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An error in the shape of Hubble’s primary mirror prompted the development of a corrective
device known as COSTAR. Installed in place of an existing instrument during the first
servicing mission, COSTAR contained a mechanical arm of optics that was deployed into the
telescope’s light path, correcting its focus.

Called the Wide Field and Planetary Camera 2 (WFPC2), this

instrument was meant for installation by astronauts at a future
date. Optics experts realized they could build corrective optics
into this camera to counteract the flaw in the primary mirror. Meanwhile, Hubble

scientists and engineers devised a set of nickel- and quarter-sized mirrors to remedy
the effects of the primary mirror on Hubble’s other instruments. Labeled the Corrective Optics
Space Telescope Axial Replacement (COSTAR), this device could be deployed into the light paths of the
telescope’s other instruments to focus their images properly.

In December 1993, astronauts installed COSTAR during a series of spacewalks. This ambitious endeavor successfully restored
Hubble ’s vision to the designers’ original expectations. On subsequent days during the mission, astronauts also upgraded
various components of the spacecraft including ESA-provided solar arrays and associated control electronics. During the many

years following that historic first servicing mission, Hubble has amassed a spectacular data treasure trove for the world—
thousands of clear, deep views of the universe. Astronomers from around the world have used the telescope to answer some of
the most pressing astronomical questions of our time, and its discoveries have also spawned a host of follow-up investigations.

As new technology became available, Hubble ’s innovative, modular design enabled astronauts to upgrade and enhance
it through four additional servicing missions. In 1997, Servicing Mission 2 vastly improved Hubble ’s spectroscopic
capabilities with the insertion of the Space Telescope Imaging Spectrograph (STIS). Using it, astronomers confirmed
the existence of supermassive black holes in the centers of galaxies and also showed that black-hole masses are

tightly correlated with the masses of the surrounding ancient stellar population. During the 1997 service call, the
addition of the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) opened Hubble ’s view of the universe
to a new spectral regime—those wavelengths slightly longer than visual light. This near-infrared sensitivity has
helped astronomers untangle the complex processes in the early universe that led to the formation of galaxies,

including our own Milky Way.

During Servicing Mission 3A in 1999, spacewalking astronauts enhanced many of Hubble ’s subsystems—replacing its
central computer; adding a new, solid-state data-recording system to replace its aging magnetic tape drives; and swapping

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