NASA - National Aeronautics and Space Administration

Image above: The SOFIA flies a second checkout flight from Waco, Texas (NASA photo by Jim Ross)

The Stratospheric Observatory for Infrared Astronomy, or SOFIA made its debut at Dryden June 27 following three successful checkout flights in Waco, Texas, where major modifications had been completed by L-3 Communications Integrated Systems.

The arrival at Dryden marked a new day in transitioning work with the aircraft from significant modification to the start of flight tests, completion of subsystems integration and, eventually, to the task of exploring the heavens.

The SOFIA still has a way to go before routinely engaging in science flights. Progress is measurable, however, and flight tests that will validate the structural modifications to the aircraft should begin this fall, according to Bob Meyer, SOFIA program manager.

The largest of the extensive modifications involved cutting a sizeable hole in the aft fuselage for installation of the infrared telescope and a special door that will protect it. The first phase of flights will be made with the door to the telescope closed. Later flights will include telescope door-open flights. The SOFIA project is a joint venture of NASA and the German Aerospace Center, or DLR. NASA provided the Boeing 747SP specially modified aircraft and will conduct flight and mission operations, while the Germans contributed the telescope, which has a primary mirror measuring more than eight feet in diameter. In addition to the most advanced telescope of its kind - one Meyer calls an engineering marvel - the Germans also provided upgraded engines and subsystems as well as a new coat of paint for the aircraft.

Although it will be years before full-scale science operations begin, Meyer said science flights have been scheduled during the second of three phases of flight tests, when the critical door of the NASA 747SP is ready to be opened in flight. Flight tests are scheduled to take about a year, but installation and integration of aircraft subsystems may take two to three. First observations made with the 45,000-pound telescope system during mission conditions are expected in 2009.

Image above: Members of the SOFIA program leadership include, from left, John Carter, Ed Austin, Bob Meyer and Eric Becklin. Aircraft and science aspects of the program will be co-managed by NASA's Dryden and Ames research centers, respectively. (NASA Photo by Tom Tschida)

"As soon as possible, we want a science instrument on the plane to get some science data," Meyer said. "Dryden is working diligently to get the observatory flight-tested, to get to the science as quickly as possible."

With that goal in mind, shifts have been doubled in an effort to accelerate deferred maintenance work and installation of key subsystems and instrumentation, said John Carter, SOFIA aircraft project manager.

With a series of checkout flights already completed - including the flight to Dryden, which did not exceed 20,000 feet in altitude - attention now turns to completing and integrating key subsystems, including installation of hardware and motors needed to open and close the door that shields the telescope. "We've gained a tremendous amount of confidence and understanding of the way the airplane truly works and flies and it has increased our confidence for the next flight phase, in which we're going to expand to the entire SOFIA envelope," Carter said.

Research flights with the telescope door closed may begin as early as fall. After those initial flights it will be about eight more months before the aircraft is flown with the door open, and observatory work can then begin to ramp up.

"We have to have the cavity insulation finished," Carter said. "We have an air duct to an auxiliary power unit that needs to be installed. We'll need to have an initial mission control and communications system, and we'll have to have the cavity door-drive system functioning."

The cavity insulation shields the aircraft's interior against outside temperatures, and reduces the effects of the aircraft's movements during flight on the telescope as well as reducing light reflection that could also impact it, he added.

Image above: SOFIA interior layout. (Illustration courtesy NASA/DLR)

Some of the most extensive modifications include a 16-foot hole for the telescope door - the largest opening ever made on a 747 -and the re-routing of the aircraft's flight control cables to accommodate the door. Those cables extend to the vertical and horizontal control surfaces. Flight control cables also will be instrumented to measure tension caused by thermal expansion. Another key modification was addition of a bulkhead to reinforce the aircraft's structure.

"It's a tremendous accomplishment to get the airplane here," Carter said. "It's the result of some terrific collaboration among Ames, Dryden, the German Aerospace Center, L-3 Communications Integrated Systems and the Universities Space Research Association," an Ames contractor. "We look forward to beginning a very exciting trip here, and the most difficult flying tasks are yet to come."

Ed Austin, SOFIA science project manager at Ames Research Center, Moffett Field, Calif., said that Ames has primary responsibility for management and oversight of the observatory's science program, including the missions to be accomplished onboard and the operation of ground facilities. Ames' responsibilities also include the integrated telescope, science instruments and software, and observatory functions.

In addition, as part of Carter's aircraft project, Ames personnel are assisting with the telescope cavity door design work, fabrication of its control system and installation and integration work. Key tasks for the Germans will be telescope checkout and test.

The observatory aircraft will feature several unique systems. "The mission control system software ties the science instruments, telescope cavity door and aircraft systems together to use the airplane to point the telescope at a particular celestial object and keep it focused on that object," Austin explained.

The principal advantage of an airborne versus land-based observatory is in the infrared study of the skies. At altitudes of about 41,000 feet, the aircraft is flying above more than 99 percent of atmospheric water vapor, which obscures the infrared spectrum when it is viewed through an Earth-based telescope. In addition, the SOFIA has a distinct advantage over space-based satellites and space telescopes in that it can be deployed quickly in the event of, say, a comet's appearance and can engage in missions around the globe without the costs of repositioning a space-based telescope. Built to be a sensitive telescope in the infrared and submillimeter spectrum, it is slightly larger than the Hubble Space Telescope, which was designed primarily for observations in the visual and ultraviolet portion of the electromagnetic spectrum.

"We can open up some wavelengths that are impossible to see from any ground-based observatory," Austin said. "We also can fly low-technology-readiness-level instruments because we can integrate the instruments with the telescope, fly the mission and return to our base of operations the following day or following morning. We can afford to use these state-of-the-art instruments that you can't fly in a space-based mission because of technology risks."

Wavelengths are ranges on the electromagnetic spectrum under which astronomical phenomena can be seen. For example, visible light is what can be seen with the naked eye, while infrared light shows a heat signature that can "peer" through dust and atmospheric water vapor that might obscure what can be seen in the infrared spectrum.

Mobility makes the SOFIA a valuable asset.

"It really is a benefit," Austin continued. "We plan to go into the Southern Hemisphere to see the galactic center and as we have targets of opportunity - events like occultation - we can position the aircraft anywhere in the world to take advantage of some really unique things that ground-based observatories are likely not able to get. We also will use the kinds of high-technology instruments at low-technology-readiness levels that the space guys are not likely to have."

An occultation is an astronomical phenomenon observed when a planet or moon passes across the line of sight to another body. An eclipse of the sun is an occultation; such events are used by astronomers to make observations that can't be made under other conditions. One example of the type of information astronomers can glean through an occultation is that, when Pluto is positioned between the Earth and a star, the presence of Pluto's atmosphere is revealed. The SOFIA is expected to be an improvement over the storied and now-retired Kuiper Astronomy Observatory aircraft that for 21 years was operated by Ames Research Center, said SOFIA Chief Scientist Eric Becklin.

"One of the things that SOFIA can do that Kuiper couldn't do is - because of its large aperture, it actually has a clearer view of the universe. We'll have a sharper view. In fact, it will be the sharpest view we'll have at some of the wavelengths we're looking at," he said.

Image above: SOFIA exterior view. (Illustration courtesy Tony Landis/Dryden Flight Research Center)

Researchers can't be certain what they'll find with the new airborne observatory but judging from past experiences, Becklin said, the possibilities are, well, galactic.

"The most exciting science is really trying to understand the chemistry and, potentially, the biology that's going on in space, and really getting to the heart of the question, did life form here on Earth, or did it form out in space?" he said.

The SOFIA alone won't offer answers to how life began on Earth, but mission planners expect that the science conducted on the aircraft could contribute to new ways of looking at the universe.

There are advantages to using infrared telescopes like the one featured on the SOFIA to study the universe versus using other wavelengths.

"An advantage of infrared [versus other wavelengths] is that it 'peers' through the dust that's out in space," Becklin said. "There's a lot of dust in space; it's between stars. The view that we get of the universe in the optical or ultraviolet (wavelength) is biased by dust. SOFIA will probe right through that dust.

"In the visible and ultraviolet, you're mainly looking at stars. When you look in infrared you see stars, but also see (more clearly) the dust and gas those stars formed from or are throwing off as they die. You really get a different view of the universe when you look in the infrared."

The SOFIA is expected to be a key component of the NASA astrophysics program, aimed at exploring fundamental questions about the universe. The SOFIA will help astronomers learn more about the birth of stars, the formation of solar systems, the nature and evolution of comets, the origins of complex molecules in space, how galaxies form and change and the mysterious black holes at the center of some galaxies - including our own.

Modifications to the Boeing 747SP airframe to accommodate the telescope, other mission-specific equipment and the large external door were made by L-3 Communications Integrated Systems of Waco, Texas.

The science portion of the SOFIA program will be planned by Ames Research Center and managed by Universities Space Research Association, or USRA, of Columbia, Md., and the Deutsches SOFIA Institut, or DSI, of the Universität Stuttgart, Germany.

Jay Levine
X-Press Editor