SOFIA—the 747SP with the big eye

SOFIA—the 747SP with the big eye

NASA operates a Boeing B-747SP (see the previous post for a description of this unique 747 variant) so that a big eye can be carried aloft for SOFIA (Stratospheric Observatory for Infrared Astronomy) — the big eye is, as you likely infer, a telescope which senses within the infrared portion of the light spectrum. This telescope is quite large and more capable than those based on land or in orbit. SOFIA is a cooperative mission between the USA’s NASA and Germany’s Deutsches Zentrum für Luft- und Raumfahrt (DLR, or the German Aerospace Center). DLR built the quite large IR telescope which has a diameter of 2.5m (100 inches) and weighs 20,000kg (44,100 lbs) — operating within the range of  0.3–1600 μm (microns). It is a Bent Cassegrain/Nasmyth design and serves to gather information from nebular gas clouds which is fed to instruments aboard the NASA’s 747SP. One of these instruments is known as GREAT, an acronym for German Receiver for Astronomy at Terahertz (frequencies), though there are many other instruments, as well. Recently the frequency was nearly doubled from ~2 THz to 4.1 THz vastly increasing the richness sensed by the telescope.

NASA’s Clipper Lindbergh, the platform for SOFIA, in flight with the cavity door opened (note “DLR” on the tail which is the other half of the team for SOFIA)—NASA photo by Jim Ross

So, why fly a telescope?

The answer is simple, frugal and pragmatic.  The telescope can be positioned nearly anywhere in the world (so celestial events can be observed at the optimum coordinate) and it is above 99% of the Earth’s atmosphere (eliminating nearly all of its adverse effects). Aircraft vibrations are zeroed out with actuators which sense these vibrations and counteract them, effectively providing a vibration free base.

SOFIA’s 2.5 meter diameter IR telescope doing what it was designed to do—NASA photo by Jim Ross

What about the aircraft?

The aircraft (N747NA) was originally built for Pan American Airways in 1977 and christened Clipper Lindbergh. Later it was sold to United Airlines and retired thereafter. Later acquired by NASA it was fitted for flight and modified to carry the large telescope aloft in a fuselage bay located between the wing and the tail. A large hatch can be rotated upward to expose the telescope to observe the heavens as well as to expose what is known as “the cavity” to the harsh conditions of the stratosphere. The aircraft is designed to fly 900 mission per year at an altitude range of 39,000–45,000 feet (~11,800–~13,600 meters) with as many as 25 persons on board for eight hours of observation at a time—all at -60º C (-76º F) and 800kph (500 mph). Clipper Lindbergh was refitted after 2011 with most of the science system wiring replaced (15,000 connections were rewired), three times more power made available to the scientific instruments, the telescope mirror cleaned, the cavity door improved as well as the cavity’s environmental control (better keeping water as well as water vapor out) and the cockpit was transformed from analog based to digitally based (i.e., a glass cockpit).

One of SOFIA’s instruments, attached to the telescope at the forward bulkhead of the cavity, is cooled with liquid nitrogen as the sensors are more sensitive the cooler they are—NASA photo by Carla Thomas

Why the science?

The IR telescope is the pointed end of the stick investigating the chemical reactions which have occurred (since the light received was emitted ages ago the past tense seems appropriate to use) so that galaxy evolution, planetary system formation and the chemical intricacies of stellar gas clouds can be fathomed.

SOFIA’s Clipper Lindbergh near the ATC tower in Christchurch, New Zealand—NASA photo by Carla Thomas

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Additional References

SOFIA Stellar—Stellar SOFIA: Southern Hemisphere missions mark new day for the program, The Dryden Express, Oct 2013, Vol 5 No 8 (2.6Mb)

SOFIA self-guided tour—Stellar SOFIA, 2013, NASA (216kb)

SOFIA_Mercury—NASA’s New Airborne Observatory Sees “First Light”, Nicholas A. Veronico, 2010, Summer issue of Mercury (1.8Mb)

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(author’s note)

Nicholas Veronico works for NASA on the SOFIA project as a writer as well as a photographer and we have seen his work before, as he is a prolific author. Read the book reviews for Hidden Warbirds and for Hidden Warbirds II—you’ll be pleased by the stories he has written of the recovery/restoration of WW II aviation wrecks with his particular skill at going beyond the easy and the obvious.