One afternoon more than four decades ago, University of Tennessee astronomer Gary Flandro, then a Caltech graduate student working at the Jet Propulsion Laboratory in Pasadena, was playing with numbers, as scientists and astronomers do. He realized that in 1977 the outer planets – Saturn, Jupiter, Neptune and Uranus – would be in a rare alignment – the first since Thomas Jefferson’s days.
Using the gravity of each planetary encounter, a spacecraft could photograph, then slingshot past and beyond each planet, enabling the robots to make a grand tour and visit them all on one mission of interplanetary exploration.
Thus began the amazing, revelatory and romantic voyage of Voyager I and Voyager II, which are still out there voyaging as the farthest man-made objects ever to leave Earth.
This month, scientists and stargazers widely mourned the demise of the Voyagers’ offspring, Cassini. The NASA mission to Saturn leaves some 13 years’ worth of invaluable data and images in its wake.
This month, scientists and stargazers widely mourned the demise of the Voyagers’ offspring, Cassini, on Saturn. But the Voyager project that inspired it is still going strong. As you read this, in fact, Voyager I continues its journey away from home at 10 miles per second deeper into the vast darkness of interstellar space outside our solar system, with Voyager II off on a tangent of its own.
But the Voyager project that inspired it is still going strong. As you read this, in fact, Voyager I continues its journey away from home at 10 miles per second deeper into the vast darkness of interstellar space outside our solar system, with Voyager II off on its own tangent beyond Pluto.
Like E.T. they “phone” home every day, sending back data on magnetic fields and solar winds from places mankind may never visit. Voyager I is already reading the fields of stars we can only see as dots of light in the night sky.
The speed of light is 186,000 miles per second, or almost eight times around the equator in a flash. Even at that speed, Voyager’s messages of discovery take 18.5 hours to reach home and another 18.5 hours for NASA/JPL scientists to acknowledge we’re still listening.
So faint are the signals – a trillionth of a watt – they must be captured and enhanced by NASA’s Deep Space Network. That’s a worldwide array of nearly football-field-sized dishes staring skyward from Madrid, Canberra and the Mojave Desert observatory at Goldstone, outside Barstow, positioned so one of them can always hear the identical craft that each weighed 1,760 pounds on Earth.
“I have a great fondness for these instruments,” said Suzanne Dodd, the latest of many Voyager project managers since their 1977 launches. “They have the problems of any senior citizen, but still keep on.”
Set aside the incredible engineering involved. The Voyagers’ discoveries are legion:
First volcanoes beyond Earth (Jupiter’s moon Io), first detection of lightning beyond Earth (Jupiter), discovery of 23 unknown moons, plus first images of rings around Uranus, Neptune and Jupiter and icy plumes shooting 50 miles into space from an ocean beneath the frozen crust of Jupiter’s moon Europa, among other revelations.
Half the world’s population was yet to be born when Voyager I took flight 40 years ago this month. The twin craft were built with 1970s technology, meaning the cellphone you may be reading this on has 240,000 times the memory of each Voyager. Crucially, however, the memory was re-programmable.
Due to the distances involved, there was no time for instructions. The Voyager probes had to know what to do and where to aim their cameras every few years each time they encountered a planet.
Because of the darkness in deep space, solar panels couldn’t work. So the Voyagers are powered by plutonium-238, whose decaying heat runs their generators. But the radioactive metal has a half-life of only 88 years, meaning it’s about halfway through its half-life.
No one anticipated these intrepid little guys lasting so long. Power production wanes four watts a year. Nothing to see visually out there, so Voyagers’ cameras are already shuttered. Soon, heaters and other instruments will follow. Dodd hopes to squeeze another seven to ten years of life yet.
That may silence the explorers – but will not end their lives. “We did the best we could with a little luck,” says Ed Stone, a project scientist from the start.
Put this in your cellphone calendar: Eventually, each Voyager will go into orbit around the center of our Milky Way. Each one of those orbits will take 225 million Earth years.
Andrew Malcolm is an author and veteran national and foreign correspondent. Follow him on Twitter @AHMalcolm.