NASA’s super 747 SOFIA: The world’s biggest flying observatory

Editor’s Note: Chris Sloan is managing editor and senior partner of Airways Magazine and This is a condensed version of his three-part series about flying aboard NASA’s 747SP flying observatory SOFIA, published on

Story highlights

NASA's rare 747SP flying observatory -- the world's biggest -- costs $100,000 an hour to fly

The "Vampire Jet's" huge telescope door opens mid-flight to study Mars and Jupiter's moon Titan

PALMDALE, California CNN  — 

Some people chase celestial bodies. I chase airliners.

Like chasing a comet, there are few airliners more desirable or out of reach than the Boeing 747SP.

This 747 is rare.

Out of more than 1,500 747s built, only 45 SPs rolled off the assembly line. Fewer than five examples remain airworthy today.

It’s essentially a 747-200 model, except it’s 47 feet shorter.

The “SP” stands for Special Performance – and it lived up to its name. In its day, the SP could fly faster, higher, and longer-range than any other airliner.

To realize my ambition of flying on an SP, I’d have to look to the stars.

NASA’s SOFIA, a 747SP-21 was originally built to carry passengers on ultra-long haul routes. Now it’s used to carry the world’s only flying infrared astronomy laboratory and flying infrared telescope.

Very simply put, SOFIA (Stratospheric Observatory for Infrared Astronomy) is used to observe light in the infrared spectrum that’s not visible to the naked eye.

What does it do?

Most telescopes as we know them observe light that’s visible to the naked eye.

SOFIA is important because – according to SOFIA’s team – it studies infrared light sources that have never been studied.

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.

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, visible light is concealed by clouds of gas and dust in space. But, infrared light can reach and be read by a telescope – if it’s an infrared telescope.

That’s where SOFIA comes in.

It provides data that can’t be picked up by any other telescope on the ground or in space … at least in the known galaxy.

Pamela Marcum, NASA’s SOFIA project scientist, said the goals of the overall mission include “studying objects spanning the full gamut of astronomical topics including planets, moons, asteroids and comets in our solar system; star and planet formation; extra-solar planets and the evolution of planetary systems; the interstellar medium and interstellar chemistry; the nucleus of the Milky Way galaxy, and nearby normal and active galaxies.”

SOFIA is a true multi-use observatory. Its instruments consist of cameras, spectrometers, and photometers. They operate at different infrared wavelengths. Some are dedicated to studying specific astronomical science phenomena.

Other instruments serve a more general role but are capable of acquiring data simultaneously with another more specialized instrument.

Why does NASA need a flying telescope?

Water vapor blocks infrared light energy and 99% of the world’s water vapor exists below 39,000 feet. So, the higher altitude you fly, the drier it gets and the more optimal it is for infrared observation.

Allan W. Meyer, a SOFIA flight planner who has been conducting airborne astronomy since 1975, said 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,” Meyer said.

SOFIA’s platform, leveraging a plane versus a satellite in space like the orbiting Hubble telescope, has definite advantages, says Randolf Klein, SOFIA instrument scientist.

Unlike satellites, a plane “can fly to any longitude or latitude on the planet to observe a special event.”

SOFIA’s signature visual cue is the bulge at the back of the fuselage. A 172-inch-wide by 226-inch-tall door is located on the plane’s left side. Inside that door the telescope sits in an unpressurized part of the plane that has an effective diameter of 2.5 meters (about 8 feet).

There’s a reason why the telescope resides on the left side of the aircraft.

“All airplane observatories have telescopes on left side,” said Meyer. It’s the best side of the aircraft for observing during westerly flight. “You can slow down the rising and setting of objects when flying west,” he said.

A former Pan Am airliner

In the late 1970s, Boeing pitched NASA on the idea that an airborne telescope could be mounted on a 747. It took until 1996 for NASA and DLR (The German Aerospace Center) to partner up and create SOFIA.

Next, they just needed to find the right plane.

The 747SP that would become SOFIA first flew with Pan American World Airways on April 25, 1977 – christened as Clipper Lindbergh on the 50th anniversary of Charles Lindbergh’s historic first solo flight across the Atlantic.

In 1986 as Pan Am sold its Asian route network to United Airlines, the plane flew with United for nearly a decade. Then it was mothballed in the Nevada desert, where NASA found it.

This SP was relatively youthful in terms of hours and age. NASA purchased it on February 5, 1997. It took 13 years to remodel the plane, install new equipment, put in retractable fuselage doors and to test it.

Finally, on November 30, 2010, SOFIA embarked on its first full science research flight.

One hour of flight = $100,000

Even with the backing of 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 $85 million per year in US funding and $20 million from DLR. Each of the 100 missions works out to nearly $1 million.

At an average of 10 hours per flight mission and 1,000 flight hours per year, each hour in flight costs in the vicinity of $100,000.

The Vampire Jet

The plane is based inside a former B-1 bomber plant at NASA’s Armstrong Flight Research Center, in Palmdale California – except during the Northern Hemisphere summer, when it’s based at Christchurch, New Zealand.

During our February 2016 flight, we would study 10 waypoints for 10 targets, including Jupiter’s moon Titan and the planet Mars. Our route would take us across the western two-thirds of the continental US – from California to Missouri and Indiana, Washington state down to Nevada and New Mexico.

Because SOFIA only performs observation missions at night, it’s often called the Vampire Jet.

The telescope doesn’t gather valuable data in daylight. Also, exposing the telescope to direct sunlight would destroy its optics and create a fire hazard.

The penthouse

Upon entering the aircraft, we encountered a cabin that was an almost overwhelming dichotomy of a long-since-passed 1970s long-haul airliner, futuristic NASA mission control, and the International Space Station.

No tour of a 747 is complete without a visit to the penthouse.

We wound our way up the 1970s vintage spiral 747 staircase to discover the most intimate of intimate upper decks: A shortened upper cabin consisting of Lufthansa Business class seats.

This space army definitely travels on its stomach. Our open plane galley includes a microwave oven, refrigerator, and a table overflowing with high energy snacks, jerky, and an avalanche of junk food.

SOFIA’s mid-cabin is where the aircraft dons the appearance of NASA mission control, with consoles, computers, and monitors displaying esoteric data, alien user interfaces, and celestial images galore.

Our crew of 25 souls included a pilot, co-pilot, flight engineer, navigator and 21 members of the science contingent.

I spotted no one playing Minecraft or surfing the web. Why surf the web when you can surf the solar system?


We take our seats and, at 8:08 p.m. local time, the doors are closed.

Co-pilot Ace Beall radios the tower: “NASA 747 heavy ready to taxi to runway 2-5.”

The only thing pumping more than the four mighty Pratt & Whitney engines are our hearts, with adrenaline.

With no traffic on the field, at 8:35 p.m., the engines spool up to begin our takeoff. Right on schedule.

Because it’s not being used as a passenger jet, the plane’s low weight lets it thrust into the cool desert air in less then 40 seconds.

There are no relief pilots during our nearly 10-hour flight, and aside from quick trips to the lavatory and walks through the cabin, the pilots are on duty the entire journey.

One pilot dons his oxygen mask as it’s mandatory to wear them above 41,000 feet and SOFIA will eventually reach an altitude of 43,000 feet.

Opening the door during mid-flight

As we climb, scientists run multiple checklists and prepare for the scheduled 6 hours and 55 minutes of observation time. Once the telescope door opens, the work can be intense. There are no real breaks.

At observation altitude, the cabin is kept in the mid-60 degrees Fahrenheit. The crew puts on their sweaters and jackets.

Turbulence can cause the telescope to de-lock from its target. But even during moderate, choppy turbulence, it stays stable due to its spherical bearing, shock absorbers and gyroscopes.

“Up to moderate turbulence, the telescope can still make reliable observations,” says SOFIA pilot Capt. Manny Antimisiaris.

If turbulence increases from moderate to heavy, the telescope will go into standby mode. After the turbulence passes, then its tracking target has to be reacquired. Normally, the telescope operators adjust it at intervals of 30 minutes to keep it on target.

NASA had told us proudly that, when SOFIA’s telescope door opens at 35,000 feet, there would be no detectable buffeting inside the cabin.

To prove their point, at 9:02 p.m., when the door opens, no one tells us.

Sure enough, there was no detectable turbulence.

On the flight deck, a green light on the flight engineer’s panel indicates that the telescope door is open.

Astonishingly, with the door open, there’s only a 2% increase in fuel burn, thanks to the door’s air flow design.

Chalk it up to science!

On the main deck, things get a bit busier as the science observations begin.

Mission Director Randy Grashuis and the flight crew operate in perfect synchronicity to facilitate the viewing of specific targets. The telescope is so precisely balanced that it appears to be moving, when in fact, the airplane is moving around the telescope.

Grashuis directs the flight crew to remain on course and to be exactly on time for each of the observation points.

The telescope “has 6 degrees of movement of cross elevation so we have to keep the star within the 6 degrees. We ask for 1 degree course changes about every four to five minutes,” Grashuis says.

This is vividly demonstrated as galaxies and stars are displayed across monitors throughout cabin.

It’s an ethereal, surreal sight.

Mission accomplished

At 5:55 a.m., the de-throttling of the engines indicates our initial descent and that our scientific mission will be drawing to a close.

Dawn begins to subtly paint the horizon as the fuselage door closes, putting the telescope to bed.

The closing sequence takes less than 1 minute and is imperceptible.

With flaps fully deployed on approach, we touch down on time – at 6:22 a.m. – after 9 hours, 46 minutes aloft.

SOFIA certainly made it clear to me – as it has to many in the scientific community – that the sky is no longer the limit for telescopes.

A certain eye in the sky called the 747SP has made certain of that.