Complex sentence: Originally, "Voyager 2" was planned as Mariner 12 of the Mariner program however, due to congressional budget cuts, the mission was scaled back to be a flyby of Jupiter and Saturn, and renamed the Mariner Jupiter-Saturn probes.
Split into simpler sentences: Originally, "Voyager 2" was planned as Mariner 12 of the Mariner program. However, due to congressional budget cuts, the mission was scaled back to be a flyby of Jupiter and Saturn, and renamed the Mariner Jupiter-Saturn probes.