N747NA
N747NA is the former NASA registration carried by the Boeing 747SP-21 that served as the Stratospheric Observatory for Infrared Astronomy (SOFIA). Built as manufacturer serial number 21441 and Boeing line number 306, the aircraft flew for Pan Am as N536PA and United Airlines as N145UA before conversion into a joint NASA–German Aerospace Center (DLR) airborne observatory. It completed its final science flight on 29 September 2022 and its final aircraft flight to Tucson on 13 December 2022. It is preserved at the Pima Air & Space Museum in Arizona.[1][2][3]
Identity and registration history
The airframe is a Boeing 747SP-21, the shortened, long-range Special Performance member of the Boeing 747 family. Boeing identified it as manufacturer serial number 21441 and production line number 306. It made its first flight on 25 April 1977.[1][4][3]
| Period | Registration | Operator or role |
| 1977–1986 | N536PA | Pan American World Airways |
| 1986–1995 | N145UA | United Airlines |
| 1997–2004 | N145UA | Acquired for the SOFIA programme; modification period |
| 2004–2022 | N747NA | NASA/DLR SOFIA research aircraft |
| From 2022 | N747NA displayed | Preserved at Pima Air & Space Museum |
The FAA's current N-number inquiry lists N747NA as a number reserved by NASA's Armstrong Flight Research Center rather than an active aircraft registration. The preserved aircraft continues to display the mark. Current legal registration status and the markings painted on a museum airframe are therefore separate facts.[5][3]
Airline service
Pan Am received the aircraft as N536PA on 6 May 1977. On 20 May, Anne Morrow Lindbergh named it Clipper Lindbergh in honour of Charles Lindbergh, fifty years after his solo transatlantic flight. NASA renewed the name during the SOFIA programme.[4][6]
United Airlines purchased the aircraft on 13 February 1986 and re-registered it N145UA. It remained in passenger service until United placed it into storage near Las Vegas in December 1995.[1][3]
The Universities Space Research Association acquired the stored aircraft on 27 October 1997 for the planned airborne-observatory programme. Although NASA later operated the aircraft and Pima summarises the acquisition as a NASA purchase, the detailed NASA history attributes the 1997 purchase to USRA. The distinction reflects the programme's contracting structure, not two different airframes.[1][3]
Selection for SOFIA
SOFIA succeeded NASA's Lockheed C-141 Kuiper Airborne Observatory. A 747SP offered a high cruise altitude, long endurance and a wide fuselage capable of carrying the large telescope and mission crew. The programme was organised as an 80/20 partnership between NASA and DLR: DLR supplied the telescope and supported maintenance, while NASA managed the aircraft, programme and science operations with USRA and the German SOFIA Institute.[7][8]
The ability to return after every mission distinguished SOFIA from a space telescope. Instruments could be removed, serviced and replaced, while deployments allowed the aircraft to observe from latitudes and regions unavailable from its Palmdale base.[7]
Conversion into an airborne observatory
L-3 Communications modified the 747SP at Waco, Texas. The most visible change was a large door in the aft port fuselage covering the telescope cavity. The telescope remained isolated from the pressurised forward cabin by a pressure bulkhead and observed directly through the open cavity while the aircraft cruised at approximately Mach 0.84.[9][3]
The German-built telescope had a 2.7 m primary mirror and an effective observing aperture of 2.5 m. Including its support structure, it weighed approximately 17–20 tonnes depending on the definition used. A hydrostatic bearing and gyroscopic pointing system isolated it from much of the aircraft's motion. The opening measured about 18 by 13.5 ft; substantial structural reinforcement and revised aft-fuselage contours were required around it.[7][9][1]
The cabin was divided into flight-deck, mission-control, education and equipment areas rather than an airline passenger layout. Four Pratt & Whitney JT9D-7J turbofans powered the aircraft. The operational ceiling of about 45,000 ft placed the observatory above more than 99 per cent of atmospheric water vapour that blocks much infrared radiation at ground level.[4][7]
Flight testing and entry into science service
The modified SOFIA aircraft made its first flight on 26 April 2007. This was not the airframe's first flight—the unmodified 747SP had flown thirty years earlier—but the first flight in its observatory configuration.[10][1]
NASA and its partners progressively expanded the test envelope. The telescope cavity door was first opened in flight on 18 December 2009. First-light observations followed in May 2010, and the first science flight using the FORCAST infrared camera took place on 1 December 2010.[11][12]
SOFIA achieved full operational capability in 2014. Science missions normally lasted about ten hours and operated from altitudes of 38,000–45,000 ft. Deployments included repeated southern-hemisphere campaigns from Christchurch, New Zealand, giving access to the southern sky.[7][2]
Scientific role
The observatory studied wavelengths and targets that are difficult or impossible to observe through the lower atmosphere. Its interchangeable instruments performed imaging, spectroscopy and polarimetry across the infrared and submillimetre spectrum. Research covered star formation, interstellar magnetic fields, galactic centres, planets, moons, comets and occultations.[7][13]
One widely reported result came from an August 2018 observation of the Moon. SOFIA's FORCAST instrument detected the 6.1-micrometre spectral signature of molecular water in the sunlit Clavius Crater region, distinguishing H2O from hydroxyl. NASA announced the result in 2020 as the first confirmation of water molecules on the Moon's sunlit surface.[14]
Other work mapped magnetic fields in star-forming regions and galaxies, examined the circulation of gases in Jupiter's atmosphere, studied whether comets delivered carbon to planets and observed Pluto's atmosphere. These examples reflect the aircraft's scientific role; they are not performance claims about the 747 itself.[13]
Retirement
NASA and DLR ended SOFIA operations after the 2022 observing campaign. The aircraft completed its last science mission overnight on 28–29 September 2022 after eight years at full operational capability and roughly twelve years of airborne science observations.[2][7]
On 13 December 2022, N747NA flew from NASA Armstrong's Palmdale facility to Davis–Monthan Air Force Base in Tucson for transfer to the neighbouring Pima Air & Space Museum. This ferry sector was the airframe's final flight and must be distinguished from the final science flight in September.[2][3]
Preservation at Pima
The Pima Air & Space Museum preserves the complete aircraft outdoors in its final NASA/DLR markings. Its collection entry records registration N747NA, previous registrations N145UA and N536PA, serial number 21441, and the telescope installation.[3]
The museum offers interior access on selected tour dates rather than continuously. The telescope door is normally closed for preservation, so historic photographs with the door open show an operational configuration that visitors should not assume is routinely displayed.[15][3]
N747NA should not be confused with NASA 905, registration N905NA, the first Space Shuttle Carrier Aircraft. Both were modified 747s operated by NASA, but N747NA was a shortened 747SP astronomical observatory and never carried a Space Shuttle orbiter.[7][16]
Timeline
| Date | Event |
| 25 April 1977 | First flight as Boeing 747SP-21 N536PA |
| 6 May 1977 | Delivered to Pan Am |
| 20 May 1977 | Named Clipper Lindbergh |
| 13 February 1986 | Purchased by United Airlines and re-registered N145UA |
| December 1995 | Withdrawn and stored by United |
| 27 October 1997 | Acquired by USRA for the SOFIA programme |
| 1998 | Major structural modification work began in Waco |
| 2004 | N747NA registration introduced |
| 26 April 2007 | First flight in SOFIA configuration |
| 18 December 2009 | First flight with telescope cavity door open |
| May 2010 | First-light observations |
| 1 December 2010 | First science flight |
| 2014 | Achieved full operational capability |
| August 2018 | Observed molecular water on the Moon's sunlit surface |
| 28–29 September 2022 | Final science flight |
| 13 December 2022 | Final aircraft flight, Palmdale–Tucson |
| 2023 | Entered preservation at Pima Air & Space Museum |
Data-quality notes
N747NA is the SOFIA 747SP, not Shuttle Carrier Aircraft N905NA.
Manufacturer serial number 21441 and Boeing line number 306 are separate identifiers.
The airframe's original 1977 first flight and its first post-conversion flight in 2007 are retained separately.
NASA's detailed history attributes the 1997 purchase to USRA; the museum's simplified NASA-acquisition wording describes the same programme transfer.
The 2.7 m primary mirror and 2.5 m effective aperture are different telescope measurements.
The final science flight in September 2022 preceded the final ferry flight in December.
The FAA currently records N747NA as reserved, while the museum aircraft continues to carry the mark.
Related pages
Sources
SOFIA: The Stratospheric Observatory for Infrared Astronomy — NASA History Office, 2025
SOFIA mission — NASA Science
NASA's retired SOFIA aircraft finds new home at Arizona museum — NASA, 8 December 2022
Boeing 747SP “SOFIA” — Pima Air & Space Museum
SOFIA aircraft facts — NASA/USRA SOFIA programme
The SOFIA aircraft and its modification — NASA Technical Reports Server
N747NA aircraft inquiry — Federal Aviation Administration, accessed 29 August 2026
Image source and rights: The Stratospheric Observatory for Infrared Astronomy — NASA/Jim Ross, public domain, Wikimedia Commons
.jpg){kind=link}