SOFIA - a Stratospheric Observatory for Infrared Astronomy

SOFIA is an airborne observatory de­ signed to address fundamental questions relating to galactic and extragalactic as­ tronomy, and to the origin and evolution of the solar system. Much of the radiant energy in the Universe lies at infrared wavelengths which are not observable using ground-based telescopes. SOFIA will provide ready and frequent access to these wavelengths with spatial and spec­ tral resolutions that will not be matched this century. SOFIA comprises a telescope, with an overall diameter of 2.7 m and an effective aperture diameter (entrance pupil) of 2.5 m, operating from a Boeing 747 aircraft at altitudes between 41000 and 45000 feet. It will provide astronomers with rou­ tine access to infrared, far infrared and submillimetric wavelengths unavailable on the ground, and with the means to ob­ serve transient astronomical events from anywhere in the world. The project is currently being studied jointly by NASA and the German Science Ministry (BMFT), Phase B studies on air­ craft modification and the telescope system having been completed in 1989 (Phases C and D should start at the end of 1990). The overall concept is based on 15 years of experience with NASA's Kuiper Airborne Observatory (KAO) which SOFIA will replace in the mid 1990's. However, SOFIA'S wavelength range covers nearly four decades of the electromagnetic spec­ trum, from the visible, through the infrared and submillimetric, to the microwave region. It will thus be roughly ten times more sensitive for compact sources than KAO, enabling observations of fainter objects and measurements at a higher spectral resolution. The angular resolving power for wavelengths above 30 microns will be three times larger, permitting more detailed imaging in the far infrared.