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.

Comments

Mount tinfoil Hats!

[R2.0]

Sounds like it would make a great surveillance platform, too. It's in the name of science, after all.

Re:Mount tinfoil Hats!

[bornyesterday]

one of these days, people will realize that the aluminum and tinfoil companies have been coerced by the government into impregnating their materials with microscopic brain-scanning devices and that wearing tinfoil hats has actually been increasing the effectiveness of the governments ability to read the minds of its conspiracy theorist and overly private citizens.

Earth-observing?

[Scutter]

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?

Re:Vibration?

[Quantos]

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.