Voyage of The Voyagers: First Quarter-Century
On August 20, 1977, the compact disk, the microwave oven, and the fax machine were tools that could only be glimpsed on the technological horizon. Email was not part of any global Post Office’s pledge to deliver. Indeed the sports’ world had yet to witness golfer Tiger Woods’ first baby steps. But 25 years ago, a pair of spacecraft started out to show the Earth’s immediate solar neighborhood that at least one planet was capable of producing a hardware record of itself–complete with the likes of recorded music from Mozart, Bach and Chuck Berry.
In 1977, setting off to probe Jupiter and Saturn, Voyager 1 launched August 20 and Voyager 2 launched Sept 5, 1977. Today the twin spacecrafts are literally the farthest human-made object. Beyond the horizon of human imagination even one generation before it–the Voyager series celebrates their first quarter century of exploration.
As the spacecraft venture to the ends of the solar system, remote-control reprogramming has endowed their electronics to gain greater capabilities than they possessed when they left the Earth. Their two-planet mission to Jupiter and Saturn doubled to become four, including Uranus and Neptune. Their five-year lifetimes first stretched to 12 and today, twenty-five and counting.
Credited with some of the most spectacular images of the Giant Planets–Jupiter and Saturn– the Voyagers also discovered active volcanoes on one of Jupiter’s moons, Io. When flying by Neptune, the Voyagers notably photographed an atmospheric storm of near planetary proportions.
But even with these historical milestones, the semi-retired Voyager mission today still performs more than just its own maintanence, but indeed targets two key, remaining jobs. First, at least one of the Voyagers (likely Voyager I) will find the far edge of any solar influence (boundary where the Sun’s wind meets its equal as interstellar wind).
Break on Through to the Other Side
The science of finding the solar boundary, or what’s beyond the Sun’s particle wind (called the heliopause) is daunting. Already the most distant Voyager 2 is 85 times the Earth-Sun distance (85 Astronomical Units, or 1 AU=93 million miles). The closer Voyager I is 68 AU. The technical definition of the heliopause is the place where the expanding solar bubble of wind is exactly counterbalanced by the inward interstellar wind. Where solar and interstellar fluences meet, is a region of our solar neighborhood far beyond the known planets.
Talking like a 70’s show
But in addition to their remaining science goals, the Voyagers had a strong cultural story to tell. Both spacecrafts shipped out with a high-density record of life on Earth. They literally carried a gold record to tell our history. Largely inspired by Carl Sagan’s unique mix of curiousity and skepticism towards extraterrestrial investigations, the voyagers carried a ‘message in a bottle’ version for future posterity. The voyagers’ audio record from our planet was meant, someday, to convey concisely some pieces of the cultural story of Earth’s civilization, its politics, biology, astronomy and art.
Identical golden disks were fastened to each of the Voyagers, engraved with ambient sounds of our planet — a kiss, a mother’s lullaby, wind and water — as well as images, written greetings from former U.S. President Jimmy Carter and former U.N. Secretary General Kurt Waldheim.
"As the Secretary General of the United Nations, an organization of the 147 member states who represent almost all of the human inhabitants of the planet Earth. I send greetings on behalf of the people of our planet. We step out of our solar system into the universe seeking only peace and friendship, to teach if we are called upon, to be taught if we are fortunate. We know full well that our planet and all its inhabitants are but a small part of this immense universe that surrounds us and it is with humility and hope that we take this step." :: Click to hear
-Kurt Waldheim, Secretary General, United Nations
Every Earthlings’ 90 Minutes of Fame
The golden records also include 90 minutes of music, running the gamut from Bach’s Second Brandenburg Concerto and Mozart’s The Magic Flute to rock icon Berry’s version of his own "Johnny B. Goode."
There are also symbolic descriptions of the spaceships’ origins and instructions on how the records are to be played. A key challenge of all such attempts to communicate even basic knowledge is some agreement on what kind of player to use, a primer of sorts that instructs how to read a message at the embryonic stage before any language agreement or alphabet has been set.
Talking beyond Pluto
As is always the case considering travel beyond our solar neighborhood, distance is measured for both space and time. If the time is 25 years, the space is billions of miles.
As Voyager-1 and Voyager-2 search for the boundary of our sun’s influence they continue to push the boundaries of our exploration envelope. Practically speaking, this quest also pushes the operating skills of the Deep Space Network that tries to keep after the Voyagers. The Canberra Australia antenna (70 m, or 230 ft in diameter) is one of only three transmitting dishes that make up the communication hub of all interplanetary missions. But only Canberra has enough signal strength (20 kW) to track the Voyagers and send basic commands for up to 12 hours every day.
To establish active communication channels, that lag or time component (even back to the 1970’s for receiving hardware) necessarily also involves a great spatial distance. For example, the Voyager command sequence is now measured in the unique quantity of ‘light-hours’. Almost twelve light-hours, for a radio signal travelling at the speed of light (186,000 miles per second), initiates a beep to Voyager from Earth.
As Byron Yetter, Telecommunications and Mission Services Manager of the Voyager Project, describes the technical challenges, indeed near impossibility, of such 11 ‘light-hour communication’, the analogy is akin to "throwing a baseball across thousands of miles of ocean, and being able to get that baseball to pass through a very small port-hole window of a moving cruise ship."
A command signal sent from one of the Deep Space Network (DSN) antennas, traveling at light-speed towards Voyager-1, actually takes 11 hours and 38 minutes, to reach Voyager-1’s receiver. A command signal going to Voyager 2 takes a little shorter trip. A command transmitted to Voyager 2 only takes 9 hours and 17 minutes to reach Voyager 2’s receiver. Compare this to sending a signal to Mars, a command going to the Global Surveyor spacecraft, in orbit around Mars would only take about 50 times less, or 15 minutes.
What’s Next: To infinity and beyond
When initially launched, the Voyager missions to Jupiter and Saturn were considered mission-capable for around 5-year lives. But after 25 years, there is a good chance that another 25 years for their tour is on-course. Voyager project manager Ed Massey recently concluded: "I don’t think anybody expected we would still be here 25 years later though we probably could go another 25 years."
Assessing their key radio-isotope generators that power the on-board battery, Massey evaluates: "We don’t run out of electrical power until about 2020", or at least for Voyager I, around 43 years towards its lifetime of some communication with its originating star, Sol, and its home planet, the Earth.
Indeed if the Voyager’s ‘message-in-a-bottle’ ever reaches some hard-to-imagine shore, the travels of those tiny crafts will spin up their own golden-oldies. How the tunes of Chuck Berry, Mozart and Bach came to arrive there will make quite a story.