COSTAR being inserted into Hubble during the First Servicing Misson.	Two images taken of the same region before and after the correction of Hubble's aberration with COSTAR.

COSTAR is not really a science instrument; it is a corrective optics package that displaced the High Speed Photometer (HSP) during Servicing Mission 1 in December 1993. COSTAR was designed to optically correct the effects of the primary mirror's aberration for three of the first generation of instruments aboard Hubble:

• Faint Object Camera (FOC)
• Faint Object Spectrograph (FOS)
• Goddard High Resolution Spectrograph (GHRS)

All the other instruments, installed since HST's initial deployment, were designed with their own corrective optics. When the FOC was replaced by the Advanced Camera for Surveys (ACS) during Servicing Mission 3B in March 2002, COSTAR had also fulfilled its task and was no longer needed. It will be replaced by the new Cosmic Origins Spectrograph (COS) instrument during the upcoming Servicing Mission 4.

	FGS - Fine Guidance Sensors
	FOC - Faint Object Camera