Mark McKee writes:
The Space Shuttle will soon be retired. Many of you on this list may recall an old computer called the DEC PDP 11, from the days before PCs. Big monstro machines that used 9-Track reel to reel tape to load programs. Did you know that these computers are still on the Space Shuttle? Why haven't they yanked them out and replaced them with say, Mac minis? Imagine how much weight that would save? Well, if only it were that simple. The Shuttle is a complex, integrated system, and obviously, you can't just swap out old parts for new without affecting thousands of other sub-systems, which is why they still fly, at least for one more year with the good old PDP 11. NASA calls it locking in the technology.
It was five redundant "System/4 Pi" computers from the IBM Federal Systems Division in Owego, New York that implemented fly-by-wire for the Shuttle Orbiter (aka Space Shuttle), not a DEC PDP 11. (My wife and I worked at this IBM plant in Owego back in those days, but not on this particular project.) IMHO, the innovation in obtaining reliable operation from the component parts of the day continues to amaze me. Here is a reference that at least mentions one innovation, the redundant computation with near real time, hardware implemented voting. There should also be references somewhere to how the software loaded into the redundant systems was written by independent teams to implement protection from a human error introduced by just one of the teams. If someone knows of equally cool ways to deploy software solutions today when "failure is not an option", please let me know. By the way, the IBM Federal Systems Division at Owego is no more. This operation was sold to Lockheed Martin.
The initial Shuttle orbiter avionics data processing system was provided by IBM' s Federal Systems Division under contract to the Space Division of Rockwell International Corp.
Five IBM computers — four of which were arranged in a redundant configuration, with a fifth computer acting as a backup unit — allowed early Shuttle missions to continue even if multiple failures were experienced. The computers cross-checked each other more than 500 times a second. In flight, the Shuttle orbiter was controlled by electrical signals generated by the digital computers — a concept called fly-by-wire — and sent to hydraulic-driven actuators.
Developed at IBM's Owego, N.Y., facility, the onboard computers were part of an Advanced System/4 Pi, avionics computer series. Input/Output Processors, also built in Owego, acted as an interface between the computers and other orbiter systems.