00:00In 2023, NASA lost a spacecraft. Not a new one. A machine that had been flying for 46 years,
00:0724 billion kilometers from home, and it suddenly went silent. The team had exactly one way to
00:12reach it, and it required aiming a signal at a patch of sky smaller than a coin held at arm's
00:16length. They pointed, they fired, and then they waited 37 hours to find out if anything was still
00:21alive out there. It was. And that should not be surprising. This spacecraft has been surviving
00:28its own death for almost half a century. Voyager 2 was designed to last 5 years. It has been
00:33speaking to us for nearly 50. It has only 68 kilobytes of memory, less than the key fob in
00:38your pocket. It has no brakes. It is moving at 60,000 kilometers an hour and it will never come
00:44back. And right now, on any given day, roughly 10 people on the entire planet are keeping it alive.
00:50The story starts with a grad student and a pencil. 1964, Jet Propulsion Laboratory, California.
00:56A young engineer named Gary Flandreau is doing trajectory math by hand, the old way, on paper.
01:02And he spots something hidden in the numbers. Jupiter, Saturn, Uranus and Neptune are about
01:08to line up in a way that happens once every 176 years. The last time it happened, the United States
01:13did not exist. What that alignment means is this. A spacecraft can use each planet's gravity the way
01:19a pool player uses the cushion. Get bounced from one to the next, gaining speed for free,
01:24never burning fuel. Fly the four outer planets without that alignment and it takes 30 years.
01:30With it, 12. Flandreau's math got to the right desk, and a program called Grand Tour was born.
01:36For spacecraft, one sweep of the entire outer solar system. Then it got cut in half. After Apollo
01:42landed, Congress lost interest in space fast, and the money went to the space shuttle.
01:47For spacecraft became two, and the official mission shrank to Jupiter and Saturn.
01:51So the engineers at JPL did something they were not supposed to do.
01:55They quietly designed both spacecraft to go all the way.
01:58On paper, a simple tour of two planets. In the wiring, a Grand Tour of Four.
02:04In the summer of 1977, they launched. Voyager 2 went first, on August 20th, taking the slower,
02:10longer road. 16 days later, Voyager 1 followed on a fast track to Jupiter and Saturn.
02:16Two machines, designed to back each other up. If one failed, the other could still bring the data home.
02:22And bolted to the side of each one was something that had no business being on a scientific instrument.
02:27A gold-plated copper record. It is not a recording device. It is a letter.
02:32One hundred and fifteen images, human anatomy, the double helix, the position of the sun among nearby pulsars.
02:38Twenty-seven pieces of music, from Beethoven's fifth to a Guqin piece played by the Chinese master Guan Pingu.
02:44Greetings in fifty-five languages.
02:46In Mandarin, the voice says, Hope you are all well, we miss you very much, please come visit when you
02:52have time.
02:53The record was designed by Carl Sagan.
02:55But the strangest thing on it came from his wife, Andrew Yen.
02:58On the day they recorded, she was hooked up to an EEG, letting her brainwaves be captured.
03:03And what she was thinking about, deliberately, was what it feels like to fall in love.
03:07The most private human emotion, encoded as an electrical signal, now traveling outward at 17 kilometers a second.
03:14The cover is etched with a map and a lump of high-purity uranium.
03:17Any civilization that finds it can measure the uranium's decay and calculate exactly when it was made.
03:22Then the machines started delivering.
03:251979, Voyager 1 reaches Jupiter.
03:27The Great Red Spot in close-up for the first time, a storm wide enough to swallow two Earths.
03:33But what actually broke the scientists was Io.
03:36The camera caught a plume of material erupting 300 kilometers above the surface.
03:40The first active volcano ever found beyond Earth.
03:43No textbook predicted it.
03:45Entire branches of planetary science had to be rewritten in the time it took one photograph to travel back.
03:51Then Saturn.
03:52Voyager 1 flew through the ring system and found that those clean, solid-looking rings were actually thousands of chunks
03:57of
03:57ice and debris, and in places only 10 meters thick.
04:00And Titan, Saturn's largest moon, turned out to have an atmosphere thicker than Earth's, denser than its own parent planet.
04:07Voyager 2 went further, and alone.
04:101986, Uranus.
04:12It remains the only spacecraft ever to visit.
04:151989, Neptune.
04:17Still the only one.
04:18Almost everything humanity knows about those two worlds comes from a single flyby, decades ago.
04:24February 14, 1990.
04:26Voyager 1 is past Neptune, about to leave the planets behind forever.
04:30Carl Sagan asks for one last thing.
04:33Turn the camera around.
04:34Look back.
04:36The engineers resisted.
04:38The camera had done its job.
04:40Pointing it at the sun risked damage.
04:42Sagan argued, and he won.
04:44Voyager turned, and took 60 frames, and one of them became the most famous image ever made by a machine.
04:50Earth.
04:51A single pale blue dot, less than a pixel wide, caught in a shaft of scattered sunlight.
04:56Sagan wrote about it later.
04:58Look at that dot.
04:59That's here.
05:01That's home.
05:02That's us.
05:03On it, everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived
05:09out their lives.
05:10Every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young
05:17couple in love, every mother and father, every inventor and explorer, every teacher of morals, every corrupt politician, every superstar,
05:24every supreme leader.
05:25On a moat of dust, suspended in a sunbeam.
05:28After that photo, Voyager 1's camera was switched off.
05:32Not broken.
05:33Off, to save power.
05:35That is the moment the mission changes.
05:37It stops being exploration.
05:39It becomes survival.
05:41Voyager does not run on solar panels.
05:44Out there, the sun is just one more star.
05:47Each spacecraft carries three radioisotope thermoelectric generators, powered by plutonium, 238.
05:53The decay heat becomes electricity.
05:55At launch, each had about 470 watts.
05:59Plutonium loses roughly 4 watts a year.
06:0150 years later, there are about 220 watts left.
06:05Not enough to run a microwave.
06:07So the engineers keep making the cruel choice.
06:10Turn something off.
06:1111 science instruments at launch.
06:14Today, 3.
06:15Each shutdown is like taking away one of the spacecraft's senses.
06:19First it goes blind.
06:21Then death.
06:22A machine flying toward eternity, having its eyes closed one at a time.
06:26And then there is the communication, which should be impossible.
06:29Voyager transmits at 23 watts.
06:32That is about the power of a refrigerator light bulb.
06:35It has to cross more than 22 billion kilometers of vacuum.
06:38By the time the signal arrives, it has faded to less than a billionth of a billionth of a watt.
06:43Weaker than the energy in a digital watch battery.
06:46To catch it, NASA built three giant dishes, 120 degrees apart.
06:50Goldstone in California.
06:52Madrid in Spain.
06:54Canberra in Australia.
06:56The deep space network.
06:57Wherever the earth turns, one of them is pointed at the right patch of sky.
07:01The largest is 70 meters across.
07:04Its receiver is cooled to minus 269 degrees Celsius, for degrees above absolute zero, so
07:09that the thermal noise of the electronics themselves does not bury the signal.
07:13And it takes almost 24 hours for a command to reach Voyager 1, and another 24 to hear back.
07:18You send a command on Monday, you find out if it worked on Wednesday.
07:22Every rescue is a bomb defusal with a two-day delay.
07:25Voyager 2 nearly died early.
07:27Eight months after launch, a scheduling error meant nobody sent it a signal for a week.
07:32Its software concluded the main receiver had failed and switched to the backup.
07:36The backup had a dead capacitor.
07:38It could never lock onto Earth's frequency.
07:40The engineers fired an emergency command to switch back, but the spacecraft was already
07:45confused and the main receiver burned out in the process.
07:47Eight months into a 50-year mission, Voyager 2 was left with a crippled receiver.
07:51However, the engineers at Madrid came up with something absurd.
07:55They manually swept frequencies, one at a time, hunting for the exact band the broken
07:59capacitor could still lock onto.
08:01It took hours.
08:02They found it.
08:04And that is the channel Voyager 2 has been using ever since.
08:07A spacecraft talking to Earth for nearly 50 years through a broken receiver, on a frequency
08:11nobody designed.
08:132020, Voyager 2, during a routine maneuver, ran two high-power systems at once.
08:18Power spiked.
08:19The safety software shut down every science instrument to prevent the whole spacecraft from
08:23burning out.
08:24And with a 17-hour one-way delay, the team spent a full week waking instruments back up
08:29one at a time.
08:30Voyager 1 started sending garbage.
08:32The attitude control data was unreadable, pure noise.
08:36Engineers spent months hunting it down, and the cause was almost funny.
08:39The spacecraft had started writing its data into a backup computer that had failed years
08:43earlier.
08:44The dead machine scrambled everything and passed it along.
08:47The fix was telling it, politely, to use the other computer.
08:51That single instruction took two days to deliver and confirm.
08:54July 2023, and this one was serious.
08:57A routine command sequence had an error, and Voyager 2's antenna tilted two degrees off
09:02Earth.
09:02Two degrees sounds trivial.
09:04At 24 billion kilometers, it means the signal misses.
09:07The spacecraft went silent.
09:10Worse, Voyager 2 had left the solar system heading south, and of the three deep space
09:15network dishes, only Canberra can reach it.
09:17One dish.
09:18One spacecraft pointed away from home.
09:21Silence for nearly two weeks.
09:23Then an engineer at Canberra found, inside the background noise, a faint signal.
09:28Like a heartbeat.
09:29It was alive.
09:30The next day they pushed the transmitter to 250% power and shouted at it.
09:35One instruction, turn the antenna back.
09:3837 hours later, the signal was back.
09:41It was not over.
09:43November 2023.
09:44A chip inside Voyager 1's flight data system failed.
09:48Possibly age.
09:50Possibly a cosmic ray.
09:51That chip held about 3% of the spacecraft's critical memory, and when it died, every piece
09:56of science and engineering data turned into binary noise.
09:59The spacecraft was still flying.
10:01We just could not understand a word it said.
10:04Five months of nothing.
10:06Then a team at JPL pulled out paper schematics from the 1970s and went through the code line
10:10by line.
10:11Their solution, break the damaged program into pieces and store the pieces in different
10:15working parts of the memory, stitched back together so they would run as one.
10:19Every patch took a day and a half to test, because every patch took a day and a half to
10:23reach the spacecraft.
10:24April 2024, engineering data returned.
10:27In June, all four instruments were back online.
10:3048 years in, they brought it back again.
10:33The plutonium keeps decaying.
10:35The team expects to keep operating until 2027, the 50th anniversary.
10:40Maybe 2028.
10:42Possibly 2030.
10:43Not much longer.
10:45In a few years the last instrument will be switched off, and the signal will get weaker,
10:49and weaker, until it disappears into the background noise of the universe.
10:53But silence is not the same as gone.
10:55Voyager has no brakes, and space offers almost no resistance, so both spacecraft will keep going
11:00at 17 kilometers a second, forever.
11:02In about 40,000 years, Voyager 1 will pass within 1.6 light-years of the star Gliese 445.
11:09In 296,000 years, Voyager 2 will drift near Sirius, the brightest star in our sky.
11:15Two small machines carrying human music, human languages, human images, and the brainwaves
11:20of a woman thinking about falling in love, moving through interstellar space.
11:24When the last city on earth is dust.
11:26When the sun swells into a red giant and swallows Mercury and Venus.
11:30Voyager will still be flying.
11:32It is the evidence that we were here.
11:34A letter dropped into the dark, with no return address.
11:37And right now, 24 billion kilometers away, they are still talking.
11:42Listen.
11:43That is the sound of something that left in 1977 and never stopped.
12:02That is, that is, that is, that is, that is the sound of something that we were here.
