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The little spacecraft that could.
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Boldly still going
Launched in 1977, Voyager is NASA’s longest-running mission. The twin spacecraft Voyager 1 and Voyager 2 are also the most distant human-made objects, currently cruising along in interstellar space.
It’s not always smooth sailing. On Jan. 25, 2020, Voyager 2 suddenly went dark. A glitch during a routine maneuver caused an automatic shutdown of its scientific instruments. Because Voyager 2 is now 11.5 billion miles (18.5 billion km) from Earth, there’s no such thing as a quick fix—messages take 17 hours each way to transmit—but by Feb. 5, 2020, engineers had everything back online. A similar shutdown occurred in 1998, and in 2010 a piece of errant code made transmissions unintelligible. It doesn’t help that the spacecraft are running on ancient technology, and the mission’s last original engineer retired in 2015.
But Voyager isn’t done quite yet. Let’s gaze at where it’s been—and where it’s going.
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Jul. 1, 1972: Work begins on the project that will become Voyager.
March 1977: The Voyager name is chosen.
Aug. 20, 1977: Voyager 2 launches from Kennedy Space Center in Florida.
Sept. 5, 1977: Voyager 1 lifts off. Despite launching second, it will reach Jupiter first, so it gets to be No. 1.
Mar. 5, 1979: Voyager 1 reaches Jupiter.
Nov. 9, 1980: Voyager 1 reaches Saturn.
Jan. 24, 1986: Voyager 2 reaches Uranus for its first close-up.
Aug. 25, 1989: Voyager 2 reaches Neptune, another first.
Feb. 17, 1998: Voyager 1 surpasses Pioneer 10 as the most distant human-made object.
Aug. 13, 2012: Voyager 2 becomes NASA’s longest running mission, passing Pioneer 6’s record of 12,758 days.
Aug. 25, 2012: Voyager 1 becomes the first human-made object to enter interstellar space.
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In 1965, NASA Jet Propulsion Laboratory intern Gary Flandro was working on “gravity assist” calculations for Mariner 10’s journey to Venus and Mercury. When he looked into whether the same concept would work for sending spacecraft to the outer planets, Flandro realized Jupiter, Saturn, Uranus, and Neptune would all be aligned on the same side of the sun in the 1980s—a phenomenon that only occurs every 176 years.
NASA got approval for two Jupiter-Saturn missions in 1972. Voyager was initially a four-year program, and the spacecraft were only supposed to last five years. But once Voyager 2 rounded Saturn with all its instruments still functioning, NASA secured funding for the trip to Uranus, and later Neptune and beyond. After flying more than 7 billion km (4.3 billion miles), Voyager 2 approached the eighth planet from the sun within seconds of its scheduled arrival and within 100 km (62 miles) of where engineers had planned.
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By the digits
815 kg (1,797 lb): Weight of each spacecraft at launch
>10,000: Trajectories considered for the two spacecraft
1,500: Engineers who built Voyager
3.5 seconds: Time the rocket that launched Voyager 1 on its path to Jupiter had left before running out of fuel
14.5 billion miles: Distance from Earth Voyager 1 has traveled
38,027 miles per hour: Voyager 1’s estimated velocity with respect to the sun
21 hours, 35 minutes: Time it currently takes light and radio waves to travel from Voyager 1 to Earth
10: Number of scientific instruments on Voyager 1
4: Number of those instruments still functioning
69.63 kilobytes: Combined memory of a Voyager spacecraft’s computers—enough to store an average internet jpeg file
$865 million: Total cost of the mission through Voyager 2’s Neptune flyby
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This one weird trick!
Traveling between planets takes a really, really, really long time. But if you’re planning a multi-planet tour, it’s possible to use the gravity of one to hasten your journey. For example, by coming up on Jupiter from behind, the Voyager spacecraft were pulled along its orbital path, giving them a burst of speed and altering their trajectories toward Saturn. This “gravity assist” cut Voyager 2’s total travel time to Neptune from 30 years to 12.
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Voyager’s scientific impact has been monumental—NASA calls it “the most scientifically productive mission ever.” Its discoveries include Jupiter’s rings, 23 new outer planet moons, active volcanoes on Jupiter’s moon Io, lightning on Jupiter, and geysers on Neptune’s moon Triton. NASA also learned that Jupiter’s moon Europa likely has a liquid ocean underneath an icy surface, Saturn’s moon Titan has an Earth-like atmosphere with seas of methane and ethane, and Uranus’s magnetic poles are close to its equator.
Despite the interstellar mission feeling a bit “anticlimactic” after the thrills of the outer planets (then-mission controller Bruce Brymer likened the letdown to postpartum depression in 1989), Voyager’s more recent findings are no less remarkable. It determined the boundary of the heliosphere, the protective bubble of solar wind that encompasses the solar system, and showed there are previously unknown layers between the heliosphere and interstellar space.
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On Feb. 14, 1990, after traveling more than 4 billion miles (6.4 billion km), Voyager 1 snapped its final photos, a series of six planets and the sun known as the “Solar System Family Portrait.” Astronomer Carl Sagan poetically called Earth—barely the size of a single pixel in the image above—a “pale blue dot,” driving home how small our planet is in the universe.
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NASA tasked Carl Sagan with crafting a message from Earth that would travel with each spacecraft. The resulting Golden Record comprises 115 images, human and nature sounds, greetings in 55 languages, messages from US president Jimmy Carter and UN secretary general Kurt Waldheim, and an eclectic selection of music—everything from traditional songs from around the world to classical standards to Chuck Berry’s “Johnny B. Goode.”
(The behind-the-scenes story of the Golden Record—featuring a Carl Sagan love quadrangle, John Lennon’s tax woes, and future rock/hip-hop producer and record executive Jimmy Iovine—is worth exploring.)
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Women working on the Voyager mission planned their pregnancies for the three- to five-year periods when the spacecraft were traveling between planets.
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Million-dollar question: When will Voyager stop working?
Given the age of the spacecraft, their continued functionality is a bit precarious. “We’re always one failure away from losing the mission,” engineer Suzanne Dodd told Wired in 2013.
Voyagers’ generators produce about 40% less energy than they did at launch. In order to continue transmitting data, the spacecraft needs heat to keep instruments from freezing and power to orient their antennas toward Earth. Voyager 1 began shutting off equipment to conserve power in 1990 and Voyager 2 followed in 1991. Ed Stone, the mission’s project scientist, said in October 2019 that the spacecraft may not be able to continue powering their instruments “in another five years or so.”
Voyager could still send engineering data after all the scientific instruments are turned off. We’ll receive the last transmissions in 2036, when the spacecraft will be too far away for Earth’s antennae to pick up their signals.