Atlantis computer goes down: Fixed by 'nauts
Space pilots turn hands to a bit of zero-G sysadmin work
Commander Chris Ferguson and pilot Doug Hurley have fixed space shuttle Atlantis' General Purpose Computer (GPC) 4, which clapped out last night requiring transfer of its duties to another of the shuttle's quintet of GPCs.
The pair have reloaded software into the unit and it has "been added to the common set of GPCs and is operating normally, processing data".
NASA elaborates: "Mission Control is evaluating the 'dump' of data from the computer that Atlantis transmitted earlier this morning to determine what caused the Thursday evening failure. GPCs 1, 2 & 4 are in 'run' and GPC 3 is in 'standby'. All four of the primary computers are processing data."
The agency describes the GPC (pictured) as "slow" and packing "little memory compared to modern home computers", specifically "a storage capacity of one megabyte". It "runs at a speed of 1.4 million instructions per second". However, NASA does quite reasonably note that "no one straps the latest-and-greatest desktop computer inside a machine that vibrates like an old truck on a washboard road while requiring it to get a spacecraft into orbit and back safely".
The GPCs' software is similarly lean and robust. NASA says: "The shuttle's primary flight software contains about 400,000 lines of code. For comparison, a Windows operating system package includes millions of lines of source code."
This modest package processes data from the shuttle's "myriad sensors" via 24 input/output links, subjecting them to "elaborate mathematical algorithms to determine when to swivel the three main engines during launch, how much to move the elevons on the wings for landing, and which thrusters to fire in space to set up a rendezvous with the International Space Station, for example".
"Open the pod bay doors GPC4"
"I'm sorry, Dave. I'm afraid I can't do that"
Tried, Trusted, Tested.
Why would anyone even think that slapping a random chip up there would be a good idea? Yeah, for everyday entertainment, or casual use, or non-essential admin work, but for life-critical functions?
Hell, they've *already* got four of the things doing nothing but double-checking each other's calculations, and it's an incredibly hostile environment (think what happens if there's a tiny bit of condensation - you can't just open a window, not to mention flying through varying EM fields, cosmic rays, and potentially unstable power - and tech support is several months away). By comparison, the liftoff was nothing.
I'd much rather they were using these old clunkers, presumably with chips that have 30+ year errata's, billions of hours of real-world testing in commercial and industrial environments and production lines established for decades, than trying to slap an Intel with an undiscovered FDIV bug up there. Plus the old chips were predictable to an extreme degree (down to the individual cycle). Modern chips are multi-core, have vast caches, unpredictable bus intersections and all sorts of problems. That's not what you want. And 1.4MHz is more than fast enough for doing anything critical, it's going to be vastly outweighed by the time for that action to actually have a physical effect.
I think it's absoutely bloody fantastic.
Lesson in reliability and code efficiency. Computer absolutely fit-for-purpose. Doesn't play games, surf the web, let you watch porn. It flies the shuttle, exactly what it was designed for.
Remember Apollo 11? How much "intelligence" that machine had? Nowadays we slide a gig. of RAM into our machines, and think nothing. They had "core rope".
Times change, but acheivements do not.