The Insane Engineering Behind Voyager 1

Author: Better Stack · Watch on YouTube

Video authored by the channel shown, not by IANIA; all rights belong to the creator. Transcript and summary generated automatically; the original-language content is preserved.

Original language: English

Original video: The Insane Engineering Behind Voyager 1 · Channel: Better Stack · 07:47 · Watch on YouTube

Topics: Software engineering with AI, AI infrastructure and hardware, Robotics and autonomous systems

Summary

Voyager 1 is approaching a distance of one light-day from Earth, despite operating with computers launched in 1977 and only about 69,000 bytes of memory across six units. The video explains how its onboard computers work and how engineers repaired a failed memory chip in 2024 by manually relocating code and sending updates across the vast distance. It also describes the recovery of thrusters in 2025 and the spacecraft’s gradual loss of power, which will eventually silence it. NASA’s Horizons system can be used to check Voyager 1’s position and signal delay.

Key points

Voyager 1 launched in 1977 and is traveling at nearly 38,000 miles per hour.
A light-day is about 16 billion miles, and radio commands take roughly a day to reach Voyager 1, with another day for a reply.
Three onboard computers handle command execution and fault monitoring, antenna pointing, and data collection and transmission; each has a spare.
The six computers have around 69,000 bytes of memory in total, and their software is written in assembly.
After a memory chip failed in 2023, engineers identified the problem in 2024 and worked around the corrupted memory by moving code and updating its references.
Engineers translated the software changes into binary by hand and restored engineering data in April 2024, followed by science data in May.
In March 2025, the team successfully brought back thrusters that had been considered unusable since 2004.
Voyager 1’s plutonium power source loses about 4 watts each year; eight of its ten instruments are now off.
NASA expects at least one instrument to keep operating into the 2030s and says its dishes should be able to hear Voyager 1 until 2036.
NASA’s Horizons system can provide Voyager 1’s distance and signal travel time; Earth’s orbit means the delay sometimes shrinks temporarily.

Chapters

Start	Chapter	Summary
00:00	Voyager 1’s distance and onboard computers	The video introduces Voyager 1’s approaching one-light-day distance from Earth, explains its communication delay, and outlines its compact, redundant computer system.
01:32	A tiny, rewritable computer system	The video describes the computers’ limited memory and assembly software, and explains that Voyager’s code can be rewritten during the mission.
03:04	Repairing the failed memory chip	After a data computer fault, engineers identified a failed chip and manually moved and reconnected code to restore readable engineering and science data.
05:11	Restoring the thrusters	With backup thrusters clogging and a key communications dish facing downtime, the team tested and successfully revived the long-idle main thrusters.
06:45	Power, remaining mission, and tracking	The video covers Voyager 1’s dwindling power and instrument shutdowns, its expected remaining lifespan, and how to track its distance and signal delay with Horizons.

Quotes

a single photo on your phone is bigger than that. — 02:03

A single chip had died, and about 3% of the computer’s memory was completely corrupted. — 03:36

The fix was to move the code somewhere else, but there wasn’t a single free gap big enough to hold all 256 words. — 04:08

The thrusters were working again after 21 years — 06:13

Concepts and entities

Voyager 1, NASA, assembly, Deep Space Network, Horizons, JPL, plutônio

Full transcript (original language)

00:00 On the 18th of November, Voyager 1 will be 1 light day away from Earth and the furthest away thing humans have ever created. That means at light speed, a message from us now takes a full day to reach it. But, it’s running on the same computers it launched with in 1977 with less than 70 kilobytes of memory between them and NASA is still patching its code today. In fact, in 2023, a memory chip on board died and the team had to move code around it from more than 15 billion

00:30 miles away. So, in this video, let’s take a look at the software running on Voyager 1, how NASA is still able to patch it, and where it is in space exactly right now. So, of course, light is the fastest thing there is. It gets from the moon to us in about a second, from the sun in 8 minutes. A light day is how far it goes in 24 hours and that’s about 25.9 billion kilometers or 16 billion miles. Voyager 1 launched in 1977 and it’s

01:02 taken just over 49 years to get there, moving at nearly 38,000 miles an hour. Radio travels at the same speed of light, too. It’s just a lower frequency of the electromagnetic spectrum. So, every command the team sends takes a day to get there and then they have to wait another day to get a response back. Last year, the team even brought back to life a set of thrusters that had been declared dead since 2004 and we’ll get to that bit later on. So, let’s take a look at the computers on board. But, before we do, guys, if you enjoy videos

01:32 like this and want to see more, you do us a massive favor by subscribing so we can keep delivering free content every single day. Now, let’s get back to the video. Voyager is way too far away to fly by hand because by the time anyone on Earth reacted, a day would have passed. So, it flies itself using three separate computers. One runs a list of commands and then watches for faults. One keeps the spacecraft and its antenna pointed at Earth and the third collects all of the data, packs it up, and then sends it home. Each of the three computers also comes with a spare, which

02:03 was very good thinking of the engineers back then. And if we add up the memory in all six, you get around 69,000 bytes. And for reference, a single photo on your phone is bigger than that. NASA, in their own FAQ, call it small potatoes. It’s all written in a form of assembly. Space was so tight that when the pointing computer launched, it had just two words of memory left free. One of the two programmers who wrote the data computer’s code later said, “We didn’t worry about top-down or structured. We just defined functions.” The big difference though from Apollo is

02:33 that this memory can be rewritten. I made a video on Apollo 11 recently, and that code was woven into the hardware, so it could never change. Voyager was designed so that the team could send up new programs during the mission. And during the Jupiter flyby in 1979, they sent up 18 of them. So, what exactly happens when one of those computers break? On the 14th of November, 2023, the data coming back from Voyager 1 stopped making sense at all. The spacecraft was still receiving commands and carrying them out, but what

03:04 came back was just repeating patterns of ones and zeros. The fault was in the data computer that packs everything up and sends it home. The team could talk to Voyager, but they couldn’t read anything and send it back. In March 2024, they sent a command they call a poke, which nudged the data computer into running different parts of its software. Two days later, the signal changed. An engineer at NASA’s Deep Space Network, which manages the big dishes on Earth that talk to spacecrafts like Voyager, worked out that the new signal was a dump of the data computer’s entire memory, the code and all of its

03:36 variables. The team compared it with a dump from before the problem started, and in April, they found the cause. A single chip had died, and about 3% of the computer’s memory was completely corrupted. So, how the hell do you fix a dead chip from 15 billion miles away? Well, you can’t replace it, so you just stop using it. The computer’s memory is split into slots called words, and each word is 16 bits. The broken chip held one bit from each of the 256 words in a row. So, when it died, every one of those words had a bad bit. So, all 256

04:08 of them were broken. And the code stored in those words was a set of routines that got called from all over the rest of the program. The fix was to move the code somewhere else, but there wasn’t a single free gap big enough to hold all 256 words. So, the team split the code into pieces, put each piece in whatever small gap they could find, and then updated every place in the program that called it, so it pointed to new locations. They had to do this without an assembler. The team said, “I no longer have any of the conventional software development tools one might expect.” So, they translated every

04:39 change into binary by hand. There’s no test machine for Voyager anymore, either. One of them said it was the first time they’d loaded flight software onto a spacecraft without thoroughly testing it on the ground first. in two steps. On the 18th of April, 2024, they sent up the code that packs the engineering data, the health readings from the spacecraft itself. Two days later, that data came back, readable for the first time in 5 months. In May, they moved the code for the science data, and by June, every instrument that was still switched on was sending data again. Now,

05:11 back to those broken thrusters. Voyager keeps its antenna pointed at Earth using tiny thrusters, and the tiny fuel tubes inside them are slowly clogging up. A rubber inside the fuel tank sheds silicon dioxide, and the opening has shrunk from a quarter of a millimeter down to around 0.035 mm, about half the width of a human hair. Back in 2004, the main set of thrusters that roll the spacecraft stopped working after two small heaters inside them lost power. And so, the team decided they were most likely unfixable.

05:42 The team had been using the backups ever since, but then in 2025, they were clogging up, too. And to add to the pile of problems, a 70-m dish in Canberra, Australia, was the only dish with enough power to send commands to Voyager, and it was about to go offline for upgrades from May 2025 until February 2026. So, the team went back to the dead thrusters with a new idea. Maybe the heaters were fine, and a glitch had just flipped a switch to the wrong position. It was risky because if the spacecraft drifted while they were working on it,

06:13 the old thrusters would fire on their own, and if the heaters were still off when that happened, it would cause a small explosion. On the 20th of March, 2025, the team watched the result come in, and within 20 minutes, they saw the heater temperature rise dramatically. The thrusters were working again after 21 years, and the propulsion lead called it such a glorious moment. So, what will finally stop it? Well, Voyager runs on the heat of decaying plutonium, and it loses about 4 W of power every single year. To keep enough power to run, the team keeps switching things off. In

06:45 February 2006, a roll where the spacecraft turns in place around its long axis nearly tripped the spacecraft’s low-voltage shutdown, and in April, they turned off another instrument. Eight of Voyager 1’s 10 instruments are now off, so only two are still taking data. NASA expects at least one of the instruments to keep going until the 2030s, and our dishes should be able to hear it until 2036 until it goes quiet forever. Now, you can check where Voyager is yourself. NASA’s JPL runs a system called Horizons

07:15 that works out where planets and spacecraft are, and you can ask it with a single curl command. Voyager 1 is target -31, and I’ve asked it for its distance and how long its signal takes to reach us. Right now, that’s just under 1,440 minutes, and on the 18th of November, it goes past 1,440 minutes, or exactly 24 hours. Something I didn’t expect is that the Voyager isn’t always getting further away from us. Earth goes round the Sun, so every few months we catch up to it a little bit and the delay shrinks by a

07:47 couple of minutes. Voyager was only designed to last 5 years and it’s been flying for 49. The people looking after it have moved its code around a dead chip by hand and brought back thrusters that had been dead for 21 years. Horizon is free to use and I’ll leave a link below. And if you enjoy videos like this, then subscribe to see more.