04 September 2013


I've long held that spaceships in games like Traveller have more in common with submarines than aircraft or anything NASA has flown.

The environment outside is very inhospitable.

Long periods of time without contact with the outside world in hyperspace.

Long response times in normal space should there be an emergency, basically if you can't fix it on your own, you're probably going to die.

This leads to thinking about other little details.

Submarines have a "christmas tree" showing the status of every single break in the hull.

A Traveller ship should have the same system.

Then there's the perennial favorite hatch of the Traveller universe; the iris valve.

It looks like a camera shutter.  A shutter that's 1.5m in diameter.  I just don't see something like that being something that works well.  With pressure on one side an vacuum on the other there's a lot of force on those plates sliding against each other.  Lots of surface area for leaking too.

A powered swinging hatch might be a better idea.  Even a single panel sliding door is well, a lot less complicated.

Simple is good when you've got hot vacuum on the other side of the door and Spaceman 3rd Class Somedood in charge of maintaining and closing it.

Of course, an iris valve could be five or six individual hatches that are pivoting open and the iris effect is from them having the pivot points arranged in radial symmetry.  That means the complicated hatch is the way it is for redundancy.  Any single panel will close the entire opening and only one needs to close to seal.  That also means that only one needs to fail to open to trap you.  This one also takes up the most space in the coaming to allow the panels to retract.  A normal shutter's door just has a bit of overlap at the center and no door covers the whole opening.

It's very telling that iris type closures aren't used in piping.  Butterfly and gate valves are about it.

Addendum:  From my LiveJournal April 5, 2009.

Sliding doors and iris-valves are neat, but would be complicated. Think about the materials you need to use to prevent things like vacuum welding. 
I have described sliding hatches that had double doors. Each face moves towards the center, away from the jamb so that in case there's pressure on one side and not the other, the vacuum side will be pressed more firmly in its coaming and cannot be slid into its pocket until both sides are centered. 
Swinging hatches are likely to be more common. If you put a geared mechanism on the door, the pressure will not prevent it from opening or closing (nor will high g-loads). But what keeps a bone head from opening it at the wrong time? 
I propose a simple diaphragm bolt. Springs hold it centered if there's pressure on both sides. If there's a pressure drop, the air pushes the diaphragm against the springs and the bolt slides into the opening mechanism and prevents it from opening. This same mechanism can also be used to trip the closing mechanism. I envision the slider looking like an emergency stop button. Slap it, the spring loaded door closes FAST. Vacuum pulls it, door closes. What if you need to open it? You pull it out, and hold it while the door opens. You could override the closure mechanism by wedging something under the button, there might even be something built in for that. No lights, you can feel for the button. If it's down you know the other side is in vacuum.


  1. I think the big draw with iris valves is that they automatically close in case of pressure breach, can be controlled from the bridge (of course this also means they can be hacked to open at the wrong time...), and do that cool Star Trek open/close.

    I rather like the idea of a solid hatch that is on tracks/runners opposite the direction of suspected pressure loss and settles into a "detent" when sealed. To unseal, just undog the hatch, push/pull out of detent, and slide to the side.

    This way the hatch still automatically close in case of vacuum, takes no interior wall space like an iris valve would, and effectively is only as large as a double door.

    1. Any powered hatch can close automatically.

    2. GURPS at TL13 (3e) likes membrane airlocks. Those are "cell-like curtain membranes made of a bioplastic that are selectively permeable to atmosphere."

      There's even a real patent for such a curtain, but the materials aren't ready for it yet.

      Even with such I'd want a nice solid hatch to cover it on the outside at the very least.

    3. Any powered hatch can close automatically, but in my mind (and I am not an engineer, obvs) a swinging door would have more potential failure points and more chances to get caught on something than would a sliding door.

  2. I've thought that if I were able to build Traveller type starships, or even just spaceships with artificial gravity, I'd start looking at ex-submariners to retrain as crew. I've thought that starships would have a lot in common with submarines myself. We're thinking alike---is that a good or a bad thing?

    1. I prescribe a fifth of top shelf Scotch and see if the pattern persists. If so, it was good. If not, then the Holy Wiskey has purged the wrongness from our thoughts.


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