Passive primary mirror concept for SOFIA

The Stratospheric Observatory for Infrared Astronomy is a planned 2.5 meter telescope that will be installed in a modified Boeing 747 aircraft and operated at altitudes above 40,000 feet. The telescope requires a primary mirror with an areal density of less than 70 kg/m(superscript 2) which can operate at elevations from 15 degrees to 70 degrees, and reach thermal equilibrium at -40 degrees C in less than 2 hours. A passive lightweighted monolithic primary mirror design with no active figure control has been shown to be a key element in meeting these requirements. A comparison of mirror designs using alternate mirror materials will be described.