What was the Apollo 11 guidance computer bug?

A sequencing error in P63 routine: code read a stale register during DSKY interrupt windows, risking 0.3-0.8 degree attitude errors in lunar descent.

Did the Apollo 11 bug affect the moon landing?

No. Timing missed the glitch window; 1202 alarm inadvertently cleared it.

Verify sequencing rigorously, even in 'simple' systems. Use formal methods for critical code — interrupts don't care about eras.

📦 Open Source

Even the code that nailed the Moon landing hid a nasty bug. Good thing it slept through Armstrong's giant leap.

DevTools Feed Apr 07, 2026 3 min read

Apollo 11 code hid a real bug that could've skewed lunar landing attitude by up to 0.8 degrees. 𝕏
It never triggered due to lucky timing and another bug's side effect. 𝕏
Lessons for today: formal verification beats luck in mission-critical software. 𝕏

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Originally reported by dev.to