Voyager 1 logged yet another milestone in space history August 17 when it crossed an invisible boundary that marks 100 astronomical units (AU) from the Sun -- about 15 billion kilometers (9.3 billion miles) out there -- farther away than any human-made object has ever gone in space. It's headed now for interstellar space. Voyager 2, at 80 AU, is about six years behind.
Nearly 30 years after the twin Voyager spacecraft took off from Cape Canaveral, the mission has become a legend in its own time, rewriting the planetary science books, and introducing us to our own diverse neighborhood. The twins, meanwhile, have become the poster children of space exploration, still communicating after all these years and sending data home regularly via the Deep Space Network.
“One of our objectives was to explore interstellar space, and following the successful Saturn flyby in 1981, the mission was renamed the Voyager Uranus Interstellar Mission," said Voyager Chief Scientist Ed Stone, professor of physics and director of the Space Radiation Laboratory at the California Institute of Technology (Caltech), and a former director of the Jet Propulsion Laboratory (JPL), where the mission was designed and is being managed. "This was a boldly optimistic goal because we knew neither how long it would take to reach interstellar space nor how long the spacecraft would continue operating beyond their original 4-year mission to Saturn which is only 10 AU from the Sun. It is indeed remarkable that the Voyager spacecraft have already operated 7 times longer and 10 times further from the Sun than originally planned," he said.
"With some luck, the two will reach interstellar space while they still have electrical power," continued Stone, who has been the project scientist on the mission since 1972, overseeing the efforts of 11 teams of scientists in their studies of Jupiter, Saturn, Uranus, and Neptune. "Whether they reach interstellar space or not under power, they will be -- and [Isaac] Newton tells us this -- humankind's first interstellar probes, the first objects launched from Earth to reach interstellar space. Crossing into interstellar space will be a major milestone in our journey from Earth into the Milky Way."
Together, Voyager 1 and Voyager 2 -- twin probes launched on September 5, 1977 and August 20, 1977 -- represent the most successful planetary exploration mission of all time. In their flybys of all the outer planets, and dozens of other planetary bodies, the Voyagers set the benchmark in planetary exploration on an undertaking that has come to be deemed as one of NASA’s greatest triumphs.
The two 1-ton spacecraft returned more knowledge-changing data than any mission before or since: stunning photographs that consistently revealed our solar system to be much more diverse, complex, and beautiful than anyone ever imagined, and a veritable bounty of scientific information to go along with them.
Even now, both Voyager spacecraft are still communicating with Earth. Many of their instruments are still functioning, as the two spacecraft head in different directions out of the solar system on their "Interstellar Mission." Voyager 1 has now passed the termination shock, where the solar wind abruptly slows down as it pushes against the interstellar medium.