On-orbit alignment of the spectrograph channels of the Corrective Optics Space Telescope Axial Replacement (COSTAR)

The corrective optics space telescope axial replacement (COSTAR), designed to restore the high image quality that was originally expected from the Hubble Space Telescope, was successfully installed in the observatory during the first HST servicing mission in December 1993. While verification testing in the lab has shown that the imaging performance of COSTAR is nearly ideal, realization of the expected high spatial resolution of the COSTAR-corrected images depends strongly on the ability to align the COSTAR mirrors with respect to the telescope and axial science instruments. We report on the methods used in the weeks following the servicing mission to optimize the HST-COSTAR performance for the Faint Object Spectrograph and Goddard High Resolution Spectrograph channels. The relatively low spatial resolution afforded by the spectrographs as well as defects in their imaging modes presented special challenges to rapid optimization of the COSTAR correction. Nevertheless, the alignment process quickly converged and has yielded images that are superior to the COSTAR specifications.