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Boeing 747 Modified To Act As Infrared Telescope
xyz writes "A joint project of NASA and the German Aerospace Center has developed a highly modified Boeing-747SP aircraft to carry a 2.5-meter (98.4 inch) infrared telescope. The project SOFIA (Stratospheric Observatory For Infrared Astronomy) will observe radiation in the wavelengths from 0.3 microns to 1.0 millimeters, spanning the visible, infrared, and sub-millimeter portions of the electromagnetic spectrum. The observations will be taken at an altitude of 40,000 to 45,000 feet (12 to 14 km) which is above 99.8 percent of the water vapor in Earth's atmosphere, thus giving it a greater range of observations." Update: 10/31 13:27 GMT by T : Mea culpa -- headline changed to reflect that this telescope is intended for looking out at space rather than down at the Earth.
Sounds like it would make a great surveillance platform, too. It's in the name of science, after all.
"As God is my witness, I thought turkeys could fly." A. Carlson
Boeing 747 Modified To Act As Earth-Observing Telescope
FTFW:
SOFIA is an airborne observatory that will study the universe in the infrared spectrum.
So, by "Earth-observing", what you meant was "everything EXCEPT Earth", right?
"Tell me doctor, with all of your defenses, are there any provisions for an attack by killer bees?"
Been there, done that, in 1974 even
http://en.wikipedia.org/wiki/Kuiper_Airborne_Observatory
The telescope will be exposed to the elements during flight: this photo of the telescope installation shows that the aircraft will be flying around with a 3x3 m hole in its fuselage.
The buffetting and general vibration levels must be huge.
here is how they plan to compensate.
It will probably be mounted on some kind of stabilized gimbal mount, much like the kind used to mount cameras to helicopters. A helicopter mount has to deal with probably 100x the vibration that a 747 in smooth air would have. Keep in mind they are going to not only be able to pick which days they fly, but pick the location as well. It won't be very hard for them to find good conditions. Example of helicopter mount here
This is taken from the SOFIA site.
At visible wavelengths, it is neither atmospheric turbulence, the refractive action of mobile air cells which push light rays around, overhead (actually there is not much air left overhead) that causes the blurring problem, nor the aircraft and telescope shaking that causes the problem, but rather the "shear layer" stream of air shooting past the open airplane cavity where the telescope sits, at 500 mph. This air motion worsens the resolution (the opposite of blurring) to 3 arc secs at visible wavelengths.
But the problem at the long wavelengths is different - it's diffraction. Basically, the far-infrared light observed by SOFIA passes through the shear stream of air unperturbed. But this light has such a long wavelength, 100x to 1000 times the wavelength of visible light, that the SOFIA telescope is of insufficient size to focus it sharply, and blurriness results. At wavelengths in the far-infrared, like 60 micrometers, there is significant blurring due to this effect. The telescope is actually held extremely steady while observing occurs, even in turbulence. It's held about as stable as a mountaintop telescope sitting on a 10 meter cement foundation, but diffraction still blurs the image.
So how do you do this? First, you isolate the telescope from the airplane by mounting it on a spherical pressurized oil bearing. The plane shakes and quakes, but the telescope doesn't feel it. Second, you direct the wind away from the telescope by shaping the side of the airplane so as to deflect it, and install a little deflector fence on the edge of the telescope cavity as well. Third, you stabilize the telescope against sudden motion (wind does get through) by spinning three orthogonal gyroscopes which are rigidly attached to the structure, and fourth, you steer the telescope so as to keep it steady, by tracking a distant star and giving the telescope magnetical nudges to point it toward a fixed direction.
Some people are only alive because it's against the law for me to hunt them down and kill them.
Vibration transferred from the plane is relatively straightforward to solve (although it can expensive to do it to tolerance). The biggest challenge that caused the most delay (years) for SOFIA was the layer of air that was happy to be going around the side of the plane and then suddenly sees a 3m gap in the side of the plane. This led to a significant amount of turbulence and both shaking of the telescope and degradation of the "seeing" (the sharpness of images through the atmosphere and optics; in this case the very local atmosphere). Significant redesign and careful consideration of the exact shape, baffling, etc. of the hold and telescope mount was necessary to overcome this problem.