The Stratospheric Observatory for Infrared Astronomy (SOFIA) is an airborne observatory consisting of a specially modified Boeing 747SP with a 2.7-m telescope, flying at altitudes as high as 13.7 km (45,000 ft). Designed to observe at wavelengths from 0.3 µm to 1.6 mm, SOFIA operates above 99.8% of the water vapor that obscures much of the infrared and submillimeter. SOFIA has seven science instruments under development, including an occultation photometer, near-, mid-, and far-infrared cameras, infrared spectrometers, and heterodyne receivers. SOFIA, a joint project between NASA and the German Aerospace Center DLR, began initial science flights in 2010 December, and has conducted 30 science flights in the subsequent year. During this early science period three instruments have flown: the mid-infrared camera FORCAST, the heterodyne spectrometer GREAT, and the occultation photometer HIPO. This article provides an overview of the observatory and its early performance.

The Stratospheric Observatory for Infrared Astronomy (SOFIA) has recently concluded a set of engineering flights for Observatory performance evaluation. These in-flight opportunities are viewed as a first comprehensive assessment of the Observatory's performance and are used to guide future development activities, as well as to identify additional Observatory upgrades. Pointing stability was evaluated, including the image motion due to rigid-body and flexible-body telescope modes as well as possible aero-optical image motion. We report on recent improvements in pointing stability by using an active mass damper system installed on the telescope. Measurements and characterization of the shear layer and cavity seeing, as well as image quality evaluation as a function of wavelength have also been performed. Additional tests targeted basic Observatory capabilities and requirements, including pointing accuracy, chopper evaluation and imager sensitivity. This paper reports on the data collected during these flights and presents current SOFIA Observatory performance and characterization.

Results are presented from a pilot survey of 3.3 m PAH emission from planetary nebulae using FLITECAM, an instrument intended for airborne astronomy with SOFIA. The observations were made during ground-based commissioning of FLITECAM's spectroscopic mode at the 3 m Shane Telescope at Lick Observatory. Direct-ruled KRS-5 grisms were used to give a resolving power (R) $ 1700. Targets were selected from IRAS, KAO, and ISO sources with previously observed PAH emission at longer wavelengths. AGB stars and PNe with C/O ratios <1 were also added to the target list in order to test PAH detection thresholds. In all, 20 objects were observed. PAH emission was detected in 11 out of 20 observed targets.

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FLITECAM, a near-infrared instrument being developed at the UCLA Infrared lab, will be the first light infrared instrument for NASA's SOFIA aircraft. In addition to its imaging capability, FLITECAM has been equipped with three direct-ruled KRS-5 grisms, allowing observations in 9 spectral bands, and giving nearly continuous spectral coverage from 1 to 5.5 microns. The design favors regions of the spectrum that are heavily attenuated except at high altitudes. The grisms are used with a dual-width long slit to yield a spectral resolution of R~1700 at high resolution and R~ 900 at low resolution. This resolution is better than that of the IRAS, ISO or KAO spectrometers, and covers a spectral regime left unsampled by the Spitzer Space Telescope. When used on the SOFIA, FLITECAM's spectroscopic mode will allow astronomical investigation of near-infrared features at a low water vapor overburden. The grism spectroscopic mode has been demonstrated on the Shane 120 inch telescope at Lick Observatory by observations of astronomical targets of interest, especially the PAH feature at 3.3 microns in HII regions and young planetary nebulae.