The Galileo spacecraft was launched by NASA in 1989 aboard Space Shuttle Atlantis. Its original mission was designed to use a direct Hohmann transfer. However, Galileo's intended booster, the cryogenically fueled (Hydrogen/Oxygen) Centaur booster rocket was prohibited as a Shuttle "cargo" for safety considerations following the loss of the Space Shuttle Challenger. Forced to substitute a lower delta V capable solid rocket upperstage, the IUS, instead of ascending directly to Jupiter, Galileo flew by Venus once and Earth twice in order to reach Jupiter in December, 1995.