I have a confession to make. I have never had much interest in astronomy or space, even to the degree that I avoid science fiction. I realize in many aviation circles, this makes me some sort of heretic. I am an AvGeek of course; I just tend to appreciate flight more at 30,000 feet rather than 30,000 light years away.
While some chase celestial bodies, I chase airliners, and like chasing a comet, there are few more desirable or out of reach than the Boeing 747SP.
Since you’re reading Airways, I probably don’t need to remind you why this rare bird is such an object of AvGeek lust. But I will anyway.
Well, for one it is rare. Out of over 1,500 747s built, only 45 SPs rolled off the Everett line. The SP, which stands for “Special Performance,” is essentially a 747-200 but 47 feet shorter. The SP, with its taller 65-foot, 5-inch VTP (vertical tail-plane) to add stability to the shorter fuselage, looks stubby and disproportionate compared to any other Queen of the Skies variant.
But for its day, the performance was special. The SP could fly faster, higher, and longer-range than any other airliner. Its range of 6,625 miles made it ideal for pioneering nonstop long-haul routes such as New York JFK – Tokyo Narita.
The type entered service in 1976 for launch customer Pan Am on that very route. Over the years, airlines such as American, Braniff, TWA, South African, Qantas, United, and Iran Air acquired first and second-hand examples for very niche, ultra-long haul missions.
With its reduced payload capability, it was never really an economical aircraft to operate. and with the arrival of the second generation ultra-long-range aircraft like the 747-400, MD-11, and A340, the 747SP was doomed.
Qantas and South African Airways were the last front-line operators, finally phasing it out of their fleets over a decade ago.
With fewer than five examples still airworthy today, the dwindling options were pretty much non-obtainable. The Sands 747SP in VIP configuration is for ferrying casino high rollers (I am not one!), Iran Air still flies a 747SP in passenger service, but for many reasons I won’t be boarding a Homa Bird anytime soon, if ever.
So that left me with one option to fulfill this ambition. I would have to look to the stars to realize my out-of-the-world experience of flying an SP. Not that any 747SP is ordinary, but the object of my desire is extra-ordinary, as well as other-worldly: NASA’s SOFIA, a 747SP-21 originally built to carry passengers on ultra-long haul routes but is now used to carry the world’s only flying infrared astronomy laboratory and flying infra-red telescope.
The feminine name SOFIA is an acronym for Stratospheric Observatory For Infrared Astronomy. Very simply put, SOFIA is used to observe light in the infrared spectrum that’s not visible to the naked eye.
What I didn’t realize at the time was, of course, that as an unintended but welcomed consequence, I would become pretty mesmerized by astronomy and space (or what I understood about it) – a science I had been fairly ambivalent about. I know… I know… heresy!
With respect to this publication and websites’ scope of coverage and my own less then erudite grasp of the heavens, this article will look at the SOFIA mission more from an aviation perspective. But the science is the raison d’être for this one-of-a-kind platform, and it’s fascinating at that, so I will attempt to do it some sort of justice.
Please bare with me as our time-space continuum jumps between air (planes) and space. And if you’re a devotee’ of all things NASA, Carl Sagan, Cosmos, and Stephen Hawking, please excuse me when I describe the science in layman’s terms.
A Universe of Scientific Possibilities
To understand why a Boeing 747SP became the world’s only flying infrared telescope, we need to summon our astrophysics acumen and turn back the clock, not quite millions of years ago back to the Big Bang Theory but the 1970s.
Telescopes have been around for hundreds of years since the days of Galileo. They have advanced to orbiting space telescopes like the famed Hubble. Most telescopes as we know them are, to one degree or another, star gazing magnifying glasses. In other words, they observe light visible to the naked eye.
According to the SOFIA Team, the importance of SOFIA is “Studying the infrared light that has never been studied. Studying the universe using only visible light gives us a very limited view, as you can see from the two images on the right. Visible light, the light you see with your eyes – reveals only part of the universe. Astronomers observe many other types of “light” to expand our views of the universe. SOFIA is designed to observe the infrared universe.”
Are you with me? Now this is where things get a bit more scientifically wonky. Infrared light energy is just one strata of the electromagnetic spectrum. This includes visible light, X-rays, radio waves and other forms. Many objects in space emit almost all of their energy at infrared wavelengths. But they are invisible in visible light.
In other instances, the visible light is concealed by clouds of gas and dust in space. But, infrared light can reach and be read by a telescope, as long as it is an infrared telescope, and there is where SOFIA comes in.
SOFIA’s observations occur at wavelengths between .3 and 1000 microns. Its ability to study infrared wavelengths of between 30 and 240 microns provide data that can’t be picked up by any other telescope on the ground or in space…at least in the known galaxy.
Stay with me. It’s getting good. This infrared observatory studies many different kinds of astronomical objects and phenomena, which NASA identifies as:
- Star birth and death
- Formation of new solar systems
- Identification of complex molecules in space
- Planets, comets and asteroids in our solar system
- Nebulae and dust in galaxies (or, ecosystems of galaxies)
- Black holes at the center of galaxies
- Planets, comets, astrochemistry, planetary nebulae, galactic center, supernovae, and star formation.
OK, that’s all and well and good, but why do we need a flying telescope? The answer to that one is pretty simple. Water vapor blocks infrared light energy and 99% of the world’s water vapor exists below 39,000 feet. The higher altitude you fly, the drier it gets and the more optimal it is for infrared observation. Makes sense, right?
Allan W. Meyer, a SOFIA Flight Planner who has been conducting airborne astronomy since 1975, puts it more scientifically: “The less water vapor, the better the observation. Water vapor refracts the photons, which makes it harder to detect photons at higher frequencies.”
According to Meyer, the seasons matter as well, which is why SOFIA shifts between hemispheres to be able to observe in winter year round: “Winter is more optimum because the nights are longer, there’s less water vapor in the atmosphere, and there’s less turbulence.”
SOFIA’s platform, leveraging a plane versus a satellite in space like the Hubble, has its definite advantages, says Randolf Klein, SOFIA Instrument Scientist, “We can fly to any longitude or latitude on the planet to observer a special event like an occultation of a star by Pluto. We flew directly into the shadow.”
The History of SOFIA: A Journey that took Light Years
SOFIA’s interstellar saga of a sojourn began over 40 years ago in an era when the Apollo moon missions were winding down, succeeded by Spacelab and Apollo-Soyuz capturing the imaginations of earthlings. The first permanent airborne observatory was called the Kuiper Airborne Observatory (KAO). First taking to the air in 1974, KAO was a Lockheed NC-141A Starlifter with a 36” telescope mounted onboard.
In 1977, Boeing presented a study to NASA suggesting that a large airborne telescope could be mounted in a 747. In 1980, it was proposed to be mounted in a 747SP and NASA began allocating funding in 1985.
Pioneering, risky, and costly government projects can move at a glacial pace and SOFIA was no exception. NASA and the US government needed a funding and technology partner, but that would come later.
The pace gradually began to pickup. In March 1990, wind tunnel tests began to study the effects of the opening telescope door on the airframe. Just over a year later, Computational Fluid Dynamics (CFD) studies on placing the door at the aft section of the airplane were performed. Consideration was given to whether engine exhaust would affect the infrared picture generated by the telescope. With no notable interference noted, the aft section of the airplane became the new focal area for the potential installation.
To validate this, in January 1992, measurements of infrared interference were made using a NASA Learjet with mounted cameras focused on the exhaust coming from a NASA Boeing 747-100 Shuttle Carrier Aircraft (SCAL). In October 1995, the Kuiper C-141 completed its last observation flight, just as more wind tunnel tests were completed for the 747SP.
It took nearly a decade for NASA to find a partner to take this great leap. In 1996, NASA and DLR (The German Aerospace Center) signed a memorandum of understanding (MOU) to create SOFIA. Their first task was to find the ideal 747SP platform. They found an ex-United Airlines example languishing in the deserts of Nevada: N145UA (MSN 21441 • LN 306)
SOFIA, registered N747NA is a 747SP-21, originally delivered to Pan American World Airways on May 6, 1977 as N536PA. Having first flown on April 25, 1977, she was christened as Clipper Lindbergh on May 20, 1977, on the 50th anniversary of Charles Lindbergh’s solo flight across the Atlantic Ocean.
Anne Morrow Lindbergh got the honors to christen her, and she is again named that today. In 1986 as Pan Am sold its Asian route network to United, N536PA was re-registered as N145UA and joined the United Airlines fleet.
It was the only 747SP in the United fleet to be painted in the carrier’s distinctive Battleship Grey livery. She “flew the friendly skies” for nearly a decade before finally being supplanted by incoming 747-400s. N145A was then mothballed in the Nevada desert in October 1994 with decidedly bleak prospects. The scrap yard, not the skies, appeared to be her next destination.
With this SP being relatively youthful in terms of hours, cycles, and age, she was given a new life when NASA purchased her on February 5, 1997. She was then flown to NASA Contractor L3’s facilities in Waco, Texas, and eventually re-registered as N747NA in 2004. The SOFIA dedication ceremony was held at NASA Ames in April 1997.
In 1999, the platform flew four “calibration flights” to confirm the airplane’s flight characteristics in terms of stability. With the ceilings raised in the aft cabin and the telescope door installed, the modified aircraft structure was completed in 2002. The legacy HF (High Frequency) antennas at the wingtips were removed, and the DLR telescope arrived at Waco from Germany.
On April 21, 2004, the pressurization proving test was conducted on the airplane to ensure the new pressure bulkhead was secure. This was not only a test of the aircraft’s own new structural integrity but also of the telescope assembly’s ability to support the cabin pressure. The test produced 680,000 pounds of axial loading on the bulkhead and 105,000 pounds on the telescope. The airplane had strain gauges installed to measure this.
In 2004, Evergreen International Airlines was selected to operate and maintain the 747SP, though eventually these duties would be taken over by Lufthansa Technik in Hamburg, Germany.
A year later, continuing checks of the fuel system’s integrity began, as well as landing gear swings. Ten years after NASA first took delivery of the SOFIA 747SP, the highly modified Baby Jumbo finally completed its first test flight at Waco, and was then ferried to NASA’s Dryden Flight Research Center at Edwards AFB for more flight testing.
Upon arrival, the airplane was christened once more as “Clipper Lindbergh,” by Charles’ grandson Erik.
In 2008, the telescope primary mirror was removed for coating and then reinstalled. One year later, the airplane flew for the first time with retractable fuselage door known as the URD (Upper Rigid Door and Lower Flexible Door) 100% open.
During tests, the telescope door didn’t completely close five times. Since then during missions, it has only been stuck open once. The warnings indicated the door was fully open, but it was actually only slightly ajar.
Finally, on November 30, 2010, SOFIA embarked on its first full science research flight, with the FORCAST (Faint Object infraRed CAmera) instrument installed. In September 2011, she flew her first North Atlantic deployment, visiting DLR in Cologne-Bonn and Stuttgart.
Even with the backing of significant deep-pocketed partners, the SOFIA program was nearly cancelled in 2006 before it ever flew, and nearly cancelled in 2013 due to budget cuts. The program costs $85 million per year in U.S. funding and $20 million from DLR. Each of the 100 missions amortizes out to nearly $1 million. At an average of 10 hours per flight mission and 1000 flight hours per year, each hour in flight costs in the vicinity of $100,000.
Over 400 people support the program. Clearly, the SOFIA program is not inexpensive and is often on the cutting board, constantly having to justify its scientific value. Before SOFIA ever took to the skies, the 11-year development project cost $1.1 billion. Budget cuts notwithstanding, the program is designed to last twenty years.
Part Two: Exploring SOFIA, the Flying Observatory
In part two of this story, we’ll explore in detail this unique 747SP, as the crew and staff make the preparations prior to its mission.