Support Structure Project for the Constellation-X Mirrors

Project Results

With ten percent of the edge covered, a number of holding configurations are possible. It was determined that the position of the tabs should be symmetrical, held equally spaced along the edges of the mirror. The remaining variable to be determined was the number of holds needed. Simulations were run for mirrors with the number of holds varying from one to ten, positioned equally and symmetrically. Figure 1 below depicts changes in von Mises stress caused by changes in this variable. Changing the number of pads along the top and bottom edges is considered independently from changing the number of pads along side edges, and the two are graphed together. Trends show a cyclic dip in stress values as the number of pads increases, showing a minimum at five pads for top and bottom edges, and two pads for side edges.

Along the top and bottom edges of the mirror, there appears to be a general decrease in von Mises stress, reaching a minimum at five holds. Along the side edges, there appears to be no trend, but a minimum appears at two holds. Figure 2 shows changes in resonant frequency, revealing a general upward trend as the number of holds increases. It appears, however, that for holds along the sides, no significant increases in eigenfrequency appear for more than three holds, and for top and bottom edges, no significant increases appear for more than seven holds. Again, the case of holds along sides was considered independently from holds along top and bottom edges and graphed together. It appears that the eigenfrequency increases as number of pads increases for both cases. For holds along sides, this increase loses significance after three holds; for holds along top and bottom, the leveling out appears around seven holds.

For all configurations, eigenfrequency values were above 50Hz, and von Mises stress values were below 108Pa, falling within GSFC constraints. These simulated trends suggest that an optimal number of pads along the sides is two, and an optimal number of pads along the top and bottom is five. This agrees with the finite element analysis performed by NASA engineers (see Figure 3).