The Most Unusual Boeing 747? Meet NASA’S SOFIA Flying Telescope

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The Boeing 747 is an iconic aircraft, and the 747SP holds a special place in many an avgeek’s heart. But this 747SP is even more special than most. For a start, its full of scientists and has an almost 20-ton telescope in the back. Here’s what you need to know about the Stratospheric Observatory for Infrared Astronomy, also known as SOFIA.

SOFIA flying telescope
NASA’s SOFIA flying telescope. Photo: Pxhere

Meet SOFIA

From its outside appearance, the NASA Boeing 747 looks very much like any other. For the avgeeks, it’s already exciting, as it’s the rare and unusual SP version, a shorter model often used for VIP services. Although some might have royalty on board, no other 747SP on Earth has a 17-ton infrared telescope mounted in its fuselage.

SOFIA in hangar
SOFIA carries a 17-ton telescope. Photo: NASA

The Stratospheric Observatory for Infrared Astronomy, more concisely named by its acronym SOFIA, is a joint project between NASA and the German Aerospace Center (DLR). It is the successor to Kuiper, NASA’s previous airborne space observatory which was retired in 1995.

Just like Kuiper did, SOFIA has been created to undertake infrared astronomy in flight, something which is near on impossible to do from the ground due to the water vapor in the atmosphere. SOFIA, when cruising at around 40,000 – 45,0000 feet, flies above this vapor, allowing for crisp, clear images of space as seen in the infrared spectrum.

The telescope onboard this special aircraft is a 2.5m reflector telescope, with a 2.7m primary mirror. It looks out of a large door in the port side of the aircraft near the tail.

SOFIA
SOFIA’s telescope looks out of a custom door at the rear. Photo: NASA

The 747SP

SOFIA is not a new aircraft. In fact, according to Planespotters, it’s of a grand old age of 42.8 years old. The 747SP was originally delivered to Pan American World Airways on the 6th May 1977, and was passed over to United Airlines on the 13th of February 1986. It arrived with NASA in October 1997, and has even had its original name restored to its fuselage – Clipper Lindbergh.

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Of course, you can’t just install a gigantic telescope on a 747 without some serious modifications. For this, NASA enlisted the help of Raytheon, a specialist intelligence and information company headquartered in Dulles, Virginia. Raytheon began work on the adaptation of SOFIA back in 1998.

SOFIA door open
The addition of a door did not affect the aerodynamics of the 747. Photo: NASA

One of the major modifications carried out to the SP was the installation of a 5.5m tall, 4.1m wide sliding door in the aircraft’s fuselage. This allows it to be opened in flight to allow the telescope access to the sky. The telescope itself is located behind a pressurized bulkhead, so that the rest of the cabin can remain pressurized for the comfort of the scientists on board.

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The focal point of the telescope is, however, housed in the pressurized section of the plane. Also in the pressurized section, and in the mid-section of the aircraft, is the main mission control and science operations area. Further forward, the aircraft houses an education and public outreach area.

Most of the seats on SOFIA have been removed, although it can still carry around 20 people on its scientific flights. Although the aircraft may sometimes experience turbulence, the telescope has been designed to not be affected by this, as its mountings allow it to ‘float’ and avoid the bumps on board.

The objectives and achievements of SOFIA

The purpose of SOFIA Is to provide us with never before seen observations of space. Unlike space telescopes, which go up into orbit, never to return, SOFIA has the added advantage of being back on the ground at the end of every mission. This means that, over its lifetime, the aircraft can have new and improved upgrades to its on board equipment added, as well as receiving the best of care and maintenance for its engines and avionics.

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Swan Nebula
The Swan Nebula as seen by SOFIA. Photo: NASA

At the start of this year, SOFIA returned us with previously unseen images of what NASA calls a ‘star factory’. The Swan Nebula, located around 5,000 light-years away, is thought to be the core of the Milky Way, and was observed in full infrared color and  in amazing detail, thanks to SOFIA.

The aircraft has been flying since 2010 and is planned to be operational until the early 2030s. By then, this grand old 747SP will be well over half a century old. And it’s no quiet retirement for the airliner either – NASA plans to operate around 100 observation flights a year with SOFIA, each one taking around eight to 10 hours.

Have you ever seen SOFIA? Let us know in the comments.

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