Dr. H. Philip Stahl is a Senior Optical Physicist at NASA MSFC currently leading an effort to mature technologies for a new large aperture telescope to replace the Hubble Space Telescope. Previous assignments include Mirror Technology lead for the James Webb Space Telescope. Dr. Stahl is a leading authority in optical metrology, optical engineering, and phase-measuring interferometry. Many of the world's largest telescopes have been fabricated with the aid of high-speed and infrared phase-measuring Interferometers developed by him, including the Keck, VLT and Gemini telescopes. Dr. Stahl is a Fellow of SPIE, Fellow of OSA, member of AAS and IAU. He was the 2014 SPIE President and an ICO Vice-President (2005-11). He earned his PhD (1985) and MS (1983) in Optical Science at the University of Arizona Optical Sciences Center. He earned a BA in Physics and Mathematics from Wittenberg University in 1979.
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Predictive Thermal Control (PTC) technology to enable thermally stable telescopes: year three status
Habitable-zone exoplanet observatory (HabEx) baseline 4-m telescope design and predicted performance
Specific cost estimating relationships (CERs) have been developed which show that aperture diameter is the primary cost driver for large space telescopes; technology development as a function of time reduces cost at the rate of 50% per 17 years; it costs less per square meter of collecting aperture to build a large telescope than a small telescope; and increasing mass reduces cost.
OTA Cost ~ (X) D (1.75 ± 0.05) λ (-0.5 ± 0.25) T-0.25 e (-0.04) Y
Specific findings include: space telescopes cost 50X to 100X more ground telescopes; diameter is the most important CER; cost is reduced by approximately 50% every 20 years (presumably because of technology advance and process improvements); and, for space telescopes, cost associated with wavelength performance is balanced by cost associated with operating temperature. Finally, duplication only reduces cost for the manufacture of identical systems (i.e. multiple aperture sparse arrays or interferometers). And, while duplication does reduce the cost of manufacturing the mirrors of segmented primary mirror, this cost savings does not appear to manifest itself in the final primary mirror assembly (presumably because the structure for a segmented mirror is more complicated than for a monolithic mirror).
Engineering specifications for large aperture UVO space telescopes derived from science requirements
Summary of the NASA science instrument, observatory, and sensor system (SIOSS) technology assessment
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This course summarizes aspheric component testing techniques, including: profilometry, interferometry, and geometric ray tests. Both null and non-null configurations are presented as well as specialized techniques: phase-measuring interferometry; CGH, two-wavelength, and infrared interferometry; sparse-array sampling; moire interferometry; and the Ronchi test.
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