Corrective Optics Space Telescope Axial Replacement
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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. 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.