Quote from: Lar on 06/13/2016 11:28 amQuote from: lamontagne on 06/13/2016 10:28 amA few more stiffeners addedIf you make the spaceframe 6 sided, it wastes a bit more space around the cylinder than an 8 sided one, but the containers can be packed much more easily as a regular hexagon tiles a surface, but a regular octagon does not, it leaves square shaped hollows.I like rectangular containers better, and will again advocate for standard 20 foot sizes that are compatible with the current terran system. we want there to be so much freight that avoiding transship repack or difficulties interfacing with terran container handlers becomes important.Why on earth (!) would you need to be compatible with Terran containers? So they fit on trucks, or trains, or ships? No reason to do that, and very likely to damage the containers anyway. Make the containers fit the task, not the task fit the containers.And as for measuring in Feet - I though the world had got over using imperial for things like this?
Quote from: lamontagne on 06/13/2016 10:28 amA few more stiffeners addedIf you make the spaceframe 6 sided, it wastes a bit more space around the cylinder than an 8 sided one, but the containers can be packed much more easily as a regular hexagon tiles a surface, but a regular octagon does not, it leaves square shaped hollows.I like rectangular containers better, and will again advocate for standard 20 foot sizes that are compatible with the current terran system. we want there to be so much freight that avoiding transship repack or difficulties interfacing with terran container handlers becomes important.
A few more stiffeners added
It will still cost on the order of $100-1000/kg to ship stuff to the surface of Mars, even with full-scale colonization. That means it's worth putting stuff in much lighter containers, more optimized for Mars.
Unlike the Moon, Mars has lots of available carbon. So ISRU manufacture of carbon-carbon containers on Mars would be more easily accomplished than an aluminum one. Just ship the resins. Possibly use some aluminum by vacuum deposition on the inner surface for increasing pressure integrity or for handling cryo liquids like LOX. Would not require a lot and the aluminum feedstock could also be shipped. Result would be more containers for a lot less total weight and volume used in shipping.The intent is to initially start being able to manufacture habitats and storage locally using same designs and materials that the containers are built from. So this means picking materials for the container that are easily obtainable early in the colonization process. Later new designs using other materials with new shapes and sizes not previously shippable would be possible. This also means that in the long run its not the weight that is so important for the containers but what and how they are made. Later after the colony has started being able to use ISRU for their own container manufacture the ones being shipped from Earth can change to a new material (lighter) to increase effective cargo shipped. This also means that the most important item for containers are their shape size and fittings, not the materials they are made from. The materials can change but not shape, size and fittings.
I'd like to suggest that whatever container design that is developed might be sized (and shaped) to tessellate in the large hypothetical cargo hold of a BFS as laid out above but ALSO be sized to fit inside the payload fairing of the F9/FH system. Currently the fairing is sized for payloads up to 4.6m in diameter (according to the F9 user guide) but I'd propose that it may be possible to squeeze something like a 5m diameter (corner to corner) hexagonal structure into an outer shell that has the same external dimensions as the current fairing - or at least shares the 5.2m external diameter to retain commonality.ISTM that something along these lines would allow F9/FH to stay relevant in the event that these containers become an in-space standard. Admittedly it's not exactly Mars-optimised but there's no reason why sizing for existing launch vehicles has to preclude effectiveness on Mars.
Containers are not strong in torsion, the single wheel arrangement proposed would twist them out of shape.They are always handled and supported using spreader beams, than hold them at their ISO corners, so the forces are always normal. Even on trailers, they are actually supported by a small structural frame beneath the container.In an MCT architecture, they would be handled by cranes with spreader beams, as they are on Earth.I expect there would be shorter half length versions as well.
At the very least, use carbon fiber shipping containers. They're 42% lighter than aluminum containers, which are themselves lighter than steel. The difference in cost is only about $5000.http://compositesmanufacturingmagazine.com/2014/04/can-carbon-fiber-composites-future-material-shipping-containers/You'll save at least a ton or so, which works out to just $5/kg, easily worth it. Don't haul heavy steel shipping containers to Mars. Mars has a lot of iron already.
I do think the 20' size is reasonably close to a good overall size (since you could fit 4 next to each other in a 15m diameter with several meters of space around for structure, cargo doors (if they open by moving inwards and sliding around the inside like an inside out van door), etc. Would likely end up not being exactly ISO sized, might be taller, might be shorter, might by wider, narrower, etc, but the 20' container is a pretty good starting point.
Part of the whole point about the shipping containers is that they somewhat protect the cargo inside. This way, the containers don't need a roof. They can be moved around during rain or snow or wind. They don't need to be constantly protected from the elements.I personally think you'd want the containers at least partially pressurized, maybe even with some semi-passive thermal shielding (or carefully chosen paint). This way they can be left outside totally exposed to vacuum and even the harsh sunlight of space and the dusts of Mars. You could have, say, an BFS launch a bunch of these things into LEO, they can be stacked and interlocked. Multiple loads. Say, 6 BFS landings worth (600t). Then a single BFS can dock with the stack, boost from LEO toward Mars, do a small aerocapture or propulsive maneuver for capture. Then the MCT leaves the stack in Mars orbit, goes to the surface with one payload, drops it off, refuels, goes back up, repeats the process.The advantage there is that you can use one MCT per couple synods for multiple payloads. And in this could be extended by refueling in high orbit, allowing you to send like 10 or 20 MCT landings' worth per MCT. Again, it'd take like 2 synods per round-trip, but by stacking the cargo like this, you could vastly increase the amount of cargo you could send per MCT in its lifetime.