Proceedings Article | 23 June 2006
Proc. SPIE. 6267, Ground-based and Airborne Telescopes
KEYWORDS: Diffraction, Telescopes, Mirrors, Contamination, Sensors, Control systems, Electroluminescence, Vignetting, Bismuth, Aerodynamics
The 2.5 meter (m) effective diameter telescope on SOFIA - the Stratospheric Observatory for Infrared Astronomy - will operate in an open-port cavity which will be closed below operating altitudes by a cavity-door assembly. When
operating, the telescope will view the sky through an aperture defined by an aperture assembly (AA) with a nearly
rectangular opening extending 112 inches (2.84 m) in elevation (roll) and 129 inches (3.27 m) in cross-elevation. The
aperture will be servo-controlled in roll to track the telescope elevation (EL), and the aircraft heading will be adjusted to
maintain the telescope centered on the aperture in cross-elevation (XEL). An upper rigid door (URD) and lower
flexible door (LFD) move with the aperture to minimize the opening into the cavity containing the telescope. This paper
describes basic parameters of the door system, and estimates possible science impacts of its specification, configuration
and planned operation. Topics included are the geometry, expected aerodynamic disturbances, control system, gear life,
influences of radiative and diffraction effects on science instrument performance, testing, operational considerations,
and development status. As designed, the door system is expected not to limit the performance of science instruments or
observatory operational efficiency, but several potential concerns are considered. These include modulation of stray
and diffracted radiation, reliability, and maintainability.
