SOFIA

SOFIA (for Stratospheric Observatory for Infrared Astronomy) is an aircraft-based infrared observatory that was operated by NASA and the German Aerospace Center (DLR) from 2010 to 2022. The aircraft is a Boeing 747SP, which cruises at 41,000 feet (12500 meters, 40% more altitude than the top of Mount Everest), high enough that 85% of the full range of infrared is visible. The opening for the telescope (which is opened at altitude) has no glass. The telescope is 2.5 meters in diameter, is built to be very light and compact, using a very short focal length. SOFIA instruments:

• EXES - mid-IR echelle spectrometer.
• FIFI-LS - far-IR imaging grating spectrometer.
• FORCAST - mid-IR camera & grism spectrometer.
• GREAT - far-IR heterodyne spectrometer.
• HAWC+ - far-IR bolometer camera & polarimeter.
• FPI+ - Focal Plane Imager.

Earlier listed:

• HAWC.
• FLITECAM - near-IR camera.

Undergoing development:

• HIRMES - mid-IR bolometer spectrometer.

SOFIA's last day of operation was September 30, 2022. In theory, it could be revived, but there doesn't seem to be sufficient interest at the necessary levels. Through its life, there had been periodic proposals to terminate SOFIA operation given its high operating cost and the limited observation it carries out, which would free money for astrophysical missions judged more effective. SOFIA had the advantage over space telescopes regarding telescope and instrument maintenance and upgrades during its lifetime, and it cost considerably less to develop and initiate than space telescopes. However, it had higher ongoing cost maintaining and operating the aircraft, and its observations were limited by the amount of time that the jet could be flown and by the weather.

However SOFIA did offer spectral bands that are not covered by any other comparable telescope: much of the infrared spectrum is blocked from ground telescopes and not covered by current space telescopes, such as the James Webb Space Telescope. There does exist one considerably-smaller (61-cm) ground telescope in Antarctica covering some of the missing wavelength-range, the High Elevation Antarctic Terahertz Telescope (HEAT). An obvious notion is a future space telescope that would cover the bands that SOFIA covered and some such space telescopes have been proposed (FIRSST, OST, PRIMA, SALTUS, SPICA), any of which would be launched well into the 2030s. In the nearer term are some balloon-based telescope projects (GUSTO, and to some degree, TIM) covering some of what SOFIA covered.

The SOFIA 747's call sign is NASA747 and tail number is N747NA.