Segmented mirror systems

In the two-segment mirror systems of Barrington-Leigh and Rosenbaum (1974) and Haselgrove et al (1977) each segment is adjusted with respect to the other and has individual bending mechanisms. 

Two-mirror telescopes are the most common optical design for ground based telescopes. These systems require a parabolic or hyperbolic primary mirror. As mentioned before, more complex optical systems can accommodate a spherical primary with its attendant simplifications, but several additional mirrors are needed to correct the spherical aberration, and the light loss and alignment complexity makes this configuration less commonly used. Here we will assume that a non spherical primary is needed and we will discuss the resulting surface shapes that segments will have. 

One way to segment applications for lightweight mirrors is to use the altitude of the system as a criterion. This leads to three different categories, each being characterized by specific cost tradeoffs. 

A sophisticated computer-controlled support system keeps the mirror segments in the desired position. The finishing of the off-axis aspheric segments is performed by stressed mirror polishing, a newly developed process for which the initially round meniscus-shaped blanks of 1.9 m diameter are mechanically deformed in such a way that a desired aspheric surface results after the stress is relieved. 

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