When one looks at a container (a normal sized one, not one of the bigger ones in the deWulf setting), one of the most complex parts of a container is the doors. No surprise, as they have to be water tight (reasonably), have effective latching mechanisms, and can be locked with any number of tools. A spaceborne container has to do all of these things, but be capable of dealing with forcible changes in pressure, as well as be built to a more robust standard (since maintaining a constant pressure is a concern, it has to be able to take some damage and not spring a leak).
This doodle is looking a bit at the way that the doors of a Space Container™ might differ from a normal container. Normal containers have locking cams at the top and bottoms, with a large lever handle to lock and unlock them. instead, this is done with powered pins on the above container (like a vault door). While a normal container has just some loops in the levers for a seal (pin or strap), this container uses a small integrated security computer.
While this is a cool idea, a part of me also acknowledges that this really is an overengineered solution to a comparatively simple problem, and I’m not really sure that this is a canon solution to smaller shipping containers that are in fact space-rated. One challenge that this design really doesn’t handle well (or at all, really) is that the container’s contents would be pressurized, while in space the outside would be a vacuum. This would mean that there’s a pressure differential that wants to make the doors swing outwards, which is the same way that they’re designed to open. So the locking system would have to be fighting against that. And the actual seals would have to be working against it as well. It would be much simpler if the space-rated containers had doors that opened inwards (then the pressure works to keep the doors securely closed). But that cuts into internal volume. More thinking on this is required (perhaps an integral roller door?)
4 thoughts on “Sketches – Container Doors”
Hi, This is interesting. Shouldn’t the container have a mechanism to equalize the pressure inside with current pressure/vacuum outside? Is such mechanism practical? But considering the force of vacuum the challenge is great if one wishes not to subject the content of container to vacuum and pressure fluctuation. Dad ________________________________
Pressure equalization would definitely be a part of the overall container design. Realistically, it would get built into the floor or ceiling of the container (probably the floor all things considered). The mechanism itself is fairly practical, as it’s assumed that the container wouldn’t be accessed from a vacuum, so it would only have to equalize with something in the neighborhood of 1 atmosphere (or 14.7 PSI or 101.3 kPA). Assume that it would have to handle pressures say… 20% on either side? Probably even more than that, as you have human cities like Potosi at 4000m elevation at around 87 kPA (approx). Given that you’re also just working to equalize to whatever’s outside, it wouldn’t require much more than a few valves and some regulators to give a nice steady bleed instead of one great big WHUMPF.
Hi The door could possibly be of sliding type just as watertight doors on ships. In this way sealing against any external force would be easy. But you have to keep in mind that if the container is allowed to have even an atmospheric pressure inside, opening such container would firstly require the crew to equalize the pressure or vacuum with that of the outside. How Nasa solved the same problem of sealing cargo space on the space shuttles? That is if they ever went higher than 100 km above the surface of the earth. Hahaha. Dad ________________________________
The challenge with sliding pressure doors is that you don’t have the space to accommodate the door for it to slide (since the container doesn’t have more structure above or to the sides to house it). I was thinking of having some kind of a rolling shutter door that would roll into the roof of the container (kind of like a garage door or a security gate), but the challenge then is making sure that the door remains airtight and then operable once pressure has been equalized (vacuum welding and rubber seal degradation come to mind as potential problems). Such problems could be solved by some kind of “sci-fi bullshit technology”, but I’d rather not rely on that if I don’t have to.
As far as the space shuttle goes however, while the cargo hold was tightly fitted and aerodynamic, the main bay wasn’t actually airtight. It would compress and decompress as the shuttle flew. And even at 100 km up, that’s above about 99.99% of the atmosphere. Not quite a vacuum, but getting close enough certainly.