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Telescope in the sky

by Bruno Van de Casteele

March 10, 2013

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Donate Imagine that you can get your hands on a Boeing 747. What would you do? Well, probably not what NASA did: they cut a 10-by-10 foot hole in the back of the airplane, and installed a big telescope in it.

That is indeed the SOFIA mission, short for Stratospheric Observatory For Infrared Astronomy and active since 2010. It is a joint collaboration between the US and Germany. And don't worry about the hole... they put back a sliding "door" that weighs over 1,4 tons.

It makes sense indeed, to haul a 100 inch telescope designed for infrared astronomy to a height of more than 40 000 feet, well above most of the water vapor on Earth. And given the temperatures at that height, it helps cooling, too (the telescope bay has to be cooled before take-off to avoid changes in the mirror's shape).

But there is one thing that really impresses me. I have once flown on a Jumbo, and found it behaving like a school bus on a bumpy road. Maybe related to the mountains in Afghanistan or the Caucasus, but even in better conditions one wonders indeed how they can precisely keep faraway astronomical objects in focus. As Wikipedia describes it, this is achieved both by bearings that isolate it from the airplane, and an ingenious "system of gyroscopes, high speed cameras, and magnetic torque motors to compensate for motion". Basically, this ensures that the telescope is locked into the object, even if the airplane around it rocks and rolls (source).

It is indeed a very good way to study infrared objects. Given our atmosphere, most of the infrared light is filtered out, but astronomers rely on it to help study for instance how stars are created. The airplane, at 330 million dollar build costs, is cheaper than a satellite. And because it returns to Earth after mission, it is easier to service and upgrade scientific instruments. Nice!

by Bruno Van de Casteele

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