SOFIA and other flying telescopes

Meet Sofia. The fattest flying telescope around.

A flying telescope… wait, -what?

Infrared imagery of the cosmos is very limited on the earth’s surface. That is because the larger part of the light is absorbed by water vapor in the atmosphere. This is one of the reasons that the Hubble and Spitzer telescopes were developed. Being in space, these famous telescopes can avoid the distortions caused by the atmosphere that group telescopes suffer.
However, flying into space isn’t the only solution. By making the telescope fly in the stratosphere, 99.8% of the water pollution that blur the infrared waves is avoided. What’s more, flying telescopes have the advantage of being mobile. An orbiting telescope has less mobility, since you can’t dramatically change its orbit, or take it back home for adjusting and amelioration. On the other hand, a traditional ground telescope can’t observe every phenomenon we want it to, because of its very limiting directional constraints. An airplane can always be at the right place on the right time. It can be at any coordinate in the world in a matter of hours.

Galileo

Three telescopes successively pioneered airborne astronomy before Sofia. The first one was NASA’s Convair CV 990 named Galileo, acquired and modified by the space administration as a airborne laboratory to research aeronautics and astronautics and to study the earth’s andionosphere. In the mid-sixties, NASA let an astronomer from University of Arizona named Gerard Kuiper (and his team) to peer out the glass windows with telescopes. Despite the small size of the telescopes brought on board, despite the turbulences distorting the images and despite the severely reduced quantity of infrared light received due to thewindow’s glass, Kuiper and his team managed to prove the importance of airborne astronomy. They discovered the presence of ice in Saturn’s rings and proved wrong the (then-widespread) theory that Venus’ clouds are composed ofwater vapor.
However, Galileo tragically collided in mid-air with a Navy patrol plane in April 1973 (while on a mission to test instruments tracking migratory sea mammals). Both aircrafts crashed killing all-but-one man.

LJO

The first airplane to be acquired and modified with core mission of observing stars was the LJO (Lear Jet Observatory). While the jet was modified for astronomy, it wasn’t very functional and was very uncomfortable. The plane wasn’t fully pressurized, the crew had to wear oxygen masks and sit on the floor to make observations. Observations could only be made during little more than one hour per flight. Still, LJO followed Galileo’s legacy and took the very first far-infrared spectrum of the famous Orion Nebula, discovered that Saturn and Jupiter have internal sources of heat (they radiate more energy into space than they receive light from the Sun).

KAO

Galileo’s and the LJO’s observations lead NASA to design a larger airborne telescope. This time, they wanted it to be radical. In 1974, they acquired a Lockheed C-141 Starlifter produced back in 1966 as a demonstration model. Lockheed then modified it to host the 91.5-cm telescope. In 1975, they named the plane Kuiper Airborne Observatory (KAO) in homage to Kuiper, who died two years earlier. The KAO produced images of higher quality than the two previous planes, and carried many more instruments. It still wasn’t a very reassuring place to be: oxygen masks were constantly hanging from the ceiling in case the cabin would depressurize, the thermal insulation wasn’t very effective so the temperature inside the plane dropped heavily. The plane’s acoustic insulation was so pitiful the crew had to communicate with microphone headsets. Nevertheless, the KAO made important discoveries. During a stellar occultation on March 10, 1977, astronomers James Elliot, Douglas Mink and Edward Dunham discovered Uranus’s 9 rings (the discovery was serendipitous, given the fact that they were planning on studying the planet’s atmosphere). Astronomers onboard the KAO also provided the first proof that comets are “dirty snowballs” (water being an essential component), that Pluto has a superficial methane atmosphere, and so on.

SOFIA

The idea to fly an even larger telescope in a jumbo jet was first officially stated by NASA in 1984. NASA studied the feasibility of the project around 1986. The KAO had to retire in 1995 so NASA could have sufficient funds for this next airborne telescope they called the Stratospheric Observatory For Infrared Astronomy (SOFIA !). In 1996 NASA contracted USRA (Universities Space Research Association) to acquire and manage a Being-747. The German Space Center (DLR) made the 2.5 telescope. It was shipped by an Airbus Beluga aircraft from Germany to the Waco, Texas on September 4, 2002. The DLR will conduct 20% of the observation time. In 2004, USR contracted Evergreen International Airlines to operate and maintain the Aircraft. According To USRA’s official press release, “Evergreen International Airlines will provide operational support, flight crews and training and dispatch, while Evergreen Air Center will provide heavy maintenance and support.” Evergreen already had substantial experience with NASA, having operated at the time NASA’s Being-747 Space Shuttle carriers for 12 years.
The major engineering difficulty in the project was designing the telescope’s “door”. A huge hole had to be cut right into the Boeing-747′s fuselage so the telescope can nakedly observe the universe (a transparent seal would severly reduce the quality of the images taken). However, the hole has to be closed to protect it when it isn’t taking images.. Therefore, a team of engineers had to invent a system so the plane’s fuselage could open and close in midair without ruining the planes aerodynamics and without causing vibrations that would distort the images taken. Program manager Cliff Imprescia explains: “You just don’t open doors on airplanes flying at Mach 0.8 at 40,000 feet. [...] Say you’re driving your car down the highway. If you open your window a certain amount, you get a vibration that affects your eardrums. We had to reassure ourselves that wouldn’t happen with SOFIA.”

SOFIA2

Furthermore, the telescope has to be assembled on a spherical bearing so as to prevent the inevitable turbulence to distort the images. When the plane vibrates, the telescope is balanced by a highly developed torque control system to float around that sphere. “We have a clever vibration isolation system,” project scientist Pamela Marcum explains. “The mirror is mechanically isolated from the plane. Shock absorbers, serving the same purpose as those found in a automobile, surround the giant bearing that bears the telescope’s weight, isolating the mirror from vibration in all directions.”
SOFIA’s telescope opened to the stars for the first time during the night of August 18 to 19, 2004. The telescope flew for the first time on April 26, 2007. It will open to the stars while flying for the first time in spring 2010. It will make its first scientific research in 2011, and will be fully operational in 2014.
As you can see, it is a very slow process. However SOFIA will be a considered a legendary telescope around 2020, just like we regard Hubble Space Telescope today. Both NASA and the German Space Agency are very optimistic on the telescope’s future discoveries. Pamela Marcum declared “this telescope will help us figure out how planets form and how our own solar system came to be.” Normal telescopes cannot see through the dense clouds of dust (orbiting young stars) that from planets. With its exceptional capability of observing infrared light, SOFIA will collect invisible light that comes directly from objects inside the clouds. It will be able to locate precisely fundamental elements such as oxygen, methane, and carbon dioxide.
Given the discoveries made by Galileo, the Lear Jet Observatory and the Kuiper Airborne Observatory, and given the magnitude of the SOFIA telescope compared to these previous telescopes, we have good reasons to think SOFIA will make dozens of awe-inspiring discoveries in the next two decades. Combined with the upcoming James Webb Space Telescope (JWST), SOFIA could revolutionize our understanding of the universe.

Here’s a nice animation I stumbled upon showing the aircraft’s structure and design: