM was to determine if they could accurately predict, using analytical models, how the various composite components would hold up. “We wanted to know if we could predict the weight accurately from a computer aided design (CAD). We predicted the weight of the CCM at 1,441 pounds and then actually measured it two years later at 1,496 including 50 lbs of strain gauges—that’s pretty close!” says Kirsch. He says one reason they were able to get that close was because they didn’t have to accommodate changes that might be required for other subsystems.