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Does the Space Shuttle’s Computer Really Run on Just One Megabyte of RAM?

Our experts tackle your nagging questions

By Christopher Mims Posted 02.03.2009 at 11:16 am 31 Comments

Vintage Tech The shuttle’s pea brain is smart enough to control a launch. Sandra Joseph/Kevin O’Connell/NASA

It’s true: The brain of NASA’s primary vehicle has the computational power of an IBM 5150, that ’80s icon that goes for $20 at yard sales. According to NASA and IBM, the shuttle’s General Purpose Computer (GPC)—which controls, among other things, the entire launch sequence—is an upgrade of the 500-kilobyte computer the shuttle flew with until 1991.
Such an antiquated computer works just fine for NASA. The shuttle doesn’t need to support a powerful graphics engine or create PowerPoint presentations or store MP3s. It focuses entirely on raw functions—thrusters on, thrusters off—which, though mathematically complex, don’t require the juice that a user interface like Windows calls for. The GPC has flown so many missions with hardly a hiccup that there’s no reason to replace it, even if it is just 0.005 percent as powerful as an Xbox 360. Besides, a complete overhaul would be horrendously expensive. The GPC’s software would have to be completely reconfigured for a modern computer and tested until proven flawless.
For proof that you shouldn’t fix a space computer if it ain’t broke, consider Russia’s Soyuz space capsule, which since 1974 has been running Argon-16 flight-computer software with just six kilobytes of RAM. In 2003 the Russians rewrote some of the spacecraft’s software, which experts suspect led to its subsequent crash-landing in a desert in Kazakhstan.