The Stratospheric Observatory for Infrared Astronomy (SOFIA), a highly modified Boeing 747SP (SP stands for Special Performance), conducts missions 38,000 feet above the Earth – providing an amazing platform for studying the universe in the infrared spectrum
Stationed at NASA’s Armstrong Flight Research Center’s facility in Palmdale, California, SOFIA is an 80/20 partnership between NASA and the German Aerospace Center (DLR), with NASA providing the plan and crews and the DLR providing the reflecting telescope. Equipped with an effective diameter of 2.5 meters (100 inches), it is the world’s largest airborne observatory, and it provides scientists with the capability to make observations that are impossible for even the largest and highest ground-based telescopes to capture.
Flying telescopes may not be commonplace, but they are hardly a new idea. SOFIA is merely the latest and largest in a line of airborne observatories going back to the 1920s, when eclipse chasers first carried a modest instrument aboard a two-seat biplane. SOFIA’s most recent ancestor is the Kuiper Airborne observatory (KAO), a converted C-141 aircraft with a 36-inch mirror that flew missions from 1974 to 1995. The idea to use a 747SP as a telescope platform goes back at least to the late 1970s at NASA. Technical challenges, years of delays and cost overruns nearly ended the project more than once, but SOFIA’s construction eventually prevailed. Test flights began in 2010, it made its first scientific observations in 2011, and it achieved full operational capability in 2014.
The plane’s storied history actually dates back to 1977 when Pan American World Airways first acquired the aircraft for commercial service. Pan Am had a penchant for naming their aircraft after famous clipper ships, giving this one a special name – Clipper Lindbergh –in honor of the famous aviator. On the 50th anniversary of Lindbergh’s historic solo flight from New York to Paris, Lindbergh’s widow, Anne Morrow Lindbergh, personally christened the aircraft and officially placed it into service on May 6, 1977. Erik Lindbergh, Charles Lindbergh’s grandson, re-christened it in 2007. To honor this history, SOFIA still carries the name “Clipper Lindbergh” on its side today.
One of the 12 research pilots behind the controls of the SOFIA is former Air Force and current Jet Linx Pilot Mike “Spike” Tellier. “I have to pinch myself. I get to walk out to a plane that says ‘NASA’ on the tail,” Tellier exclaimed. The aircraft lives in Armstrong Flight Research Center’s Building 703, located on Air Force Plant 42 property, which holds a personal affection for Tellier. “I flew the swing-wing supersonic B-1 built by Rockwell International in Palmdale, California, which was in the same hangar where SOFIA lives. It’s a really cool déjá vu!”
Tellier’s journey to becoming a research pilot for SOFIA can be described as ‘meant to be.’ He retired from an illustrious career in the Air Force in 2008 and found Jet Linx in 2012. During his tenure with the Air Force flying the Boeing E-4, Tellier and his colleagues attended academics and 747 simulator training up to three times per year in Denver at United Airlines. “One of the guys I worked with in the simulator, Tim Sandon, was an Air Force Reservist and also an academic instructor who worked for United Airlines. Somewhere along the way in the late ’90s, he had mentioned SOFIA,” Tellier recalled. “Fast forward to April 2015 when I saw the job posting online… I immediately reached out to him.”
Although the job Tellier initially sought candidacy for was converting to the ER-2 position, Sandon informed him they would be hiring for SOFIA later in the year. “Sure enough, October 2015 I received an email from Tim and he said, ‘The ad is going live tomorrow so if you’re still interested, get your resume and credentials in.’”
Tellier jumped at the opportunity, and in December he received a phone call from the hiring manager of a company called i3 (Integration Innovation, Inc.) requesting a phone interview. “Todd Dagget, who is also a retired Air Force pilot, called and we chatted for about an hour,” Tellier recalled. Dagget noted the process was just beginning, as a formal interview would be up next – at United Airlines in Denver.
Tellier’s impressive career had prepared him for the interview of a lifetime. “It was a one-hour panel interview with Dagget, Sandon, and the Chief Pilot of SOFIA at the time, Dave Fedors, plus an hour in the simulator which was my old friend from my Air Force days,” Tellier described. “A few weeks later, I received the thumbs up. It was all coming full circle for me, all the folks that I had crossed paths with over the years were placed in my life for a reason and had a hand in bringing me to that exact moment to land a job on SOFIA. Again, I need to keep pinching myself! I’m so darn thankful!”
Seen from the exterior with its telescope cavity closed, SOFIA looks like a normal jumbo jet – one that is reminiscent of another heavily modified Boeing 747, Air Force One. The 2.5-meter telescope is mounted within the rear fuselage behind a new pressure bulkhead. Once SOFIA reaches cruising altitude, the cavity door raises giving the telescope’s observing end an unobstructed view of the skies while its operator remains safely inside the pressurized cabin. Mission control and scientists sit on the main deck of the aircraft, and educational and outreach passengers reside in the cabin where first-class seats would sit on a traditional airliner.
SOFIA’s long-haul design is an added operational advantage. With a range of 6,600 nautical miles, the aircraft can be in the right place at the right time to observe significant celestial events. “All missions are flown overnight. April of last year  we flew a 10-hour mission out of Palmdale, and coincidentally saw the Northern Lights – Aurora Borealis,” Tellier explained. “The show was just mesmerizing!”
At 41,000 feet, scientists aboard SOFIA study the universe in the infrared spectrum that is not available to the naked eye. Erick Young, former director of SOFIA Science Center, now senior science advisor at Universities Space Research Association (USRA), explained the infrared light phenomena to QUEST in 2012. “The appearance of things that we can see in visible light is primarily because things are hot enough to give off light at visible light wavelengths,” Young described. “If you get things too cold, then things look redder and redder and eventually they’re so red that the human eye can’t see them anymore. And then what we are actually sensing is a different kind of light called infrared – basically the heat radiation that’s coming from objects.” What SOFIA can look at are not things that are thousands of degrees hot, but things that are hundreds or tens of degrees above absolute zero. And it turns out that there’s a lot of that material in the universe – the dust, planets like the Earth, clouds in space. They’re too cold to normally emit in visible light, but by looking in the infrared, SOFIA scientists are able to sense them, detect them, and measure their properties.
“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,” Young continued to explain. “The main thing that blocks the infrared light from reaching the ground is water vapor in the Earth’s atmosphere. If we want to observe these wavelengths, we have to get to some place where there’s no water vapor. SOFIA flies above more than 99% of the water vapor in the atmosphere.”
Prepping for each mission takes approximately three hours, including crew and mission briefings where the science for the night is announced. “Last October we did a trip where we deployed the airplane to Florida for a week,” Tellier recalled. “It was for one mission on one night – the occultation of Triton, Neptune’s largest moon. In this event, Earth, Triton and a star all sat in a line… just like an eclipse, except it’s encompassing a moon of a planet and a star behind it.” The occultation presented a rare opportunity for the science team to detect possible changes in Triton’s atmosphere. “Triton’s atmosphere hadn’t been looked at in about 15 years, so they wanted to see what our instruments would see it as and to also see if it had changed at all.”
Mission planners are typically not required during science missions – however, for this event, a mission planner was necessary, and for good reason. “They have to refine the navigation solution as the event gets really close,” Tellier divulged. “I think we ended up airborne refiling some points three different times during that mission before we captured about a two minute window of actual full occultation and I heard the mission director yell, ‘We nailed it! We can see the sparkle!’”
SOFIA’s flexibility offers scientists an immeasurable amount of opportunity to explore the universe on a much larger scale compared to other infrared telescopes that have been launched into space. Future missions may potentially unravel fundamental questions about the creation and evolution of the universe, including how stars and planets are formed, how organic materials necessary for life form and evolve, and the nature of the black hole at the center of our Milky Way galaxy. In addition, SOFIA’s Airborne Astronomy Ambassadors (AAA program), a highly sought after hands-on program, offers middle and high school teachers and science museum educators an opportunity to experience scientific and astronomical research working side-by-side with scientists during missions.
“I look at my role with NASA and where I am with Jet Linx and simply love the position I am in with both,” Tellier remarked. “I would miss the person-to-person part of flying I enjoy with Jet Linx because I love the personal side of what we do. My interactions with passengers, especially the aircraft owners, is on a first name basis – and I love that!”