SOFIA, the Stratospheric Observatory for Infrared Astronomy, is the largest airborne observatory in the world, studying the universe at infrared/far-infrared (also called terahertz) wavelengths, capable of making observations that are impossible for even the largest and highest ground-based telescopes. SOFIA is an 80%/20% partnership of NASA and DLR, consisting of an extensively modified Boeing 747SP aircraft carrying a reflecting telescope with an effective diameter of 2.5 meters. SOFIA is based at NASA's Dryden Aircraft Operations Facility in Palmdale, California. During its planned 20 year lifetime, SOFIA also will inspire the development of new scientific instrumentation and foster the education of young scientists and engineers.
SOFIA contributes significantly to answering major scientific questions in the following areas: evolution of the Solar System, planetary atmospheres, star formation, physics and chemistry of the interstellar medium.
GREAT is a first-generation German SOFIA instrument, developed and maintained by the Max-Planck Institute for Radio Astronomy (MPIfR) and KOSMA at the University of Cologne, in collaboration with the Max Planck Institute for Solar System Research and the DLR Institute of Planetary Research. GREAT is a heterodyne receiver for spectroscopic observations in the far- infrared/terahertz spectral regime at frequencies between 1.25 and 5 terahertz (wavelengths of 60 to 220 microns), which are not accessible from the ground due to absorption by water vapor in the atmosphere. At the department of Experimental Planetary Physics the high frequency channel of GREAT is being developed. It operates at a frequency of 4.7 THz.
The main research goal is the detection of the fine-structure line of atomic oxygen (OI), which is major cooling line in both the galactic and extragalactic interstellar medium and a probe of physical parameters in photo-dissociation regions. The local oscillator of the high frequency channel is based on a frequency-stabilized quantum-cascade laser and a superconducting nanostructured hot electron bolometric mixer.
SOFIA/GREAT Special Issue , Astronomy & Astrophysics (Volume 542, May 10, 2012). (http://www.aanda.org/index.php?option=com_toc&url=/articles/aa/abs/2012/06/contents/contents.html)