back to article Space station astronauts pop outside to replace crippled computer

Two astronauts aboard the International Space Station have taken a wander over the outside of the station to replace a critical backup computer that conked out. MDM NASA doesn't do beige boxes, it prefers grey Flight engineers Rick Mastracchio and Steve Swanson swapped out the multiplexer/demultiplexer (MDM) control box in …


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  1. Mark 85

    The train may move slowly,

    but the tracks really fly.

  2. Yet Another Anonymous coward Silver badge

    Delivery time

    So does it take longer to get a replacement delivered than it takes the INS to get spares from its office 7miles away?

  3. Don Jefe

    Solid Design

    About 11 years ago I was in the middle of the very complicated task of working with the architects who I had chosen to build my flagship facility. It had to look normalish from the outside, suitably opulent and techy inside, but never let people forget it was still a machine shop. A very advanced machine shop designed to design, engineer and build extremely complex 'stuff'. Stuff we need to test before we build so IBM built us this monstrous computer to run simulations and designed the fairly good size data center that lives under the complex.

    That's all cool. Yeah. I always wanted a bunch of robots living on top of a giant computer, things were good. IBM built a second, scaled down, offsite backup facility in my mountain bunker in the mountains of Tenessee but still more redundancy was needed. 'You're too close to DC' they said. 'If something goes tragically wrong you might not be able to keep operating your business if the US was invaded or a catastrophic natural disaster occurred' they threatened stated.

    Years of experience told me not to point out the fact that a man with a fortified mountain bunker is probably thinking something other than going to work if there's an invasion or another volcano incident, it hurts their brains if you tell them you might not be concerned with money (IBM people are notoriously single minded you know). At any rate, They still wanted more redundancy though and proposed a small version of our simulation system that ran solely on power the facility could produce. Maybe located on the back of the property and accessible though the service tunnels to the compression pit.

    'Fuck no' I says at that point. 'If we're going through all this trouble and two NBC fortified bunkers aren't enough there's no way I'm leaving a second system with tunnel access out there that some foreign invader or Morlock (they access the surface through volcanos and they scare me) can just go switch it on and steal all my IP (that made good sense to the IBM guys, they love IP). Here's what I want'

    Drawing on the knowledge of my friends at NASA and the vast amount of sci-fi I've assimilated over the decades I knew what had to be done. The backup had to be in the most inaccessible place possible, need special tools to activate and have a cunning and lethal set of challenges one would have to undergo before even thinking about starting the backup.

    The whole fucking bit you know. Special, individually tailored isolation suits would have to be procured, years of training, advanced applied and theoretical knowledge in many fields would be a must for access. The tools alone would be extremely rare, symbols of a more refined, bygone age.

    Since I don't have a space station the backup was suspended in the middle of a .5km deep pit and accessible only from two narrow catwalks, each 30m long. After passing all the previous challenges one still has to inch around a large cylinder of unknown purpose and pull the lever on the back to start the backup. The guards will have found you by then so you'll probably have to shoot your way out.

    It's that kind if thinking that makes NASA and I such great partners. No middle of the road mucking about for us, hell no! Look at the middle of any road, that's where all the things that have been run over now live. If you're going to do something do it big and let the English see you do it, that's what I always say.

    1. frank ly

      Re: Solid Design

      Are any of your books available in libraries?

    2. Wzrd1 Silver badge

      Re: Solid Design

      Ah, so you're the guy with the little bunker!

      I got a real steal on my larger complex. You can see the secondary cooling system purge periodically. It took years of inserting fiction in various texts, but people now buy "Old Faithful" as a regular geyser.

      When some geologists came along poking about, we started turning on and off the secondary and tertiary systems, now they think that it's a really big caldera! LOL!

      If you want, we can link side tunnels, I have a tramway not too far from the Smokies. We're installing one of the new Hitachi super trains soon, can't be late for a weekend on the beach! We can divert one of them your way and you can pop by some evening.

      Maybe we can think of some more deviltry to disturb those silly geologists.

      1. Don Jefe

        Re: Solid Design

        I guess that means there are three regulars on this site that have bunkers. I was only aware of one other. He and I have a bilateral agreement so we always have a place to go on either coast should the situation require it. You should sign on (I hope yours is in Canada). We can call it the Trilateral Commission or something suitably three sided.

        1. John Brown (no body) Silver badge

          Re: Solid Design

          "We can call it the Trilateral Commission or something suitably three sided."

          If you're going to link the bunkers by train, how about calling yourselves the Amtrack Federation?

          That leaves room for future growth without having to keep renaming things.

          1. Don Jefe
            Thumb Up

            Re: Solid Design

            That Sir, is genius! Maybe I'll tweak it a bit and do Amtrak Confederation and I can position it as the balancing force to the evil Amtrak Federation.

        2. Michael Thibault

          Re: Solid Design

          >We can call it the Trilateral Commission or something suitably three sided.

          Tricorne, perhaps. Salut!

    3. Phil O'Sophical Silver badge

      Re: Solid Design

      the backup was suspended in the middle of a .5km deep pit and accessible only from two narrow catwalks, each 30m long.

      What, no pirahna fish or crocodiles?

      Give the white cat a stroke for me.

    4. Anonymous Coward
      Anonymous Coward

      Re: Solid Design

      So now you just need to hire Indiana Jones as your IT guy.

  4. Tom 64

    It looks suspiciously like an AE-35 unit

    HAL: I've just picked up a fault in the AE35 unit. It's going to go 100% failure in 72 hours.

    1. MacroRodent

      Re: It looks suspiciously like an AE-35 unit

      I have always wondered why the AE35 had to be in a location reachable only by a spacewalk, except that the plot of the "2001" required it. But what plot point requires that ISS computer to be outside?

      1. David Knapman

        Re: It looks suspiciously like an AE-35 unit

        I think space inside the station is reserved for things that benefit from having access to warmth and atmosphere. Computers don't (yet) need either.

        1. Vulch

          Re: It looks suspiciously like an AE-35 unit

          Actually the computers do like having atmosphere, it's a real bugger keeping them cool without. The ones outside usually have to be hooked in to the ammonia cooling system which also needs regular EVA maintenance.

      2. EddieD

        Re: It looks suspiciously like an AE-35 unit

        I thought the AE35 unit were the servos for the communications antenna that kept it pointing the right way, and would therefore be on the antenna itself.

      3. Graham Marsden

        @MacroRodent - Re: It looks suspiciously like an AE-35 unit

        > I have always wondered why the AE35 had to be in a location reachable only by a spacewalk,

        JOOI, in "The Lost Worlds of 2001" one of the proposed plot-lines which wasn't used was that HAL tries to kill all the Discovery's crew by opening both inner and outer airlock doors simultaneously.

        The hibernating astronauts are killed, but Bowman manages to get to an emergency on-board survival shelter with its own independent oxygen supply.

        Having them need to do a spacewalk instead was more dramatic and allowed Kubrick and Clarke to set-up the situation where Frank Poole repeats the spacewalk and is then killed by the Pod.

    2. southpacificpom

      Re: It looks suspiciously like an AE-35 unit

      HAL: Well, I don't think there is any question about it. It can only be attributable to human error. This sort of thing has cropped up before, and it has always been due to human error.

  5. Julian Taylor

    In this day and age, surely they could make a computer a bit smaller than 'microwave' size especially since there are almost 50 of them? Couldn't someone come up with a simple array - hell even a 2u rack would be smaller than that ...

    1. David Knapman

      I suspect big and bulky is actually a bonus when you're trying to manipulate things in a spacesuit. You don't want to be dealing with anything that requires fine dexterity to fit.

      1. Don Jefe

        I would have put the computer inside the space station. Kind of done away with any maintenance requirements for dexterity and spacesuit altogether...

        On a less blindingly obvious tack, if you're going to insist on keeping your computer on the outside of your space station then it's a good idea for it to be well shielded. There's all sorts of stuff zipping around in space that's rarely found in the regular Human household. Sol will attempt ~15 direct assaults every day and by proxy attack constantly. There's also a big overheating problem in space you know. A really, really big overheating problem with electronics in space and wee enclosures aren't great for managing heat. You also want important stuff bolted to the exterior of your spacehouse to be quite robust and resilient to physical damage from things like astronaut restraint systems, tools on wrist tethers that bang around on the outside, hard, when astronauts work on anything and other such things. But don't let the dimensions fool you, astronauts are tiny, so it looks a lot bigger than it really is.

        The most important part though is that all space computers must be comprised of really long rail mounted cards that allow for easy rerouting of power from shields to life support and those rail systems are extremely bulky.

        1. Christoph

          It sounds like the sort of box that has lots of wires going to/from it. Maybe they thought putting it on the outside was better than putting that many holes in the pressure containment?

          1. Simon Harris

            "Maybe they thought putting it on the outside was better than putting that many holes in the pressure containment?"

            and maybe because it was controlling equipment on one of the trusses, having the multiplexer/demultiplexer unit outside saved a ton of wiring back to the crew modules.

            Here's a description of the architecture of the system:


    2. cray74

      By the time you're done layering on requirements for insulation, vacuum operation, accessibility by space suit gloves, compatibility with existing mounting points on external station structures, backup power supplies, redundant components, and cooling and heating, computers less powerful than your smartphone tend to grow to the size of microwave ovens.

  6. Gene Cash Silver badge

    Speaking of speed...

    By the way, those bad boys use 386SX-16s with a separate math coprocessor. Zoom!

    1. John Smith 19 Gold badge
      IT Angle

      Re: Speaking of speed...

      "By the way, those bad boys use 386SX-16s with a separate math coprocessor. Zoom!"

      AFAIK the ISS MDM's are split into "tiers."

      Only the Tier 1 MDM's have processors.

      The rest collect (multiplex) and distribute (demultiplex) data from the network, 1553b on the Shuttle, Ethernet (I think) on the ISS. The clue is in the name. It's just that NASA's ideas on architecture have changed over time and things have become "smart."

      Embedded design rules apply. slow, known, stable, predictable >> Fast, high power, unreliable.

      They get the job done.

      1. Simon Harris

        Re: Speaking of speed...

        Apparently the failed unit is 13 years old.

        Wonder whether Honeywell will be telling NASA they're no longer supporting it, and they should be upgrading to the new MDM 8.1 with a wizzy touch interface!

    2. Don Jefe

      Re: Speaking of speed...

      True story. When I was doing my undergrad the 'micro PC' was just becoming a thing and it was cool for the geeks to have computers in their dorm rooms, so there was always talk in the (still smoker friendly) commons and the math coprocessor was seen as an important geek ugrade. Computers were never my field and I didn't want to be scorned by the geeks (I played with LASERS, I wasn't a geek at all :) so I didn't ask them what this apparently important piece if equipment was for.

      I searched for about two days, through company listings and parts suppliers (in those book things where such information was stored) and finally became infuriated that I couldn't find this mystery part. So I asked a professor where MathCo was based as I wanted to research their products to see if I could make money with them.

      He had the most curious look on his face then he laughed to tears. Bastard (I jest). I was very serious then and he thought it was hilarious that I has spent two days looking for processors made by MathCo. MathCo in my home state made pre-K math oriented coloring books, and appeared in no parts supplier catalogs. I felt so stupid.

  7. Phil O'Sophical Silver badge


    I'm still trying to work out how a snorkel can be useful in a zero-G environment.

    1. Don Jefe

      Re: Snorkels

      It's a real shame nobody onboard understood what the Russians were trying to say. Now that you've pointed it out it seems so obvious why they were so upset when all they got was a helmet with a snorkel before going into the airlock.

    2. ragnar

      Re: Snorkels

      The water sticks to surfaces (i.e. faces, faceplates etc.) in zero g, it doesn't sink to the bottom. It should be possible to point the end of the snorkel to an 'empty' part of the helmet and breathe, if the area around your mouth is covered.

      Unless it's just tied directly into the oxygen tank I guess.

  8. Field Marshal Von Krakenfart
    Paris Hilton

    With a maximum speed of one inch per second

    Have the operating rights for the train been sold to Virgin Galactic?

    Paris, 'cos she knows how to move things at an inch a second.

  9. Rodrigo Valenzuela

    Oh the simplicity...

    "so the team simply slid the old one out and replaced it with a spare unit."

    Yes, very simple... just go out in the vacuum, hanging from a cable, exposed to radiations, working with gigantic gloves... yes, simple indeed.


  10. Anonymous Coward
    Anonymous Coward

    Inches, feet, miles?


    1. Swarthy

      Re: Inches, feet, miles?


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