NASA has fitted a 17-tonne telescope with an effective diameter of eight feet on a modified Boeing 747 jetliner that the US space agency is using as a flying observatory to study stars.

The infrared telescope called “Stratospheric Observatory for Infrared Astronomy” (SOFIA) is mounted behind a sliding door that reveals it to the skies.

The jet can stay airborne for over 12 hours and its range is up to 6,625 nautical miles (7,624 miles).

According to NASA, “The data provided by SOFIA cannot be obtained by any other astronomical facility on the ground or in space.”

SOFIA is mobile, so it can better spot transient space events like supernovae and comets.

The telescope, built with the help from German Aerospace Centre (DLR), can easily be repaired or reprogrammed when necessary.

NASA plans SOFIA — now in Germany for its last extensive maintenance and refitting leg — to launch in 2015 which will keep flying for another 20 years, wired.com reported.