Flying with the top down

Put a huge scope in an old 747, and you can almost see forever

By , Special to The Christian Science Monitor

Right now, tucked away near the Bay Area in California, NASA scientists are building an entire astronomical observatory in a 747 airplane.

You may have noticed that astronomers tend to build their telescopes in the most out-of-the-way places. All major ground-based observatories are perched on top of desert mountains or on icy plateaus near the South Pole. The highest observatory on Earth is on the top of Mauna Kea in Hawaii. At 14,000 feet, astronomers working there routinely pass out from lack of oxygen. Why put yourself through that?

Astronomers aren't just trying to go to places with good weather, they're trying to go to places with comparatively little air.

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If you're on Earth looking up at the stars, that light had to pass through the atmosphere to get to you. And if you're an astronomer who's trying to make very accurate measurements, all those air currents make the stars look wobbly and distorted, as if you were looking through the hot air rising above a barbecue. The problem is even worse than that, because air absorbs most of the radiation we get from space before it ever gets to us. Objects in space put out radiation in all forms of light, from gamma-rays and x-rays to microwaves and radio. Pretty much all of that gets taken out by our atmosphere, which is good for us, but bad for astronomy.

Cut to the early 1970s, with a bunch of astronomers trying to think out of the box. They wanted to build an observatory to look at infrared light coming from space. Infrared light is what we commonly think of as heat, and it's what most night-vision cameras "see." The reason you can see people in the dark is that these special cameras can image the heat coming from their bodies. Water vapor in our atmosphere absorbs nearly all infrared light from space, so for the longest time, this aspect of the universe was invisible. Even the highest mountains on Earth weren't above enough water vapor to see much infrared light.

So, the astronomers reasoned, why not go higher than that? What if we put a telescope in an airplane and fly above the water vapor? Thus was born the Kuiper Observatory, a modified C-141 aircraft with a 36-inch telescope inside the plane. The telescope itself floated on a cushion of air, allowing it to track stars accurately, despite the vibrations and turbulence of the aircraft. The astronomers stayed in a separate, pressurized cabin, and conducted their experiments.

Now cut to the mid-'80s: a bunch of astronomers trying to think big. What if you put a really big telescope in an even bigger aircraft? What if you put a really big telescope in a 747?

I found out the answer about a year ago in Austin, Texas, at an astronomy convention. A few friends and I went to the Raytheon aircraft modification plant in Waco. A tour had been arranged for us to see the initial modifications to the 747 that would someday be SOFIA, the Stratospheric Observatory for Infrared Astronomy. NASA had obtained an old 747SP aircraft from United Airlines. The plane was in the process of being completely gutted.

I was having the usual queasy reaction of walking through a stripped-down aircraft (I didn't really want to know that 747s are controlled by old, rusty-looking cables and pulleys strung along the interior walls), when my eyes turned to an outline painted on the wall. The painted lines were to guide the workers to cut the hole in the airplane for the telescope to look out. Honestly, my jaw dropped open.

The hole is big enough to drive an 18-wheeler through. It starts about midway up the aircraft and continues all the way over the zenith of the fuselage. The hole will be big enough to accommodate a 2.5 meter-diameter (8 foot) telescope that is currently being built by the German space agency.

The side of this 747 will open up like a garage door to allow a giant telescope to peer out into space. The astronomers will again be in a comfortable, pressurized cabin, and they're even planning to invite teachers and reporters along for the ride.

I may understand the physics of flying, but doesn't such a gaping hole in the plane weaken its structure? How will it handle sudden turbulence or crosswinds? Of course, the engineers assure everyone that, even with the hole, the plane will be stronger than it will ever need to be. That may be so, but the scientists are trying to get the engineers to fly on SOFIA's first flight, just for good measure.

Even with the rather cock-eyed engineering, SOFIA will be a tremendous boon to science. The infrared telescope will be able to peer deep into vast dust clouds to witness the birth of stars and planetary systems. Its sensitive spectrographs might even allow us to search for the chemistry of life on distant worlds. It is practically guaranteed to revolutionize the field of infrared astronomy. It will allow us to probe the origins of the universe and ourselves. It will not, however, earn you any frequent-flyer miles. The people at SOFIA asked United Airlines about that (honestly).

SOFIA will take off from Moffett Field in Sunnyvale, Calif., fly around for eight hours conducting scientific observations, and then land at the same airport. Where, exactly, have you have gone? Well, only to the edge of the universe and back. See for yourself - check out SOFIA's Web site at http://sofia.arc.nasa.gov/

Michelle Thaller is an astrophysicist who works for NASA in Los Angeles.

(c) Copyright 2000. The Christian Science Publishing Society

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