The Voyager Missions – Still Calling Home after 37 Years

The Voyager spacecraft were launched by scientists from the Jet Propulsion Laboratory in 1977 with the audacious goal of flying past the four outermost planets in our Solar System over a period of 12 years – at a time when it was still proving difficult to fly spacecraft on year-long journeys to the closer planets. In fact the reason there are two Voyagers is because JPL thought at least one might not survive. But due to some inspired design decisions by JPL researchers, a host of back-up systems, “and a lot of good luck,” both spacecraft spectacularly completed the first parts of their missions and now, 37 years later, are still sending back data as they head off into interstellar space. Along the way they caused a “revolution in our understanding of the Solar System,” Ed Stone, the former JPL director, told LAWAC members on Wednesday night.

Stone, who has been the chief scientist in charge of the Voyager mission since it was first planned in 1972, gave a remarkable presentation about what is still an outstanding achievement of American space technology. He reminded the audience that our entire space program was barely 20 years old at the time they planned the Voyager mission – “we couldn’t imagine then that these spacecraft would last for more than 40 years.” Under their current trajectories, Voyager 1, now 12 billion miles away, and Voyager 2, 10 billion miles away, are expected to start shutting down some instruments by 2020, and to finally go offline in 2025. But even then they will keep orbiting the center of the Milky Way galaxy every 225 million years, held in place by the galaxy’s own gravity, for billions of years. “They will be our silent ambassadors to the Milky Way.”

It all started in 1965 when a Caltech graduate student who was working at JPL in Pasadena realized that there would soon be a rare alignment of the four outermost planets, Jupiter, Saturn, Uranus and Neptune, that it would occur only once in 176 years, and that it would require a launch from Earth in a small window between 1976-78. It seemed a long shot, but starting in 1972 JPL began building not one but two spacecraft to make the journey. “The reason we had two was that [the criterion for] mission success was one spacecraft making the four-year journey to Saturn – that’s how risky it was! Fortunately both made it and they kept going,” said Stone.

As they passed by the four planets and their moons, the Voyagers found the first volcanos ever recorded outside Earth on Jupiter’s moon Io, ten times more active than those on our own planet. “Suddenly our terracentric view of the Solar System became clearly a bit limited,” said Stone. Before Voyager the only know liquid oceans were here on earth – but Voyager found liquid oceans on Europa, another moon of Jupiter, beneath its frozen surface. They also found a nitrogen atmosphere on Saturn’s moon Titan, and erupting geysers on Neptune’s moon Triton, at the chilly temperature of 390 degrees Fahrenheit below zero. “It gave us a whole new view,” said Stone.

Having passed the outlier, Neptune, in 1989, Voyager 2 joined Voayger 1 on their dual tracks out of the heliosphere that encapsules the Solar System and towards interstellar space – buffeted by an interstellar wind that travels at 1 million miles per hour. Voyager 1 reached the boundary on August 25 2012, and is now sending back measurements of the particles and the magnetic field of the Milky Way, which are quite different to the readings inside our Solar System. The Voyager’s radio communications, which are sent out by their weak 23 watt transmitters at the very low speed of 160 bits a second (far slower than the old phone modems) are still picked up by NASA’s Deep Space Network of antennas that are located in California, Spain and Australia.

Asked about life outside our planet, Stone said he thought “there is life in lots of places – maybe even in our own solar system. It’s hard to believe it’s not out there because there are so many planets – it is our challenge to find which planets might be able to support microbial life.” He dismissed the possibility of the Chinese sending a human mission to Mars before the US. “I hope it will happen some day but I don’t think it will happen for the next few decades – and it will have to be an international mission, because it will be so complicated.”

Of course as Ed Stone’s remarkable career and that of his colleagues shows, “complicated” is what JPL does best.