00:00:00.040 In 2015, NASA put out a job posting looking for a software engineer with a specific set of skills.
00:00:06.800 The person had to be an expert in FORTRAN and Assembly
00:00:10.237 two programming languages from the 40s and 50s that most young graduates don't know.
00:00:15.800 The job was to join the very small team of people working on the Voyager space probes.
00:00:21.349 Incredibly, both voyagers still run on their original 50-year-old computers
00:00:26.421 which have just 70 kilobytes of memory.
00:00:28.911 It might not sound like much, but it was enough to navigate both space probes through our solar system
00:00:34.860 and make incredible discoveries along the way.
00:00:38.464 Unsurprisingly, things do go wrong with Voyager's computers.
00:00:42.664 Just last year, Voyager 1 started sending back garbled Telemetry data about its orientation in space
00:00:48.804 On top of that, the thrusters in charge of keeping Voyager pointing in the right direction
00:00:53.519 were starting to show signs of fatigue.
00:00:55.708 Every time the thrusters are used, tiny pieces of hydrazine fuel get stuck in the pipes.
00:01:01.240 This has built up over time causing blockages in the system.
00:01:05.007 Voyager is already on its backup thrusters
00:01:07.854 and so if these failed it would be the end for Voyager.
00:01:11.637 At a distance of 15 billion miles, there is no way of clearing the tubes
00:01:16.961 but in order to slow down the buildup and fix the Telemetry problem
00:01:21.242 the small team in charge of Voyager began writing a software update
00:01:24.902 that would be sent across our universe to fix it.
00:01:27.696 There are three main computers on board Voyager.
00:01:30.409 The main computer controls all of the major instruments, maintains its health and temperature
00:01:34.684 and also controls the other two computers.
00:01:37.218 The second computer is in charge of Voyager's orientation
00:01:40.391 so it looks for predetermined reference points
00:01:43.373 and fires the thrusters to keep Voyager's antenna pointing towards Earth.
00:01:47.500 The third computer is in charge of storing and handling all of the scientific data
00:01:52.200 and images taken by Voyager's instruments.
00:01:55.011 Voyager doesn't have an operating system
00:01:57.351 and any kind of programming language would take up two too much space
00:02:01.100 but this isn't the first time Voyager has been updated.
00:02:04.206 At Neptune, the light was 900 times dimmer than it was at Earth
00:02:09.317 so in order to take pictures
00:02:11.209 Engineers had to reprogram the camera to take longer exposures.
00:02:15.699 Once it left Neptune, NASA began shutting down things like the camera
00:02:19.774 and various scientific instruments to save power
00:02:22.840 but with just 70 KB of memory on board its computer, having lines of code for dead instruments was a waste of space.
00:02:30.105 And so the Engineers completely rewrote Voyager's code
00:02:33.800 and performed a software update to make sure it continued to live for the foreseeable future.
00:02:39.258 But how does NASA update such old hardware from 15 billion miles away?
00:02:45.148 To understand how difficult this is we need to know how the software works on Voyager.
00:02:50.388 Voyager runs the latest version of NordVPN
00:02:54.239 Not really, NordVPN wouldn't fit on Voyager's computers, but if it did it would do a great job of protecting Voyager
00:03:01.244 from online threats. Whenever you are connected to Wi-Fi, especially public Wi-Fi, your data is constantly at risk
00:03:08.169 from hackers. With NordVPN you can become instantly protected with just a single click.
00:03:14.457 How many times have you gone to watch a YouTube video or Netflix series
00:03:18.219 only to find it's blocked in your country? With NordVPN all you need to do is connect to one
00:03:23.760 of the 5,000 servers and suddenly all the content you've been missing will appear.
00:03:29.419 NordVPN has also launched 'Meshnet' the safest way to connect to all of your devices no matter where you are
00:03:36.524 in the world. It acts like a local area network and creates a secure way to directly access things
00:03:42.680 like personal servers and share files around the world. NordVPN works on every major platform
00:03:49.200 and can be installed on up to six devices at one time. To get NordVPN's 2-year plan plus 4 months
00:03:56.160 for free visit nordvpn.com/primalspace.
00:04:00.477 in order to do a software update on Voyager, NASA needs to install the new code into its computers.
00:04:07.539 Perhaps the coolest thing about Voyager's computers is the memory.
00:04:11.164 Each computer has its own plated wire memory, which stores Voyager's code in its most basic form
00:04:17.022 ones and zeros
00:04:18.462 This memory consists of a physical grid of wires and thin metal plates.
00:04:23.320 Each intersection point can be thought of as a single bit of memory and it can store either a one or zero.
00:04:30.070 By passing a current through one of the plates and a specific wire, it would create a magnetic field.
00:04:35.495 If the magnetic field is in this direction, it is considered a zero. if it goes in the opposite direction, it's a one.
00:04:43.131 By passing a current in the opposite direction, it would change the direction of the magnetic field
00:04:48.436 and flip the bit to a zero.
00:04:50.596 By doing this for every point
00:04:52.345 you could save these ones and zeros into the memory.
00:04:55.847 This design was a great choice at the time
00:04:58.190 because it meant that even if the power went out, the ones and zeros would still be saved to the memory.
00:05:04.276 It also meant that each bit could be updated.
00:05:07.386 With just 70 kilobytes of total memory onboard Voyager
00:05:10.957 the engineers have to be extremely efficient with their code.
00:05:14.353 Along with this basic machine code
00:05:16.935 Voyager has its own pseudo code. Basically a series of shortcut commands
00:05:21.359 that can be triggered to carry out repetitive tasks without taking up too much memory.
00:05:26.179 An interpreter onboard the main computer reads the ones and zeros. Once it comes across a predetermined code
00:05:33.000 it initiates the pseudo code to carry out a command. This saves lots of memory and allows many
00:05:38.720 tasks to be automated without writing out long lines of code.
00:05:42.724 But the problem is that humans can't code in just ones and zeros.
00:05:46.816 And so a more advanced language is needed to actually write the code for Voyager.
00:05:51.554 On Earth, Voyager software was originally written in Assembly Language with a little bit of FORTRAN.
00:05:57.172 Assembly is a very simple language that can be understood by humans, but is much closer to
00:06:02.360 the basic ones and zeros of machine language.
00:06:05.153 Once the code is complete it gets compiled into machine code
00:06:09.000 which can be sent to Voyager using the deep space network.
00:06:12.493 The data is sent to Voyager at a rate of 16 bits per second
00:06:16.449 and it takes almost an entire day to actually reach Voyager.
00:06:20.519 The computers onboard Voyager are interrupt-driven.
00:06:23.399 This means that the software goes through its usual list of instructions until it gets interrupted
00:06:28.584 When an update is sent to Voyager, it carries an interrupt signal.
00:06:32.460 When Voyager receives this, it tells the main computer to stop what it's doing and instead work on the update instructions.
00:06:39.509 It then unloads the new code into the memory
00:06:42.520 flipping all the bits to their new position. The code is then read through to check that everything
00:06:47.320 is correct and then the main computer kicks it into gear and returns to normal operations.
00:06:52.797 Over the years Voyager has received a long list of updates and patches to fix and improve how it operates.
00:06:59.365 In 1995 an update was written that would basically restart certain components if they failed.
00:07:05.481 In 2014, some 20 years after the code was written, this code saved Voyager 1 when a piece
00:07:11.720 of hardware malfunctioned. In 2010 a single bit of Voyager's memory was flipped, changing a zero
00:07:18.120 to a one. This caused computers to lose sync with each other and the commands started happening two
00:07:23.080 and a half hours later than expected. A software update was sent up to flip the faulty bit back
00:07:28.640 into its correction position. It's amazing stories like these that have allowed these iconic space
00:07:33.640 probes to survive almost 50 years in space. It's incredible that the physical wires, transistors
00:07:40.160 and hardware onboard Voyager's computers are still operating as intended after all this time.
00:07:46.845 And now for the Primal Space giveaway.
00:07:49.475 The winner of the previous giveaway is Yasmine. Congratulations!
00:07:53.515 In the next video we'll be giving away this Primal Space designed Voyager poster. All you need to do
00:07:59.080 is sign up at the link below, like the video and leave a comment saying where you would send a
00:08:04.560 Voyager 3 if it launched today.
00:08:06.939 Thank you very much for watching and I'll see you in the next video.
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