Apr. 24-29, 1990: During the flight of the Space Shuttle Discovery (STS-31) the crew deployed the Hubble Space Telescope. Soon after deployment, controllers found that the telescope was flawed by a "spherical aberration," a mirror defect only 1/25th the width of a human hair, that prevented Hubble from focusing all light to a single point.

At first many believed that the spherical aberration would cripple the 43foot-long telescope, and NASA received considerable negative publicity, but soon scientists found a way with computer enhancement to work around the abnormality and engineers planned a servicing mission to fully correct it with an additional instrument.

Even with the aberration, Hubble made many important astronomical discoveries, including striking images of galaxy M87, providing evidence of a potentially massive black hole.