What was the name of the instrument installed in orbit to correct the spherical aberration?

Answer

COSTAR (Corrective Optics Space Telescope Axial Replacement)

The primary fix was packaged into a new instrument called the Corrective Optics Space Telescope Axial Replacement (COSTAR), designed to intercept the imperfect beam and introduce opposite optical defects.

What was the name of the instrument installed in orbit to correct the spherical aberration?

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