We found an undocumented bug in the Apollo 11 guidance computer code
juxt.pro
April 7, 2026
10 min read
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Summary
A bug was discovered in the Apollo Guidance Computer's gyro control code that has been undetected for fifty-seven years, causing a resource lock that silently disables the guidance platform's ability to realign. The bug was identified using Claude and Allium, an open-source behavioral specification language.
Key Takeaways
- A bug was discovered in the Apollo Guidance Computer's gyro control code that had gone unnoticed for 57 years, which can disable the guidance platform's ability to realign.
- The bug involves a resource lock called LGYRO that is not released during an emergency procedure, causing subsequent gyro torque attempts to hang indefinitely.
- The bug was identified using Allium, an open-source behavioral specification language, which distilled 130,000 lines of AGC assembly into 12,500 lines of specifications.
- The Apollo Guidance Computer's source code has been publicly available since 2003, allowing extensive scrutiny and analysis by developers and researchers.
