It is expected that the next generation of large ground based astronomical telescopes will need large fast-steering/tip-tilt mirrors made of ultra-lightweight construction. These fast-steering mirrors are used to continuously correct for atmospheric disturbances and telescope vibrations. An example of this is the European Extremely Large Telescope (E-ELT) M5 lightweight mirror, which is part of the Tip-Tilt/Field-Stabilization Unit. The baseline design for the E-ELT M5 mirror, as presented in the E-ELT Construction Proposal, is a closed-back ULE mirror with a lightweight core using square core cells. Corning Incorporated (Corning) has a long history of manufacturing lightweight mirror blanks using ULE in a closed-back construction, going back to the 1960’s, and includes the Hubble Space Telescope primary mirror, Subaru Telescope secondary and tertiary mirrors, the Magellan I and II tertiary mirrors, and Kepler Space Telescope primary mirror, among many others. A parametric study of 1-meter class lightweight mirror designs showed that Corning’s capability to seal a continuous back sheet to a light-weighted core structure provides superior mirror rigidity, in a near-zero thermal expansion material, relative to other existing technologies in this design space. Corning has investigated the parametric performance of several design characteristics for a 3-meter class lightweight mirror blank for the E-ELT M5. Finite Element Analysis was performed on several design scenarios to obtain weight, areal density, and first Eigen frequency. This paper presents an overview of Corning ULE and lightweight mirror manufacturing capabilities, the parametric performance of design characteristics for 1-meter class and 3-meter class lightweight mirrors, as well as the manufacturing advantages and disadvantages of those characteristics.
A thermal imaging zoom system has been developed for the mid wave infrared band with greater than 30X zoom range.
The zoom system provides continuous changes in the field of view from the narrow field of view to the wide field of
view. Athermalization was also a key feature included in the design. An active thermal compensation approach is being
used to cover a broad thermal range. A preloaded rail approach is used to maintain boresight and vibration requirements.
The final optical layout and mechanical design resulted in a system suitable for tactical and other harsh environments.
The current design is very compact for the extremely large zoom range but, the lens layout also provides adequate space
for folding. In this way the zoom system can be easily configured for applications with compact space claims such as
small turrets or gimbals. The fundamental optical design has also been found to be capable of accommodating different
camera formats (focal plane array size and F number).