Our Spaceflight Heritage: 40 years after launch, NASA’s twin Voyager spacecraft continue to return valuable data
Well past their expected lifetime, and farther from Earth than any other human-designed spacecraft, the Voyager robotic explorers are approaching another significant milestone: 40 years of operation. The two interplanetary travelers, each launched in 1977, have traveled billions of miles and expanded humanity’s understanding of the Solar System and beyond.
Beginning in the 1960s, scientists realized that a coincidental alignment of the outer planets would allow a visit by a single spacecraft. Utilizing a gravitational assist by each, the spacecraft would be able to alter its trajectory and speed to allow the encounters with very little expenditure of fuel.
This plan, coined the Grand Tour, was initially to be a single spacecraft with multiple, redundant systems designed to survive the journey. High costs, however, induced a change to the program resulting in the twin Voyager spacecraft – each with a primary mission to Jupiter and Saturn, with an extended mission to the remaining outer planets on the table should funding and conditions allow.
Though christened the first of the line, Voyager 1 was actually the second of the pair to launch. Lifting off from Launch Complex 41 (LC-41) atop a Titan IIIE rocket on September 5, 1977, the spacecraft was set on a course to visit the two largest planets in the Solar System: Jupiter and Saturn.
Reaching the Jovian system 18 months later, Voyager 1 provided data leading to many monumental discoveries.
One of the most surprising findings was the presence of active volcanoes on Jupiter’s moon Io. These features – the first of their kind found anywhere beyond Earth – were unexpected and were determined to be the primary source of material interacting with Jupiter’s strong magnetic field.
After collecting scientific and photographic data on other moons in the Jovian system, Voyager 1 continued on its journey to Saturn, a destination nearly 20 months and 401 million miles (646 million kilometers) distant.
Adding to the observations already collected by Pioneer 11, Voyager 1 made its fair share of discoveries at the Ringed Planet. Unexpectedly, Saturn was found to have a significantly different concentration of helium in its upper atmosphere as compared to Jupiter. This discrepancy may be attributed to the helium molecules sinking through the lighter hydrogen and collecting deeper in the planet.
Beyond the planet itself, a primary target in the Saturnian system was the moon Titan. Long known to harbor a thick atmosphere, the moon was such a vital target that mission planners opted to plot a trajectory to allow for the best observations of Titan rather than travel a path that would have taken it to Pluto in 1986.
Voyager 2, though second in number, was launched 16 days before its speedier sibling. Perched atop a Titan IIIE, the interplanetary spacecraft lifted off from LC-41 at the Cape Canaveral Air Force Station on August 20, 1977.
Like its counterpart, Voyager 2‘s early targets included Jupiter and Saturn. However, unlike Voyager 1, Voyager 2‘s trajectory allowed for some flexibility – the spacecraft could be repositioned to make further observations of Titan, or it could be adjusted to also visit the outermost planets, Uranus and Neptune.
At Jupiter, Voyager 2 witnessed the same volcanic activity on Io, as well as discovered a few, faint rings around the gas giant. Data collected at Europa lead scientists to believe the ice-encrusted moon holds a deep below the surface, and several new moons were discovered before the spacecraft sped out of the system on its way to Saturn.
Upon reaching the second-largest planet in the Solar System more than two years later, Voyager 2 confirmed many of Voyager 1‘s discoveries, in addition to collecting atmospheric and temperature data.
With its primary mission complete, Voyager 2 was given the go-ahead to begin its extended mission by visiting Uranus and Neptune.
The spacecraft became the first man-made object to visit Uranus (January 1986) and Neptune (August 1989), providing scientists with their first-ever close observations of the two planets, and earning the record of being the first spacecraft to fly by four different planets.
Communicating with the Voyagers
In order for NASA to communicate with the two Voyager spacecraft, the space agency had to expand its Deep Space Network (DSN) of radio communication antennas.
One legacy of those antennas used for the Voyager mission is still visible in the Mojave Desert, California: NASA’s Goldstone Deep Space Communications Complex.
At Goldstone, in the 1970s, construction crews began building new dishes and expanding old ones to enable NASA to communicate with the two probes as they traveled farther out into deep space. These dishes now dominate the landscape; the largest of them is 230 feet (70 meters) in diameter – a “true colossus”, which was expanded from its original 210-foot (64-meter) width.
The smaller dishes at the complex are 112 feet (34 meters) in diameter, which were also increased in size from their original 85-foot (26-meter) diameters.
Expansions of antenna dishes were also carried out at NASA’s other DSN sites around the world, located in Madrid (Spain) and Canberra (Australia). The Voyager program helped to accelerate these upgrades to the network.
“In a sense, Voyager and the DSN grew up together,” said Suzanne Dodd of NASA’s Jet Propulsion Laboratory (JPL), director of the Interplanetary Network Directorate and Voyager’s project manager since 2010. “The mission was a proving ground for new technology, both in deep space as well as on Earth.”
By the late 1970s, NASA began to explore the concept of antenna arrays by combining the signals from multiple dishes pointed toward the Voyager probes, thereby giving them the equivalent sensitivity of one giant antenna.
All good things must come to an end
With their primary missions complete, and their planetary targets investigated, the two spacecraft began their journey into interstellar space.
Indeed, Voyager 1 – now more than 13 billion miles (20.92 billion kilometers) from Earth and on a “northbound” trajectory out of the Solar System – was the first of the pair to reach interstellar space, generally accepted to have occurred on August 25, 2012.
Voyager 2, traveling slightly slower than its partner, is on a “southbound” exit, but it will probably not reach interstellar space until late 2019 or early 2020.
Though the spacecraft have exceeded expectations, their power supply continues to drain and will no longer be able to provide electricity to the explorer’s scientific instruments by the mid-2020s. Moreover, the computers and systems designed to support operations rely on an increasingly rare skill: the ability to work with 1970s-era hardware.
“The technology is many generations old, and it takes someone with 1970s design experience to understand how the spacecraft operate and what updates can be made to permit them to continue operating today and into the future,” stated Suzanne Dodd in a release issued by NASA.
Nevertheless, the two groundbreaking spacecraft have provided invaluable information to scientists.
“I believe that few missions can ever match the achievements of the Voyager spacecraft during their four decades of exploration,” noted Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at NASA, in the release. “They have educated us to the unknown wonders of the universe and truly inspired humanity to continue to explore our solar system and beyond.”
Video courtesy of NASA Jet Propulsion Laboratory
Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.