One of the prevailing criticisms of the U.S. space shuttle program is that it is comprised of antiquated equipment. Designed in the 1970s, built in the 1980s, and with two decades of operational fatigue on the fleet, Discovery, Endeavor, and Atlantis aren’t cutting edge technology in any respect — especially their computer systems. The space program is an exercise in proven, cost-effective, work-horse tech, rather than the latest and greatest innovations.

We’ve come a long way since the days of Apollo.

When Apollo 11 set forth for the moon in 1969, it carried with it what were then arguably the two most advanced computers ever built. The Apollo Guidance Computer — two of which went on every manned moon mission — was the first computer to use integrated circuitry and was thus the first modern embedded computer system ever put to use. Custom-designed by MIT and purpose-built by Raytheon, the Apollo Guidance Computer was the basis for the world’s first fly-by-wire systems, which in turn directly influenced the design of the space shuttle’s flight control systems.

Not bad for a 2 MHz, 16-bit system with a four kilobit RAM allotment and 32K of fixed memory. (And that was the Block II advanced model; earlier Apollo shakedown missions used an even more limited Block I design.) The Apollo Guidance Computer had a 19-key calculator-style keyboard that astronauts used to program the system with two-digit commands. Bear in mind, the first commercially available pocket calculator wasn’t sold until 1967, when Texas Instruments debuted a basic function model (add, subtract, multiply, and divide) for about $100. A calculator-esque interface was cutting edge for 1969.

That isn’t to say the Apollo Guidance Computer — advanced as it was for its era — was error free. The AGC that ran the Apollo 11 lunar module’s Primary Navigation, Guidance, and Control System (PNGCS, pronounced pings) malfunctioned during the first lunar descent. Fortunately, the error codes 1201 and 1202 didn’t faze Buzz Aldrin and Neil Armstrong when they popped up, informing the astronauts of a critical buffer overflow. (Two radar systems were feeding the Apollo Guidance Computer data simultaneously due to an error in flight protocol.) The Apollo Guidance Computer simply popped into a failover mode and — because the system was designed with 15 percent spare memory capacity in case of error — the mission went off without a hitch. If the Apollo Guidance Computer had thrown a 404 error, it might have been a different story.


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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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