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Soon after Hubble began sending back images in 1990, scientists discovered the telescope's primary mirror had a flaw called spherical aberration. The outer edge of the mirror was ground too flat by a depth of 4 microns, which is roughly equal to one- fiftieth the thickness of a human hair. The flaw resulted in images that were fuzzy because some of the light from the objects being studied was being scattered. After the amount of aberration was understood, scientists and engineers developed WFPC2 and COSTAR, which were installed in Hubble during the first space shuttle servicing mission in 1993.
COSTAR deployed corrective optics in front of three of Hubble's first generation instruments - the Faint Object Camera, the Goddard High Resolution Spectrometer, and the Faint Object Spectrograph. COSTAR could not correct the vision for the Wide Field/Planetary Camera (WFPC) currently on Hubble. So, a replacement instrument, which was already in work as an upgrade, was hastened to completion as WFPC2. WFPC and WFPC2 were built by
WFPC2 was separately fitted with corrective optics to compensate for the scattered light from the primary mirror. This allowed the camera to record razor-sharp images of celestial objects - from nearby planets to remote galaxies -- for more than 15 years. A landmark observation was the Hubble Deep Field taken in 1995. This long-exposure captured the light of 4,000 galaxies stretching 12 billion years back into time.
WFPC2 was one of Hubble's main cameras until the Advanced Camera for Surveys was installed in 2002. WFPC2's 48 filters allowed scientists to study precise wavelengths of light and to sense a range of wavelengths from ultraviolet to near-infrared light.
COSTAR and WFPC2 were removed from Hubble in 2009 during the fifth and final shuttle servicing mission and returned to Earth. COSTAR's removal made way for the Cosmic Origins Spectrograph. WFPC2 was replaced by Wide Field Camera 3.
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