This false color plot was generated by finite element modeling. It shows y-axis displacement of each point in a cross-section of a flat tilted disk. This model assumed a 100-mm diameter beryllium disk with a thickness of 12.5 mm spinning at 30,000 rpm. The deflection is about 600 nm; if the disk were aluminum it would be nearly 3600 nm, because aluminum is half again as dense and 4x less stiff than beryllium. A comparable disk would be required to implement Tank’s design from the previous slide, and the modeling shows that it would be difficult to maintain the necessary optical flatness.