The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a 2.7 meter telescope (with an effective aperture of 2.5 m) carried aboard a Boeing 747SP aircraft. It is the successor to the smaller Kuiper Airborne Observatory (KAO), which was operated by NASA.
SOFIA is a joint project of NASA and the Deutsches Zentrum für Luft- und Raumfahrt (DLR, the German Space Agency). Flight operations are being conducted out of the NASA Armstrong Flight Research Center in Palmdale, California. The SOFIA Science Center (SSC), responsible for overseeing the scientific output of the mission, is located at the NASA Ames Research Center in Moffett Field, California. The Science Mission Operations are jointly managed by the Universities Space Research Association (USRA) for NASA and by the Deutsches SOFIA Institut (DSI), in Stuttgart, for DLR. Aircraft operations are handled by NASA Armstrong.
The observing altitudes of SOFIA are between 37,000 and 45,000 feet, above 99% of the water vapor in the Earth's atmosphere. The telescope and instruments provide imaging and spectroscopic capabilities in the 0.3-1600 µm wavelength range, making SOFIA one of the premier infrared/sub-millimeter astronomical facilities. The telescope is located in an open cavity in the rear section of the aircraft, with a view out of the port side. Observations can be done at elevations between +20 and +60 degrees. The telescope is inertially stabilized and the pointing accuracy is about 0.5 arcseconds. The seeing is expected to be diffraction limited at all wavelengths longward of about 15 µm. There will be about 8 hours of observing time on each flight, and at full operations capability there will be three flights per week. SOFIA is expected to have a lifetime of 20 years.
SOFIA has 6 instruments, both imagers and spectrographs, covering a wide range in wavelength and spectral resolution. These include four Facility Science Instruments (FSIs), FORCAST, FIFI-LS, FPI+, and HAWC+, which are maintained and operated by Science Mission Operations (SMO), two Principal Investigator-class Science Instruments (PSIs), GREAT and EXES, maintained by the respective instrument teams. FSIs and PSIs are available to all General Investigators. Additionally, SOFIA will carries a Water Vapor Monitor, which is used to measure the precipitable water vapor level along a fixed line of sight. The resulting values will be used to calibrate the data obtained using the science.
The U.S. share of the overall observing time is 80%. This US time will be awarded based on peer review of proposals submitted in response to periodic proposal calls. The calls will be open to both the US and international astronomical communities. The remaining 20% of the time will be allocated to the German astronomical community. Observing on SOFIA will be done in service, or queue, mode and it is not required that General Investigators be present on the aircraft while their observations are being obtained. However, the program will invite one or more General Investigators on each flight.
SOFIA offers astronomers a unique platform, providing regular access to the entire mid-infrared/far-infrared wavelength range. With a wide range of instruments, SOFIA complements ground based facilities such as Keck, Gemini, JCMT and ALMA as well as current and future space-based IR missions (Spitzer, Herschel, JWST). The capabilities of SOFIA and its potential are described in several Design Reference Mission case studies and in the "Science Vision" document, which are available here. By including new instruments and upgrades to existing instruments regularly, SOFIA will retain its state-of-the-art capabilities. Via this instrument program SOFIA will enable the development of the technology required for future infra-red instrumentation.