The two Voyager spacecraft were launched, taking advantage of rare planetary alignment in the 1970s. The alignment of Jupiter, Saturn, Uranus, and Neptune, which happens every 176 years, reduced the travel time to Neptune to just 12 years from 30 years. After completing their four-year planned mission, the two spacecraft kept going. Today, Voyager 1 and Voyager 2 are the farthest human-made objects in space. They are still functional, but their power levels are dropping at the rate of 4 watts per year.
