Launched in 1990, the Hubble Space Telescope promised to expand mankind's knowledge of the universe but when the first images from the telescope were received, astronomers were hugely disappointed. The main mirror had been ground incorrectly during manufacture leaving a spherical aberration which resulted in out of focus images. NASA was left with a $4.7 billion egg on its face. After much study and rehearsal, Space Shuttle Endeavour was launched in 1993 on an ambitious mission to correct the telescope's optics as well as other maintenance items. Mission STS-61 was carried out between December 2 and 13. Over the course of 5 spacewalks, the astronauts made the repairs to the telescope. The number of spacewalks in a single mission is still a record today. It was a resounding success; the optical problem was corrected and the telescope has provided crystal clear imagery not possible from ground based telescopes. The discoveries made by the telescope have greatly expanded mankind's knowledge of the universe.