DALLAS — NASA's now-retired Stratospheric Observatory for Infrared Astronomy (SOFIA) aircraft will have a permanent home in Tucson, Arizona's Pima Air & Space Museum.

Following guidelines for the disposal of excess government equipment, NASA decided where to house the plane after its mission was complete after eight years of science. On Tuesday, December 13, the aircraft is anticipated to fly from NASA's Armstrong Flight Research Center in Palmdale, California, to Tucson.

Pima, one of the biggest aerospace museums in the world, is planning for when and how the SOFIA aircraft will eventually be on public display.

Along with its own restoration facility where new aircraft like SOFIA are prepared for museum immortalization after their arrival, Pima also has six hangars, 80 acres of outdoor display grounds, and more than 425 aircraft from all over the world.

“The SOFIA mission has a powerful potential to inspire, from its discoveries about the unknown in our universe to the engineering achievements that broke new ground, to the international cooperation that made it all possible,” said Paul Hertz, senior advisor for the Science Mission Directorate at NASA Headquarters in Washington.

Mr. Hertz added, “We are excited SOFIA will continue to engage a diverse new generation of scientists, engineers, and explorers.”

The SOFIA Mission

Flying into the stratosphere at 38,000–45,000 feet puts SOFIA above 99% of Earth’s infrared-blocking atmosphere, allowing astronomers to study the solar system and beyond in ways that are not possible with ground-based telescopes. In 2010, SOFIA was used to observe its first astronomical targets, the planet Jupiter and the Messier 82 galaxy.

Since then, the aircraft has made various deployments across the globe to observe and image faraway galaxies and planets, primarily in the Southern Hemisphere.

Earlier this year, the aircraft traveled to Chile, where it captured unique images of two galaxies in the Milky Way, the Large Cloud and the Small Magellanic Cloud, which scientists predict could merge with our galaxy within billions of years.

The History of SOFIA

SOFIA’s interstellar saga of a sojourn began 45 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). KAO was a Lockheed NC-141A Starlifter with a 36” telescope mounted onboard. The type took to the skies for the first time in 1974.

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 pick up. 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 (UA) example languishing in the deserts of Nevada: N145UA (MSN 21441 • LN 306).

From Pan Am to NASA

SOFIA, registered N747NA is a Boeing 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 the 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.

SOFIA Calibration, Test Flights

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 (EZ) 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's primary mirror was removed for coating and then reinstalled. One year later, the airplane flew for the first time with a 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.

First Research Flights

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 canceled in 2006 before it ever flew, and nearly canceled in 2013 due to budget cuts. The program costs US$85m per year in U.S. funding and US$20m from DLR.

Each of the 100 missions amortizes out to nearly US$1m. At an average of 10 hours per flight mission and 1000 flight hours per year, each hour in flight costs in the vicinity of US$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 US$1.1bn. Budget cuts notwithstanding, the program is designed to last twenty years.

SOFIA completed its science program and ended operations on September 29, 2022.

https://airwaysmag.com/nasa-conclude-b747sp-sofia/

Featured image: SOFIA on her last visit to NASA AMES in mid-October before the airshow down at Edwards AFB, which was opened only for NASA employees and families. Photo: Yifei Yu/Airways