The possibility for an expendable rocket to be used was also suggested, if the spacecraft was designed to meet certain constraints.[1] On March 12, 1987, the mission was rescheduled for launch in 1992, in lieu of other backlogged missions (Galileo, Magellan, Ulysses) after the Space Shuttle Challenger disaster.[2] Along with a launch delay, budget overruns necessitated the elimination of two instruments to meet the 1992 planned launch.[3][4] As the development matured, the primary science objectives were finalized as:[3][5][6]