Corrective Optics Space Telescope Axial Replacement

The Corrective Optics Space Telescope Axial Replacement (COSTAR) is the instrument designed to correct Hubble Space Telescope's spherical aberration for light focused at the FOC, FOS and GHRS instruments. Built by Ball Aerospace Corp., it replaced the High Speed Photometer (HSP) during the first Hubble Servicing Mission in 1993.

Later instruments, installed after HST's initial deployment, were designed with their own corrective optics. COSTAR was removed from HST in 2009 during the fifth servicing mission and replaced by the Cosmic Origins Spectrograph. It is now on exhibit in the Smithsonian's National Air and Space Museum.