Telescopes on the ground â€“ while having all sorts of good qualities â€“ have the disadvantage of peering through the whole of the atmosphere when looking at the stars. Space-based telescopes like Hubble are an effective way around this, but launching a telescope into space and maintaining it is not exactly cheap. What about something in between the two?

This is where SOFIA (Stratospheric Observatory for Infrared Astronomy) flies in. SOFIA is a converted 747SP airliner that used to carry passengers for United Airlines and Pan Am, but now only has one voyager: an infrared telescope.

SOFIA recently completed the first phase of flight tests to determine its structural integrity, aerodynamics and handling abilities. This first series of tests were done with the door through which the telescope will peer closed, and open-door testing will begin in late 2008.

What makes SOFIA valuable is its ability to fly high in the stratosphere for observations, at around 41,000 feet (12.5km). This eliminates the atmosphere in between the ground and space, which causes turbulence in the light coming through, and also absorbs almost completely some wavelengths of infrared light.

Cloudy nights, normally the bane of observational astronomy, will not impede the ability of SOFIA. Other advantages are that scientists will be able to add specialized observing instruments for specific observations, and fly to anywhere in the world.

The telescope is 10 feet across, and weighs around 19 tons. It will look through a 16-foot high door in the fuselage to study planetary atmospheres, star formation and comets in the infrared spectrum.

During this stage of testing, the ability of the telescope to compensate for the motion and vibrations of the airplane was checked. After the first open-door tests are run this year, the mobile observatory will begin making observations in 2009, and will be completely operational in 2014.

SOFIA is a cooperation between NASA, who will maintain the plane, and the German Aerospace Center, who built and will maintain the telescope.

Source: NASA Press Release