We found an undocumented bug in the Apollo 11 guidance computer code
by henrygarner on 4/7/2026, 10:25:12 AM
https://www.juxt.pro/blog/a-bug-on-the-dark-side-of-the-moon/
Comments
by: buredoranna
Still my all time favorite snippet of code.<p><pre><code> TC BANKCALL # TEMPORARY, I HOPE HOPE HOPE CADR STOPRATE # TEMPORARY, I HOPE HOPE HOPE TC DOWNFLAG # PERMIT X-AXIS OVERRIDE </code></pre> <a href="https://github.com/chrislgarry/Apollo-11/blob/master/Luminary099/LUNAR_LANDING_GUIDANCE_EQUATIONS.agc" rel="nofollow">https://github.com/chrislgarry/Apollo-11/blob/master/Luminar...</a>
4/7/2026, 1:20:25 PM
by: ChicagoBoy11
For anyone who liked this, I highly suggest you take a look at the CuriousMarc youtube channel, where he chronicles lots of efforts to preserve and understand several parts of the Apollo AGC, with a team of really technically competent and passionate collaborators.<p>One of the more interesting things they have been working on, is a potential re-interpretation of the infamous 1202 alarm. It is, as of current writing, popularly described as something related to nonsensical readings of a sensor which could (and were) safely ignored in the actual moon landing. However, if I remember correctly, some of their investigation revealed that actually there were many conditions which would cause that error to have been extremely critical and would've likely doomed the astronauts. It is super fascinating.
4/7/2026, 1:06:20 PM
by: jwpapi
Has someone verified this was an actual bug?<p>One of AI’s strengths is definitely exploration, f.e. in finding bugs, but it still has a high false positive rate. Depending on context that matters or it wont.<p>Also one has to be aware that there are a lot of bugs that AI won’t find but humans would<p>I don’t have the expertise to verify this bug actually happened, but I’m curious.
4/7/2026, 11:53:18 AM
by: josephg
Super interesting. I wish this article wasn’t written by an LLM though. It feels soulless and plastic.
4/7/2026, 11:06:59 AM
by: riverforest
Software that ran on 4KB of memory and got humans to the moon still has undiscovered bugs in it. That says something about the complexity hiding in even the smallest codebases.
4/7/2026, 12:32:03 PM
by: chrisjj
> The specs were derived from the code itself<p>Oh dear. I strongly suggest this author look <i>specification</i> up in a dictionary.
4/7/2026, 1:13:01 PM
by: MeteorMarc
Are there any consequences for the Artemis 2 mission (ironic)?
4/7/2026, 1:03:34 PM
by: yodon
This is so insightfully and powerfully written I had literal chills running down my spine by the end.<p>What a horrible world we live in where the author of great writing like this has to sit and be accused of "being AI slop" simply because they use grammar and rhetoric well.
4/7/2026, 11:48:20 AM
by: wg0
Someone please amend the title and add "using claude code" because that's customary nowadays.
4/7/2026, 11:56:23 AM