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Modern Telescopes AS4100 Astrofisika Pengamatan Prodi Astronomi 2007/2008 B. Dermawan Slide 2 To Dreamers, Then, Now, and Always Majewski Slide 3 Trends in Modern Telescope Development Light gathering power Quality & sensitivity of the instruments efficiency Resolution (image quality & sensitivity) efficiency Majewski Bely Slide 4 Trends in Modern Telescope Development Instrument Sensitivity - Improvement in optical design, optics, detectors - New inventions (fiver optics, holographic gratings) - Finding appropriate sites Resolution - Quick & automatic guiding - Improved understanding of the effects of seeing - Locating observing sites for better seeing - Improvement in mirror & dome design - Active mirror figure & atmospheric compensation - Space-based platforms - Interferometry Majewski Bely Slide 5 Large Mirrors: Shapes, Materials & Types Telescope f-ratio Majewski Fast primaries: cost driver, smaller tube stiffer, smaller wind cross-section, secondary mirror smaller Bely Difficult decisions: type & construction of primary mirror, rest of optical train, tel. Structure/size/control, instrument optical design, size of dome, potentially the site of the tel., overall cost Slide 6 Large Mirrors: Shapes, Materials & Types Mirror substrate Majewski Considerations: Available in large quantities, castable in large size Long term stability of shape Polishable & be able to be coated Rigidity: sustain cooling, withstand constant motion, not deformable, segmented mirrors are low-rigidity such as space telescopes Good thermal behavior: homogeneous mirror focal length, low Coefficient of Thermal Expansion (CTE), high thermal conductivity & low density & spec. heat, for active shape mirror high thermal diffusivity Slide 7 Large Mirrors: Shapes, Materials & Types Mirror substrate Majewski Bely Slide 8 Large Mirrors: Shapes, Materials & Types Lightweighting mirror Majewski Lighter mirrors without sacrificing rigidity - Compression on the top surface and tension on the bottom - Middle section can be removed honeycomb Bely Slide 9 Large Mirrors: Shapes, Materials & Types Lightweighting mirror Majewski HST LBT, abell.as.arizona.edu/~hill/mirror Bely Slide 10 Large Mirrors: Shapes, Materials & Types Segmented mirrors Majewski Size limited of monolithic mirrors: fabrication facilities, difficult to achieve substrate homogeneity, handling & transport difficulties, max. 4-m sized space telescope Advantages of segmented mirrors: lower mass, shorter thermal time constants compared to monolithic mirror of same size, ability to "change out" segments, unlimited aperture sizes Slide 11