<a href="https://github.com/chrislgarry/Apollo-11/blob/master/Comanche055/P30-P37.agc#L62" rel="nofollow">https://github.com/chrislgarry/Apollo-11/blob/master/Comanch...</a><p>I feel like "BEWARE"... is, given the context, what we would now likely call "load-bearing"<p><pre><code> COMPTGO EXTEND # USED TO COMPUTE TTOGO
QXCH PHSPRDT6 # ** GROUP 6 TEMPORARY USED .. BEWARE **
</code></pre>
(edit: formatting)
This is such an interesting peek into the engineering of these sort of systems with very constrained resources at the time. Like any random file you open contains little pragmatic design decisions like this<p><a href="https://github.com/chrislgarry/Apollo-11/blob/master/Comanche055/LUNAR_AND_SOLAR_EPHEMERIDES_SUBROUTINES.agc" rel="nofollow">https://github.com/chrislgarry/Apollo-11/blob/master/Comanch...</a><p># THE POSITION OF THE MOON IS STORED IN THE COMPUTER IN THE FORM OF
# A NINTH DEGREE POLYNOMIAL APPROXIMATION WHICH IS VALID OVER A 15
# DAY INTERVAL BEGINNING SHORTLY BEFORE LAUNCH. THEREFORE THE TIME
# INPUT BY THE USER SHOULD FALL WITHIN THIS 15 DAY INTERVAL.<p>Better be back home in 15 days! ;)
The Apollo program set a requirement for a fourteen day mission from the beginning. None of the missions lasted that long; the longest was Apollo 17 at 12 and a half days.<p>The Space Shuttle flight software used an interpolating polynomial for the solar ephemeris, with coefficients that were valid 10+ years (I've forgotten the exact number). The solar position was an input to the atmosphere model used to compute on-orbit drag, which itself was itself an interpolating function for data generated by a model with higher fidelity. I could go on. The pattern of using interpolation formulas to save memory and CPU cycles was (is) a common one.<p>People would be surprised by the amount of data required for on-board guidance and navigation software. Some of it is non-mission specific, but much of it must be generated for each mission. During the Shuttle era, these parameters were called I-Loads (for Initialization, of course) and were a separate memory load from the flight software itself.
The LM landing algorithm was also based on a polynomial, with "time-to-go" as the variable. Problems would occur if that variable went negative.
Given the constant launch delays how could they justify hard coding a 15 day window like this?
The coefficients are stored in writable memory as input data. Only the structure and degree of the polynomial are hard-coded in the program. So if the launch is delayed you just change the data.<p>Of course, the justification is that compute and memory were at an extreme premium on the spacecraft. Accurately predicting the position of the moon at <i>arbitrary</i> times requires more complicated calculations. You can dramatically optimize the calculation by fitting a polynomial approximation which is valid for the length of the mission. And there's no reason to waste resources fitting that polynomial in space when it could be done on the ground, using much more powerful machines.<p>The AGC is what tends to get the press. It's easy to forget that the Apollo program relied on a cutting-edge <i>distributed</i> hardware and software stack, most of which was in Mission Control at the Real Time Computing Center.
It wasn't hardcoded. The exact mission parameters (mission clock, moon position, orbital parameters, etc) were uploaded by mission control the morning of the launch. From that point, they had 15 days. The longest Appolo mission was 12.5 days.
And I'm scared to hardcode some negligible config value that will never change
Happy 10-year anniversary to this repo being shared on HN.<p>Most significant discussion: <a href="https://news.ycombinator.com/item?id=12048945">https://news.ycombinator.com/item?id=12048945</a>, 652 points, 145 comments on July 7, 2016<p>All previous submissions: <a href="https://news.ycombinator.com/from?site=github.com/chrislgarry">https://news.ycombinator.com/from?site=github.com/chrislgarr...</a>
For an terrific AGC deep dive, I can’t recommend Marc’s restoration videos enough. The work they did was incredible:<p><a href="https://youtube.com/playlist?list=PL-_93BVApb59FWrLZfdlisi_x7-Ut_-w7" rel="nofollow">https://youtube.com/playlist?list=PL-_93BVApb59FWrLZfdlisi_x...</a>
Not sure in which video (pretty sure it was one of Marc's videos) it was mentioned, but what I found particularly interesting is that they restored the source code by just cherry picking patches documented elsewhere until the output matched the documented checksums...
This remains to be my go-to example for how YouTube can be a remarkably effective and valuable platform for the kind of enthusiast whose interests have exceeded the bounds of typical documentaries and media produced for the general public.<p>It’s sadly getting more difficult to surface these kinds of examples, as we’re seeing a lot of lowest common denominators and slop-py channels run by people who only want to be YouTube content mills, rather than people who have expertise to share and who learned to leverage YouTube as a means to those ends.
and Master Ken and co...
More here (linked in the repo):<p>Original scans (featuring Margaret Hamilton!)<p><a href="https://28gpc.csb.app/" rel="nofollow">https://28gpc.csb.app/</a><p>The Virtual AGC Project
Spaceborne Computer Systems<p><a href="https://www.ibiblio.org/apollo/" rel="nofollow">https://www.ibiblio.org/apollo/</a><p><i>The purpose of this project is to provide the original flight software and emulations of the onboard guidance computers flown in historical spacecraft, so that the flight software can be run on computers commonly available to the public today. The particular emphasis is on the Apollo Guidance Computer (AGC) flown in lunar missions in the 1960's and 1970's.</i><p>Wikipedia on the hardware:<p><a href="https://en.wikipedia.org/wiki/Apollo_Guidance_Computer" rel="nofollow">https://en.wikipedia.org/wiki/Apollo_Guidance_Computer</a>
As other commenters have pointed out, some of the comments in there are pretty scary. I guess the astronauts didn't have to read the code:<p>`TC WHIMPER -1 # YES. DONT DO POODOO. DO BAILOUT.`
To see the code in action (and learn many good things about Apollo computer) please watch this: <a href="https://www.youtube.com/watch?v=B1J2RMorJXM&pp=ygUPYXBvbGxvIGNvbXB1dGVy" rel="nofollow">https://www.youtube.com/watch?v=B1J2RMorJXM&pp=ygUPYXBvbGxvI...</a>
Clicking around the code, it mentions a page with images... even more clicking around got me to this page/image: <a href="https://www.ibiblio.org/apollo/Block1.html#DSKY" rel="nofollow">https://www.ibiblio.org/apollo/Block1.html#DSKY</a> / <a href="https://www.ibiblio.org/apollo/Block1ControlPanelDSKY.jpg" rel="nofollow">https://www.ibiblio.org/apollo/Block1ControlPanelDSKY.jpg</a><p>Damn, a control panel to input values, probably straight to the CPU. I guess the astronauts didn't have to learn assembly, but imagine a programmer having to recite all the raw code (I guess the commands (verbs) are numeric as well) to debug something, all the way at the moon.
The DSKY was the main input system for the AGC, and commands were inputted using the verb/noun system. Verb says what you want to do, and Noun says what you want to do that verb to.<p>For example, "Verb 35 Enter" lights every single segment and light on the DSKY, to make sure they're all working. "Verb 16 Noun 17 Enter" displays the IMU measurements, "Verb 16 Noun 36 Enter" displays the current time and "Verb 16 Noun 43 Enter" displays the current GPS lat/long. Verb 16 indicates to display something as decimal, and the noun indicates what to display.<p>Other commands could be used to input data, or set what program the AGC was running, for example if you wanted to change the current running program to 67, that would be "Verb 37 Enter 67 Enter"
While I know about the DSKY, I keep wondering if they were the first ones, i.e. inventing that way of entering data into a computer and others copied it later on, or if it was a already a more widespread and known pattern and the AGC copied it.<p>I <i>know</i> that other machines existed that used a similar system. I recall being asked, circa summer 2009 or so, to set up extensions on a quite old PABX that was configured that way.<p>The PABX was a huge electrical box full of giant PCBs stuck into a backplane (S-100 or maybe something proprietary?). I didn't get a good look tough, the box was mounted under the ceiling, directly above a desk with a terminal that you used for configuring it. There was a binder with laminated, typewritten cards, documenting "verbs" and "nouns" that you entered into a numeric keypad. As said, it worked like the Apollo DSKY, but the "display" was single slot that you had to squint through at just the right angle to make out faint numbers on a mirror, aimed downwards at some back projection thingy.
The funniest thing is that DSKY was, IIRC, a "temporary solution" that became the norm, and despite all the platitudes today it was apparently hated by astronauts.
For a superb video explaining what the AGC did and what WENT WRONG during the moon landing including the error codes:l, see: <a href="https://youtu.be/B1J2RMorJXM?si=Ad1UYojAtee2ktr3" rel="nofollow">https://youtu.be/B1J2RMorJXM?si=Ad1UYojAtee2ktr3</a>
Really cool to see this digitized and archived, it's such an important piece of history and really one of the earliest digital ic bases computers.
Well, I have no idea how complete this is, but perhaps a neat Christmas-time-project for anyone with seemingly unlimited tokens to take this and let it build up a simulator, using the real code to drive simulated machinery.
Great to see the AGC assembly code and knowing that Apollo 11 is coded purely in assembly. Not sure if it has any compiler. Also found <a href="https://github.com/virtualagc/virtualagc" rel="nofollow">https://github.com/virtualagc/virtualagc</a> while searching for compiler.
The assembler you're looking for, is called YUL. [0]<p>You can find much of that code here [1], but unless you have a Honeywell, it isn't much help. yaYUL is a modern remake, and can assemble most of the Apollo code.<p>[0] <a href="https://www.ibiblio.org/apollo/Documents/agcis_13_yul.pdf" rel="nofollow">https://www.ibiblio.org/apollo/Documents/agcis_13_yul.pdf</a><p>[1] <a href="https://klabs.org/history/software/yul/" rel="nofollow">https://klabs.org/history/software/yul/</a>
> knowing that Apollo 11 is coded purely in assembly<p>Of course. According to Wikipedia, it was <i>introduced</i> in 1966, so it's development must have been started earlier. Also according to Wikipedia higher-level languages like Fortran and Cobol were <i>introduced</i> in 1957/58. They were a cutting-edge technology of the era.<p>So programmers of the day would have been comfortable with assembly, and the inefficiency and novelty of higher-level languages would have probably been a bad fit for the application.<p>> Not sure if it has any compiler.<p>What you're looking for is an assembler.
Part of the AGC ROMs implemented a virtual machine for things like matrix multiplication. So, a higher level of abstraction was available but it was still very much coded in its own assembly language.
Strange that no one took the effort to fix yaYUL to read the YUL format, but instead of adapting the transcription of the source to match the 'quirks' of yaYUL.
In 1969, they had not invented lowercase yet.
the code that landed humans on the moon has 72k stars on github and your startup's monorepo still can't pass CI on the first try
Not the same goals, risks, monetary budget, time budget.<p>If your goal was to absolutely prevent any errors and you would go great lengths to do it, you would.<p>Just look at any safety critical systems: medical, transportation. There has been some incidents, but some systems do work really well that are developed today.
> monetary budget<p>I’ve never attempted to calculate it, but I’ve always felt that the money lost from major incidents must outweigh the additional engineering time spent doing things right. Of course, that assumes that the engineering skill exists, and that the deliberate choice is being made to push out sub-optimal code in favor of velocity (which is then negated by the incidents anyway).
I think I read somewhere around here the code could be run today on something as low powered as the chip that runs the USB charger for an iphone<p>So yeah I'd like to see that lol
looks like its not hard to read assembly code
Orion on Artemis has a bunch of really cool stuff like redundant computers but it's certainly jarring to go from Verbs and Nouns of Apollo to seeing them tapping on screens with a GUI
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Ok, someone evaluate it with Fable and vibecode it better. Remember "make no mistake".