Marshall Space Flight Center of the launch vehicle. Finally, on April 24, 1990, on Mission STS-31, Shuttle "Discovery" launched the Hubble telescope successfully into its planned orbit. Almost immediately it was realized that the optical performance was not as expected; analysis of the flawed images showed that the primary mirror had been ground to the wrong shape, resulting in spherical aberration. Fortunately, the Hubble telescope had been designed to allow in-space maintenance, and in December 1993, mission STS-61 carried astronauts to the Hubble to make corrections and change some components. A second repair mission, STS-82, was made in February 1997, and a third, STS-103,
Spitzer Space Telescope environment was poorly suited to an onboard infrared telescope due to contamination from the relatively "dirty" vacuum associated with the orbiters. By September 1983 NASA was considering the "possibility of a long duration [free-flyer] SIRTF mission". "Spitzer" is the only one of the Great Observatories not launched by the Space Shuttle, as was originally intended. However, after the 1986 Challenger disaster, the Centaur LH2–LOX upper stage, which would have been required to place it in its final orbit, was banned from Shuttle use. The mission underwent a series of redesigns during the 1990s, primarily due to budget considerations. This resulted