How did the Apollo flight computers get men to the moon and back ?
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How did the Apollo flight computers get men to the moon and back ?

August 29, 2019

There has been much speculation by some as to how the flight computer aboard the Apollo missions managed to get men to the moon when it had just a tiny fraction of a computing power of something like a modern smartphone. But this is quite misleading as it was not one solitary computer controlling the Apollo craft there were four computers and there were no fancy touchscreens GUI’s or other things in a typical computer of today to waste resources on. The first of the 4 computers was the Saturn Launch Vehicle Digital Computer (LVDC). This got the rocket from the launch pad to the Earth orbit. Then there was the Apollo guidance computer or AGC this is the one that most people think of. There were in fact two of them one in the command module to get from Earth orbit to the moon and in back again the second was in Lunar Lander and would control the landing and then the ascent back to the command module and docking. The fourth computer was one which was never used on any missions because it would control an emergency abort and ascent should something happen during the descent to the moon surface like the landing computer failing or they ran out of fuel. The Apollo guidance computer wasn’t as dumb as many make it out to be. As time went by in Apollo’s development the tasks that it was meant to do increased in both number and sophistication. This in turn created ever more issues with the limited resources available. One of the biggest problems was the limited amount of memory due to technological limitations of the time. This meant that the programmers had to make use of every single Byte available. The AGC also had a unique operating system. Systems like unix, linux ,windows and Apple iOS are in control and share out time to the program. In the AGC the program’s controlled how much time they got depending on how important they were, so in the case of an emergency the highest priority programs would get the most amount of time and non-essential operations were dropped to free up resources which became the basis mission-critical systems for all manned missions afterwards. The computer had a performance somewhere around that of the first generation of personal computers like the Apple II, Commodore pet Commodore 64, the ZX spectrum which will all arrive ten years later in the late 1970s. It had 2k of RAM and 36k the fixed storage rope core memory or ROM. Now this was woven by hand and took months to assemble, so any software bugs were literally woven into the system. A comparison between the Apollo guidance computer and say an iPhone 6 is tricky because the AGC was not a general-purpose computer it was built for a very specific task and had a unique operating system that and also over 48 year gap in the technologies used mean that we can only get a very rough estimate on the difference in performance. The Apple iPhone 6 has an ARM A8 processor which has about 1.6 billion transistors in it, the agc had just 12300. This iPhone 6 has one Gigabyte of RAM, about 488,000 times that of the AGC and this one 128 Gigabytes of non-volatile storage about 3.5 million times after the AGC. As for the performance the iPhone 6 is maybe somewhere between 4 and 30 million times faster than the AGC depending upon what type of calculations are being done and if you include the iPhones GPU, it will be even more. So if you had to fly back to the moon in an Apollo craft and given the choice would you trust your life to a couple of iPhones in place of the AGC because you would actually have more computing power in just one of these than the whole of NASA had during all the Apollo missions. However if your iphone crashed you would be in big trouble whereas the ancient AGC was designed to recover from crashes and overloads and continue by itself in essence it was designed to be crash-proof, something that is needed in a mission critical situation. The problem we have here is in the context in which we see the Apollo computer today. We are now surrounded by computers hugely more powerful and we don’t give them a second thought. It’s very difficult for most people who are not computer engineers or assembly language programmers to imagine how you could do anything with such limited resources. What we forget is at the time of the design in 1962 that this was to be the first embedded computer. It was a huge leap forward in miniaturized computing from something the size of a large room to a size of a briefcase. It would also be a giant leap forward for software programming and the first time that software would be used for real-time problem solving that will be key to the entire mission. If it fails people could die but this development was far from easy, it said that if the designers had known in 1961 what they learned later or had a complete specification when given the contract to make it, they would have most likely concluded that it was just not have been possible with early 1960s technology. The contract for the design development construction of the Apollo guidance navigation systems and software was given to the Massachusetts Institute of Technology, MIT in August 1961 instead of NASA’s normal computer contractors IBM. But there was no specifications given in the contract because no one at NASA really knew what the requirements of an Apollo computer would be at that early stage. As the project developed throughout the 1960s it became apparent that the task was going to be much more difficult than they first considered and by the mid to late sixties the problems in the computers development were in danger of sinking being entire Apollo program if they couldn’t get the AGC to work. By the time of testing in 1966 for the ill fated Apollo 1, it became apparent that the bugs in the software meant that the AGC could not be relied upon to do the navigational course calculations as it was just not accurate enough something but could put the craft in the wrong orbit when it returned to earth. It was decided that IBM mainframe computers on the ground would do the course calculations then send them to the AGC in the command module to be implemented. This way round known limitations could be worked around with much more powerful ground-based computers and the results sent to be a AGC’s. However the command module had to be capable of working independently if the ground link was broken, like when it was flying behind the moon or if someone tried to actually jam the signal, so using a combination of the inertial guidance system and the built-in sextant to check the star positions they could still navigate without the ground link Data. As for the Lander the round-trip delay of 1.5 seconds for the signals to get to the moon and in back to earth would have been too long for the ground control to remotely lander’s descent stage because the feedback needed to be in real time. To this end the descent stage AGC would work with the landing radar and the astronauts to land on the moon this led to the Apollo 11 landing almost been aborted when design bug in the landing radar which had been left on standby during the descent in case of an emergency abort, created a flood of signals and overloaded the AGC setting off computer error code alarms just before the landing. Due to the AGC design instead of crashing or locking up like we might expect to our iPhone or a normal computer to do, it dropped all but the most important tasks before then restarting itself. This was not a fault it was called Reset Protection, the AGC was designed so but all the current data it was working on was stored, this meant but it could be turned off and on again or reset at any time and it would just continue to work from where it left off, a bit like when your PC goes in to sleep mode and then comes back again but much much quicker. These features saved the mission from aborting and allowed Armstrong to control the orientation of the lander whilst the AGC controlled the descent to a successful landing. It’s things like this that made what is now about as powerful as the microcontroller in a toaster get men to the moon and safety back again six times. It also created a paradigm shift not only in space exploration but also computing for the future and as always thanks for watching and please subscribe, rate and share.

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  1. I’m impressed. This is a clear explanation for a general audience of some complex information — especially, of just what was going on with the LEM’s computer, and the repeated error codes, during Eagle’s descent. The explanation is so good, I almost understood what happened in that episode!

  2. Couldn’t use an iPhone the battery wouldn’t last lol

    Nah but seriously we still haven’t been back since, how sad is that.

  3. So the next Moon mission won’t cost very much if all the computing can be handled by a couple of iPhone 6’s.

  4. Next time they're going to send a rocket load of sandwich makers.. and they will be black, trans, and of course butch

  5. 4:30 It's also astounding at how wasteful modern forward thinking computing is. Little regard is given to the size of the program or the resources it consumes. Just buy more or bigger CPU's, more powerful GPU, more RAM, etc. Bloat ware is rampant and no longer a real consideration today. However if you look at the retro computing communities they are doing astounding things on retro hardware things the original creators and programmers never dreamed of. These retro programmers are squeezing every ounce out of retro hardware based on new techniques that didn't exist back then and armed with a better understanding of the systems than of days past. I wonder what amazing things will be done with our current computing resources when the retro communities of the future have a crack at it.

  6. So you couldn’t watch funny fail videos on youtube on the way to the moon? What a bummer that wouldn’t been.

  7. L'orbita bassa e sparita 🤣😂🤣😂🤣😂🤣😂😂😂😂😂non si va e non si viene….🤡🤡🤡🤡🤡

  8. I always chuckle when people say you'd need a NASA computer to run this and that. NASA has such lengthy procedures to certify computer hardware space worthy that everything that is sent up into space could be a decade behind current computers at launch. To see the opposite here was quite surprising.

  9. the idea that you can manoeuvre a Saturn five rocket with sextant that is 100s of years old, Bligh staring at the stars from the other side of the moon instead of the deck of the Bounty,

  10. Great video. I still think you would make a fantastic Bond villain, unfortunately the new 007 is a black female SJW. The world is going to hell quickly.

  11. 😄😄😄😄 come on.. We don't have the technology to go back to the moon what the bunch of bullocks

  12. With today's technology we should be going to the moon every month……and yet NASA said they have lost the technology to return….hmmmm

  13. I guess in reliability parameter AGC will beat linux, apple and Windows by million times. i have i5, 8 gen, 16 GB with Windows 10 and still i am shaky while i am doing a video call with clients abroad as my Windows 10 crashes atleast one time in day and i always pray it does not crash atleast during the call with a bad experience

  14. Not sure the AGC wasn't a general purpose computer… It did limited tasks because that's what was needed, but in theory it could do anything

  15. I have some rocking horse shit if anyone wants it for their garden…
    So the landers had these four little computers… Then what the F were all those in NASA for?
    NO MAN ever walked on the moon.
    It was filmed by KUBRIK. full stop.

  16. "Houston, the Eagle has landed. …Houston?"
    "Wait what? Sorry Eagle.. we were playing Pong. Say again, what's your status?"

  17. How does this limey know jack shit about all this they dont even have a fake space program to bilk there citizens out of billions the lovely queen just takes it

  18. I always enjoy watching your great videos full of information and accessible to non specialist. Guess what?! I've just realized that I did subscribe to your channel. This is no longer the case. I'm in.👍🏿😊

  19. Excellent presentation! It shows that NASA, as well as other aerospace agencies across the world, at that time and even to just a few years ago used computing as a tool to assist humans, not to replace human input all together.

  20. Fantastic great bit of info there, makes me want to visit the space museum to see all technology used in the Apollo missions.

  21. 4 calculators was all that’s required to guide the craft? That’s incredible. Makes you wonder why we haven’t been able to go back. Losing the telemetry data along with the technology didn’t help. We’ve got better technology and communications now, but according to NASA we are still working on how to protect humans from the massive amounts of radiation in the Van Allen belts.

  22. Simple, if you want to avoid crash then don't use apple or windows os, that way you don't end up being a pancake on the surface of the moon.

  23. Droid, I am very lost here, how is it possible to navigate via sextant without a horizon. I am familiar with this navigation instrument, not having used one however, understanding the principle. Again, though it is completely reliant on measuring celestial objects in relation to the horizon. Please explain or direct me to a further vid on this.

  24. How did the Apollo flight computers get men to the moon and back ?   Simple answer?  They did not  !!   Anyone who believes man has been to the moon or space station or space shuttle is just plain "STUPID"

  25. Take that, ignorant hoax-accolytes. But they never want facts to get in the way of their insane fantasies.

  26. bollocks! they never went past low orbit. they cant get past the van allen belts. not with a 10cm thick aluminium hull

  27. Back in the early 1980's I used my parts bin 8088 (1st generation?) PC and a single 360 floppy to surf the internet. It would display the entire front page of the New York Times in less then two seconds. However, the title was ASCI text. Eventually the links went from this [NEW YORK TIMES] [EDITORIALS] to this [LINK]. It was a serious impediment to actual information retrieval for a long time.

    I used a file transfer program called CrossTalk to dial up a Unix internet computer. Both CrossTalk and my Personal
    Word Perfect word processor fit on a single 360 floppy and would load into a full sized 1 megabyte RAM card on start up and everything was fast after that. I used a daisy wheel printer at 13 characters per second which was slower then dot matrix printers but had laser printer resolution of course.

  28. AGS was actually used during missions. IIRC it was used during Apollo 13. IIRC it was also used during gimbal lock on one mission.
    AGC was actually a GPC.

  29. Since that computer was powerfull enough to calculate positions and movements of objects in 3 dimensions in real time it would have been poosible to build a few thosound of them to computer animate the moonlanding instead. I wounder if that also would have costed 40 bilion usd? Thank God that Nixon fellow was an honest President and never would have thought about stealing tax dollars like that.

  30. This is brilliant. It does need to be put in context. As anyone who worked with dos based computers recalls, we used to be able to do a lot more when resources were devoted to the program instead of the interface. My no hard drive 512k ram one 720 floppy Toshiba T1000 did some great productivity software stuff without the burden of running a GUI

  31. What utter rubbish! It really is the case that if you keep repeating fictionalised stories and nonsense people will eventually start believing. No one will doubt whatever set of ridiculous facts you present.

  32. this is a particularly fascinating area of the Apollo program for me. The sheer ingeniousness of how they designed and built the computers to enable craft to travel to and land on the moon. In a way, they had to be smarter than today's system designers and developers, because of the extremely limited computing power available.

  33. Ok, one of my friends just explained this to me in less than a minute..
    Or, as he put it, in "my money.." He basically said, with the computing power they had at their disposal to get to the moon, it would take approximately 3 days to download a tit and around 2 months for a low res, 5 minute jazz flick.. His eloquent descriptive terminology, however crude, has enlightened me to just how bloody lucky they were to get there and back..! Hats off to them, and especially to the ground crew who are often the unsung heroes in these endeavours.

  34. The "Executive" routine prioritized every "task" it was responsible to complete. Usually, it could get through all of the tasks assigned to it…but on Apollo 11, during the final approach phase of the landing…the Rendezvous radar inputs began swamping the AGC's computational time. It turned out there was an electrical phase problem with the two A/D converters tasked with reading azimuth and elevation of the radar. The two CDU's wound up being supplied with power at different phases. This made the information coming into the AGC incorrect. The AGC kept trying to drive the Rendezvous Radar to it's proper setting to acquire the Command Module…but was constantly being fed incorrect feed back info from the Radar. Luckily the Rendezvous Radar information was of a lower priority than solving the landing equations and while the DSKY gave a quite upsetting "Malfunction Code"…the codes soon passed and after Neil Armstrong, took command of a portion of the landing responsibility, the "MC's" ceased occurring…and the landing was successful.

  35. They didn't, it's fake.

    Once you use low tech to go to the moon once it explodes and you cant go back to the moon ever again…

  36. R.A.H. was once talking with some NASA engineers about the lunar orbit of one of the spaceships in either Rocket Ship Galileo, or The Man Who Sold the Moon. The mentioned how accurate it was to the one used by NASA's lunar missions (only off by a few degrees), the Engineers we're then shocked when he told the he used a slide rule to make the calculations because back in 1946-1948 there were only about 2 or three computers, and since he was a civilian didn't have access to them, so he used the old fashioned way to make the calculations.

  37. Hmm, why "iPhone" and not just "mobile phone"? Was it important to the story to use a brand instead of a generic term?
    /end rant

  38. Imagine taking off from the moon.

    Bij hand control. No computer timing.

    And you have to time it to something that is rotating around the moon..

    And you have to connect to it.. fly to wards it. Not ram it.
    So you can fly back to earth.

    Your moonlander is not an airplane. Refuel midair is Nice, but connect your moonlander on something in moon-orbit?!

    Well, you now know the moonlanding is fake.

  39. Sure. They went to another planet and back 50 years ago with a Commodore 64. Landing on another planet is sci-fi today.

  40. No two-minute waste of time getting to the point. Thank you for knowing how to present a video, most don't know how to do it.

  41. The Apollo Abort Guidance System was actually used, by the way. It was tested on Apollo 9, accidentally activated on Apollo 10, used during lunar ascent gimbal lock on Apollo 11, and used for most of the return trip of Apollo 13 (including several engine burns).

  42. Ridiculous, no one has been to the moon and no one will ever get there.

    The task of Nasa is just like those of Hollywood,

    they create false scenarios about the nature of the earth,

    its creation and what surrounds us – also called cosmos.

    Only the naive, the gullible and the credulous fall into this nonsense.

    Nasa is an instrument of power that constantly supplies humanity with scientifically substantiated lies,
    to hide our true origin and destiny.

    You as the creator of this post, do you seriously believe that they flew to the moon,
    within a tin can and a calculator, who you want to sell this scrap?

    Wake up.

  43. Speed vortex lines. Empty space is a uniform speed vortex line. And earth is a 11km speed vortex curvature. What is 11km. Diameter of earth is 10km extra 1km. So anything less than 10000 km/sec gets trapped in suns gravity space and reaches sun.

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