voyager 1 and 2 now

NASA's Voyager 1 spacecraft finally phones home after 5 months of no contact

On Saturday, April 5, Voyager 1 finally "phoned home" and updated its NASA operating team about its health.

NASA's interstellar explorer Voyager 1 is finally communicating with ground control in an understandable way again. On Saturday (April 20), Voyager 1 updated ground control about its health status for the first time in 5 months. While the Voyager 1 spacecraft still isn't sending valid science data back to Earth, it is now returning usable information about the health and operating status of its onboard engineering systems. 

Thirty-five years after its launch in 1977, Voyager 1 became the first human-made object to leave the solar system and enter interstellar space . It was followed out of our cosmic quarters by its space-faring sibling, Voyager 2 , six years later in 2018. Voyager 2, thankfully, is still operational and communicating well with Earth. 

The two spacecraft remain the only human-made objects exploring space beyond the influence of the sun. However, on Nov. 14, 2023, after 11 years of exploring interstellar space and while sitting a staggering 15 billion miles (24 billion kilometers) from Earth, Voyager 1's binary code — computer language composed of 0s and 1s that it uses to communicate with its flight team at NASA — stopped making sense.

Related: We finally know why NASA's Voyager 1 spacecraft stopped communicating — scientists are working on a fix

In March, NASA's Voyager 1 operating team sent a digital "poke" to the spacecraft, prompting its flight data subsystem (FDS) to send a full memory readout back home.

This memory dump revealed to scientists and engineers that the "glitch" is the result of a corrupted code contained on a single chip representing around 3% of the FDS memory. The loss of this code rendered Voyager 1's science and engineering data unusable.

The NASA team can't physically repair or replace this chip, of course, but what they can do is remotely place the affected code elsewhere in the FDS memory. Though no single section of the memory is large enough to hold this code entirely, the team can slice it into sections and store these chunks separately. To do this, they will also have to adjust the relevant storage sections to ensure the addition of this corrupted code won't cause those areas to stop operating individually, or working together as a whole. In addition to this, NASA staff will also have to ensure any references to the corrupted code's location are updated.

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On April 18, 2024, the team began sending the code to its new location in the FDS memory. This was a painstaking process, as a radio signal takes 22.5 hours to traverse the distance between Earth and Voyager 1, and it then takes another 22.5 hours to get a signal back from the craft. 

By Saturday (April 20), however, the team confirmed their modification had worked. For the first time in five months, the scientists were able to communicate with Voyager 1 and check its health. Over the next few weeks, the team will work on adjusting the rest of the FDS software and aim to recover the regions of the system that are responsible for packaging and returning vital science data from beyond the limits of the solar system.

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Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.

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• Robb62 'V'ger must contact the creator. Reply
• Holy HannaH! Couldn't help but think that "repair" sounded extremely similar to the mechanics of DNA and the evolution of life. Reply
• Torbjorn Larsson *Applause* indeed, thanks to the Voyager teams for the hard work! Reply
• SpaceSpinner I notice that the article says that it has been in space for 35 years. Either I have gone back in time 10 years, or their AI is off by 10 years. V-*ger has been captured! Reply

Admin said: On Saturday, April 5, Voyager 1 finally "phoned home" and updated its NASA operating team about its health. The interstellar explorer is back in touch after five months of sending back nonsense data. NASA's Voyager 1 spacecraft finally phones home after 5 months of no contact : Read more

evw said: I'm incredibly grateful for the persistence and dedication of the Voyagers' teams and for the amazing accomplishments that have kept these two spacecrafts operational so many years beyond their expected lifetimes. V-1 was launched when I was 25 years young; I was nearly delirious with joy. Exploring the physical universe captivated my attention while I was in elementary school and has kept me mesmerized since. I'm very emotional writing this note, thinking about what amounts to a miracle of technology and longevity in my eyes. BRAVO!!! THANK YOU EVERYONE PAST & PRESENT!!!

• EBairead I presume it's Fortran. Well done all. Reply

SpaceSpinner said: I notice that the article says that it has been in space for 35 years. Either I have gone back in time 10 years, or their AI is off by 10 years. V-*ger has been captured!

EBairead said: I presume it's Fortran. Well done all.

• View All 13 Comments

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Voyager 1, After Major Malfunction, Is Back From the Brink, NASA Says

The farthest man-made object in space had been feared lost forever after a computer problem in November effectively rendered the 46-year-old probe useless.

By Orlando Mayorquín

Several months after a grave computer problem seemed to spell the end for Voyager 1, which for nearly a half century had provided data on the outer planets and the far reaches of the solar system, NASA announced on Thursday that it had restored the spacecraft to working order.

“The spacecraft has resumed gathering information about interstellar space,” NASA said in its announcement about Voyager 1, the farthest man-made object in space.

Since the problem surfaced in November, engineers had been working to diagnose and resolve the issue, a tedious and lengthy process complicated by the fact that it takes almost two days to send and receive information from Voyager 1, which was the first man-made object ever to enter interstellar space and is currently more than 15 billion miles from Earth.

The space community had been holding its breath since last year as the prospect of fixing the aging probe appeared as dire as ever.

In February, Suzanne Dodd, the Voyager mission project manager, said the problem, which hindered Voyager 1’s ability to send coherent engineering and science data back to Earth, was “the most serious issue” the probe had faced since she began leading the mission in 2010.

Voyager 1 and its twin probe, Voyager 2, were launched in 1977 on a mission to explore the outer planets. NASA capitalized on a rare alignment in the solar system that enabled the probes to visit the four outer planets — Jupiter, Saturn, Uranus and Neptune — by using the gravity of each to swing to the next.

Its planetary mission a success, Voyager 1 continued its journey toward the edge of the solar system, and in 1990 it snapped a fabled photo of the Earth — a tiny speck in an infinite darkness that became known as the “pale blue dot.”

In 2012, the probe became the first to cross into interstellar space and had since, along with its twin, which followed six years later, collected data about the heliosphere, the space around the sun directly under the sun’s influence.

Perhaps as profound as the pale blue dot, each spacecraft is equipped with a golden phonograph record loaded with sound recordings and images showing humanity and life on Earth, begging to one day be discovered by another civilization.

The outlook for recovering Voyager 1 improved substantially in April , when NASA reported that it had managed to get the probe to send back “usable” data about its engineering systems and its health. That was followed by news late last month that the team had restored functionality to two of Voyager 1’s science instruments, allowing it to send back science data and continue its mission.

On Thursday, the agency announced that it had brought the remaining instruments back online and restored Voyager 1 to its normal operations.

Still, Voyager 1’s new lease on life may not last very long. NASA has previously estimated that the nuclear-powered generators on Voyager 1 and Voyager 2 were likely to die around 2025. But Voyager 1 has already demonstrated that it can beat the odds. Ms. Dodd hopes both Voyager spacecraft can reach the mission’s 50th anniversary in 2027.

Orlando Mayorquín is a breaking news reporter, based in New York, and a member of the 2023-24 Times Fellowship class , a program for journalists early in their careers. More about Orlando Mayorquín

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Is Pluto a planet? And what is a planet, anyway? Test your knowledge here .

Interstellar Mission

Voyager 1 reached interstellar space in August 2012 and is the most distant human-made object in existence.

Mission Statistics

Launch Date

Sept. 5, 1977

About the mission

Voyager 1 reached interstellar space in August 2012 and is the most distant human-made object in existence. Launched just shortly after its twin spacecraft, Voyager 2, in 1977, Voyager 1 explored the Jovian and Saturnian systems discovering new moons, active volcanoes and a wealth of data about the outer solar system.

Voyagers 1 and 2 were designed to take advantage of a rare planetary alignment that occurs only once in 176 years and remain the most well traveled spacecraft in history. Both spacecraft carry a sort of time capsule called the Golden Record, a 12-inch gold-plated copper disk containing sounds and images selected to portray the story of our world to extraterrestrials.

Instruments

• Imaging system
• Infrared interferometer spectrometer
• Ultraviolet spectrometer
• Triaxial fluxgate magnetometer
• Plasma spectrometer
• Low-energy charged particles detectors
• Cosmic Ray System (CRS)
• Photopolarimeter System (PPS)
• Plasma Wave System (PWS)

Mission Highlights

Sept. 1, 2013

Interactive 3D model of Voyager 1. View the full interactive experience at Eyes on the Solar System .

Voyager 1 live position and data

This page shows Voyager 1 location and other relevant astronomical data in real time. The celestial coordinates, magnitude, distances and speed are updated in real time and are computed using high quality data sets provided by the JPL Horizons ephemeris service (see acknowledgements for details). The sky map shown in the background represents a rectangular portion of the sky 60x40 arcminutes wide. By comparison the diameter of the full Moon is about 30 arcmins, so the full horizontal extent of the map is approximately 2 full Moons wide. Depending on the device you are using, the map can be dragged horizondally or vertically using the mouse or touchscreen. The deep sky image in the background is provided by the Digitized Sky Survey ( acknowledgements ).

Current close conjunctions

List of bright objects (stars brighter than magnitude 9.0 and galaxies brighter than magmitude 14.0) close to Voyager 1 (less than 1.5 degrees):

Additional resources

• 15 Days Ephemerides
• Interactive Sky Map (Planetarium)
• Rise & Set Times
• Distance from Earth

Astronomy databases

• The Digitized Sky Survey, a photographic survey of the whole sky created using images from different telescopes, including the Oschin Schmidt Telescope on Palomar Mountain
• The Hipparcos Star Catalogue, containing more than 100.000 bright stars
• The PGC 2003 Catalogue, containing information about 1 million galaxies
• The GSC 2.3 Catalogue, containing information about more than 2 billion stars and galaxies

Object Search

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Voyager 1 and 2: The Interstellar Mission

An image of Neptune taken by the Voyager 2 spacecraft. Image credit: NASA

NASA has beautiful photos of every planet in our solar system. We even have images of faraway Neptune , as you can see in the photo above.

Neptune is much too distant for an astronaut to travel there with a camera. So, how do we have pictures from distant locations in our solar system? Our photographers were two spacecraft, called Voyager 1 and Voyager 2!

An artist’s rendering of one of the Voyager spacecraft. Image credit: NASA

The Voyager 1 and 2 spacecraft launched from Earth in 1977. Their mission was to explore Jupiter and Saturn —and beyond to the outer planets of our solar system. This was a big task. No human-made object had ever attempted a journey like that before.

The two spacecraft took tens of thousands of pictures of Jupiter and Saturn and their moons. The pictures from Voyager 1 and 2 allowed us to see lots of things for the first time. For example, they captured detailed photos of Jupiter's clouds and storms, and the structure of Saturn's rings .

Image of storms on Jupiter taken by the Voyager 1 spacecraft. Image credit: NASA

Voyager 1 and 2 also discovered active volcanoes on Jupiter's moon Io , and much more. Voyager 2 also took pictures of Uranus and Neptune. Together, the Voyager missions discovered 22 moons.

Since then, these spacecraft have continued to travel farther away from us. Voyager 1 and 2 are now so far away that they are in interstellar space —the region between the stars. No other spacecraft have ever flown this far away.

Where will Voyager go next?

Watch this video to find out what's beyond our solar system!

Both spacecraft are still sending information back to Earth. This data will help us learn about conditions in the distant solar system and interstellar space.

The Voyagers have enough fuel and power to operate until 2025 and beyond. Sometime after this they will not be able to communicate with Earth anymore. Unless something stops them, they will continue to travel on and on, passing other stars after many thousands of years.

Each Voyager spacecraft also carries a message. Both spacecraft carry a golden record with scenes and sounds from Earth. The records also contain music and greetings in different languages. So, if intelligent life ever find these spacecraft, they may learn something about Earth and us as well!

A photo of the golden record that was sent into space on both Voyager 1 and Voyager 2. Image credit: NASA/JPL-Caltech

More about our universe!

Where does interstellar space begin?

Searching for other planets like ours

Play Galactic Explorer!

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July 1, 2022

21 min read

Record-Breaking Voyager Spacecraft Begin to Power Down

The pioneering probes are still running after nearly 45 years in space, but they will soon lose some of their instruments

By Tim Folger

NASA/JPL-Caltech

I f the stars hadn't aligned, two of the most remarkable spacecraft ever launched never would have gotten off the ground. In this case, the stars were actually planets—the four largest in the solar system. Some 60 years ago they were slowly wheeling into an array that had last occurred during the presidency of Thomas Jefferson in the early years of the 19th century. For a while the rare planetary set piece unfolded largely unnoticed. The first person to call attention to it was an aeronautics doctoral student at the California Institute of Technology named Gary Flandro.

It was 1965, and the era of space exploration was barely underway—the Soviet Union had launched Sputnik 1, the first artificial satellite, only eight years earlier. Flandro, who was working part-time at NASA's Jet Propulsion Laboratory in Pasadena, Calif., had been tasked with finding the most efficient way to send a space probe to Jupiter or perhaps even out to Saturn, Uranus or Neptune. Using a favorite precision tool of 20th-century engineers—a pencil—he charted the orbital paths of those giant planets and discovered something intriguing: in the late 1970s and early 1980s, all four would be strung like pearls on a celestial necklace in a long arc with Earth.

This coincidence meant that a space vehicle could get a speed boost from the gravitational pull of each giant planet it passed, as if being tugged along by an invisible cord that snapped at the last second, flinging the probe on its way. Flandro calculated that the repeated gravity assists, as they are called, would cut the flight time between Earth and Neptune from 30 years to 12. There was just one catch: the alignment happened only once every 176 years. To reach the planets while the lineup lasted, a spacecraft would have to be launched by the mid-1970s.

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READY FOR LAUNCH: Voyager 2 undergoes testing at NASA’s Jet Propulsion Laboratory before its flight ( left ). The spacecraft lifted off on August 20, 1977. Credit: NASA/JPL-Caltech

As it turned out, NASA would build two space vehicles to take advantage of that once-in-more-than-a-lifetime opportunity. Voyager 1 and Voyager 2, identical in every detail, were launched within 15 days of each other in the summer of 1977. After nearly 45 years in space, they are still functioning, sending data back to Earth every day from beyond the solar system's most distant known planets. They have traveled farther and lasted longer than any other spacecraft in history. And they have crossed into interstellar space, according to our best understanding of the boundary between the sun's sphere of influence and the rest of the galaxy. They are the first human-made objects to do so, a distinction they will hold for at least another few decades. Not a bad record, all in all, considering that the Voyager missions were originally planned to last just four years.

Early in their travels, four decades ago, the Voyagers gave astonished researchers the first close-up views of the moons of Jupiter and Saturn, revealing the existence of active volcanoes and fissured ice fields on worlds astronomers had thought would be as inert and crater-pocked as our own moon. In 1986 Voyager 2 became the first spacecraft to fly past Uranus; three years later it passed Neptune. So far it is the only spacecraft to have made such journeys. Now, as pioneering interstellar probes more than 12 billion miles from Earth, they're simultaneously delighting and confounding theorists with a series of unexpected discoveries about that uncharted region.

Their remarkable odyssey is finally winding down. Over the past three years NASA has shut down heaters and other nonessential components, eking out the spacecrafts' remaining energy stores to extend their unprecedented journeys to about 2030. For the Voyagers' scientists, many of whom have worked on the mission since its inception, it is a bittersweet time. They are now confronting the end of a project that far exceeded all their expectations.*

“We're at 44 and a half years,” says Ralph McNutt, a physicist at the Johns Hopkins University Applied Physics Laboratory (APL), who has devoted much of his career to the Voyagers. “So we've done 10 times the warranty on the darn things.”

The stars may have been cooperating, but at first, Congress wasn't. After Flandro's report, NASA drew up plans for a so-called Grand Tour that would send as many as five probes to the four giant planets and Pluto. It was ambitious. It was expensive. Congress turned it down. “There was this really grand vision,” says Linda Spilker, a JPL planetary scientist who started working on the Voyager missions in 1977, a few months before their launch. “Because of cost, it was whittled back.”

Congress eventually approved a scaled-down version of the Grand Tour, initially called Mariner Jupiter-Saturn 1977, or MJS 77. Two spacecraft were to be sent to just two planets. Nevertheless, NASA's engineers went about designing, somewhat surreptitiously, vehicles capable of withstanding the rigors of a much longer mission. They hoped that once the twin probes proved themselves, their itinerary would be extended to Uranus, Neptune, and beyond.

“Four years—that was the prime mission,” says Suzanne Dodd, who, after a 20-year hiatus from the Voyager team, returned in 2010 as the project manager. “But if an engineer had a choice to put in a part that was 10 percent more expensive but wasn't something that was needed for a four-year mission, they just went ahead and did that. And they wouldn't necessarily tell management.” The fact that the scientists were able to build two spacecraft, and that both are still working, is even more remarkable, she adds.

In terms of both engineering and deep-space navigation, this was new territory. The motto “Failure is not an option” hadn't yet been coined, and at that time it would not have been apt. In the early 1960s NASA had attempted to send a series of spacecraft to the moon to survey future landing sites for crewed missions. After 12 failures, one such effort finally succeeded.

GOLDEN RECORD: Each Voyager carries a golden record ( left ) of sounds and images from Earth in case the spacecraft are intercepted by an extraterrestrial civilization. Engineers put the cap on Voyager 1’s record before its launch ( right ). Credit: NASA/JPL-Caltech

“In those days we always launched two spacecraft” because the failure rate was so high, said Donald Gurnett, only partly in jest. Gurnett, a physicist at the University of Iowa and one of the original scientists on the Voyager team, was a veteran of 40 other space missions. He spoke with me a few weeks before his death in January. (In an obituary, his daughter Christina said his only regret was that “he would not be around to see the next 10 years of data returning from Voyager.”)

When the Voyagers were being built, only one spacecraft had used a gravity assist to reach another planet—the Mariner 10 probe got one from Venus while en route to Mercury. But the Voyagers would be attempting multiple assists with margins of error measured in tens of minutes. Jupiter, their first stop, was about 10 times farther from Earth than Mercury. Moreover, the Voyagers would have to travel through the asteroid belt along the way. Before Voyager there had been a big debate about whether spacecraft could get through the asteroid belt “without being torn to pieces,” McNutt says. But in the early 1970s Pioneer 10 and 11 flew through it unscathed—the belt turned out to be mostly empty space—paving the way for Voyager, he says.

To handle all these challenges, the Voyagers, each about the size of an old Volkswagen Beetle, needed some onboard intelligence. So NASA's engineers equipped the vehicles' computers with 69 kilobytes of memory, less than a hundred thousandth the capacity of a typical smartphone. In fact, the smartphone comparison is not quite right. “The Voyager computers have less memory than the key fob that opens your car door,” Spilker says. All the data collected by the spacecraft instruments would be stored on eight-track tape recorders and then sent back to Earth by a 23-watt transmitter—about the power level of a refrigerator light bulb. To compensate for the weak transmitter, both Voyagers carry 12-foot-wide dish antennas to send and receive signals.

“It felt then like we were right on top of the technology,” says Alan Cummings, a physicist at Caltech and another Voyager OG. “I'll tell you, what was amazing is how quickly that whole thing happened.” Within four years the MJS 77 team had built three spacecraft, including one full-scale functioning test model. The spacecraft were rechristened Voyager 1 and 2 a few months before launch.

Although many scientists have worked on the Voyagers over the decades, Cummings can make a unique claim. “I was the last person to touch the spacecraft before they launched,” he says. Cummings was responsible for two detectors designed to measure the flux of electrons and other charged particles when the Voyagers encountered the giant planets. Particles would pass through a small “window” in each detector that consisted of aluminum foil just three microns thick. Cummings worried that technicians working on the spacecraft might have accidentally dented or poked holes in the windows. “So they needed to be inspected right before launch,” he says. “Indeed, I found that one of them was a little bit loose.”

Credit: Graphic by Matthew Twombly and Juan Velasco (5W Infographic); Consultants: John Richardson (principal investigator, Voyager Plasma Science, Massachusetts Institute of Technology, Center for Space Research) and Merav Opher (professor, Department of Astronomy, Boston University)

Voyager 1 reached Jupiter in March 1979, 546 days after its launch. Voyager 2, following a different trajectory, arrived in July of that year. Both spacecraft were designed to be stable platforms for their vidicon cameras, which used red, green and blue filters to produce full-color images. They hardly spin at all as they speed through space—their rotational motion is more than 15 times slower than the crawl of a clock's hour hand, minimizing the risk of blurred images. Standing-room crowds at JPL watched as the spacecraft started transmitting the first pictures of Jupiter while still about three or four months away from the planet.

“In all of the main conference rooms and in the hallways, they had these TV monitors set up,” Spilker says. “So as the data came down line by line, each picture would appear on a monitor. The growing anticipation and the expectation of what we were going to see when we got up really, really close—that was tremendously exciting.”

Cummings vividly recalls the day he caught his first glimpse of Jupiter's third-largest moon, Io. “I was going over to a building on the Caltech campus where they were showing a livestream [of Voyager's images],” he says. “I walk in, and there's this big picture of Io, and it's all orange and black. I thought, okay, the Caltech students had pulled a prank, and it's a picture of a poorly made pizza.”

Io's colorful appearance was completely unexpected. Before the Voyagers proved otherwise, the assumption had been that all moons in the solar system would be more or less alike—drab and cratered. No one anticipated the wild diversity of moonscapes the Voyagers would discover around Jupiter and Saturn.

The first hint that there might be more kinds of moons in the heavens than astronomers had dreamed of came while the Voyagers were still about a million miles from Jupiter. One of their instruments—the Low-Energy Charged Particle [LECP] detector system—picked up some unusual signals. “We started seeing oxygen and sulfur ions hitting the detector,” says Stamatios Krimigis, who designed the LECP and is now emeritus head of the space department at Johns Hopkins APL. The density of oxygen and sulfur ions had shot up by three orders of magnitude compared with the levels measured up to that point. At first, his team thought the instrument had malfunctioned. “We scrutinized the data,” Krimigis says, “but there was nothing wrong.”

The Voyagers' cameras soon solved the mystery: Io had active volcanoes. The small world—it is slightly larger than Earth's moon—is now known to be the most volcanically active body in the solar system. “The only active volcanoes we knew of at the time were on Earth,” says Edward Stone, who has been the project scientist for the Voyager missions since 1972. “And here suddenly was a moon that had 10 times as much volcanic activity as Earth.” Io's colors—and the anomalous ions hitting Krimigis's detector—came from elements blasted from the moon's volcanoes. The largest of Io's volcanoes, known as Pele, has blown out plumes 30 times the height of Mount Everest; debris from Pele covers an area about the size of France.

The twin spacecraft took a grand tour through the giant planets of the solar system, passing by Jupiter ( 1 , 2 ) and Saturn ( 5 , 6 ) and taking the first close-up views of those planets’ moons. Jupiter’s satellite Europa ( 3 ), for instance, turned out to be covered with ice, and its moon Io ( 4 ) was littered with volcanoes—discoveries that came as a surprise to scientists who had assumed the moons would be gray and crater-pocked like Earth’s. Voyager 2 went on to fly by Uranus ( 7 ) and Neptune ( 8 ), and it is still the only probe to have visited there. Credit: NASA/JPL ( 1 , 2 , 4 , 5 , 6 , 8 ); NASA/JPL/USGS (3); NASA/JPL-Caltech ( 7 )

Altogether, the Voyagers took more than 33,000 photographs of Jupiter and its satellites. It felt like every image brought a new discovery: Jupiter had rings; Europa, one of Jupiter's 53 named moons, was covered with a cracked icy crust now estimated to be more than 60 miles thick. As the spacecraft left the Jupiter system, they got a farewell kick of 35,700 miles per hour from a gravity assist. Without it they would not have been able to overcome the gravitational pull of the sun and reach interstellar space.

At Saturn, the Voyagers parted company. Voyager 1 hurtled through Saturn's rings (taking thousands of hits from dust grains), flew past Titan, a moon shrouded in orange smog, and then headed “north” out of the plane of the planets. Voyager 2 continued alone to Uranus and Neptune. In 1986 Voyager 2 found 10 new moons around Uranus and added the planet to the growing list of ringed worlds. Just four days after Voyager 2's closest approach to Uranus, however, its discoveries were overshadowed when the space shuttle Challenger exploded shortly after launch. All seven of Challenger 's crew members were killed, including Christa McAuliffe, a high school teacher from New Hampshire who would have been the first civilian to travel into space.

Three years later, passing about 2,980 miles above Neptune's azure methane atmosphere, Voyager 2 measured the highest wind speeds of any planet in the solar system: up to 1,000 mph. Neptune's largest moon, Triton, was found to be one of the coldest places in the solar system, with a surface temperature of −391 degrees Fahrenheit (−235 degrees Celsius). Ice volcanoes on the moon spewed nitrogen gas and powdery particles five miles into its atmosphere.

Voyager 2's images of Neptune and its moons would have been the last taken by either of the spacecraft had it not been for astronomer Carl Sagan, who was a member of the mission's imaging team. With the Grand Tour officially completed, NASA planned to turn off the cameras on both probes. Although the mission had been extended with the hope that the Voyagers would make it to interstellar space—it had been officially renamed the Voyager Interstellar Mission—there would be no photo ops after Neptune, only the endless void and impossibly distant stars.

ERUPTION: The discovery of the volcano Pele, shown in this photograph from Voyager 1, confirmed that Jupiter’s moon hosts active volcanism. Credit: NASA/JPL/USGS

Sagan urged NASA officials to have Voyager 1 transmit one last series of images. So, on Valentine's Day in 1990, the probe aimed its cameras back toward the inner solar system and took 60 final shots. The most haunting of them all, made famous by Sagan as the “Pale Blue Dot,” captured Earth from a distance of 3.8 billion miles. It remains the most distant portrait of our planet ever taken. Veiled by wan sunlight that reflected off the camera's optics, Earth is barely visible in the image. It doesn't occupy even a full pixel.

Sagan, who died in 1996, “worked really hard to convince NASA that it was worth looking back at ourselves,” Spilker says, “and seeing just how tiny that pale blue dot was.”

Both Voyagers are now so far from Earth that a one-way radio signal traveling at the speed of light takes almost 22 hours to reach Voyager 1 and just over 18 to catch up with Voyager 2. Every day they move away by another three to four light-seconds. Their only link to Earth is NASA's Deep Space Network, a trio of tracking complexes spaced around the globe that enables uninterrupted communication with spacecraft as Earth rotates. As the Voyagers recede from us in space and time, their signals are becoming ever fainter. “Earth is a noisy place,” says Glen Nagle, outreach and communications manager at the Deep Space Network's facility in Canberra, Australia. “Radios, televisions, cell phones—everything makes noise. And so it gets harder and harder to hear these tiny whispers from the spacecraft.”

Faint as they are, those whispers have upended astronomers' expectations of what the Voyagers would find as they entered the interstellar phase of the mission. Stone and other Voyager scientists I spoke with cautioned me not to conflate the boundary of interstellar space with that of the solar system. The solar system includes the distant Oort cloud, a spherical collection of cometlike bodies bound by the sun's gravity that may stretch halfway to the closest star. The Voyagers won't reach its near edge for at least another 300 years. But interstellar space lies much closer at hand. It begins where a phenomenon called the solar wind ends.

Like all stars, the sun emits a constant flow of charged particles and magnetic fields—the solar wind. Moving at hypersonic speeds, the wind blows out from the sun like an inflating balloon, forming what astronomers call the heliosphere. As the solar wind billows into space, it pulls the sun's magnetic field along for the ride. Eventually pressure from interstellar matter checks the heliosphere's expansion, creating a boundary—preceded by an enormous shock front, the “termination shock”—with interstellar space. Before the Voyagers' journeys, estimates of the distance to that boundary with interstellar space, known as the heliopause, varied wildly.

“Frankly, some of them were just guesses,” according to Gurnett. One early guesstimate located the heliopause as close as Jupiter. Gurnett's own calculations, made in 1993, set the distance at anywhere from 116 to 177 astronomical units, or AU—about 25 times more distant. (One AU is the distance between Earth and the sun, equal to 93 million miles.) Those numbers, he says, were not very popular with his colleagues. By 1993 Voyager 1 already had 50 AU on its odometer. “If [the heliopause] was at 120 AU, that meant we had another 70 AU to go.” If Gurnett was right, the Voyagers, clipping along at about 3.5 AU a year, wouldn't exit the heliosphere for at least another two decades.

That prediction raised troubling questions: would the Voyagers—or the support of Congress—last that long? The mission's funding had been extended on the expectation that the spacecraft would cross the heliopause at about 50 AU. But the spacecraft left that milestone behind without finding any of the anticipated signs of interstellar transit. Astronomers had expected the Voyagers to detect a sudden surge in galactic cosmic rays—high-energy particles sprayed like shrapnel at nearly the speed of light from supernovae and other deep-space cataclysms. The vast magnetic cocoon formed by the heliosphere deflects most low-energy cosmic rays before they can reach the inner solar system. “[It] shields us from at least 75 percent of what's out there,” Stone says.

The Voyager ground team was also waiting for the spacecraft to register a shift in the prevailing magnetic field. The interstellar magnetic field, thought to be generated by nearby stars and vast clouds of ionized gases, would presumably have a different orientation from the magnetic field of the heliosphere. But the Voyagers had detected no such change.

Gurnett's 1993 estimates were prescient. Almost 20 years passed before one of the Voyagers finally made it to the heliopause. During that time the mission narrowly survived threats to its funding, and the Voyager team shrank from hundreds of scientists and engineers to a few dozen close-knit lifers. Most of them remain on the job today. “When you have such a long-lived mission, you start to regard people like family,” Spilker says. “We had our kids around the same time. We'd take vacations together. We're spanning multiple generations now, and some of the younger people on Voyager were not even born [when the spacecraft] launched.”

The tenacity and commitment of that band of brothers and sisters were rewarded on August 25, 2012, when Voyager 1 finally crossed the heliopause. But some of the data it returned were baffling. “We delayed announcing that we had reached interstellar space because we couldn't come to an agreement on the fact,” Cummings says. “There was lots of debate for about a year.”

Although Voyager 1 had indeed found the expected jump in plasma density—its plasma-wave detector, an instrument designed by Gurnett, inferred an 80-fold increase—there was no sign of a change in the direction of the ambient magnetic field. If the vehicle had crossed from an area permeated by the sun's magnetic field to a region where the magnetic field derived from other stars, shouldn't that switch have been noticeable? “That was a shocker,” Cummings says. “And that still bothers me. But a lot of people are coming to grips with it.”

When Voyager 2 reached the interstellar shoreline in November 2018, it, too, failed to detect a magnetic field shift. And the spacecraft added yet another puzzle: it encountered the heliopause at 120 AU from Earth—the same distance marked by its twin six years earlier. That did not jibe with any theoretical models, all of which said the heliosphere should expand and contract in sync with the sun's 11-year cycle. During that period the solar wind ebbs and surges. Voyager 2 arrived when the solar wind was peaking, which, if the models were correct, should have pushed the heliopause farther out than 120 AU. “It was unexpected by all the theorists,” Krimigis says. “I think the modeling, in terms of the findings of the Voyagers, has been found wanting.”

Now that the Voyagers are giving theorists some real field data, their models of the interaction between the heliosphere and the interstellar environment are becoming more complex. “The sort of general picture is that [our sun] emerged from a hot, ionized region” and entered a spotty, partly ionized area in the galaxy, says Gary Zank, an astrophysicist at the University of Alabama in Huntsville. The hot region likely formed in the aftermath of a supernova—some nearby ancient star, or perhaps a few, exploded at the end of its life and heated up the space, stripping electrons off their atoms in the process. The boundary around that region can be thought of as “kind of like the seashore, with all the water and the waves swirling and mixed up. We're in that kind of turbulent region ... magnetic fields get twisted up, turned around. It's not like the smooth magnetic fields that theorists usually like to draw,” although the amount of turbulence seen can differ depending on the type of observation. The Voyagers' data show little field variation at large scales but many small-scale fluctuations around the heliopause, caused by the heliosphere's influence on the interstellar medium. At some point, it is thought, the spacecraft will leave those roiling shoals behind and at last encounter the unalloyed interstellar magnetic field.

Or maybe that picture is completely wrong. A few researchers believe that the Voyagers have not yet left the heliosphere. “There is no reason for the magnetic fields in the heliosphere and the interstellar medium to have exactly the same orientation,” says Len A. Fisk, a space plasma scientist at the University of Michigan and a former NASA administrator. For the past several years Fisk and George Gloeckler, a colleague at Michigan and a longtime Voyager mission scientist, have been working on a model of the heliosphere that pushes its edge out by another 40 AU.

Most people working in the field, however, have been convinced by the dramatic uptick in galactic cosmic rays and plasma density the Voyagers measured. “Given that,” Cummings says, “it's very difficult to argue that we're not really in interstellar space. But then again, it's not like everything fits. That's why we need an interstellar probe.”

McNutt has been pushing for such a mission for decades. He and his colleagues at Johns Hopkins recently completed a nearly 500-page report outlining plans for an interstellar probe that would launch in 2036 and potentially could reach the heliosphere within 15 years, shaving 20 years off Voyager 1's flight time. And unlike the Voyager missions, the interstellar probe would be designed specifically to study the outer edge of the heliosphere and its environs. Within the next two years the National Academies of Sciences, Engineering, and Medicine will decide whether the mission should be one of NASA's priorities for the next decade.

An interstellar probe could answer one of the most fundamental questions about the heliosphere. “If I'm looking from the outside, what the devil does this structure look like?” McNutt asks. “We really don't know. It's like trying to understand what a goldfish bowl looks like from the point of view of the goldfish. We [need to] be able to see the bowl from the outside.” In some models, as the heliosphere cruises along at 450,000 mph, interstellar matter flows smoothly past it, like water around the bow of a ship, resulting in an overall cometlike shape. One recent computer model, developed by astronomer Merav Opher and her colleagues at Boston University, predicts that more turbulent dynamics give the heliosphere a shape like a cosmic croissant.

“You can start multiple fights at any good science conference about that,” McNutt says, “but it's going to take getting out there and actually making some measurements to be able to see what's going on. It would be nice to know what the neighborhood looks like.”

Some things outlive their purpose—answering machines, VCRs, pennies. Not the Voyagers—they transcended theirs, using 50-year-old technology. “The amount of software on these instruments is slim to none,” Krimigis says. “There are no microprocessors—they didn't exist!” The Voyagers' designers could not rely on thousands of lines of code to help operate the spacecraft. “On the whole,” Krimigis says, “I think the mission lasted so long because almost everything was hardwired. Today's engineers don't know how to do this. I don't know if it's even possible to build such a simple spacecraft [now]. Voyager is the last of its kind.”

It won't be easy to say goodbye to these trailblazing vehicles. “It's hard to see it come to an end,” Cummings says. “But we did achieve something really amazing. It could have been that we never got to the heliopause, but we did.”

Voyager 2 now has five remaining functioning instruments, and Voyager 1 has four. All are powered by a device that converts heat from the radioactive decay of plutonium into electricity. But with the power output decreasing by about four watts a year, NASA has been forced into triage mode. Two years ago the mission's engineers turned off the heater for the cosmic-ray detector, which had been crucial in determining the heliopause transit. Everyone expected the instrument to die.

“The temperature dropped like 60 or 70 degrees C, well outside any tested operating limits,” Spilker says, “and the instrument kept working. It was incredible.”

The last two Voyager instruments to turn off will probably be a magnetometer and the plasma science instrument. They are contained in the body of the spacecraft, where they are warmed by heat emitted from computers. The other instruments are suspended on a 43-foot-long fiberglass boom. “And so when you turn the heaters off,” Dodd says, “those instruments get very, very cold.”

How much longer might the Voyagers last? “If everything goes really well, maybe we can get the missions extended into the 2030s,” Spilker says. “It just depends on the power. That's the limiting point.”

TINY SPECK: Among Voyager 1’s last photographs was this shot of Earth seen from 3.8 billion miles away, dubbed the “Pale Blue Dot” by Voyager scientist Carl Sagan. Credit: NASA/JPL-Caltech

Even after the Voyagers are completely muted, their journeys will continue. In another 16,700 years, Voyager 1 will pass our nearest neighboring star, Proxima Centauri, followed 3,600 years later by Voyager 2. Then they will continue to circle the galaxy for millions of years. They will still be out there, more or less intact, eons after our sun has collapsed and the heliosphere is no more, not to mention one Pale Blue Dot. At some point in their travels, they may manage to convey a final message. It won't be transmitted by radio, and if it's received, the recipients won't be human.

The message is carried on another kind of vintage technology: two records. Not your standard plastic version, though. These are made of copper, coated with gold and sealed in an aluminum cover. Encoded in the grooves of the Golden Records , as they are called, are images and sounds meant to give some sense of the world the Voyagers came from. There are pictures of children, dolphins, dancers and sunsets; the sounds of crickets, falling rain and a mother kissing her child; and 90 minutes of music, including Bach's Brandenburg Concerto No. 2 and Chuck Berry's “Johnny B. Goode.”

And there is a message from Jimmy Carter, who was the U.S. president when the Voyagers were launched. “We cast this message into the cosmos,” it reads in part. “We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination, and our good will in a vast and awesome universe.”

*Editor’ Note (6/22/22): This paragraph was edited after posting to correct the description of when NASA began shutting down nonessential components of the Voyager spacecraft.

Tim Folger is a freelance journalist who writes for National Geographic , Discover , and other national publications.

AIR & SPACE MAGAZINE

Voyager, still going after all these years.

Low on power and billions of miles from Earth, NASA’s twin spacecraft keep exploring—with a little TLC from home.

Mark Strauss

The twin Voyager spacecraft, NASA’s oldest, most venerable explorers, are still continuously transmitting data back to Earth. Launched in 1977 to study the large outer planets, Voyager 1 and 2 are now, respectively, more than 13 billion and 11 billion miles from Earth, exploring the outer boundary of the heliosphere—a vast magnetic sphere created by the sun that surrounds the solar system. The 42-year-old spacecraft also present immense challenges to those responsible for their care.

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This story is a selection from the December/January issue of Air & Space magazine

The data stream from the Voyagers is continuous at a rate of 160 bits per second. (The one exception is that Voyager 1 has the ability to record data from the Plasma Wave Subsystem and transmit it at designated times.) NASA captures the data when one of the antennas in its Deep Space Network is pointed at the spacecraft, about six hours per day for each probe. The data is then transferred from the antenna site to JPL’s central mission control, and then to the project mission support office, which processes the data and makes it available to the science teams.

That data also allows JPL engineers to regularly monitor the spacecrafts’ vital signs. Seeing the health or weakness of the instruments, the engineers improvise creative fixes, working with equipment built for planetary exploration that must now adapt to the needs of an interstellar mission. “It’s repurposing systems to do things they were not designed to do, but can do,” says Dodd.

For instance, the magnetometer (MAG), which was originally designed to measure the magnetic fields of Jupiter, Saturn, Uranus, and Neptune, is now studying the interaction of the magnetic field of the sun with the magnetic field of interstellar space—and is a crucial instrument for researchers who want to learn more about the shape of the heliosphere. The MAG, though, was designed for planetary magnetic fields, which are much stronger than interstellar ones. “So it takes a lot of analysis and a lot of review to pull a weak signal out of the noise of the instrument,” says Dodd.

In addition to powering the instruments, the generators keep the heaters running. Without heat, the temperature aboard the Voyagers would plummet. While some instruments can function at the subzero temperatures in deep space, the freezing point of the spacecrafts’ propellant is around 34.5 degrees Fahrenheit. If the propellant lines freeze, engineers would no longer be able to use the probes’ thrusters to keep their antennas oriented toward Earth to transmit data. “So for about the last five years, it’s actually been a balance between power and thermal,” says Dodd.

Maintaining that balance plays out differently for each instrument. For instance, Voyagers’ cameras, the Imaging Science Subsystem, were the first to be shut down. Designed to take photos of the outer planets, “there wasn’t any more science you could get out of that instrument,” says Dodd, “and there’s a certain amount of memory space that was freed up that we could then repurpose for this longer Voyager interstellar mission.”

But sometimes the location of an instrument surpasses other concerns. For instance, there’s a digital tape recorder still running on Voyager 1 that would reduce power consumption if it were turned off, says Dodd. Instead, NASA keeps it on because the instrument generates some heat in a particular area of the probe’s central bus that helps keep the propellant lines warm.

Other instruments, such as the Cosmic Ray Subsystem (CRS)—which detects super-energetic particles—sit out on a boom away from the bus and have their own heating units. NASA shut down the CRS’ heater on Voyager 2 this past summer. Despite the extreme cold (minus 76 degrees Fahrenheit), the instrument is still functioning. “We gained two things by turning [the heater] off,” says Dodd. “We gained power...and that extra power also provided extra heat in the bus because it’s not going out to the boom now.”

With the CRS still running, scientists continue to gain valuable data. Cosmic rays are a type of high-energy particles: fragments of atoms created by supernovae outside the solar system and accelerated to nearly the speed of light that bombard Earth from all directions. “The heliosphere is a shield against all those cosmic rays that have speeds less than about 50 percent the speed of light,” says Ed Stone, who has served as project scientist for the Voyager program since 1972.

Despite its success in keeping the Voyagers going, NASA has reached the point where it is one anomaly away from losing the spacecraft. JPL engineers were very concerned when they discovered that the primary attitude thrusters on both spacecraft had degraded. “The way a thruster shows age is it starts to pulse many more times to get the same amount of thrust,” says Dodd. To keep the Voyagers oriented toward Earth to transmit data, the JPL engineers have instead fired up another set of thrusters that were used for trajectory correction maneuvers and haven’t been used since the planetary flybys early in the mission.

“I always tell people, my personal goal is to have a spacecraft that celebrates its 50th anniversary from launch,” says Dodd. With more than a little luck, the Voyagers might make it.

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Voyager 1 and 2, Humanity’s Interstellar Envoys, Soldier On at 45

Today is the 45th anniversary of the launch of Voyager 1, one of humanity’s iconic twin emissaries to the cosmos. (Its sibling, Voyager 2, launched a couple of weeks earlier.) Now in the dark, far reaches of interstellar space—more than 10 billion miles from home, where our sun looks like any other bright star—the pair are still doing science. They carry with them the Golden Records, bearing the sounds and symbols of Earth, should some extraterrestrial ever rendezvous with one of the spacecraft and become curious about its distant sender.

“I’ve been following the arc of Voyager over my career,” says Linda Spilker, Voyager’s deputy project scientist at NASA’s Jet Propulsion Laboratory, who started at the agency in 1977, the year the probes launched. “I’m amazed at how long both of these spacecraft, Voyager 1 and Voyager 2, have been able to keep going and return unique science about new places that no spacecraft has visited before. And now they’ve become interstellar travelers. How cool is that?”

The two car-sized probes, each with a 12-foot antenna mounted on top, had one primary task: to visit the gas giants in our own solar system. After their launches, the Voyagers’ paths diverged, but they both took advantage of a rare planetary lineup, snapping groundbreaking photos as they flew by Jupiter, Saturn, Uranus, and Neptune and revealed tantalizing details about the planets’ moons. By the end of 1989, they’d completed that mission. In 1990, Voyager 1 capped it by turning around and taking a poignant image of our own world, which astronomer and science communicator Carl Sagan dubbed the Pale Blue Dot .  

“Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, has lived out their lives,” Sagan wrote. The image of the Earth from a cosmic perspective—a mere “mote of dust suspended in a moonbeam,” as he put it—became nearly as memorable as the Earthrise photo taken by an Apollo 8 astronaut showing the planet as seen from the moon.

The two probes, which run on nuclear-powered systems called radioisotope thermoelectric generators (RTGs), kept flying. Our solar system has no clear boundary, but in the 2000s they crossed the “termination shock,” where solar wind particles abruptly slow below the speed of sound due to pressure from the gas and magnetic fields in interstellar space. Then in the 2010s, they breached the heliopause, the boundary between the solar wind and the interstellar wind. 

With four instruments operating on Voyager 1 and five aboard Voyager 2, they now have a new job: measuring the magnetic field strength, the density of the plasma, and the energy and direction of charged particles in the environment they’re traveling through. “The purpose of the interstellar mission is to measure the sun’s effects as we go further and further from Earth. We’re trying to find out how the sun’s heliosphere interacts with interstellar space,” says Suzanne Dodd, project manager of the Voyager interstellar mission at JPL. Voyager 1 is currently 14.6 billion miles from home, and Voyager 2 is 12.1 billion miles away, but for perspective, the nearest star is some 25 trillion miles away. (NASA maintains a tracker of their journeys .) It’s a remarkable coda for their mission, decades after the probes completed their main goals. 

But they’ve always had a secondary task: conveying a message to any aliens from beyond the solar system who might one day peek inside a craft. Each one carries a Golden Record, which looks like vinyl but is made of metal. A team of scientists and artists, including Sagan and Frank Drake , who died last Friday, packed music, nature sounds, messages, photos, and more on each record—and they included players and instructions, should anyone find them. The ambitious project seeks to tell a story about humanity, what humans aspire to, and our world. It includes the music of Bach and Chuck Berry, and images of families, homes, and scientific advances. “The purpose of the record was to try to answer questions that we would have,” says Jon Lomberg, a scientific artist and the designer for the Golden Records team. “What were the beings like who sent it? What do they look like? What do they act like? What was their world like? So it’s really a self-portrait.”

Unlike the search for extraterrestrial intelligence , or SETI, the records are not designed to be a prelude to first contact. In fact, the Golden Records might be found millions of years from now, perhaps when human civilizations no longer exist. “It’s more like finding a fossil,” says Lomberg. “You can’t talk to the dinosaurs. This is a relic—our obituary in a way, the memento that we were once here.”

The Voyager probes were preceded by the Pioneer missions, which carried small metal plaques with symbolic messages . (The pair of Pioneers left the solar system in the 1980s and ’90s, but they’re no longer functioning.) But no space mission since has incorporated a similar record of humanity—though NASA’s New Horizons , for example, which flew by Pluto in 2015, offered another chance. That was a missed opportunity, Lomberg says, although it might still be possible to send a digital message to the spacecraft’s computer. That would be durable, but it would not last as long as the Golden Records.

The Voyagers have had a tangible influence on space exploration ever since. Their success inspired NASA and other agencies to revisit the outer planets, especially Jupiter and Saturn, and their myriad moons. These subsequent missions include Galileo , Juno , Cassini , and the European Space Agency’s Huygens lander, plus new probes in the works, such as the Europa Clipper , Dragonfly , ESA’s JUICE, and potential voyages to Uranus and Saturn’s moon Enceladus .

The Voyagers influenced pop culture too. The first Star Trek movie in 1979 included an alien spacecraft called “V’ger,” which was actually an altered fictional “Voyager 6.” Voyager and the Golden Records have turned up in TV shows like Saturday Night Live , The West Wing , and—of course— The X-Files . The composer Dario Marianelli even wrote a Voyager-inspired violin concerto.

The pair of spacecraft have lasted far longer than anyone imagined—and, Dodd says, the instruments are working and the data is still great. But they’re showing signs of age. In May, she and her team encountered a glitch in Voyager 1’s telemetry data, which would normally provide information to scientists back home about what the probe’s instruments are doing and whether they’re working properly. The data had been coming back garbled. Addressing the issue was complicated by the vast distance involved, since messages to and from Voyager 1 now take nearly 22 hours. 

Then last week, the team figured out what was wrong. Apparently, the attitude control system had suddenly started sending the telemetry data through the wrong computer, which was no longer working properly. They resolved the problem by routing the data back to the correct computer. “The spacecraft is healthy, it’s happy. It’s returning science data just beautifully,” Spilker says.

Even if Dodd, Spilker, and their colleagues can keep resolving these kinds of technical issues, however, the spacecraft have a more enduring problem: their power supplies. Their RTG systems provide power by converting heat from the radioactive decay of plutonium-238 into electricity. But after 45 years, the fuel is now generating 4 watts less per year. Dodd and her team have turned off any systems and instruments not involved in the interstellar mission—and in 2019, they started turning off heaters in some of the instruments that are still running. That added a couple of years to the spacecrafts’ lifespans.

Nevertheless, the Voyager probes might only have a few years, or perhaps a decade, left in them. Eventually, their dwindling power won’t be sufficient to run their instruments. “At that point, the Voyagers will become our silent ambassadors,” Spilker says.

As they hurtle at 35,000 miles per hour into the unknown with their powered-down machines, they will still carry humanity’s message in a bottle. “The Golden Record, a piece of human civilization, a piece of technology with a 1970s stamp on it—that is going to persevere. It’s not degrading. It’s going to last for billions of years. It’s going to outlast the planet that it came from. That’s mind-blowing kind of stuff,” says Jim Bell, a planetary scientist at Arizona State University and the author of a book on the Voyager mission’s 40th anniversary.

Bell speculates that it might not be aliens, but our own descendants, who ultimately spot the far-flung spacecraft. “My prediction is that the message really is going to be for us. We’re going to be the ones who go find it—in the far future, when it becomes easy to travel and be tourists and see the Voyagers,” he says. “We’ll be thinking: Wasn’t that one of the most amazing things we did as a species in the 20th century?”

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Voyager 1 team accomplishes tricky thruster swap

Engineers working on NASA's Voyager 1 probe have successfully mitigated an issue with the spacecraft's thrusters, which keep the distant explorer pointed at Earth so that it can receive commands, send engineering data, and provide the unique science data it is gathering.

After 47 years, a fuel tube inside the thrusters has become clogged with silicon dioxide , a byproduct that appears with age from a rubber diaphragm in the spacecraft's fuel tank. The clogging reduces how efficiently the thrusters can generate force. After weeks of careful planning, the team switched the spacecraft to a different set of thrusters.

The thrusters are fueled by liquid hydrazine, which is turned into gases and released in tens-of-milliseconds-long puffs to gently tilt the spacecraft's antenna toward Earth. If the clogged thruster were healthy it would need to conduct about 40 of these short pulses per day.

Both Voyager probes feature three sets, or branches, of thrusters: two sets of attitude propulsion thrusters and one set of trajectory correction maneuver thrusters. During the mission's planetary flybys, both types of thrusters were used for different purposes. But as Voyager 1 travels on an unchanging path out of the solar system, its thruster needs are simpler, and either thruster branch can be used to point the spacecraft at Earth.

In 2002 the mission's engineering team, based at NASA's Jet Propulsion Laboratory in Southern California, noticed some fuel tubes in the attitude propulsion thruster branch being used for pointing were clogging, so the team switched to the second branch. When that branch showed signs of clogging in 2018, the team switched to the trajectory correction maneuver thrusters and have been using that branch since then.

Now those trajectory correction thruster tubes are even more clogged than the original branches were when the team swapped them in 2018.

The clogged tubes are located inside the thrusters and direct fuel to the catalyst beds, where it is turned into gases. (These are different than the fuel tubes that send hydrazine to the thrusters.) Where the tube opening was originally only 0.01 inches (0.25 millimeters) in diameter, the clogging has reduced it to 0.0015 inches (0.035 mm), or about half the width of a human hair. As a result, the team needed to switch back to one of the attitude propulsion thruster branches.

Warming up the thrusters

Switching to different thrusters would have been a relatively simple operation for the mission in 1980 or even 2002. But the spacecraft's age has introduced new challenges, primarily related to power supply and temperature. The mission has turned off all non-essential onboard systems, including some heaters, on both spacecraft to conserve their gradually shrinking electrical power supply, which is generated by decaying plutonium.

While those steps have worked to reduce power, they have also led to the spacecraft growing colder, an effect compounded by the loss of other non-essential systems that produced heat. Consequently, the attitude propulsion thruster branches have grown cold, and turning them on in that state could damage them, making the thrusters unusable.

The team determined that the best option would be to warm the thrusters before the switch by turning on what had been deemed non-essential heaters. However, as with so many challenges the Voyager team has faced, this presented a puzzle: The spacecraft's power supply is so low that turning on non-essential heaters would require the mission to turn off something else to provide the heaters adequate electricity, and everything that's currently operating is considered essential.

Studying the issue, they ruled out turning off one of the still-operating science instruments for a limited time because there's a risk that the instrument would not come back online. After additional study and planning, the engineering team determined they could safely turn off one of the spacecraft's main heaters for up to an hour, freeing up enough power to turn on the thruster heaters.

It worked. On Aug. 27, they confirmed that the needed thruster branch was back in action, helping point Voyager 1 toward Earth.

"All the decisions we will have to make going forward are going to require a lot more analysis and caution than they once did," said Suzanne Dodd, Voyager's project manager at the Jet Propulsion Laboratory which manages Voyager for NASA.

The spacecraft are exploring interstellar space , the region outside the bubble of particles and magnetic fields created by the sun, where no other spacecraft are likely to visit for a long time. The mission science team is working to keep the Voyagers going for as long as possible, so they can continue to reveal what the interstellar environment is like.

Provided by NASA

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Communications continue with both the Voyager 1 and 2 spacecraft nearly 34 years after their launches.  Both spacecraft continue to make measurements that will determine when they leave the sphere of influence of the sun and enter interstellar space.

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NASA's Voyager 1 probe swaps thrusters in tricky fix as it flies through interstellar space

The distant and cold Voyager 1 spacecraft did a clever thruster trick to help it phone home.

Voyager 1 , the most distant human object that is now flying through interstellar space , had thruster issues making it difficult for the spacecraft to stay pointed at Earth when calling home. Unless Voyager 1 could make a switch to a different thruster set, the 47-year-old spacecraft would sail on alone without help from Earth. Making matters worse, Voyager 1 is so old that sudden changes could damage the spacecraft.

"All the decisions we will have to make going forward are going to require a lot more analysis and caution than they once did," Suzanne Dodd, Voyager's project manager at NASA's Jet Propulsion Laboratory that manages the mission, said in a statement on Tuesday (Sept. 10).

The science of Voyager 1 is critical to space science as it tells us more about interstellar space, meaning the region of the cosmos outside of the reach of the sun 's gravity or particles. 

But the spacecraft's aging nuclear power source is much diminished, and doesn't have much power to play with. So engineers at JPL embarked on a rescue plan to help the spacecraft's pointing capabilities without risking its remaining functional science instruments.

Voyager 1 and its twin, Voyager 2 , launched on their initial missions in 1977 to study the distant solar system. They collectively flew by four largest outer solar system planets by 1989 and continue, with tweaks for their age, to send science from afar even after both exited the solar system in the early 2010s.

As with humans, aging brought changes to the Voyager systems. The fuel tube for their thrusters have been prone to clogging for more than 20 years; that happens as a rubber diaphragm in each spacecraft fuel tank degrades, creating a silicon dioxide byproduct that clogs the line.

Luckily, each Voyager has three thruster branches available for use: two attitude branches originally designed for orientation, and one trajectory correction branch made for pathway changes in space. To be clear, engineers have been overcoming the unexpected for decades by creatively repurposing parts of Voyager. This new thruster situation, however, brought additional challenges.

On Voyager 1, a fuel tube in the first attitude propulsion branch began to clog in 2002, necessitating a switch to the second branch, NASA officials wrote in the same statement . When the second branch began acting up in 2018, Voyager 1's orientation maneuvers all switched to the trajectory correction maneuver branch. 

But with use, this single branch of the trajectory correction system has been clogging severely, to an even worse extent than either attitude propulsion branch did before.

JPL therefore decided to switch back to the attitude propulsion system, but they had to do so with less power available than in 2002. Voyager 1 is running on essential systems only, and even some of its heaters have turned off. 

Between that necessary loss of some heaters — and the diminished radiant heat from fewer systems running on the spacecraft — Voyager 1's dormant attitude propulsion thruster branch was so cold that even turning it on could cause damage.

Scrutinizing Voyager 1 carefully from afar, JPL engineers determined switching one of the heaters on for an hour would be enough. The command worked and on Aug. 27, one of the attitude thruster branches successfully reoriented Voyager 1 towards Earth for the first time in six years.

Voyager 1 required another form of creative troubleshooting recently; engineers in June resolved a data transmission problem plaguing the spacecraft for months. 

Engineers at JPL plan to keep the Voyager twin spacecraft running until at least the 50th anniversary of the mission in 2027, Dodd told reporters in June at a meeting of the space science community's outer planet assessment group, according to SpaceNews.  

The group more generally deals with exploration activities in the outer reaches of the solar system; it can provide advice to NASA, but the agency does not necessarily follow recommendations, according to NASA .

Voyager 1 Team Accomplishes Tricky Thruster Swap

The spacecraft uses its thrusters to stay pointed at Earth, but after 47 years in space some of the fuel tubes have become clogged.

Engineers working on NASA’s Voyager 1 probe have successfully mitigated an issue with the spacecraft’s thrusters, which keep the distant explorer pointed at Earth so that it can receive commands, send engineering data, and provide the unique science data it is gathering.

After 47 years, a fuel tube inside the thrusters has become clogged with silicon dioxide, a byproduct that appears with age from a rubber diaphragm in the spacecraft’s fuel tank. The clogging reduces how efficiently the thrusters can generate force. After weeks of careful planning, the team switched the spacecraft to a different set of thrusters.

The thrusters are fueled by liquid hydrazine, which is turned into gases and released in tens-of-milliseconds-long puffs to gently tilt the spacecraft’s antenna toward Earth. If the clogged thruster were healthy it would need to conduct about 40 of these short pulses per day.

Both Voyager probes feature three sets, or branches, of thrusters: two sets of attitude propulsion thrusters and one set of trajectory correction maneuver thrusters. During the mission’s planetary flybys, both types of thrusters were used for different purposes. But as Voyager 1 travels on an unchanging path out of the solar system, its thruster needs are simpler, and either thruster branch can be used to point the spacecraft at Earth.

In 2002 the mission’s engineering team, based at NASA’s Jet Propulsion Laboratory in Southern California, noticed some fuel tubes in the attitude propulsion thruster branch being used for pointing were clogging, so the team switched to the second branch. When that branch showed signs of clogging in 2018 , the team switched to the trajectory correction maneuver thrusters and have been using that branch since then.

Now those trajectory correction thruster tubes are even more clogged than the original branches were when the team swapped them in 2018 . The clogged tubes are located inside the thrusters and direct fuel to the catalyst beds, where it is turned into gases. (These are different than the fuel tubes that send hydrazine to the thrusters.) Where the tube opening was originally only 0.01 inches (0.25 millimeters) in diameter, the clogging has reduced it to 0.0015 inches (0.035 mm), or about half the width of a human hair. As a result, the team needed to switch back to one of the attitude propulsion thruster branches.

Warming Up the Thrusters

Switching to different thrusters would have been a relatively simple operation for the mission in 1980 or even 2002. But the spacecraft’s age has introduced new challenges, primarily related to power supply and temperature. The mission has turned off all non-essential onboard systems, including some heaters, on both spacecraft to conserve their gradually shrinking electrical power supply , which is generated by decaying plutonium .

While those steps have worked to reduce power, they have also led to the spacecraft growing colder, an effect compounded by the loss of other non-essential systems that produced heat. Consequently, the attitude propulsion thruster branches have grown cold, and turning them on in that state could damage them, making the thrusters unusable.

The team determined that the best option would be to warm the thrusters before the switch by turning on what had been deemed non-essential heaters. However, as with so many challenges the Voyager team has faced, this presented a puzzle: The spacecraft’s power supply is so low that turning on non-essential heaters would require the mission to turn off something else to provide the heaters adequate electricity, and everything that’s currently operating is considered essential.

Studying the issue, they ruled out turning off one of the still-operating science instruments for a limited time because there’s a risk that the instrument would not come back online. After additional study and planning, the engineering team determined they could safely turn off one of the spacecraft’s main heaters for up to an hour, freeing up enough power to turn on the thruster heaters.

It worked. On Aug. 27, they confirmed that the needed thruster branch was back in action, helping point Voyager 1 toward Earth.

“All the decisions we will have to make going forward are going to require a lot more analysis and caution than they once did,” said Suzanne Dodd, Voyager’s project manager at the Jet Propulsion Laboratory which manages Voyager for NASA.

The spacecraft are exploring interstellar space, the region outside the bubble of particles and magnetic fields created by the Sun, where no other spacecraft are likely to visit for a long time. The mission science team is working to keep the Voyagers going for as long as possible, so they can continue to reveal what the interstellar environment is like.

News Media Contact

Calla Cofield Jet Propulsion Laboratory, Pasadena, Calif. 626-808-2469 [email protected]

Related Terms

• Heliophysics
• Heliosphere
• The Solar System
• Voyager Program

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