Our most familiar instrument for observing and measuring the electromagnetic spectrum, the human eye, can sense only a narrow range of energy wavelengths. These waves are 380 nanometers (violet) to about 740 nm (red). Although astronomy has it's origin in observing the universe in this part of the spectrum, there are also telescopes and instruments that measure incredibly short (and often energetic) wavelengths, such as Gamma rays and X-rays, as well as extremely long wavelengths such as radio waves. Infrared or "IR" astronomers study that expansive swath of wavelengths just below the visible range, but still above much of the radio end of the spectrum. Astronomers often break this range down into 3 categories:
Near-infrared: 800 to 8000 nm
Mid-infrared: 8000 to 30,000 nm
Far-infrared: 30,000 to 300,000 µm
[spectrum image]
But why go through the trouble of observing objects in the IR spectrum from the stratosphere, 12+ kilometers above the surface of the earth? There are several major infrared telescopes operating both on the ground and in space: _Mauna Kea Observatories_ in Hawaii, _Kitt Peak National Observatory_ in Arizona, for example.
"We put a telescope on the airplane because there are parts of the spectrum which are completely blocked and completely opaque in the Earth’s atmosphere. This was primarily in the infrared part of the spectrum," explains Young. "The main thing that blocks the infrared light from reaching the ground is water vapor in the Earth’s atmosphere. And if we want to observe many of these wavelengths, we have to get to some place where there’s no water vapor and SOFIA will fly above more than 99% of the water vapor in the atmosphere."
Flying telescopes may not be commonplace, but are hardly a new idea. SOFIA is merely the latest and largest in a line of airborne observatories going back to the 1920's, when eclipse chasers first carried a modest instrument aboard a 2-seater biplane (link). SOFIA's most recent ancestor is the the _Kuiper Airborne observatory or KAO_ (link to Ben story on KAO), a converted C-141 aircraft with a 36-inch mirror that flew missions from 1974 to 1995, and can be seen peacefully enjoying it's retirement on a nearby patch of Moffett Field tarmac. The idea within NASA to use a 747-SP as a telescope platform goes back at least to the late 1970's. Technical challenges, years of delays and cost overruns nearly ended the project more than once. But SOFIA' cosntruction eventually prevailed, test flights began in 2010, and it made it's first scientific observations this past year.
Although all science operations are managed here in the Bay Area within Moffet Field's _NASA Ames Research Center_, SOFIA's primary home is in Palmdale, California, at _NASA's Dryden Flight Research Center_. SOFIA is a collaboration between NASA and the German aerospace center, _DLR (Deutches Zentrum fur Luft-und Raumfahrt)_. The Germans provided the telescope; NASA provided the airplane and crew responsible for the science operations.
Another operational advantage of flying the instruments on a plane is flexibility. Unlike IR telescopes that we have launched into space, such as the _Spitzer Space Telescope_, SOFIA comes home every night. It can swap out, repair, or update to existing instruments as needed. To take advantage of this flexibility, SOFIA has available a collection of 9 specially-designed primary instruments to attach to the telescope, that each cover a specific range of wavelengths across and around the IR spectrum. Lastly, these instruments need not hew to the stringent weight requirements of their space-based counterparts, which saves money and allows use of instrumentation normally too big to launch on a rocket.
[instrument spectrum illustration]
After a successful run of several science test flights in 2011, SOFIA is currently in the shop for a major upgrade to its avionics systems. Upon returning later in 2012, the observatory plans to ramp up to 3 missions week by 2014, a schedule it hopes to keep for the next 20 years.
Erick Young expects that the future of IR astronomy with SOFIA is very bright - or warm, as the case may be. In fact, as the 1st generation of instruments are just being put through their paces, the _call for the second generation has already begun_ (http://soma.larc.nasa.gov/SOFIA/). "The instrumentation that’s available on the infrared is still rapidly evolving, particularly at the very long wavelengths that SOFIA operates at. The technology is still relatively in the infancy. And so one can expect that as the years go by, we’ll have huge increases in our capabilities as the technology improves. And SOFIA will definitely be able to take advantage of that."
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