Between the heavens and Earth, there is the stratosphere. It's that upper layer of the atmosphere that will be the workplace for a 747-based airborne observatory called SOFIA, which made its first science flight this week, in a joint program run by NASA and DLR Deutsches Zentrum fur Luft- und Raumfahrt (German Aerospace Center).
The telescope aboard the highly modified aircraft, NASA says, will give astronomers access to the visible, infrared, and submillimeter spectrums, without having to worry about the atmospheric issues that terrestrial telescopes face. SOFIA stands for Stratospheric Observatory for Infrared Astronomy, which would seem to give an indication of the spectrum that takes priority.
The SOFIA aircraft flies in the company of a NASA F/A-18 chase plane during a test flight in August. The telescope looks out of the door behind the left wing; the door/telescope assembly here is rotated to its maximum vertical position of 58 degrees. The 20-ton, German-built telescope has a 2.5-meter (100-inch) diameter.
The 747, acquired by NASA in 1997, made its first post-modification flight in 2007 and its first 100 percent open-door flight a year ago, in December 2009. In its previous life, it first went into service for Pan Am in 1977, and later was sold to United Air Lines.
The debut astronomy mission flight this week lasted about 10 hours, during which time the vessel's FORCAST mid-infrared camera captured this image of the core of the Orion star formation. "This two-filter false-color composite image (20 microns - green, 37 microns - red) reveals detailed structures in the clouds of star-forming material, as well as heat radiating from a cluster of luminous newborn stars seen in the upper right," NASA said.
The SOFIA aircraft made its "first light" flight in May. This composite images shows, at right, an infrared image of Jupiter--"at wavelengths of 5.4 (blue), 24 (green) and 37 microns (red)"--and the white stripe, NASA said, marks "a region of relatively transparent clouds through which the warm interior of Jupiter can be seen." At left, for comparison's sake, is roughly the same view of the big planet in the visual-light wavelength.
Caption byJon Skillings / Photo by Anthony Wesley; Infrared image: NASA/SOFIA/USRA/FORCAST Team
Also taken during the first-light flight, these images show the central portion of the galaxy M82. Where the visible-wavelength images are cluttered with stars and dust clouds (lovely though they may be), the infrared image reveals the "star-forming heart" of the galaxy, according to NASA.
Caption byJon Skillings / Photo by Visible image: N. A. Sharp/NOAO/AURA/NSF; Infrared image: NASA/SOFIA/USRA/FORCAST Team
After a rehearsal this week for the science flight, Ithaca College professor Luke Keller studies some of the data collected. Keller is a longtime member of the team working on the project's FORCAST instrument--the Faint Object Infrared Camera for the SOFIA Telescope.
In a blog post from just before Thanksgiving, Keller wrote: "Our final test included observations of the Orion Nebula (M42 for you astronomers), a region where stars are forming about 1,500 light-years from Earth. The data look so good that we expect to be able to use them for new astrophysics studies. In other words, SOFIA is ready for astronomy!"
In this photo taken during a ground-based checkout in October, researchers assess the alignment of the FORCAST instrument to the telescope's secondary mirror. Standing next to the monitor is Cornell University professor Terry Herter, principal investigator for FORCAST, which came out of Cornell's labs.
Here's a closer look at the FORCAST/telescope assembly. "FORCAST is unique," according to NASA, "in that it records energy coming from space at infrared wavelengths between 5 and 40 microns--most of which cannot be seen by ground-based telescopes due to blockage by water vapor in Earth's atmosphere."
And here's the FORCAST/telescope assembly again, from a different angle. Other first-generation instruments will eventually include EXES (Echelon-Cross-Echelle Spectrograph), GREAT (German Receiver for Astronomy at Terahertz Frequencies), and HIPO (High-speed Imaging Photometer for Occultation).
To see out of the plane, the camera relies on the view from the telescope cavity door at the rear of the fuselage.
In a blog post from mid-November, Keller wrote: "Our flight was about an hour longer than planned due to a minor problem: the telescope cavity door was stuck open (!!) due to a software glitch. Not a problem for the aircraft or pilots, but they had to slow our descent to allow the telescope mirrors to warm up from -37 C (at our cruising altitude of 42,000 feet) to 1 C on the ground. Landing with a cold telescope would have condensed ice on the mirrors, bad news for a $100,000,000 telescope! As soon as we landed, the aircraft operations engineers fixed the problem and closed the door.
In the center of this photo is the "blue, dry, and stable stratosphere" in which the SOFIA missions will take place, above the "beige-ish, wet, and turbulent troposphere," writes the SOFIA Science Center. The 747 will be flying between about 39,000 feet and 45,000 feet, above 99 percent of the water vapor in the lower atmosphere.
Caption byJon Skillings / Photo by NASA, USRA (Universities Space Research Association), and L-3 Communications Integrated Systems