Apollo 11: From one small step to interplanetary computing

Every aspect of the Apollo 11 Moon landing mission was tested and tested again to ensure it would work. “The risk was in the descent and ascent, because we had never done it before,” says Dave Proctor, who worked for IBM on the Lunar descent integrator software module.

And, just before Neil Armstrong and Buzz Aldrin were set to make the final descent, as the BBC’s 8 Days: To the Moon and back documentary recently reported, the lunar module raised a 1202 error. The error occurred because the small computer on the lunar module had very little memory, and this was being filled up by data from what Paul Adler, a lunar module software engineer, described as “a misconfiguration of the radar switches”. In effect, the computer was signalling that it was overloaded.

Armstrong asked Mission Control for clarification on the 1202 error. Jack Garman, a computer engineer at Nasa who worked on the Apollo Guidance Program Section, told Mission Control that the error could be ignored in this instance, which meant the mission could continue. Apollo 11 landed a few seconds later.