Costar

COSTAR stands for Corrective Optics Space Telescope Axial Replacement. It was a system of optical correction units created for the Hubble Space Telescope to address the spherical aberration of its primary mirror that limited image sharpness in several early instruments. COSTAR was designed to re-image the telescope’s focal plane onto corrected optics, enabling clearer and more accurate scientific observations with instruments that did not have their own corrective optics.

The COSTAR assemblies were mounted in front of affected instruments, providing precise, instrument-specific corrections. The primary beneficiaries were instruments such as the Faint Object Camera, the Faint Object Spectrograph, and the Goddard High Resolution Spectrograph, which otherwise produced blurred images due to the mirror’s aberration. The corrective optics allowed these instruments to achieve substantially improved resolution and data quality without waiting for new hardware.

Deployment and impact: COSTAR was installed during the first Hubble servicing mission in 1993, alongside the replacement of the original Wide Field and Planetary Camera with the WF/PC2, which incorporated built-in aberration correction. The combination of COSTAR and WFPC2 dramatically enhanced Hubble’s imaging performance and enabled a broad range of high-resolution astronomical observations in the 1990s and beyond.

Legacy: COSTAR represented a pivotal, if temporary, engineering solution that mitigated a fundamental flaw in the telescope’s initial design. As newer instruments with their own corrective optics were introduced, the reliance on COSTAR diminished. The installation is widely regarded as a crucial contributor to restoring Hubble’s scientific capabilities in its early operational years.