June 27, 2007, Dryden, CA-- The Stratospheric Observatory For Infrared Astronomy (SOFIA), an aircraft-mounted observatory developed by the US space agency National Aeronautics and Space Administration (NASA; Washington, DC) and the German Aerospace Center (DLR; Cologne, Germany), will be presented to the media in a debut event today at Dryden Flight Research Center on Edwards Air Force Base in California. At the heart of the telescope is a 2.7 meter mirror substrate using "Zerodur" glass-ceramic material manufactured by SCHOTT.
The material for the SOFIA telescope mirror substrate possesses a nearly zero thermal expansion coefficient, which allows it to maintain its shape and provide a constant optical basis, without distortion, despite wide temperature fluctuations. This is particularly important for SOFIA, since the telescope will operate at altitudes higher than seven miles, where the temperature can quickly drop down to minus 72 degrees Fahrenheit. The glass-ceramic is also strong enough to handle rough flying conditions and difficult landings with up to a nine fold gravitational force (9g).
To reduce the weight of the telescope as much as possible, the specially engineered Zerodur material was configured into a honeycomb shape on its non-reflecting side, reducing the mirror's weight to only 850 kg (1,874 lb) 78% less than what a similar solid mirror would weigh on a terrestrial deployed unit. The honeycomb design ensures that the mirror retains the strength and rigidity needed to endure the stress of several landings a week for decades.
Flying in the stratosphere, SOFIA will be able to collect UV radiation from 300 nm, visible light and infrared radiation up to the 1600 micron wavelength range. Even the largest ground-based telescopes are not able to collect infrared radiation in this range, because it is almost completely absorbed by atmospheric water vapor. Infrared radiation is particularly important to astronomers, as this type of radiation constitutes about half of the radiation in the universe and carries important information from the "Big Bang" and early universe.
SOFIA also offers several advantages over satellite telescopes. Since it is not restricted to a standard earth orbit it can get every cosmic event quickly on sight. SOFIA also uses a larger mirror than present satellite telescopes, where mirror size is limited due to cost considerations. SOFIA can be equipped with not only a large number but also more advanced measuring and observation instruments than satellite telescopes. And since it can be easily brought back to earth, regular maintenance is possible, which allows it to last longer.
The Zerodur glass-ceramic material has been used in mirror substrates for earthbound and orbital telescopes, including the Mars Reconnaissance Observer HiRISE (High Resolution Imaging Science Experiment) telescope, and the Keck Telescopes in Hawaii.
For more information, contact Schott North America.