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Home > News and Updates > SOFIA has first "On-Sky" Tests!


SOFIA has first "On-Sky" Tests!

On 18 August, 2004, SOFIA was towed out of its hangar and the telescope was pointed at the sky. For the very first time, light from a celestial source (in this case, the star Polaris) passed through the SOFIA telescope and was detected by the HIPO instrument, which was bolted to the scientific instrument mount.

On-sky tests were repeated on 25 August after adjustments were made to optimize the alignment of the telescope optics. Images and data below on this page were obtained as part of this second set of tests.

Telescope Assembly and HIPO instrument on-sky test crews at work in the SOFIA cabin, August 25, 2004. View looking forwards.

An image of Polaris as seen by HIPO through the SOFIA optics (with its diamond-turned aluminum backup secondary mirror). The FWHM of the primary peak seen is 2-3 arcsec. The secondary peak is most likely due to aberrations in the backup secondary mirror used in these tests that is primarily intended for use at long wavelengths. The nominal secondary mirror for SOFIA is made of polished SiC, and is expected to have much better optical quality. These images and test data are provided courtesy of Brian Taylor, Ted Dunham and the HIPO team.
Image of Polaris seen through HIPO
A contour plot of a region of the image centered on Polaris (note the axes in this image are in units of pixels - HIPO has a plate scale of 0.327 arcsec/pixel).
Countour plot of star image
A Shack-Hartmann test image corresponding to the Polaris imag above. This is used to measure the wavefront tilts across the telescope entrance pupil.
Shack-Hartmann image
A plot of tracking data taken with HIPO showing better than 0.8 arcsec RMS tracking.
Typical pointing stability during Focal Plane Imager tracking.   Data obtained 8/24/04 UT.    Plot axes units are HIPO pixels, 0.327 arcsec.

HIPO and its proud crew of designers and builders from Lowell Observatory (clockwise from upper left: Ted Dunham, Brian Taylor, Ralph Nye, and Tom Bida), can be seen in this photograph, taken from inside the aircraft cabin. HIPO is the black instrument mounted on the blue instrument mount. The SOFIA telescope is behind the white pressure bulkhead at the back and cannot be seen in this picture.


Page Last Updated: July 8, 2005

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