Which instrument utilized COSTAR externally, requiring the external unit to place corrective mirrors in its light path?

Answer

Faint Object Camera (FOC)

The Faint Object Camera (FOC) and the Goddard High Resolution Spectrograph (GHRS) required the external COSTAR unit for correction, while the WFPC2 had internal corrective optics.

Which instrument utilized COSTAR externally, requiring the external unit to place corrective mirrors in its light path?

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