The Only Reason the Voyager Probes are Still Working Today

Thanks to Speakly for sponsoring today’s video. It’s one of life’s little ironies that  it is not new, cutting-edge technology that is advancing our understanding most at the  edge of our solar system, but an old machine. It has an onboard computer with less memory than  the one inside your car’s key fob.

To this day, it is still using 8-track magnetic tape from  the 1970s – which makes it older than many of you sitting here watching this. Such is  the conundrum of deep space exploration, where vast distances and extremely  long travel times can mean that technology is antiquated by the time it  has reached its most ambitious targets. But it’s true.

That record-setting spacecraft is,  of course, the nearly 45-year-old Voyager 1 probe. Along with its twin, Voyager 2, it became the  first human-made object to reach interstellar space. It takes over 21 hours for NASA to send and  receive radio signals with Voyager 1 (covering a distance of 23 billion kilometres), versus about  20 minutes to send a radio signal to Mars.

And while it’s astonishing to think that we can still  communicate with a 3. 7-meter antenna over such an immense distance, it’s even more incredible  when you consider that the probes are relying on technology that would look more at home in a  museum than in NASA’s Jet Propulsion Laboratory! For such technology to have done so well,  lasting so long, it must have been special.

So, what secrets lie inside? How were  Voyager’s engineers able to build spacecraft capable of operating continuously  for such a long time, beating all records? I’m Alex McColgan, and you are watching Astrum. 

Join me today as we explore the technology of the Voyager probes and learn how a series of  shrewd engineering choices paved the way for the most ambitious and stunningly successful  mission in the history of space exploration. Although Voyagers 1 and 2 were initially built  for a 5-year mission to explore Jupiter and Saturn and their larger moons, their team of  forward-thinking scientists and engineers made a number of design choices that enabled the probes  to hold up over a much longer journey. To recap, after completing all of its initial objectives  on Jupiter and Saturn, the Voyager Mission team added flybys of Uranus and Neptune.

Once these,  too, were completed, NASA announced the start of the even more ambitious Voyager Interstellar  Mission, with the purpose of exploring the outer limits of the sun’s sphere of influence  and beyond. This final journey would take both probes off the ecliptic to unexplored parts of the  solar system, such as the termination shock and the denser and hotter heliosheath, before finally  crossing the heliopause into interstellar space. Let’s start with one of the most consequential  decisions: the fuel source.

Each probe is equipped with a long-lasting radioisotope thermoelectric  generator, which converts heat from the decaying plutonium 238 isotope into electric power. These  generators were capable of producing 157 Watts of electrical power upon takeoff – about enough  to power a laptop and charge a mobile phone. This might not sound like much,  but was more than Voyager needed.

While a radioisotope generator meant that power  production was in constant decline (it would halve in strength every 87. 7 years), it would  still be enough power to keep the essentials on the probes running until at least 2025.  This long-term fuel capacity was no accident.

You see, when the Voyagers launched in 1977,  NASA faced a unique opportunity: the planets would soon be in a one-in-176-year alignment that  had last occurred during Napoleon’s first reign! This rare alignment would not only allow  the Voyagers to visit Neptune and Uranus with minimal course adjustment but also give  the probes a gravity assist from each of the four outer giants they visited, thereby increasing  their effective velocity beyond what they could get from their own rocket propulsion. However,  this narrow window gave NASA a strict deadline.

There wasn’t enough time to plan follow-up  missions, and the United States Congress wouldn’t earmark enough funding for a longer expedition  (like the Grand Tour NASA first proposed). So, what did Voyager’s team do? They devised  a series of engineering feats to optimize the probes for a potentially longer mission and  fervently hoped that the funding would follow.

Each of the Voyager probes is equipped with  11 scientific instruments. Most of them have redundancies in case of machine failure, which  can be toggled on and off to conserve power. To adjust course and orientation, the  probes are equipped with gyroscopes for stabilization, referencing instruments and  16 hydrazine thrusters, including 8 backups.

Backups – and good backups at that – were  key to the voyager probes’ longevity. They proved to be vital as Voyager 2’s main  thrusters stopped working after 37 years. Its backup thrusters had to engage after 4 decades of  idleness.

And guess what? They worked perfectly, highlighting the excellent engineering that went  into them. The Voyagers also have custom-built onboard computers, which are antiquated by  today’s standards but were cutting-edge in 1977.

The probes’ wide-angle and narrow-angle lens  cameras are controlled by a Computer Command Subsystem, which has fixed programs like  fault detection and correction routines. Another key to its success lay in its computers.  Each probe had a computer called the Attitude and Articulation Control Subsystem, and no, it doesn’t  scold the Voyagers when they get sassy!

“Attitude” refers to the probes’ orientations with respect to  the Earth, without which their high-gain antennae would be unable to send or receive signals from  NASA’s Deep Space Network. This is very important, as the probes’ transmitters only have  the Wattage of a refrigerator lightbulb, and at such immense distances, their radio  signals become barely detectable whispers. To communicate with the Voyager team and vice  versa, the probes’ antennae must be facing the Earth, and the Deep Space Network must in  turn know exactly where they are.

Otherwise, they would be lost, like a needle  in a 287 billion km haystack. Each Voyager spacecraft has a 3. 7 meter antenna  for real-time transmission and an 8-track digital tape recorder capable of buffering 536 megabits  for future transmission, enough to store 100 photographs.

While this was a huge step up from  the earlier Pioneer probes, which had no onboard data storage, it’s still a fraction of what  the smartphone in your pocket can store today. Despite these limitations ,  the DTRs were built to last. Odetics, which manufactured the them,  claimed their DTRs could process over 4,000 kilometres of tape without taking  visible wear and tear.

They had to withstand the harshest environments imaginable and undergo  rigours that had never before been tested. Yet, the Voyager DTRs performed without data loss  or machine failure until they were finally taken offline to conserve power. Not bad for  machines 12 years older than the world wide web!

Durability was a chief concern during Voyager’s  planning. There are many unknowns in a mission of this magnitude. To get to Jupiter, both Voyagers  would have to pass through the asteroid belt.

Scientists once believed that this region  would shred apart any spacecraft that tried to pass through it. However, Pioneers 10 and 11 had  previously been able to pass through the asteroid belt, which emboldened Voyager’s team to repeat  the stunt. However, failure would have meant disaster before the probes had even reached their  first target.

Luckily, both probes made it through the asteroid belt unscathed (and we now know  that it is mostly empty space thanks to them)! Even with all these successes, and with  the probes performing far better than their engineers could possibly have hoped  for, as the two spacecraft travelled through the vastness between planets there was  still at least one more hurdle to cross. What would happen to the probes in the extremely  cold temperatures of interstellar space?

NASA installed multiple heaters to keep  the machinery operational. Nonetheless, as the probes’ power waned, NASA had to turn  off some of their heaters to conserve energy. When the cosmic-ray detector’s heater was turned  off two years ago, its temperature plummeted by 70 degrees Celsius.

Needless to say, sending a  repair team 23 billion kilometers into space isn’t an option. So, everyone thought the instrument  would break, but… it continued to run smoothly! The fact that the probes have operated so well  for 45 years is a testament to their resilience and engineering.

But, for any mission as long  and ambitious, there are always things no-one can predict. Not everything on the Voyager  missions has worked perfectly. Voyager’s team learned this recently when Voyager 1 started  sending mysterious scrambled signals.

I talk about this in more depth in another of my videos  (which you should check out, by the way), but at a June 2022 meeting of the National Academies of  Sciences, Engineering and Medicine, NASA announced that Voyager 1’s Attitude Articulation and Control  System had been spitting back strange sequences, like rows of zeroes that appear to be nonsense.  While the probe itself was operating normally (we knew its speed and distance, and it was  still responding to and taking commands), its telemetry data was a complete scramble. In  other words, Voyager 1 had no idea where it was.

Sadly, this turned out to be a sign of a  failing computer, and although scientists were able to find a workaround by moving over  to a backup, there will come a day when there are no backups left. Still, we have a lot to be  thankful for. Voyager 1 has travelled farther than any other human-made object, including  its twin, Voyager 2.

Its technology, although rudimentary by today’s standards, has really  shown what can be done with even simple tools. Its discoveries have been a monumental step  forward in our understanding of our solar system. When we do inevitably say goodbye to this  erstwhile friend and its twin, Voyager 2, it will be time to apply the engineering lessons of  the past, and to try and recreate the magic with a successor.

Already, there is a proposal from  Johns Hopkins’s Applied Physics Laboratory for an interstellar probe that would launch in 2036  and reach interstellar space in just 15 years. Perhaps this future probe will make it even  farther and faster than the Voyagers. Of course, even if it does, by the time it is reporting  back from the fringes of interstellar space, it, too, will be a thing of the past.

But  there is something inspiring in that. Just because it’s an old dog doesn’t mean it  isn’t really really good at what it does. Is English your native language?

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If you  like what you see, there’s even a 60% discount on the annual subscription. Click on the link  in the description below to give it a try. Thanks for watching.

If you like Voyager, check  out this video about their discoveries here. Thanks to my patrons and members for your  support, if you want to support too and have your name on this list, check the links in the  description. All the best, and see you next time.