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Voyager 1 makes stellar comeback to science operations

Engineers coax veteran probe back to health.

NASA's Voyager 1 spacecraft is back in action and conducting normal science operations for the first time since the veteran probe began spouting gibberish at the end of 2023.

All four of the spacecraft's remaining operational instruments are now returning usable data to Earth, according to NASA .

Some additional work is needed to tidy up the effects of the issue. Engineers need to resynchronize the timekeeping software of Voyager 1's three onboard computers to ensure that commands are executed at the correct times. Maintenance will also be performed on the digital tape recorder, which records some data from the plasma instrument for a six-monthly downlink to Earth.

As the 50th anniversary of Voyager 1's launch rapidly approaches, and with the probe now 15 billion miles (24 billion kilometers) from Earth, restoring functionality is quite an engineering feat.

Voyager 1's woes began in November 2023, when the spacecraft stopped transmitting usable data back to Earth. Rather than engineering and science data, NASA found itself faced with a repeating pattern of ones and zeroes, as though the spacecraft was somehow stalled.

Engineers reckoned the issue lay with the Flight Data System (FDS) and in March sent a command – dubbed a "poke" – to get the FDS to try some other software sequences and thus circumvent whatever was causing the problem.

The result was a complete memory dump from the computer, which allowed engineers to pinpoint where the corruption had occurred. It appeared that a single chip was malfunctioning, and engineers were faced with the challenge of devising a software update that would work around the defective hardware.

Dr Ed Stone, former director of JPL, Voyager project scientist, dies at 88

• Voyager 1 regains sanity after engineers patch around problematic memory
• NASA tries to jog Voyager 1's memory from 15 billion miles away
• Voyager 1 starts making sense again after months of babble

Usable engineering data began to be returned later in April, and in May the mission team sent commands to instruct the probe to keep science data flowing. The result was that the plasma wave subsystem and magnetometer instrument began sending data immediately. According to NASA, the cosmic ray subsystem and low energy charged particle instrument required a little more tweaking but are now operational.

The rescue was made all the more impressive by the fact that it takes 22.5 hours for a command to reach Voyager 1 and another 22.5 hours for a response to be received on Earth.

How much longer the Voyagers can continue to function is open to conjecture. The power supplies are gradually degrading, and engineers have been turning off non-essential systems to eke out dwindling resources for as long as possible.

Due the engineers' efforts, there is a very good chance that one or both Voyagers will continue to be operational by the time the 50th anniversary of the mission's launch rolls around in 2027.

A fitting tribute to those who designed the spacecraft, and the mission's first project scientist, Ed Stone, who died recently at the age of 88. ®

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Voyager 1 is back to life in interstellar space, but for how long?

NASA engineers have succeeded in breathing new life into Voyager 1 after the spacecraft, launched in 1977, went silent seven months ago.

NASA engineers have succeeded in breathing new life into Voyager 1 , the spacecraft launched in 1977 and once again communicating after it went silent seven months ago. But now comes another challenge: Keeping Voyager 1 scientifically useful for as long as possible as it probes a realm where no spacecraft has gone before .

Voyager 1 and its twin, Voyager 2 , are treasured at NASA not only because they have sent home astonishing images of the outer planets, but also because in their dotage, they are still doing science that can’t be readily duplicated.

They are now in interstellar space, far beyond the orbits of Neptune and Pluto. Voyager 1 is more than 15 billion miles from Earth and Voyager 2 nearly 13 billion miles. Both have passed the heliopause , where the “solar wind” of particles streaming from the sun terminates.

“They’re going someplace where we have nothing, we have no information,” NASA Deputy Administrator Pam Melroy said. “We don’t know anything about the interstellar medium. Is it a highly charged environment? Are there a lot of dust particles out there?”

Even as the Voyagers continue their journeys, engineers and scientists at the NASA Jet Propulsion Laboratory in Pasadena, Calif. are mourning the loss of Ed Stone, the scientist who guided the mission from 1972 until his retirement in 2022. Stone, a former director of JPL, died June 9 at the age of 88.

“It’s great. This is exploration. This is wonderful,” Stone told The Washington Post in 2013 when he and his colleagues determined that Voyager 1 had reached interstellar space.

Voyager 1 has four scientific instruments still operational in this extended phase of its mission, but it suddenly ceased sending intelligible data on Nov. 14. A “tiger team” of engineers at JPL spent the ensuing months identifying the problem — a malfunctioning computer chip — and restoring communication.

That laborious process is nearly complete. Data is coming from all four instruments, project scientist Linda Spilker said, though engineers are still checking to see whether data from two of the instruments is fully usable.

What no one can change, though, is the mortality of a spacecraft with a limited power supply. Voyager 1 is running on fumes, or, more precisely, on the dwindling power from the radioactive decay of plutonium.

The Voyagers have traveled so far from the sun they can’t rely on solar power and instead use a radioisotope thermoelectric generator. But an RTG doesn’t last forever. Voyager 1 and Voyager 2 will eventually go silent as they continue to cruise the galaxy. NASA scientists and engineers are hoping Voyager 1 can keep sending data until at least Sept. 5, 2027, the 50th anniversary of its launch.

“At some point, we’ll have to start turning off the science instruments one by one,” Spilker said. “Once we’re out of power, then we can no longer keep the spacecraft pointed at the Earth. And so [the Voyagers] will then continue on as what I like to think of as our silent ambassadors.”

In a sense, this is all a bonus because the primary mission for the two Voyagers was the exploration of the outer planets. Both visited Jupiter and Saturn, and Voyager 2 went on to Uranus and Neptune in what was known as the “Grand Tour” of the outer solar system, enabled by a rare orbital arrangement of the planets. The Voyagers delivered spectacular close-up images of the outer planets, and the mission ranks among NASA’s greatest achievements.

The gravitational slingshot from the planetary encounters sent Voyager 1 out of the elliptical plane of the solar system and did the same to Voyager 2 in a different direction.

About four years ago, Voyager 1 encountered something unexpected — a phenomenon scientists have dubbed a pressure front. Jamie Rankin, deputy project scientist, said the instruments on the spacecraft picked up a sudden change in the magnetic field of the interstellar environment, as well as a sudden increase in the density of particles.

What exactly caused this change remains unknown. But NASA scientists are eager to get all the data flowing normally again to see whether the pressure front is still detectable.

“Is the pressure front still there; what is happening with it?” Melroy said.

Voyager 1 is heading toward the constellation Ophiuchus, according to NASA, and in about 38,000 years, it will come within 1.7 light-years of an unremarkable star near the Little Dipper. But although it will have long gone silent, it does carry the equivalent of a message in a bottle: the “Golden Record.”

The record was curated by a committee led by astronomer Carl Sagan and includes greetings in 55 languages, sounds of surf, wind and thunderstorms, a whale song and music ranging from Beethoven to Chuck Berry to a Navajo chant. The Golden Record is accompanied by instructions for playing it, should the spacecraft someday come into the hands of an intelligent species interested in finding out about life on Earth.

“The spacecraft will be encountered and the record played only if there are advanced spacefaring civilizations in interstellar space,” Sagan said.

But that advanced spacefaring civilization might not be an alien one, NASA scientists point out. It’s conceivable that the cosmic message in a bottle could be picked up someday by a human deep-space mission eager to examine a vintage spaceship.

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.

Things are finally looking up for the Voyager 1 interstellar spacecraft

Two of the four science instruments aboard the Voyager 1 spacecraft are now returning usable data after months of transmitting only gibberish, NASA scientists have announced.

I was once sitting with my father while Googling how far away various things in the solar system are from Earth. He was looking for exact numbers, and very obviously grew more invested with each new figure I shouted out. I was thrilled. The moon? On average, 238,855 miles (384,400 kilometers) away. The James Webb Space Telescope ? Bump that up to about a million miles (1,609,344 km) away. The sun? 93 million miles (149,668,992 km) away.  Neptune ? 2.8  billion  miles (4.5 billion km) away. "Well, wait until you hear about Voyager 1," I eventually said, assuming he was aware of what was coming. He was not.

"NASA's  Voyager 1  interstellar spacecraft actually isn't even in the solar system anymore," I announced. "Nope, it's more than 15 billion miles (24 billion km)  away from us  — and it's getting even farther as we speak." I can't quite remember his response, but I do indeed recall an expression of sheer disbelief. There were immediate inquiries about how that's even physically possible. There were bewildered laughs, different ways of saying "wow," and mostly, there was a contagious sense of awe. And just like that, a new Voyager 1 fan was born.

It is easy to see why Voyager 1 is among the most beloved robotic space explorers we have — and it is thus easy to understand why so many people felt a pang to their hearts several months ago, when Voyager 1 stopped talking to us.

Related:  After months of sending gibberish to NASA, Voyager 1 is finally making sense again

For reasons unknown at the time, this spacecraft began sending back gibberish in place of the neatly organized and data-rich 0's and 1's it had been providing since its  launch in 1977 . It was this classic computer language which allowed Voyager 1 to converse with its creators while earning the title of "farthest human made object." It's how the spacecraft relayed vital insight that led to the discovery of new Jovian moons and, thanks to this sort of binary podcast, scientists incredibly identified a new ring of Saturn and created the solar system's first and only "family portrait." This code, in essence, is crucial to Voyager 1's very being.

Plus, to make matters worse, the issue behind the glitch turned out to be associated with the craft's Flight Data System, which is literally the system that transmits information about Voyager 1's health so scientists can correct any issues that arise. Issues like this one. Furthermore, because of the spacecraft's immense distance from its operators on Earth, it takes about 22.5 hours for a transmission to reach the spacecraft, and then 22.5 hours to receive a transmission back. Alas, things weren't looking good for a while — for about five months, to be precise.

But then, on April 20, Voyager 1  finally phoned home  with legible 0's and legible 1's.

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"The team had gathered early on a weekend morning to see whether telemetry would return," Bob Rasmussen, a member of the Voyager flight team, told Space.com. "It was nice to have everyone assembled in one place like this to share in the moment of learning that our efforts had been successful. Our cheer was both for the intrepid spacecraft and for the comradery that enabled its recovery."

And  then,  on May 22 , Voyager scientists released the welcome announcement that the spacecraft has successfully resumed returning science data from two of its four instruments, the plasma wave subsystem and magnetometer instrument. They're now working on getting the other two, the cosmic ray subsystem and low energy charged particle instrument, back online as well. Though there technically are six other instruments onboard Voyager, those had been out of commission for some time.

The comeback

Rasmussen was actually a member of the Voyager team in the 1970s, having worked on the project as a computer engineer before leaving for other missions including  Cassini , which launched the spacecraft that taught us almost everything we currently know about Saturn. In 2022, however, he returned to Voyager because of a separate dilemma with the mission — and has remained on the team ever since.

"There are many of the original people who were there when Voyager launched, or even before, who were part of both the flight team and the science team," Linda Spilker, a planetary scientist at NASA's Jet Propulsion Laboratory , who also worked on the Voyager mission, told Space.com in the This Week from Space podcast on the TWiT network. "It's a real tribute to Voyager — the longevity not only of the spacecraft, but of the people on the team."

To get Voyager 1 back online, in rather cinematic fashion, the team devised a complex workaround that prompted the FDS to send a copy of its memory back to Earth. Within that memory readout, operators managed to discover the crux of the problem — a corrupted code spanning a single chip — which was then remedied through another (honestly,  super interesting ) process to modify the code. On the day Voyager 1 finally spoke again, "you could have heard a pin drop in the room," Spilker said. "It was very silent. Everybody's looking at the screen, waiting and watching." 

Of course, Spilker also brought in some peanuts for the team to munch on — but not just any peanuts. Lucky peanuts. 

It's a longstanding tradition at JPL to have a peanut feast before major mission events like launches, milestones and, well, the possible resurrection of Voyager 1. It  began  in the 1960s, when the agency was trying to launch the Ranger 7 mission that was meant to take pictures of and collect data about the moon's surface. Rangers 1 through 6 had all failed, so Ranger 7 was a big deal. As such, the mission's trajectory engineer, Dick Wallace, brought lots of peanuts for the team to nibble on and relax. Sure enough, Ranger 7 was a success and, as Wallace once said, "the rest is history." 

Voyager 1 needed some of those positive snacky vibes. 

"It'd been five months since we'd had any information," Spilker explained. So, in this room of silence besides peanut-eating-noises, Voyager 1 operators sat at their respective system screens, waiting. 

"All of a sudden it started to populate — the data," Spilker said. That's when the programmers who had been staring at those screens in anticipation leapt out of their seats and began to cheer: "They were the happiest people in the room, I think, and there was just a sense of joy that we had Voyager 1 back."

Eventually, Rasmussen says the team was able to conclude that the failure probably occurred due to a combination of aging and radiation damage by which energetic particles in space bombarded the craft. This is also why he believes it wouldn't be terribly surprising to see a similar failure occur in the future, seeing as Voyager 1 is still roaming beyond the distant boundaries of our stellar neighborhood just like its spacecraft twin,  Voyager 2 .

To be sure, the spacecraft isn't fully fixed yet — but it's lovely to know things are finally looking up, especially with the recent news that some of its science instruments are back on track. And, at the very least, Rasmussen assures that nothing the team has learned so far has been alarming. "We're confident that we understand the problem well," he said, "and we remain optimistic about getting everything back to normal — but we also expect this won't be the last."

In fact, as Rasmussen explains, Voyager 1 operators first became optimistic about the situation just after the root cause of the glitch had been determined with certainty. He also emphasizes that the team's spirits were never down. "We knew from indirect evidence that we had a spacecraft that was mostly healthy," he said. "Saying goodbye was not on our minds."

"Rather," he continued, "we wanted to push toward a solution as quickly as possible so other matters on board that had been neglected for months could be addressed. We're now calmly moving toward that goal."

The future of Voyager's voyage

It can't be ignored that, over the last few months, there has been an air of anxiety and fear across the public sphere that Voyager 1 was slowly moving toward sending us its final 0 and final 1. Headlines all over the internet, one written by  myself included , have carried clear, negative weight. I think it's because even if Voyager 2 could technically carry the interstellar torch post-Voyager 1, the prospect of losing Voyager 1 felt like the prospect of losing a piece of history. 

"We've crossed this boundary called the heliopause," Spilker explained of the Voyagers. "Voyager 1 crossed this boundary in 2012; Voyager 2 crossed it in 2018 — and, since that time, were the first spacecraft ever to make direct measurements of the interstellar medium." That medium basically refers to material that fills the space between stars. In this case, that's the space between other stars and our sun, which, though we don't always think of it as one, is simply another star in the universe. A drop in the cosmic ocean.

"JPL started building the two Voyager spacecraft in 1972," Spilker explained. "For context, that was only three years after we had the first human walk on the moon — and the reason we started that early is that we had this rare alignment of the planets that happens once every  176 years ." It was this alignment that could promise the spacecraft checkpoints across the solar system, including at Jupiter, Saturn, Uranus and Neptune. Those checkpoints were important for the Voyagers in particular. Alongside planetary visits come gravity assists, and gravity assists can help fling stuff within the solar system — and, now we know, beyond.

As the first humanmade object to leave the solar system, as a relic of America's early space program, and as a testament to how robust even decades-old technology can be, Voyager 1 has carved out the kind of legacy usually reserved for remarkable things lost to time.

"Our scientists are eager to see what they’ve been missing," Rasmussen remarked. "Everyone on the team is self-motivated by their commitment to this unique and important project. That's where the real pressure comes from." 

Still, in terms of energy, the team's approach has been clinical and determined. 

— NASA's Voyager 1 sends readable message to Earth after 4 nail-biting months of gibberish

— NASA engineers discover why Voyager 1 is sending a stream of gibberish from outside our solar system

— NASA's Voyager 1 probe hasn't 'spoken' in 3 months and needs a 'miracle' to save it

"No one was ever especially excited or depressed," he said. "We're confident that we can get back to business as usual soon, but we also know that we're dealing with an aging spacecraft that is bound to have trouble again in the future. That's just a fact of life on this mission, so not worth getting worked up about."

Nonetheless, I imagine it's always a delight for Voyager 1's engineers to remember this robotic explorer occupies curious minds around the globe. (Including my dad's mind now, thanks to me and Google.)

As Rasmussen puts it: "It's wonderful to know how much the world appreciates this mission."

Originally posted on Space.com .

Monisha Ravisetti is Space.com's Astronomy Editor. She covers black holes, star explosions, gravitational waves, exoplanet discoveries and other enigmas hidden across the fabric of space and time. Previously, she was a science writer at CNET, and before that, reported for The Academic Times. Prior to becoming a writer, she was an immunology researcher at Weill Cornell Medical Center in New York. She graduated from New York University in 2018 with a B.A. in philosophy, physics and chemistry. She spends too much time playing online chess. Her favorite planet is Earth.

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Voyager 1 Sends Clear Data to NASA for the First Time in Five Months

The farthest spacecraft from Earth had been transmitting nonsense since November, but after an engineering tweak, it finally beamed back a report on its health and status

Will Sullivan

Daily Correspondent

For the first time in five months, NASA has received usable data from Voyager 1, the farthest spacecraft from Earth.

The aging probe, which has traveled more than 15 billion miles into space, stopped transmitting science and engineering data on November 14. Instead, it sent NASA a nonsensical stream of repetitive binary code . For months, the agency’s engineers undertook a slow process of trial and error, giving the spacecraft various commands and waiting to see how it responded. Thanks to some creative thinking, the team identified a broken chip on the spacecraft and relocated some of the code that was stored there, according to the agency .

NASA is now receiving data about the health and status of Voyager 1’s engineering systems. The next step is to get the spacecraft to start sending science data again.

“Today was a great day for Voyager 1,” Linda Spilker , a Voyager project scientist at NASA’s Jet Propulsion Laboratory (JPL), said in a statement over the weekend, per CNN ’s Ashley Strickland. “We’re back in communication with the spacecraft. And we look forward to getting science data back.”

Hi, it's me. - V1 https://t.co/jgGFBfxIOe — NASA Voyager (@NASAVoyager) April 22, 2024

Voyager 1 and its companion, Voyager 2, separately launched from Earth in 1977. Between the two of them, the probes have studied all four giant planets in the outer solar system—Jupiter, Saturn, Uranus and Neptune—along with 48 of their moons and the planets’ magnetic fields. The spacecraft observed Saturn’s rings in detail and discovered active volcanoes on Jupiter’s moon Io .

Originally designed for a five-year mission within our solar system, both probes are still operational and chugging along through space, far beyond Pluto’s orbit. In 2012, Voyager 1 became the first human-made object to reach interstellar space, the area between stars. The probe is now about eight times farther from the sun than Uranus is on average.

Over the decades, the Voyager spacecraft have transmitted data collected on their travels back to NASA scientists. But in November, Voyager 1 started sending gibberish .

Engineers determined Voyager 1’s issue was with one of three onboard computers, called the flight data system (FDS), NASA said in a December blog post . While the spacecraft was still receiving and executing commands from Earth, the FDS was not communicating properly with a subsystem called the telemetry modulation unit (TMU). The FDS collects science and engineering data and combines it into a package that the TMU transmits back to Earth.

Since Voyager 1 is so far away, testing solutions to its technical issues requires time—it takes 22.5 hours for commands to reach the probe and another 22.5 hours for Voyager 1’s response to come back.

On March 1, engineers sent a command that coaxed Voyager 1 into sending a readout of the FDS memory, NASA said in a March 13 blog post . From that readout, the team confirmed a small part—about 3 percent—of the system’s memory had been corrupted, NASA said in an April 4 update .

The core of the problem turned out to be a faulty chip hosting some software code and part of the FDS memory. NASA doesn’t know what caused the chip to stop working—it could be that a high-energy particle from space collided with it, or the chip might have just run out of steam after almost 50 years spent hurtling through the cosmos.

“It’s the most serious issue we’ve had since I’ve been the project manager, and it’s scary because you lose communication with the spacecraft,” Suzanne Dodd , Voyager project manager at JPL, told Scientific American ’s Nadia Drake in March.

To receive usable data again, the engineers needed to move the affected code somewhere else that wasn’t broken. But no single location in the FDS memory was large enough to hold all of the code, so the engineers divided it into chunks and stored it in multiple places, per NASA .

The team started with moving the code responsible for sending Voyager’s status reports, sending it to its new location in the FDS memory on April 18. They received confirmation that the strategy worked on April 20, when the first data on the spacecraft’s health since November arrived on Earth.

In the next several weeks, the team will relocate the parts of the FDS software that can start returning science data.

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Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next .

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How the most distant object ever made by humans is spending its dying days

By Rahul Rao

Posted on Apr 28, 2021 4:00 PM EDT

4 minute read

The eyes of the world might be fixed upon Mars, where last week alone, the Ingenuity helicopter took flight and the Perseverance rover made oxygen . But farther—much farther—Voyager 1, one of the oldest space probes and the most distant human-made object from Earth, is still doing science.

The probe is well into the fourth decade of its mission, and it hasn’t come near a planet since it flew past Saturn in 1980. But even as it drifts farther and farther from a dimming sun, it’s still sending information back to Earth, as scientists recently reported in The Astrophysical Journal.

For decades, Voyager has been sailing away at around 11 miles (17 kilometers) every second. Each year, it travels another 3.5 AU (the distance between Earth and the sun) away from us. Now, it’s sending messages home even as it prepares to leave this solar system behind.

There are multiple ways to think about the “edge of the solar system.” One is a boundary region called the heliopause. That’s the frontier where the solar wind (the soup of charged particles continually thrown off by the sun) is too weak to hold off the interstellar medium—the plasma, dust, and radiation that fill the bulk of space.

When Voyager 1 left Earth in 1977, nobody was certain where the heliopause was, according to Bill Kurth , an astrophysicist at the University of Iowa who has been working with Voyager 1 since before it launched. Some scientists then even thought the heliopause was as close as 10 or even 5 AU—around the orbits of Jupiter, which Voyager 1 passed in 1979, or Saturn.

In reality, the heliopause is around 120 AU away. We know this partly because Voyager 1 crossed the heliopause in August 2012, a whole three and a half decades after it departed Earth. That puts the probe well and truly in interstellar space.

[Related: Voyager 2 can finally probe the rarified plasma surrounding our solar system ]

Out here, space is filled with interstellar medium—but you’ll not see very much of it. A cube of air at sea level on Earth contains more than a trillion times as many molecules as an equal-sized cube of even the interstellar medium’s densest parts. The region that Voyager 1 is traversing is sparser still. And for the most part, it’s quiet.

But every few years, as Voyager 1 records more data about the plasma and dust out here, it finds something . For instance, in 2012 and again in 2014, Voyager 1 felt a shock. According to Kurth, what Voyager 1 recorded was a magnetic spike, accompanied by a burst of energetic electrons that caused intense, oscillating electric fields. These shocks are the most distant effects of the sun, rippling outwards even past the heliopause.

What Voyager 1 encountered in 2020 was another jump in magnetic field strength, but without those intense electrical oscillations. Scientists instead think it’s a pressure front, a much more subtle disturbance moving out into the interstellar medium. Voyager 1 previously encountered something like it in 2017.

According to Jon Richardson , an astrophysicist at MIT who wasn’t an author on the paper, this latest finding shows that Voyager 1 is still capable of surprising scientists. Normally, he says, the probe would need to experience a shock in the surrounding plasma to measure its density. But with observations like this one, scientists have found a way to use Voyager 1 to continually monitor that density—over 13 billion miles away from us.

Richardson also says the findings show that Voyager 1 continues to feel the sun’s tendrils, billions of miles past the heliopause. “The sun is still having a major effect,” he says, “far outside the heliosphere.”

Meanwhile, Voyager 1 is still within the sun’s gravitational influence. In about 300 years, scientists expect, Voyager 1 will start to enter the inner edge of the Oort cloud, that shroud of comets which stretches as far as several light-years away.

We’ve never actually seen evidence of the Oort cloud, but sadly, Voyager 1 likely won’t be the one to reveal it. The probe is quite literally living on borrowed time. Plutonium-238, the radioisotope that powers the probe’s generator, has a half-life of about 88 years. 

[Related: Ask Us Anything: What happens to your body when you die in space? ]

As a result, Voyager 1 is starting to lose fuel. Scientists are already having to make choices about which parts of the probe they should keep functional. By the mid-2020s, it’s likely that the probe won’t be able to power even a single instrument.

Still, scientists like Kurth hope they can eke the probe’s life out to 2027, the 50th anniversary of its launch. That, Kurth says, is a milestone that none of Voyager 1’s designers could ever have foreseen.

Latest in NASA

Voyager 1 defies the odds yet again and is back online voyager 1 defies the odds yet again and is back online.

By Andrew Paul

‘Check his pulse one more time’: NASA accidentally airs ISS emergency test ‘Check his pulse one more time’: NASA accidentally airs ISS emergency test

Voyager 1 "back in action" reporting space data after NASA fixes glitch 15 billion miles away

N ASA's Voyager 1 is back "conducting normal science operations" for the first time since a technical glitch some seven months sidelined the spacecraft, space agency officials announced.

Why it matters: The spacecraft that launched in 1977 has collected key scientific data and at more than 15 billion miles from Earth it's the farthest human-made object in space.

• Per a NASA statement announcing the fix, Voyager 1 and Voyager 2 (which launched the same year) "are the only spacecraft to directly sample interstellar space, which is the region outside the heliosphere — the protective bubble of magnetic fields and solar wind created by the Sun."
• The twin probes explored the outer planets of Jupiter, Saturn, Uranus and Neptune before starting their voyages toward interstellar space.

Driving the news: NASA announced last year that Voyager 1 was experiencing problems with its flight data system.

• "The spacecraft is receiving and executing commands sent from Earth but not returning useable data," per a post to X by the Jet Propulsion Laboratory, which many of NASA's robotic missions after the issue emerged last November.

The big picture: NASA announced in April that the mission team had partially resolved the issue by prompting the spacecraft to begin returning engineering data including information about the health and status of the spacecraft.

• They completed the next step of the repair process last month when they beamed a command to the spacecraft to begin resuming science data and two of the four science instruments returned to their normal operating modes.
• "Two other instruments required some additional work, but now, all four are returning usable science data," according to NASA's statement last week.

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NASA's Voyager 1 spacecraft is talking nonsense. Its friends on Earth are worried

Nell Greenfieldboyce

This artist's impression shows one of the Voyager spacecraft moving through the darkness of space. NASA/JPL-Caltech hide caption

This artist's impression shows one of the Voyager spacecraft moving through the darkness of space.

The last time Stamatios "Tom" Krimigis saw the Voyager 1 space probe in person, it was the summer of 1977, just before it launched from Cape Canaveral, Florida.

Now Voyager 1 is over 15 billion miles away, beyond what many consider to be the edge of the solar system. Yet the on-board instrument Krimigis is in charge of is still going strong.

"I am the most surprised person in the world," says Krimigis — after all, the spacecraft's original mission to Jupiter and Saturn was only supposed to last about four years.

These days, though, he's also feeling another emotion when he thinks of Voyager 1.

"Frankly, I'm very worried," he says.

Ever since mid-November, the Voyager 1 spacecraft has been sending messages back to Earth that don't make any sense. It's as if the aging spacecraft has suffered some kind of stroke that's interfering with its ability to speak.

"It basically stopped talking to us in a coherent manner," says Suzanne Dodd of NASA's Jet Propulsion Laboratory, who has been the project manager for the Voyager interstellar mission since 2010. "It's a serious problem."

Instead of sending messages home in binary code, Voyager 1 is now just sending back alternating 1s and 0s. Dodd's team has tried the usual tricks to reset things — with no luck.

It looks like there's a problem with the onboard computer that takes data and packages it up to send back home. All of this computer technology is primitive compared to, say, the key fob that unlocks your car, says Dodd.

"The button you press to open the door of your car, that has more compute power than the Voyager spacecrafts do," she says. "It's remarkable that they keep flying, and that they've flown for 46-plus years."

Each of the Voyager probes carries an American flag and a copy of a golden record that can play greetings in many languages. NASA/JPL-Caltech hide caption

Each of the Voyager probes carries an American flag and a copy of a golden record that can play greetings in many languages.

Voyager 1 and its twin, Voyager 2, have outlasted many of those who designed and built them. So to try to fix Voyager 1's current woes, the dozen or so people on Dodd's team have had to pore over yellowed documents and old mimeographs.

"They're doing a lot of work to try and get into the heads of the original developers and figure out why they designed something the way they did and what we could possibly try that might give us some answers to what's going wrong with the spacecraft," says Dodd.

She says that they do have a list of possible fixes. As time goes on, they'll likely start sending commands to Voyager 1 that are more bold and risky.

"The things that we will do going forward are probably more challenging in the sense that you can't tell exactly if it's going to execute correctly — or if you're going to maybe do something you didn't want to do, inadvertently," says Dodd.

Linda Spilker , who serves as the Voyager mission's project scientist at NASA's Jet Propulsion Laboratory, says that when she comes to work she sees "all of these circuit diagrams up on the wall with sticky notes attached. And these people are just having a great time trying to troubleshoot, you know, the 60's and 70's technology."

"I'm cautiously optimistic," she says. "There's a lot of creativity there."

Still, this is a painstaking process that could take weeks, or even months. Voyager 1 is so distant, it takes almost a whole day for a signal to travel out there, and then a whole day for its response to return.

"We'll keep trying," says Dodd, "and it won't be quick."

In the meantime, Voyager's 1 discombobulation is a bummer for researchers like Stella Ocker , an astronomer with Caltech and the Carnegie Observatories

"We haven't been getting science data since this anomaly started," says Ocker, "and what that means is that we don't know what the environment that the spacecraft is traveling through looks like."

After 35 Years, Voyager Nears Edge Of Solar System

That interstellar environment isn't just empty darkness, she says. It contains stuff like gas, dust, and cosmic rays. Only the twin Voyager probes are far out enough to sample this cosmic stew.

"The science that I'm really interested in doing is actually only possible with Voyager 1," says Ocker, because Voyager 2 — despite being generally healthy for its advanced age — can't take the particular measurements she needs for her research.

Even if NASA's experts and consultants somehow come up with a miraculous plan that can get Voyager 1 back to normal, its time is running out.

The two Voyager probes are powered by plutonium, but that power system will eventually run out of juice. Mission managers have turned off heaters and taken other measures to conserve power and extend the Voyager probes' lifespan.

"My motto for a long time was 50 years or bust," says Krimigis with a laugh, "but we're sort of approaching that."

In a couple of years, the ebbing power supply will force managers to start turning off science instruments, one by one. The very last instrument might keep going until around 2030 or so.

When the power runs out and the probes are lifeless, Krimigis says both of these legendary space probes will basically become "space junk."

"It pains me to say that," he says. While Krimigis has participated in space missions to every planet, he says the Voyager program has a special place in his heart.

Spilker points out that each spacecraft will keep moving outward, carrying its copy of a golden record that has recorded greetings in many languages, along with the sounds of Earth.

"The science mission will end. But a part of Voyager and a part of us will continue on in the space between the stars," says Spilker, noting that the golden records "may even outlast humanity as we know it."

Krimigis, though, doubts that any alien will ever stumble across a Voyager probe and have a listen.

"Space is empty," he says, "and the probability of Voyager ever running into a planet is probably slim to none."

It will take about 40,000 years for Voyager 1 to approach another star; it will come within 1.7 light years of what NASA calls "an obscure star in the constellation Ursa Minor" — also known as the Little Dipper.

If NASA greenlights this interstellar mission, it could last 100 years

Knowing that the Voyager probes are running out of time, scientists have been drawing up plans for a new mission that, if funded and launched by NASA, would send another probe even farther out into the space between stars.

"If it happens, it would launch in the 2030s," says Ocker, "and it would reach twice as far as Voyager 1 in just 50 years."

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Edward Stone, 88, Physicist Who Oversaw Voyager Missions, Is Dead

He helped send the twin spacecraft on their way in 1977. Decades and billions of miles later, they are still probing — “Earth’s ambassadors to the stars,” as he put it.

By Sam Roberts

Edward C. Stone, the visionary physicist who dispatched NASA’s Voyager spacecraft to run rings around our solar system’s outer planets and, for the first time, to venture beyond to unravel interstellar mysteries, died on Sunday at his home in Pasadena, Calif. He was 88.

His death was confirmed by his daughter Susan C. Stone.

Inspired by the launch of the Soviet satellite Sputnik in 1957, while he was a college student, Dr. Stone went on to oversee the Voyager missions 20 years later for the Jet Propulsion Laboratory, which the California Institute of Technology manages for NASA.

Twin spacecraft, Voyager 1 and Voyager 2 were launched separately in the summer of 1977 from Cape Canaveral, Fla. Almost five decades later, they are continuing their journeys deep into space and still collecting data.

Dr. Stone was the program’s chief project scientist for 50 years, starting in 1972, when he was a 36-year-old physics professor at Caltech. He became the public face of the project with the double launch in 1977.

Taking advantage of a gravitational convergence of four planets that occurs only once every 176 years, the spacecraft soared past Jupiter, Saturn, Uranus and Neptune.

The spacecraft produced the first high-resolution images of the four planets, the rings of Jupiter, Uranus and Neptune, lightning on Jupiter and lava lakes that revealed active volcanoes on Jupiter’s moon Io.

“We were on a mission of discovery,” Dr. Stone told The New York Times in 2002. “But we didn’t appreciate how much discovery there would be.”

In 2012, Voyager 1 became the first human-made object to pass the heliopause frontier, where the fierce solar wind of subatomic particles yields to the force of other suns. Today, Voyager 1 is estimated to be 15 billion miles from Earth and traveling at a speed of 38,000 m.p.h., according to NASA . Voyager 2 crossed the border to interstellar space in 2018.

“The two spacecraft will be Earth’s ambassadors to the stars, orbiting the Milky Way for billions of years,” Dr. Stone once said.

His leadership on the Voyager project earned him the 1991 National Medal of Science from President George H.W. Bush.

As director of the Jet Propulsion Laboratory in Pasadena from 1991 to 2001, Dr. Stone oversaw the Mars Pathfinder mission and its wheeled Sojourner rover; the Galileo space probe’s orbital mission to Jupiter; the launch of the Cassini spacecraft to Saturn and its rings and moons, a joint project involving NASA, the European Space Agency and the Italian space agency; and a new class of Earth science satellites.

Dr. Stone also served, from the late 1980s through the ’90s, as chairman of the California Association for Research in Astronomy, which built and operated the W.M. Keck Observatory in Hawaii.

In 2014, he became the founding executive director of the Thirty Meter Telescope International Observatory , also in Hawaii. He held that position until 2022, when he retired as Voyager’s chief scientist.

In a statement, Thomas F. Rosenbaum, the president of Caltech, called Dr. Stone “a great scientist, a formidable leader and a gifted expositor of discovery.”

Edward Carroll Stone Jr. was born on Jan. 23, 1936, in Knoxville, Iowa, southeast of Des Moines, and grew up near Burlington, on the banks of the Mississippi River. His father, Edward Sr., owned a small construction company, and his mother, Ferne Elizabeth (Baber) Stone, kept its books.

“Our father was a construction superintendent who enjoyed learning new things and explaining how they worked,” Dr. Stone wrote when he was awarded the 2019 Shaw Prize in Astronomy for his work on the Voyager missions.

He received an associate of arts degree in physics from Burlington Junior College (now Southeastern Community College) and earned a master’s degree and a doctorate from the University of Chicago.

Dr. Stone married Alice Trabue Wickliffe in 1962. She died in 2023. In addition to his daughter Susan, he is survived by another daughter, Janet Stone; and two grandsons.

Shortly after he began his graduate studies, the news that the Soviets had launched a satellite focused his fascination with physics on space exploration and, in particular, cosmic rays, the particles that come from stars and that travel through the universe at warp speed.

Inspired by his doctoral adviser, John A. Simpson , Dr. Stone performed his first cosmic ray experiments in 1961 while working on Discover 36, an Air Force spy satellite.

He joined Caltech’s faculty in 1964. As chairman of the university’s Division of Physics, Mathematics and Astronomy, a role he held from 1983 to 1988, he helped establish the Laser Interferometer Gravitational-Wave Observatory, which later detected ripples in space and time called gravitational waves.

Norman Haynes, who for years was Voyager’s overall project manager, once said that Dr. Stone, by dint of his scientific expertise and management skill, “revolutionized the world of project science.”

In 1990, Dr. Stone acknowledged the irony in his signature project — that even with all its discoveries, he would not see its conclusion before he died.

“I’ve been having so much fun on Voyager,” he told The New York Times Magazine, “that even if I never see the edge of the solar system, I would do it all again.”

Dr. Stone eventually got to witness the twin spacecraft’s departure from the solar system — twice.

“I keep asking myself why is there so much public interest in space,” he said. “It is, after all, just basic science in the end. The answer is that it provides us with a sense of the future. When we stop discovering new things out there, the concept of the future will change. Space reminds us that there is something left to be done, that life will continue to evolve. It gives us direction, an arrow in time.”

Sam Roberts is an obituaries reporter for The Times, writing mini-biographies about the lives of remarkable people. More about Sam Roberts

NASA's interstellar Voyager 1 spacecraft isn't doing so well — here's what we know

Since late 2023, engineers have been trying to get the Voyager spacecraft back online.

On Dec. 12, 2023, NASA shared some worrisome news about Voyager 1, the first probe to walk away from our solar system 's gravitational party and enter the isolation of interstellar space . Surrounded by darkness, Voyager 1 seems to be glitching. 

It has been out there for more than 45 years, having supplied us with a bounty of treasure like the discovery of two new moons of Jupiter, another incredible ring of Saturn and the warm feeling that comes from knowing pieces of our lives will drift across the cosmos even after we're gone. (See: The Golden Record .) But now, Voyager 1 's fate seems to be uncertain.

As of Feb. 6, NASA said the team remains working on bringing the spacecraft back to proper health. "Engineers are still working to resolve a data issue on Voyager 1," NASA's Jet Propulsion Laboratory said in a post on X (formerly Twitter). "We can talk to the spacecraft, and it can hear us, but it's a slow process given the spacecraft's incredible distance from Earth."

Related: NASA's interstellar Voyager probes get software updates beamed from 12 billion miles away

So, on the bright side, even though Voyager 1 sits so utterly far away from us, ground control can actually communicate with it. In fact, last year, scientists beamed some software updates to the spacecraft as well as its counterpart, Voyager 2 , from billions of miles away. Though on the dimmer side, due to that distance, a single back-and-forth communication between Voyager 1 and anyone on Earth takes a total of 45 hours. If NASA finds a solution, it won't be for some time .

The issue, engineers realized, has to do with one of Voyager 1's onboard computers known as the Flight Data System, or FDS. (The backup FDS stopped working in 1981.)

"The FDS is not communicating properly with one of the probe's subsystems, called the telemetry modulation unit (TMU)," NASA said in a blog post. "As a result, no science or engineering data is being sent back to Earth." This is of course despite the fact that ground control can indeed send information to Voyager 1, which, at the time of writing this article , sits about 162 AU's from our planet. One AU is equal to the distance between the Earth and the sun , or 149,597,870.7 kilometers (92,955,807.3 miles).

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From the beginning 

Voyager 1's FDS dilemma was first noticed last year , after the probe's TMU stopped sending back clear data and started procuring a bunch of rubbish. 

As NASA explains in the blog post, one of the FDS' core jobs is to collect information about the spacecraft itself, in terms of its health and general status. "It then combines that information into a single data 'package' to be sent back to Earth by the TMU," the post says. "The data is in the form of ones and zeros, or binary code." 

However, the TMU seemed to be shuffling back a non-intelligible version of binary code recently. Or, as the team puts it, it seems like the system is "stuck." Yes, the engineers tried turning it off and on again. 

That didn't work. 

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Then, in early February, Suzanne Dodd, Voyager project manager at NASA's Jet Propulsion Laboratory, told Ars Technica that the team might have pinpointed what's going on with the FDS at last. The theory is that the problem lies somewhere with the FDS' memory; there might be a computer bit that got corrupted. Unfortunately, though, because the FDS and TMU work together to relay information about the spacecraft's health, engineers are having a hard time figuring out where exactly the possible corruption may exist. The messenger is the one that needs a messenger.

They do know, however, that the spacecraft must be alive because they are receiving what's known as a "carrier tone." Carrier tone wavelengths don't carry information, but they are signals nonetheless, akin to a heartbeat. It's also worth considering that Voyager 1 has experienced problems before, such as in 2022 when the probe's "attitude articulation and control system" exhibited some blips that were ultimately patched up. Something similar happened to Voyager 2 during the summer of 2023, when Voyager 1's twin suffered some antenna complications before coming right back online again.

Still, Dodd says this situation has been the most serious since she began working on the historic Voyager mission.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Monisha Ravisetti is Space.com's Astronomy Editor. She covers black holes, star explosions, gravitational waves, exoplanet discoveries and other enigmas hidden across the fabric of space and time. Previously, she was a science writer at CNET, and before that, reported for The Academic Times. Prior to becoming a writer, she was an immunology researcher at Weill Cornell Medical Center in New York. She graduated from New York University in 2018 with a B.A. in philosophy, physics and chemistry. She spends too much time playing online chess. Her favorite planet is Earth.

Ed Stone, who led NASA's iconic Voyager project for 50 years, dies at 88

NASA's Voyager 1 glitch has scientists sad yet hopeful: 'Voyager 2 is still going strong'

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• Classical Motion There must be more to this story. Let me see if I have this right. They can receive a carrier. But the modulator gives them junk. Or possibly the processor's memory. And they can send new software. New instructions. So, why not simply use the packet data, to key the carrier on and off. OOK On and Off Keying. Telegraphy. Reply

Admin said: NASA's Voyager 1 deep space probe started glitching last year, and scientists aren't sure they can fix it. NASA's interstellar Voyager 1 spacecraft isn't doing so well — here's what we know : Read more

• Classical Motion I wish something would kick one of them back to us. I would love to see an analysis of every cubic cm of it. Reply
• billslugg Modulating the carrier wave would do no good unless the carrier knew what information to send us. The unit that failed takes the raw data and then tells the carrier what to say. Without the modulation unit there is no data to send. Reply

Classical Motion said: I wish something would kick one of them back to us. I would love to see an analysis of every cubic cm of it.

• Classical Motion I read that they were not sure if it was the modulator or the packet memory. The packet buffer. If they can send patch, it's easy to relocate that buffer into another section of memory. This can be done at several different memory locations to verify if it is a memory problem. If that works, then the modulator is ok. If the modulator fails with all those buffers, then it's the modulator. Turn off modulator. Just enable the carrier for a certain duration for a 1 bit. And turn it off for that certain duration for a 0 bit. One simply rotates that buffer string thru the accumulator at the duration rate, and use status flags to key the transmitter. Very simple and very short code. The packet is nothing more that a 128 BYTE or multiple size string of 1s and 0s. OOK is a very common wireless modulation. That's why I commented on more must be going on. And I would like to see what 30 years naked in space does to man molded matter. Reply

Classical Motion said: I read that they were not sure if it was the modulator or the packet memory. The packet buffer. If they can send patch, it's easy to relocate that buffer into another section of memory. This can be done at several different memory locations to verify if it is a memory problem. If that works, then the modulator is ok. If the modulator fails with all those buffers, then it's the modulator. Turn off modulator. Just enable the carrier for a certain duration for a 1 bit. And turn it off for that certain duration for a 0 bit. One simply rotates that buffer string thru the accumulator at the duration rate, and use status flags to key the transmitter. Very simple and very short code. The packet is nothing more that a 128 BYTE or multiple size string of 1s and 0s. OOK is a very common wireless modulation. That's why I commented on more must be going on. And I would like to see what 30 years naked in space does to man molded matter.

• damienassurre I think they should make another space craft and have it pick up voyager 1 and bring it back the info it went through would very valuable to stellar travel Reply

damienassurre said: I think they should make another space craft and have it pick up voyager 1 and bring it back the info it went through would very valuable to stellar travel

• billslugg The newer forms of memory can't be used easily in outer space as their feature size is too small and too easily corrupted by a cosmic ray. Very large, bulky features keep spacecraft memory far smaller than what earthbound computers can enjoy. As far as returning one of the Voyagers to Earth, it would take several thousand years using available technology. Better to wait for more advanced propulsion technologies. Reply
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• The Contents
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golden record

Where are they now.

• frequently asked questions
• Q&A with Ed Stone

The Voyager Planetary Mission

The twin spacecraft Voyager 1 and Voyager 2 were launched by NASA in separate months in the summer of 1977 from Cape Canaveral, Florida. As originally designed, the Voyagers were to conduct closeup studies of Jupiter and Saturn, Saturn's rings, and the larger moons of the two planets.

To accomplish their two-planet mission, the spacecraft were built to last five years. But as the mission went on, and with the successful achievement of all its objectives, the additional flybys of the two outermost giant planets, Uranus and Neptune, proved possible -- and irresistible to mission scientists and engineers at the Voyagers' home at the Jet Propulsion Laboratory in Pasadena, California.

As the spacecraft flew across the solar system, remote-control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left the Earth. Their two-planet mission became four. Their five-year lifetimes stretched to 12 and more.

Eventually, between them, Voyager 1 and 2 would explore all the giant outer planets of our solar system, 48 of their moons, and the unique systems of rings and magnetic fields those planets possess.

Had the Voyager mission ended after the Jupiter and Saturn flybys alone, it still would have provided the material to rewrite astronomy textbooks. But having doubled their already ambitious itineraries, the Voyagers returned to Earth information over the years that has revolutionized the science of planetary astronomy, helping to resolve key questions while raising intriguing new ones about the origin and evolution of the planets in our solar system.

History of the Voyager Mission

The Voyager mission was designed to take advantage of a rare geometric arrangement of the outer planets in the late 1970s and the 1980s which allowed for a four-planet tour for a minimum of propellant and trip time. This layout of Jupiter, Saturn, Uranus and Neptune, which occurs about every 175 years, allows a spacecraft on a particular flight path to swing from one planet to the next without the need for large onboard propulsion systems. The flyby of each planet bends the spacecraft's flight path and increases its velocity enough to deliver it to the next destination. Using this "gravity assist" technique, first demonstrated with NASA's Mariner 10 Venus/Mercury mission in 1973-74, the flight time to Neptune was reduced from 30 years to 12.

While the four-planet mission was known to be possible, it was deemed to be too expensive to build a spacecraft that could go the distance, carry the instruments needed and last long enough to accomplish such a long mission. Thus, the Voyagers were funded to conduct intensive flyby studies of Jupiter and Saturn only. More than 10,000 trajectories were studied before choosing the two that would allow close flybys of Jupiter and its large moon Io, and Saturn and its large moon Titan; the chosen flight path for Voyager 2 also preserved the option to continue on to Uranus and Neptune.

From the NASA Kennedy Space Center at Cape Canaveral, Florida, Voyager 2 was launched first, on August 20, 1977; Voyager 1 was launched on a faster, shorter trajectory on September 5, 1977. Both spacecraft were delivered to space aboard Titan-Centaur expendable rockets.

The prime Voyager mission to Jupiter and Saturn brought Voyager 1 to Jupiter on March 5, 1979, and Saturn on November 12, 1980, followed by Voyager 2 to Jupiter on July 9, 1979, and Saturn on August 25, 1981.

Voyager 1's trajectory, designed to send the spacecraft closely past the large moon Titan and behind Saturn's rings, bent the spacecraft's path inexorably northward out of the ecliptic plane -- the plane in which most of the planets orbit the Sun. Voyager 2 was aimed to fly by Saturn at a point that would automatically send the spacecraft in the direction of Uranus.

After Voyager 2's successful Saturn encounter, it was shown that Voyager 2 would likely be able to fly on to Uranus with all instruments operating. NASA provided additional funding to continue operating the two spacecraft and authorized JPL to conduct a Uranus flyby. Subsequently, NASA also authorized the Neptune leg of the mission, which was renamed the Voyager Neptune Interstellar Mission.

Voyager 2 encountered Uranus on January 24, 1986, returning detailed photos and other data on the planet, its moons, magnetic field and dark rings. Voyager 1, meanwhile, continues to press outward, conducting studies of interplanetary space. Eventually, its instruments may be the first of any spacecraft to sense the heliopause -- the boundary between the end of the Sun's magnetic influence and the beginning of interstellar space. (Voyager 1 entered Interstellar Space on August 25, 2012.)

Following Voyager 2's closest approach to Neptune on August 25, 1989, the spacecraft flew southward, below the ecliptic plane and onto a course that will take it, too, to interstellar space. Reflecting the Voyagers' new transplanetary destinations, the project is now known as the Voyager Interstellar Mission.

Voyager 1 is now leaving the solar system, rising above the ecliptic plane at an angle of about 35 degrees at a rate of about 520 million kilometers (about 320 million miles) a year. Voyager 2 is also headed out of the solar system, diving below the ecliptic plane at an angle of about 48 degrees and a rate of about 470 million kilometers (about 290 million miles) a year.

Both spacecraft will continue to study ultraviolet sources among the stars, and the fields and particles instruments aboard the Voyagers will continue to search for the boundary between the Sun's influence and interstellar space. The Voyagers are expected to return valuable data for two or three more decades. Communications will be maintained until the Voyagers' nuclear power sources can no longer supply enough electrical energy to power critical subsystems.

The cost of the Voyager 1 and 2 missions -- including launch, mission operations from launch through the Neptune encounter and the spacecraft's nuclear batteries (provided by the Department of Energy) -- is $865 million. NASA budgeted an additional $30 million to fund the Voyager Interstellar Mission for two years following the Neptune encounter.

Voyagers 1 and 2 are identical spacecraft. Each is equipped with instruments to conduct 10 different experiments. The instruments include television cameras, infrared and ultraviolet sensors, magnetometers, plasma detectors, and cosmic-ray and charged-particle sensors. In addition, the spacecraft radio is used to conduct experiments.

The Voyagers travel too far from the Sun to use solar panels; instead, they were equipped with power sources called radioisotope thermoelectric generators (RTGs). These devices, used on other deep space missions, convert the heat produced from the natural radioactive decay of plutonium into electricity to power the spacecraft instruments, computers, radio and other systems.

The spacecraft are controlled and their data returned through the Deep Space Network (DSN), a global spacecraft tracking system operated by JPL for NASA. DSN antenna complexes are located in California's Mojave Desert; near Madrid, Spain; and in Tidbinbilla, near Canberra, Australia.

The Voyager project manager for the Interstellar Mission is George P. Textor of JPL. The Voyager project scientist is Dr. Edward C. Stone of the California Institute of Technology. The assistant project scientist for the Jupiter flyby was Dr. Arthur L. Lane, followed by Dr. Ellis D. Miner for the Saturn, Uranus and Neptune encounters. Both are with JPL.

JUPITER Voyager 1 made its closest approach to Jupiter on March 5, 1979, and Voyager 2 followed with its closest approach occurring on July 9, 1979. The first spacecraft flew within 277,400 kilometers (172,368 miles) of the planet's cloud tops, and Voyager 2 came within 650,180 kilometers (404,003 miles).

Jupiter is the largest planet in the solar system, composed mainly of hydrogen and helium, with small amounts of methane, ammonia, water vapor, traces of other compounds and a core of melted rock and ice. Colorful latitudinal bands and atmospheric clouds and storms illustrate Jupiter's dynamic weather system. The giant planet is now known to possess 16 moons. The planet completes one orbit of the Sun each 11.8 years and its day is 9 hours, 55 minutes.

Although astronomers had studied Jupiter through telescopes on Earth for centuries, scientists were surprised by many of the Voyager findings.

The Great Red Spot was revealed as a complex storm moving in a counterclockwise direction. An array of other smaller storms and eddies were found throughout the banded clouds.

Discovery of active volcanism on the satellite Io was easily the greatest unexpected discovery at Jupiter. It was the first time active volcanoes had been seen on another body in the solar system. Together, the Voyagers observed the eruption of nine volcanoes on Io, and there is evidence that other eruptions occurred between the Voyager encounters.

Plumes from the volcanoes extend to more than 300 kilometers (190 miles) above the surface. The Voyagers observed material ejected at velocities up to a kilometer per second.

Io's volcanoes are apparently due to heating of the satellite by tidal pumping. Io is perturbed in its orbit by Europa and Ganymede, two other large satellites nearby, then pulled back again into its regular orbit by Jupiter. This tug-of-war results in tidal bulging as great as 100 meters (330 feet) on Io's surface, compared with typical tidal bulges on Earth of one meter (three feet).

It appears that volcanism on Io affects the entire jovian system, in that it is the primary source of matter that pervades Jupiter's magnetosphere -- the region of space surrounding the planet influenced by the jovian magnetic field. Sulfur, oxygen and sodium, apparently erupted by Io's many volcanoes and sputtered off the surface by impact of high-energy particles, were detected as far away as the outer edge of the magnetosphere millions of miles from the planet itself.

Europa displayed a large number of intersecting linear features in the low-resolution photos from Voyager 1. At first, scientists believed the features might be deep cracks, caused by crustal rifting or tectonic processes. The closer high-resolution photos from Voyager 2, however, left scientists puzzled: The features were so lacking in topographic relief that as one scientist described them, they "might have been painted on with a felt marker." There is a possibility that Europa may be internally active due to tidal heating at a level one-tenth or less than that of Io. Europa is thought to have a thin crust (less than 30 kilometers or 18 miles thick) of water ice, possibly floating on a 50-kilometer-deep (30-mile) ocean.

Ganymede turned out to be the largest moon in the solar system, with a diameter measuring 5,276 kilometers (3,280 miles). It showed two distinct types of terrain -- cratered and grooved -- suggesting to scientists that Ganymede's entire icy crust has been under tension from global tectonic processes.

Callisto has a very old, heavily cratered crust showing remnant rings of enormous impact craters. The largest craters have apparently been erased by the flow of the icy crust over geologic time. Almost no topographic relief is apparent in the ghost remnants of the immense impact basins, identifiable only by their light color and the surrounding subdued rings of concentric ridges.

A faint, dusty ring of material was found around Jupiter. Its outer edge is 129,000 kilometers (80,000 miles) from the center of the planet, and it extends inward about 30,000 kilometers (18,000 miles).

Two new, small satellites, Adrastea and Metis, were found orbiting just outside the ring. A third new satellite, Thebe, was discovered between the orbits of Amalthea and Io.

Jupiter's rings and moons exist within an intense radiation belt of electrons and ions trapped in the planet's magnetic field. These particles and fields comprise the jovian magnetosphere, or magnetic environment, which extends three to seven million kilometers toward the Sun, and stretches in a windsock shape at least as far as Saturn's orbit -- a distance of 750 million kilometers (460 million miles).

As the magnetosphere rotates with Jupiter, it sweeps past Io and strips away about 1,000 kilograms (one ton) of material per second. The material forms a torus, a doughnut-shaped cloud of ions that glow in the ultraviolet. Some of the torus's heavy ions migrate outward, and their pressure inflates the Jovian magnetosphere, while the more energetic sulfur and oxygen ions fall along the magnetic field into the planet's atmosphere, resulting in auroras.

Io acts as an electrical generator as it moves through Jupiter's magnetic field, developing 400,000 volts across its diameter and generating an electric current of 3 million amperes that flows along the magnetic field to the planet's ionosphere.

SATURN The Voyager 1 and 2 Saturn flybys occurred nine months apart, with the closest approaches falling on November 12 and August 25, 1981. Voyager 1 flew within 64,200 kilometers (40,000 miles) of the cloud tops, while Voyager 2 came within 41,000 kilometers (26,000 miles).

Saturn is the second largest planet in the solar system. It takes 29.5 Earth years to complete one orbit of the Sun, and its day was clocked at 10 hours, 39 minutes. Saturn is known to have at least 17 moons and a complex ring system. Like Jupiter, Saturn is mostly hydrogen and helium. Its hazy yellow hue was found to be marked by broad atmospheric banding similar to but much fainter than that found on Jupiter. Close scrutiny by Voyager's imaging systems revealed long-lived ovals and other atmospheric features generally smaller than those on Jupiter.

Perhaps the greatest surprises and the most puzzles were found by the Voyagers in Saturn's rings. It is thought that the rings formed from larger moons that were shattered by impacts of comets and meteoroids. The resulting dust and boulder- to house-size particles have accumulated in a broad plane around the planet varying in density.

The irregular shapes of Saturn's eight smallest moons indicates that they too are fragments of larger bodies. Unexpected structure such as kinks and spokes were found in addition to thin rings and broad, diffuse rings not observed from Earth. Much of the elaborate structure of some of the rings is due to the gravitational effects of nearby satellites. This phenomenon is most obviously demonstrated by the relationship between the F-ring and two small moons that "shepherd" the ring material. The variation in the separation of the moons from the ring may the ring's kinked appearance. Shepherding moons were also found by Voyager 2 at Uranus.

Radial, spoke-like features in the broad B-ring were found by the Voyagers. The features are believed to be composed of fine, dust-size particles. The spokes were observed to form and dissipate in time-lapse images taken by the Voyagers. While electrostatic charging may create spokes by levitating dust particles above the ring, the exact cause of the formation of the spokes is not well understood.

Winds blow at extremely high speeds on Saturn -- up to 1,800 kilometers per hour (1,100 miles per hour). Their primarily easterly direction indicates that the winds are not confined to the top cloud layer but must extend at least 2,000 kilometers (1,200 miles) downward into the atmosphere. The characteristic temperature of the atmosphere is 95 kelvins.

Saturn holds a wide assortment of satellites in its orbit, ranging from Phoebe, a small moon that travels in a retrograde orbit and is probably a captured asteroid, to Titan, the planet-sized moon with a thick nitrogen-methane atmosphere. Titan's surface temperature and pressure are 94 kelvins (-292 Fahrenheit) and 1.5 atmospheres. Photochemistry converts some atmospheric methane to other organic molecules, such as ethane, that is thought to accumulate in lakes or oceans. Other more complex hydrocarbons form the haze particles that eventually fall to the surface, coating it with a thick layer of organic matter. The chemistry in Titan's atmosphere may strongly resemble that which occurred on Earth before life evolved.

The most active surface of any moon seen in the Saturn system was that of Enceladus. The bright surface of this moon, marked by faults and valleys, showed evidence of tectonically induced change. Voyager 1 found the moon Mimas scarred with a crater so huge that the impact that caused it nearly broke the satellite apart.

Saturn's magnetic field is smaller than Jupiter's, extending only one or two million kilometers. The axis of the field is almost perfectly aligned with the rotation axis of the planet.

URANUS In its first solo planetary flyby, Voyager 2 made its closest approach to Uranus on January 24, 1986, coming within 81,500 kilometers (50,600 miles) of the planet's cloud tops.

Uranus is the third largest planet in the solar system. It orbits the Sun at a distance of about 2.8 billion kilometers (1.7 billion miles) and completes one orbit every 84 years. The length of a day on Uranus as measured by Voyager 2 is 17 hours, 14 minutes.

Uranus is distinguished by the fact that it is tipped on its side. Its unusual position is thought to be the result of a collision with a planet-sized body early in the solar system's history. Given its odd orientation, with its polar regions exposed to sunlight or darkness for long periods, scientists were not sure what to expect at Uranus.

Voyager 2 found that one of the most striking influences of this sideways position is its effect on the tail of the magnetic field, which is itself tilted 60 degrees from the planet's axis of rotation. The magnetotail was shown to be twisted by the planet's rotation into a long corkscrew shape behind the planet.

The presence of a magnetic field at Uranus was not known until Voyager's arrival. The intensity of the field is roughly comparable to that of Earth's, though it varies much more from point to point because of its large offset from the center of Uranus. The peculiar orientation of the magnetic field suggests that the field is generated at an intermediate depth in the interior where the pressure is high enough for water to become electrically conducting.

Radiation belts at Uranus were found to be of an intensity similar to those at Saturn. The intensity of radiation within the belts is such that irradiation would quickly darken (within 100,000 years) any methane trapped in the icy surfaces of the inner moons and ring particles. This may have contributed to the darkened surfaces of the moons and ring particles, which are almost uniformly gray in color.

A high layer of haze was detected around the sunlit pole, which also was found to radiate large amounts of ultraviolet light, a phenomenon dubbed "dayglow." The average temperature is about 60 kelvins (-350 degrees Fahrenheit). Surprisingly, the illuminated and dark poles, and most of the planet, show nearly the same temperature at the cloud tops.

Voyager found 10 new moons, bringing the total number to 15. Most of the new moons are small, with the largest measuring about 150 kilometers (about 90 miles) in diameter.

The moon Miranda, innermost of the five large moons, was revealed to be one of the strangest bodies yet seen in the solar system. Detailed images from Voyager's flyby of the moon showed huge fault canyons as deep as 20 kilometers (12 miles), terraced layers, and a mixture of old and young surfaces. One theory holds that Miranda may be a reaggregration of material from an earlier time when the moon was fractured by an violent impact.

The five large moons appear to be ice-rock conglomerates like the satellites of Saturn. Titania is marked by huge fault systems and canyons indicating some degree of geologic, probably tectonic, activity in its history. Ariel has the brightest and possibly youngest surface of all the Uranian moons and also appears to have undergone geologic activity that led to many fault valleys and what seem to be extensive flows of icy material. Little geologic activity has occurred on Umbriel or Oberon, judging by their old and dark surfaces.

All nine previously known rings were studied by the spacecraft and showed the Uranian rings to be distinctly different from those at Jupiter and Saturn. The ring system may be relatively young and did not form at the same time as Uranus. Particles that make up the rings may be remnants of a moon that was broken by a high-velocity impact or torn up by gravitational effects.

NEPTUNE When Voyager flew within 5,000 kilometers (3,000 miles) of Neptune on August 25, 1989, the planet was the most distant member of the solar system from the Sun. (Pluto once again will become most distant in 1999.)

Neptune orbits the Sun every 165 years. It is the smallest of our solar system's gas giants. Neptune is now known to have eight moons, six of which were found by Voyager. The length of a Neptunian day has been determined to be 16 hours, 6.7 minutes.

Even though Neptune receives only three percent as much sunlight as Jupiter does, it is a dynamic planet and surprisingly showed several large, dark spots reminiscent of Jupiter's hurricane-like storms. The largest spot, dubbed the Great Dark Spot, is about the size of Earth and is similar to the Great Red Spot on Jupiter. A small, irregularly shaped, eastward-moving cloud was observed "scooting" around Neptune every 16 hours or so; this "scooter," as Voyager scientists called it, could be a cloud plume rising above a deeper cloud deck.

Long, bright clouds, similar to cirrus clouds on Earth, were seen high in Neptune's atmosphere. At low northern latitudes, Voyager captured images of cloud streaks casting their shadows on cloud decks below.

The strongest winds on any planet were measured on Neptune. Most of the winds there blow westward, or opposite to the rotation of the planet. Near the Great Dark Spot, winds blow up to 2,000 kilometers (1,200 miles) an hour.

The magnetic field of Neptune, like that of Uranus, turned out to be highly tilted -- 47 degrees from the rotation axis and offset at least 0.55 radii (about 13,500 kilometers or 8,500 miles) from the physical center. Comparing the magnetic fields of the two planets, scientists think the extreme orientation may be characteristic of flows in the interiors of both Uranus and Neptune -- and not the result in Uranus's case of that planet's sideways orientation, or of any possible field reversals at either planet. Voyager's studies of radio waves caused by the magnetic field revealed the length of a Neptunian day. The spacecraft also detected auroras, but much weaker than those on Earth and other planets.

Triton, the largest of the moons of Neptune, was shown to be not only the most intriguing satellite of the Neptunian system, but one of the most interesting in all the solar system. It shows evidence of a remarkable geologic history, and Voyager 2 images showed active geyser-like eruptions spewing invisible nitrogen gas and dark dust particles several kilometers into the tenuous atmosphere. Triton's relatively high density and retrograde orbit offer strong evidence that Triton is not an original member of Neptune's family but is a captured object. If that is the case, tidal heating could have melted Triton in its originally eccentric orbit, and the moon might even have been liquid for as long as one billion years after its capture by Neptune.

An extremely thin atmosphere extends about 800 kilometer (500 miles) above Triton's surface. Nitrogen ice particles may form thin clouds a few kilometers above the surface. The atmospheric pressure at the surface is about 14 microbars, 1/70,000th the surface pressure on Earth. The surface temperature is about 38 kelvins (-391 degrees Fahrenheit) the coldest temperature of any body known in the solar system.

The new moons found at Neptune by Voyager are all small and remain close to Neptune's equatorial plane. Names for the new moons were selected from mythology's water deities by the International Astronomical Union, they are: Naiad, Thalassa, Despina, Galatea, Larissa, Proteus.

Voyager 2 solved many of the questions scientists had about Neptune's rings. Searches for "ring arcs," or partial rings, showed that Neptune's rings actually are complete, but are so diffuse and the material in them so fine that they could not be fully resolved from Earth. From the outermost in, the rings have been designated Adams, Plateau, Le Verrier and Galle.

Interstellar Mission

The spacecraft are continuing to return data about interplanetary space and some of our stellar neighbors near the edges of the Milky Way.

As the Voyagers cruise gracefully in the solar wind, their fields, particles and waves instruments are studying the space around them. In May 1993, scientists concluded that the plasma wave experiment was picking up radio emissions that originate at the heliopause -- the outer edge of our solar system.

The heliopause is the outermost boundary of the solar wind, where the interstellar medium restricts the outward flow of the solar wind and confines it within a magnetic bubble called the heliosphere. The solar wind is made up of electrically charged atomic particles, composed primarily of ionized hydrogen, that stream outward from the Sun.

Exactly where the heliopause is has been one of the great unanswered questions in space physics. By studying the radio emissions, scientists now theorize the heliopause exists some 90 to 120 astronomical units (AU) from the Sun. (One AU is equal to 150 million kilometers (93 million miles), or the distance from the Earth to the Sun.

The Voyagers have also become space-based ultraviolet observatories and their unique location in the universe gives astronomers the best vantage point they have ever had for looking at celestial objects that emit ultraviolet radiation.

The Ultraviolet Spectrometer (UVS) is the only experiment on the scan platform that is still functioning. The scan platform is parked at a fixed position and is not being articulated. The Infrared Spectrometer and Radiometer (IRIS) heater was turned off to save power on Voyager 1 on December 7, 2011. On January 21, 2014 the Scan Platform Supplemental Heater was also turned off to conserve power. The IRIS heater and the Scan Platform Heater were used to keep UVS warm. The UVS temperature has dropped to below the measurement limits of the sensor; however, UVS is still operating. The scientist expect to continue to receive data from the UVS until 2016, at which time the instrument will be turned off to save power.

Yet there are several other fields and particle instruments that can continue to send back data as long as the spacecraft stay alive. They include: the cosmic ray subsystem, the low-energy charge particle instrument, the magnetometer, the plasma subsystem, the plasma wave subsystem and the planetary radio astronomy instrument. Barring any catastrophic events, JPL should be able to retrieve this information for at least the next 20 and perhaps even the next 30 years.