Geek Trivia: Cast to the 404 winds

What kind of error did a 404 code signify within the operating system of the Apollo Guidance Computer, the first embedded system ever put to practical use, and the computer that accompanied the first human beings to land on the moon?

What kind of error did a 404 code signify within the operating system of the Apollo Guidance Computer, the first embedded system ever put to practical use, and the computer that accompanied the first human beings to land on the moon?

Error code 00404 signified an error in the AGS's Optical Alignment Telescope, such that the craft could not determine its orientation, position, or direction. Forget page not found, this 404 code essentially meant spacecraft not found. While modern 404 browser errors are not directly inspired or related to Apollo 404 errors, there is a rather poetic similarity that illustrates just how far ahead of its time the Apollo Guidance Computer really was.

All inertial measurement systems are inherently imperfect, and the IMU in the Apollo Primary Navigation, Guidance, and Control System (PNGCS) drifted by a predictable one milliradian per hour. That's why the PNGCS also had an optical sextant that realigned and reset the system at regular intervals by syncing to the positions of known constellations--the Optical Alignment Telescope. The 00404 code signified a failure in that sextant. Luckily, no Apollo mission ever suffered a major 00404 error in its Apollo Guidance Computer, though the crew of Apollo 13 did endure the rough equivalent of one when they had to make computer-unaided course corrections during their emergency return to Earth.

Being at the forefront of technological innovation is a costly business, however, and Apollo would not stay ahead of the curve forever. We mentioned earlier how the Apollo Guidance Computer's calculator-style interface and computational power were well beyond consumer-available technology in 1969. By the time the final Apollo mission was underway, consumer tech had caught up. On the Apollo-Soyuz rendezvous mission in 1975, an HP-65 programmable calculator was part of the cargo manifest for the American crew. The HP-65 served as an independent backup for the Apollo Guidance Computer, offering roughly commensurate processing power to the once-unparalleled portable system. (The HP-65 was also the first programmable calculator in space.) This, fittingly, was the last time Apollo capsules carried men into flight.

Today, the space shuttle is being phased out in favor of Project Constellation, which will see a return to Apollo-style manned capsules and rockets but with more modern computer systems. At least until those capsules, too, become outdated, which will create not just some fitting techno-historical symmetry but an innovatively internecine instance of Geek Trivia.

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