How A Tiny Mistake Destroyed America’s First Interplanetary Space Probe

Vote for this video by social sharing!
Many people have heard the story of how a small code error destroyed a rocket – the rocket was an Atlas-Agena B launched in 1962 and carrying Mariner I and the error is commonly reported as a ‘missing hyphen’. However it’s often misreported and I’ve always had questions, so I wanted to get to the bottom of the story and find out the real truths:
It’s not a hyphen, it’s an Overbar.
It wasn’t a simple fat fingered typo by a programmer.
It required a hardware failure to expose the bug.
1950’s rocket guidance technology was hella complicated.

The research for this took a long time but some of the important sources which lead me to the conclusion are detailed in my latest post at Patreon.

  1. Nikita Nedelko

    This reminds me of Stanislaw Lem’s “The Conditioned Reflex”

  2. kevin cvalciuc

    Looks like one of the computers I used in the 90’s in the military. I was designed in the 50’s and was crammed with synchros, servos and resolvers. It was a nightmare to fix when you melded it with digital systems.

  3. Brandon Burr

    Hi Scott,
    Thank you for another episode on why missions fail. I think this should be a ongoing series showing mission failures by not only the US but other countries as well. The former Soviet Union has had some failures that would great to docu,entertainment as well. It’s interesting to see how simple (or complex) some of these can be. Thanks again scott😀

  4. dapowerfulmastermind

    Ah Mariner 1&2, one of my favorite space probes! Come to think of it, I believe that the picture of Mariner 2 was the very first image I’ve ever associated with the word “satellite”.

  5. J P

    You forgot, “check yo staging!”

  6. Cole Smith

    Was it a hyphen or a minus sign? Let’s be real here, this is what’s important….
    Edit: oh it was an over-bar… I’m disappointed.

  7. Macsen Phloudio

    The infamous missing hyphen.

  8. Dave C

    A good follow-up to this would be the Ariane 5 mission in 1996, which suffered a similar fate due to a floating point error in the code. I’d love to see your take on that.

  9. Jeanne Shirow


  10. Dave K

    Nice explanation of launch error.
    I’m reading ‘Observing Earth Satellites’ by Desmond King-Hele. It briefly explains launch requirements, but only when things go right.

  11. Paul Smith

    “Aborted launch lead to Mariner crashing into the sea”. How very Kerbal to launch a sea-going research vessel via rocket on a parabolic trajectory first. ;-)

  12. Barry McWhirter

    Hey Scott how about a video explaining what caused the 4 Soviet N-1 failures, if that information is actually available. Thx FS

  13. SpinFast

    Test your entire system. Test your requirements. End to end testing is the best, DO178C and DO254 are your friends.

  14. Aaron Ray

    If you lose contact with ground control
    You will not go to space today.

  15. CaptainDuckman

    wrong specs, had them happen to me more than once…
    And usually we as coders get blamed for implementing the incorrect spec correctly, causing the system to go haywire.

  16. Damian P

    At first glance it looked like interstellar … I was like waaa

  17. Mulberryman

    Surviving Mars: Green Planet DLC
    I want to see how fast you can terraform mars and hear your thoughts on how realistic it is in the game while you do it

  18. Jack F

    Decent audio for the room an setup u have

  19. texaswilliam

    We’ve reached BECO (Best Explanation Cut-Off).

  20. Samhain Tollins

    I was expecting a CHECK YO STAGING slipped in at the end lol

  21. Sebi One

    The fact that the report had to be simplified so Congress could understand proves that the wrong people are in charge.

  22. Tim Heaver

    Another great video well researched and very in depth you really know your stuff.
    I tried to find some spare hyphens to give to you from my keyboard but looks like the hyphen burglar has got there first.

  23. QuantumBraced

    210 KHz, wow… And I thought my childhood 486 was unimaginably slow at 33 MHz.

  24. rsb

    your last advice is great for an aerospace engineer inspired by you and KSP. I still think this is the best channel

  25. Ola Leier

    Ah, the 60s. “Look, an alien life form that shows kinship to our planet! Quick, shoot it dead for entertainment!”

  26. WalesDark

    i was so sure you were going to say check yo stagin at the end, oof

  27. Timothy McDaniel

    I’d like to quibble on one bit (pun intended). In today’s terminology, we’d say that the computer words were 24 bits: as the documentation there shows, the magnitude was in 23 bits but there’s also a sign bit.
    There’s also a discrepancy between “17 instruction bits” but “18-bit, wired instructions”. I don’t have an explanation for that. The video says 38 instructions, which would be 6 bits if packed in. With 18-bit space, that would leave 12 bits, which I suppose was for register numbers, addresses of fixed constants, or immediate constants.

  28. Huntracony

    YES! Thanks you. Overbar missing in the specification makes sense, hyphen missing in a computer from 1962 does not.

  29. Nik McIntosh

    This research belongs in a history of space science journal (if such a thing exists), not on YouTube. And I mean that entirely as a compliment.

  30. Tax-return

    Dear Scott, would you ever consider narrating audiobooks? Your voice is quite enjoyable

  31. David Cox

    Amazing explanation. Thanks for sharing that bit of history.

  32. Billy Johnson

    Love the detail. Keep up the Great work!

  33. RAVEN II

    As someone studying for his diploma in Aerospace Electronics, this is a very valuable lesson

  34. Adam Wishneusky

    I love these history lessons. You make things very clear and understandable!

  35. Lenard Segnitz

    5:32 “1536 18-bit, WIRED instructions” (my own emphasis). The MOD1 computer on the ground didn’t run stored instructions. The programming had to be painstakingly hard-wired in. This is pre-punch-card stuff.

  36. ben3847

    comment section:
    something something check your staging

  37. Paul Bouchard

    How about an episode ,covering economics of buildong rocket costs and d produvtion

  38. Papi Uuhmelmehahay

    This is probably one of the most intriguing explanations I’ve heard about the failure of Mariner.

  39. RyllenKriel

    It takes a Manly Man to Manly-splain projectile dysfunction of a rocket on the first launch date. Thanks! Luckily Venus gave us another date.

  40. Lorenzo Orders

    “And check your hardware before commiting to launch”
    rocket@nasa>git commit launch

  41. lesnyk255

    In a former life I was a mainframe programmer (COBOL) at an insurance company. In rushing to meet a deadline, I accidentally omitted a period at the end of an inline subroutine. As a result, control just fell down into the next section – resulting in the company doubling its commissions to its agents that month. The agents loved me for it. Senior management, not so much.

  42. Josh Colletta

    Scott Manley I have my undergraduate Artificial Intelligence Exam tomorrow, can you make my day with a good luck!?

  43. Kalle Lammi

    You should start a new series. Why rockets fail…in Kerbal!

  44. Sebastian Jasper

    I just love your kind of humor: ”It fell into the Ocean, which is kind of apropriate … (Mariner)” – still laughing! I noticed many of these hidden jokes (with a serious explaning voice) in your vids . Love the content too!

  45. Karman Line

    Classic and brilliant Manley video. Thanks! Check Yo Coding folks

  46. ShermanHrus

    >First Interplanetary Space Probe
    By the time of Mariner-1 the soviet Venera-1 had already reached Venus

  47. Ivan

    I love these videos where you recount the full technical history of missions! So very interesting!

  48. Christopher Underhill,

    …”kind of appropriate given it’s name.”. = Perfect analogy 😄

  49. calaphos

    11:24 There might be live on Venus, so we can go there and hunt dinosaurs for sport!
    Times really have changed

  50. Minonian

    The kind of mistake which only a problem because nature is unforgiving…
    But why he is?
    Because he wants to be…

  51. Dangermouse

    Scott, Love this series!
    As a lifelong mechanic in cars and underground machines, I’ve often had to carry out post failure analysis prior to repairing the machine to prevent a repeat failure.
    Doing this on spacecraft, often with little remaining of the vehicle would be the ultimate in detection skills. 👍
    Thanks for your efforts.

  52. GhostHostMemories

    Check your program staging?

  53. rohandrummer

    After such an informative video, the only thing that comes to my mind is “I’m Scott Manley. Fly Safe!”

  54. Alpha Adhito

    Can you do Ariane 5 first flight/Cluster failure because of software design error please? You always make everthing much more interesting :)

  55. zakelwe

    Hardware issues not corrected by dodgy software … an early example 737Maxitus.

  56. Jayson Durkee

    Mariner: powered by a HECS 2 probe core!

  57. Evgeniy Zhabotinskiy

    > “Check everything.”
    >> Meh, I’ll just “revert to launch” if anything goes wrong.

  58. Peter Ebel

    Great & clear description!
    Top channel.

  59. Don Ruxton

    My college Calculus professor was part of the NASA math department that signed off on this mistake. He told us that the “Overbar” R denotes a mean value instead of an absolute value and that leaving off the bar cause the rocket to explode. Since the entire math department signed off on the equation, the entire department was fired including him. He also stated that the incident went into the Guinness Book of World records as the costliest mathematical mistake at that time.

  60. japeking1

    I’ve always thought of “Rocket Science” as pretty straightforward. Not any more….. thank you for disabusing me ;-)

  61. Josh Lyon

    Great video always, may I ask where you got that Starship model in the background?

  62. Robert Emerson

    Explained well enough for a Leyman to understand. Well done!! I’d love to see a detailed video of the “launch window”. I know a couple of the variables but think it would be great to see what all makes up a clear launch window.

  63. Francisco Domínguez Román

    Amazing explanation, graphics and video, as always. Thanks for sharing and keep going!

  64. Johiah plays games

    How long would it take that computer to process one frame of this video?

  65. calown

    I’m amazed by the forethought utilized to include a centrifugal self repairing connector module!

  66. RFC3514

    Here’s a summary for the new generations: “N00bz forgot to turn anti-aliasing on, LOL rekt!!”

  67. humanhiveanomaly

    I don’t always test, but when I do, it’s in Prod.

  68. C SMITH

    Love these stories explained by Scotty

  69. Bo Dan

    @10:50 The spin caused by the fault, fixed the fault… if ever there was something called ‘fail safe’, this should be it the benchmark.

  70. Red Ice

    11:22 That cartoon in hilarious.
    Scientist: “We’ve discovered an ancient world populated by never before seen alien dinosaurs”
    Floridaman: “I’ve got my bazooka, let’s get going!”

  71. Hudson Doty

    The first thing that popped into my head before you gave your (very awesome) hypothesis about the failure was: “They didn’t have syntax highlighting back then?”

  72. spin kick

    i love how, during the second/backup flight, the spinning forced the connector back up into place – reconnecting it. These details… wow.

  73. Pongo Ponginae

    Definitely not a missing hyphen!
    – The Punctuation Burglar

  74. Tyelor K.

    That’s super Kerbal. Mariner 2 spins at a rate almost 1 revolution per second, then regains control and manages to make it to it’s target still lol.

  75. Seth Baker

    “I must’ve put a decimal point in the wrong place or something. —-, I always do that. I always mess up some mundane detail.” -Michael Bolton

  76. maxidejf

    being a space SW developer I enjoyed this ep. very much!

  77. Teh509

    The theory of Marina 2 cable connection is the most Kerbal thing I have ever heard.

  78. MrRex2U

    0:04:22 <<-- bunch of hard wired logic... My minds-eye sees... Mr Spock...!

  79. Ikhwan Yusuf

    3:36 hey that’s my country when East and West Malaysia (Sarawak, N. Borneo later known as Sabah, and Malaya later known as Peninsular Malaysia) were to combined altogether! That is part of our history :D Great to see the news on the newspaper side-by-side with the Mariner incident.

  80. Roman Priborkin

    And check your staging.

  81. Señor Koquonfaes

    “Check your hardware before launch”
    Meanwhile, at the SLS program,
    ‘Lol just launch it tomorrow gotta pretend we’re not a decade behind schedule’

  82. kromulous

    Yeh uhm, Scott. Venus is hot because its atmosphere is 100 times thicker than earths. 90 atmospheres or so? Either way it’s a superfluid. That thickness translates into latent heat capacity. hehehe. PVT law of gasses. If venus was pure oxygen it would still be at extreme temperature, its the density. Common mistake (don’t buy hype) but awesome vid. I love the technical explanation.

  83. ShadowZone

    That Venus surface picture is from a Russian Venera probe, I believe Venera 13, if memory serves correct. It lasted longer than any other vehicle on the hellscape that is Venus’s surface.

  84. CatholicSatan

    It’s happened to me! Many years ago, when we still worked off those huge printer pages (alternate green/white) I was asked to transcribe a large program for a rocketry system from another company into our system. I did this but could not get the navigation section to work. Not a single comment in the code, so it was a bit of a battle. After about a week, I gave the code for someone else to check (trees and forests) who was up to speed on this type of navigation. A few days later, he came to me and said “You’ve put in a multiply (*) when it’s a plus (+) in this equation”. On squinting at the printout, I could see he was right, the plus had become smudged!

  85. bconneau

    Morality : coders should not be drones. Try to know some context of what you’re implementing if at all possible.

  86. Ricky Oswald

    In other words, check your staging!

  87. Touay

    “test your hardware before committing to launch” … always a good policy (cough)

  88. Matt Horkan

    Seconding my request to change the name of this segment to ~~~”Great Unscheduled Disassemblies in history”~~~. (Even if they dont include only explosions)
    Thanks illectro if you read this :D

  89. Micai Askauss

    If the hyphen was so expensive but wasn’t used, then they actually saved money!

  90. Quinten

    Just like in KSP, always Check Ya Staging.

  91. Azivegu

    I have to just say it, Mariner 2 fixed itself in the most kerbal of ways. Well done Mariner 2 xD

  92. Peter Anderson

    I think you’re correct. Those types of early computers were programmed in machine language, not in a high level text-based programming language like to today. The human programmer was, in essence, a human compiler turning specifications into machine language. The programmer probably wasn’t totally 100% aware of exactly what he was programming or why it needed to exist, just dutifully following instructions like a good compiler should.

  93. Dave King

    Scott shouldn’t that be “Check yo stagin”? Lol

  94. tehbonehead

    Scott Manley: says “…to Venus to collect data…”
    Me: hears “…to collect that sweet, sweet science…”

  95. Paul Gracey

    I was working on transistorized Navy digital computers in 1962 that were roughly three times as fast as those Burroughs machines. They were octal format so the words were 30 bits long. Same punched paper tape input with switch arrays as backup. Boot up required 18 3 bit octal digits hand entered into the switch array to start the punch tape machine which then had a more elaborate boot loader routine at the head of each program. Our computers were a type of air traffic control, and fed search radar air battle information to the missile command computers which were analogue using resolvers, differentiators and integrators that were much faster than any digital emulations of the missile flight profile could do with the computers we had at that time I was told.

  96. Илья Найдов

    Also check yo staging!..

  97. Peter Sherratt

    I’ve been meaning to ask if you could do a video on how the heck they manage to accurately guide these things – that pretty much sorts it – thanks! Would be cool to see a comparison of the 1950s way with modern ways. Fly safe 😉

  98. KvaNTy Troiden

    And as always Check Yo Staging!

  99. Iron Man

    And most importantly, don’t forget to check your staging.

  100. Don Guru de Bro

    Wants to explain a tiny coding error, goes on to explain how the whole rocket functioned – thats why you just have to love Scott! <3

Comments are closed.