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What is SOFIA?
SOFIA stands for: Stratospheric Observatory for Infrared Astronomy. It’s a partnership between NASA and Deutsches Zentrum fur Luft-und Raumfahrt (DLR), the German Space Agency. France and Switzerland have had roles in the development of Stratospheric Observatory for Infrared Astronomy, too, as the SAGEM (Société d’Applications Générales de l’Électricité et de la Mécanique) Group of France made the main mirror, and the Swiss made the secondary mirror. SOFIA is an airborne space observatory built on a re-purposed wide-body Boeing 747. The plane is stationed at Edwards Air Force Base in California.
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The Carrier - Boeing 747SP, Modified
The Boeing 747SP wide body jet that carries the observatory had to be modified to hold the 2.5 meter diameter telescope in the rear section of the plane’s fuselage. The telescope is designed for infrared observations from the stratosphere, at altitudes of around 41,000 feet (12 km) above the earth. The plane is designed for longer flights than a typical 747. It was owned by Pan American World Airways from 1977 until 1986, when it was purchased by United Airlines, where it was used until 1995. The company named L-3 Communications Integrated Systems, located in Waco, Texas, did the heavy modifications necessary to convert the craft into a flying observatory.
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Telescope Placement and Specs
The telescope is located toward the rear of the aircraft, behind the suite of science instruments in their pressurized chamber. Mission control and science operations are carried out from the center of the aircraft, and in the forward section is an education and public outreach area.
The 2.5 meter reflective telescope has a 2.7 meter diameter main mirror. The optics consist of a Cassegrain reflector design, a parabolic primary mirror, and a hyperbolic secondary mirror that can be configured remotely. The telescope looks out from a door in the side of the fuselage and is slated to carry nine instruments, collecting infrared data at wavelengths ranging from 1 to 655 micrometers. It will also carry out optical astronomy operations at 0.3 to 1.1 micrometers wavelengths. The instruments cover the near infrared (1-5 micrometers), the mid IR (5-40 micrometers) and the far IR (40-300 micrometers). Five IR spectrometers are also part of the instrument suite.
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SOFIA is the largest telescope ever installed in an aircraft. It must withstand high-speed winds, as well as the vibrations and motions from the aircraft. Before takeoff, the telescope’s cabin has to be pre-cooled to the external temperature so as to avoid changes in the shape of the optics due to temperature changes. Before the plane lands, the compartment must be filled with nitrogen gas to keep moisture from condensing on the cooled instrument.
Test flights of Stratospheric Observatory for Infrared Astronomy aircraft began in 2007 at the L-3 Waco facility. In December 2009 the aircraft made its first test flight with the telescope door fully opened for two minutes of the flight, which lasted 79 minutes total. On May 26, 2010, the SOFIA telescope took its first images of Jupiter. Science observation flights should begin in 2011, with the full schedule beginning by 2014. At that time, observation flights three or four nights a week for 20 years are predicted.
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The reason for an aircraft-based observatory is that it brings the telescopes above most of the water vapor in the Earth’s atmosphere. Water vapor blocks some IR wavelengths from reaching the ground. The aircraft will be able to travel to almost any place over the Earth’s surface, allowing experiments from both northern and southern hemispheres. SOFIA’s objectives are to study planetary surfaces and atmospheres, to investigate the composition and structure of comets, to study the chemical and physical makeup of the interstellar medium, and to explore star formation. The Stratospheric Observatory for Infrared Astronomy aircraft ops are managed by NASA, and the SOFIA Science Center is located in Mountain View, California.