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SOFIA, the Stratospheric Observatory for Infrared Astronomy, is an airborne observatory that will study the universe in the infrared spectrum. A Boeing 747-SP aircraft will carry a 2.5 m telescope designed to make sensitive infrared measurements of a wide range of astronomical objects. In 2008, SOFIA's primary mirror was demounted and coated for the first time. After reintegration into the telescope assembly in the aircraft, the alignment of the telescope optics was repeated and successive functional and performance testing of the fully integrated telescope assembly was completed on the ground. The High-speed Imaging Photometer for Occultations (HIPO) was used as a test instrument for aligning the optics and calibrating and tuning the telescope's pointing and control system in preparation for the first science observations in flight. In this paper, we describe the mirror coating process, the subsequent telescope testing campaigns and present the results.

Observations were made during the reentry of the Stardust sample return capsule on 15 January 2006 in order to calibrate the level of radiation from the capsule surface, from the bow shock, and from its wake. A sensitive cooled charge-coupled device camera was used, equipped with a grating to simultaneously record the first-order spectrum of the capsule and that of the background stars. The radiation of the capsule was dominated by the graybody radiation from the hot surface. This graybody radiation was calibrated against the known radiation of background stars. The purpose of this calibration was to provide a cross check for other instruments participating in the airborne Stardust Entry Observing Campaign. In addition, eight short-exposed images were obtained that show the development of billowing and the distortion induced by winds.