NASA bids farewell to SOFIA: the unique Boeing 747SP aircraft modified to carry a reflecting telescope made its last flight

NASA Boeing 747SP, registration N747NA, modified to carry a reflecting telescope for the Stratospheric Observatory for Infrared Astronomy (SOFIA), operated its last flight ever on Wednesday, Sep. 28, 2022.

NASA Boeing 747SP, registration N747NA, modified to carry a reflecting telescope for the Stratospheric Observatory for Infrared Astronomy (SOFIA), operated its last flight ever on Wednesday, Sep. 28, 2022. According to, the flight lasted seven hours and 57 minutes, departing from Palmdale Airport (PMD), and flying around the North Pacific Ocean.

SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a Boeing 747SP aircraft modified to carry a 2.7-meter (106-inch) reflecting telescope (with an effective diameter of 2.5 meters or 100 inches). Flying into the stratosphere at 38,000-45,000 feet puts SOFIA above 99 percent 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. SOFIA is made possible through a partnership between NASA and the German Space Agency at DLR.

NASA awarded the contract for the development of the aircraft, operation of the observatory and management of the American part of the project to the Universities Space Research Association (USRA) in 1996. The DSI (Deutsches SOFIA Institut) manages the German parts of the project which were primarily science- and telescope-related.

SOFIA’s telescope made its first light on May 26, 2010.

The observatory’s mobility allows researchers to observe from almost anywhere in the world, and enables studies of transient events that often take place over oceans where there are no telescopes. For example, astronomers on SOFIA studied eclipse-like events of Pluto, Saturn’s moon Titan, and Kuiper Belt Object MU69, the next flyby target for NASA’s New Horizons spacecraft, to study the objects’ atmospheres and surroundings.

According to NASA website, SOFIA is designed to observe the infrared universe. Many objects in space emit almost all their energy at infrared wavelengths and are often invisible when observed with visible light. In other cases, celestial clouds of gas and dust block the light emitted by more distant objects, but infrared energy pierces through these clouds. In both cases, the only way to learn about these objects is to study the infrared light they emit.

During 10-hour, overnight flights, SOFIA observes the solar system and beyond at mid- and far-infrared wavelengths gathering data to study:

  • Star birth and death
  • Formation of new solar systems
  • Identification of complex molecules in space
  • Planets, comets and asteroids in our solar system
  • Nebulas and galaxies • Celestial magnetic fields
  • Black holes at the center of galaxies

SOFIA’s telescope instruments — cameras, spectrometers, and polarimeters — operate in the near-, mid- and far-infrared wavelengths, each suited to studying a particular phenomena. Spectrometers spread light into its component colors, in the same way that a prism spreads visible light into a rainbow, to reveal the chemical fingerprints of celestial molecules and atoms. Polarimeters are sensitive to the effect magnetic fields have on dust in and around celestial objects, allowing astronomers to learn how magnetic fields affect the birth of stars and other objects.

Unlike space-based telescopes, SOFIA lands after each flight, so its instruments can be exchanged, serviced or upgraded to harness new technologies. Because these new instruments can be tested and adjusted, SOFIA can explore new frontiers in the solar system and beyond and serve as a testbed for technology that may one day fly in space.

The aircraft was operated and maintained by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California.

SOFIA was based on a Boeing 747SP wide-body aircraft that has been modified to include a large door in the aft fuselage that can be opened in flight to allow a 2.5 m (8.2 ft) diameter reflecting telescope access to the sky.

The SOFIA aircraft was a modified Boeing 747SP widebody (serial number 21441, line number 306; registration N747NA; callsign NASA747). Boeing developed the SP or “Special Performance” version of the 747 for ultra long range flights, modifying the design of the 747-100 by removing sections of the fuselage and heavily modifying others to reduce weight, thus allowing the 747SP to fly higher, faster and farther non-stop than any other 747 model of the time.

Boeing assigned serial number 21441 (line number 306) to the airframe that would eventually become SOFIA. The first flight of this aircraft was on Apr. 25, 1977, and Boeing delivered the aircraft to Pan American World Airways on May 6, 1977. The aircraft received its first aircraft registration, N536PA and Pan American placed the aircraft into commercial passenger service.

United Airlines purchased the plane on Feb. 13, 1986, and the aircraft received a new aircraft registration, N145UA. The aircraft remained in service until December, 1995, when United Airlines placed the aircraft in storage near Las Vegas.

On Apr. 30, 1997, the Universities Space Research Association (USRA) purchased the aircraft for use as an airborne observatory. On Oct.27, 1997, NASA purchased the aircraft from USRA. NASA conducted a series of “baseline” flight tests that year, prior to any heavy modification of the aircraft by E-Systems (later Raytheon Intelligence and Information Systems then L-3 Communications Integrated Systems of Waco, Texas). To ensure successful modification, Raytheon purchased a section from another 747SP, registration number N141UA, to use as a full-size mock-up.

Commencing work in 1998, Raytheon designed and installed a 5.5 m (18 ft) tall (arc length) by 4.1 m (13.5 ft) wide door in the aft left side of the aircraft’s fuselage that can be opened in-flight to give the telescope access to the sky. The telescope was mounted in the aft end of the fuselage behind a pressurized bulkhead. The telescope’s focal point is located at a science instruments suite in the pressurized, center section of the fuselage, requiring part of the telescope to pass through the pressure bulkhead. In the center of the aircraft was the mission control and science operations section, while the forward section hosts the education and public outreach area.

What’s the future for SOFIA?

Simple Flying reports;

‘According to Paul Hertz [senior advisor for NASA’s Science Mission Directorate, former Astrophysics Division director, and former SOFIA program scientist], now that SOFIA has reached the end of its active history, NASA has to follow a standard process set by the US government for the disposal of equipment that is no longer needed.

‘The Government Services Administration (GSA, the agency that manages federal property and provides contracting options for other agencies) has already put out a call for any organizations that are interested in taking the plane. Other government agencies get first dibs, added Hertz.

‘SOFIA wouldn’t be the only artifact set to end in a museum. Hertz added that NASA is anticipating other artifacts from the program that are already being dispositioned could end up in multiple museums.

‘Now the question is, to which museum could the 747 be sent? Could it be the National Air and Space Museum in Washington, the Space Center Houston, the National Museum of the United States Air Force in Dayton, or maybe another one across the US? We will have to wait and see.’

Photo credit: Jim Ross and Tony Landis / NASA

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Dario Leone

Dario Leone is an aviation, defense and military writer. He is the Founder and Editor of “The Aviation Geek Club” one of the world’s most read military aviation blogs. His writing has appeared in The National Interest and other news media. He has reported from Europe and flown Super Puma and Cougar helicopters with the Swiss Air Force.

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