Author Topic: Standardized container cargo system for Cargo MCT  (Read 23360 times)

Offline Impaler

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Re: Standardized container cargo system for Cargo MCT
« Reply #20 on: 06/07/2016 01:16 AM »
The logical container size is standard twenty foot unit used in international shipments all over the world today.  3 abreast and stacked 3 or 4 high they would easily fit in the expected vehicle and when un2l8oaded from the MCT/lander they will be movable by truck (something no one else seems to be thinking of)0.

Pressurized habitation modules might be larger, about the size of the Destiny module or a MPLM and carry an integrated 'cage' frame which allows them to be bolted down f8or transport.  I believe most cargo will be un-pressurized and pressurized containers will be almost exclusively for crew.

Offline Lar

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Re: Standardized container cargo system for Cargo MCT
« Reply #21 on: 06/07/2016 01:37 AM »
Making the containers the same standard size as terrestrial ones, as long as there are no serious technical impediments, is really thinking ahead to when there is so much cargo volume that it matters. Good point, Impaler.
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Offline biosehnsucht

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Re: Standardized container cargo system for Cargo MCT
« Reply #22 on: 06/07/2016 05:55 AM »
I will be surprised if they go with the concept of dropping off one giant 15m container, I took Elon's response of being "something like that" or whatever he said to mean the overall architecture of sending and landing a 2nd/upper stage from Earth to Mars, then sending it back as single stage to earth landing. That requires a lot of additional mass (structure for carrying G-loads between them, cosine losses and more propellant or complicated engines that can articulate out beyond the craft .. and more propellant, large parts of the MCT which are left on the surface that must be built new each flight, extra heatshield, etc...). Seems at odds with the simple and cost and/or mass optimized approach SpaceX normally takes.
Having said that, being able to directly deposit a 15m hab module or nuclear reactor etc is pretty compelling.

Regardless of how they get them there, since they can't use off-the-shelf intermodal containers, I would expect exact dimensions to be tweaked a bit (probably using purely metric and sane dimensions for starters, rather than weird odd # of mm in a given dimension because it was originally specced in imperial). They would probably also be optimized for reducing wasted volume in the cargo bay (whether it is integral to the BFS or dropped off as a separate module).

As far as moving them around on the ground, I was suggesting something like the PODS "Podzilla" : - only I would change it a bit to attach to the top of the container (much like container cranes can attach to the top of an intermodal container) rather than lift with chains hooked to the bottom (less wobbly). BEV and/or series hybrid (CH4/GOX, I'd assume) power unit on a 4-post frame with each post having a set of wheels, and method of lifting/leveling the corners (so you can pick up, move, and level the container) - possibly a hydraulic system, but possibly a pure electrical system (depending on how the trades for mass vs complexity vs ... etc go for that).

I wasn't suggesting that you could indefinately "stack" containers horizontally, but a few containers (3-5 surely) could be done this way. I wouldn't make any direct assumption about air tight seals just by bolting them together. Instead, after bolting them and covering as much exterior area as possible in soil and/or martian 'concrete' made from martian soil (leaving openings just where necessary for power/data/hatches/etc).

I would then go around all areas where there are joints (including the joints internal to a given container, not just between adjacent ones) with some sort of semi-flexible sealant appropriate to a Martian-adjacent environment (temps / pressures / etc) which would have enough give in it to not crack under the various stresses (flexing of containers as loads are moved around, temperature changes, etc), sort of like caulking around a bathtub (you don't want to use rigid grout, but a flexible seal).

Making some assumptions for what material science can provide for "martian container caulk", this should give you an air tight space, though this alone might not provide for a huge pressure differential, it should help keep dust out and provide a space with controlled environment (no wind, such as it is on Mars, and lighting whenever you need it).

Turning this into a pressure vessel may require either fancier material science than merely forming a seal, or covering it with an additional layer of some kind that would prevent pressure differentials from blowing it out. I don't think these are unsolvable problems, but probably best to leave habitats to habitats designed for it. Perhaps you could at least generate enough pressure safely to perform maintenance work on vehicles in just a jump suit of some kind with an oxygen mask (though you would need to go through a de/repressurization airlock like deep sea divers do in that case).

Offline JamesH65

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Re: Standardized container cargo system for Cargo MCT
« Reply #23 on: 06/07/2016 08:08 AM »
The logical container size is standard twenty foot unit used in international shipments all over the world today.  3 abreast and stacked 3 or 4 high they would easily fit in the expected vehicle and when un2l8oaded from the MCT/lander they will be movable by truck (something no one else seems to be thinking of)0.

Pressurized habitation modules might be larger, about the size of the Destiny module or a MPLM and carry an integrated 'cage' frame which allows them to be bolted down f8or transport.  I believe most cargo will be un-pressurized and pressurized containers will be almost exclusively for crew.

I disagree. This is something that needs to be thought about without the preconceptions of existing container systems.

As an analogy, the F9 diameter is limited by road transport considerations, which were determined by height of bridges and tunnels which are determined by sizes of vehicles going back to Roman times. (http://www.snopes.com/history/american/gauge.asp). Well, not quite true, but you get the gist.

Point is, here we have no prior history to adhere to. It's an opportunity to make the optimum mechanism.


Offline MikeAtkinson

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Re: Standardized container cargo system for Cargo MCT
« Reply #24 on: 06/07/2016 08:15 AM »
Cubic pressurised containers do not work well.

Offline envy887

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Re: Standardized container cargo system for Cargo MCT
« Reply #25 on: 06/07/2016 12:54 PM »
Cubic pressurised containers do not work well.

And I doubt anyone would seriously propose them.

Online Semmel

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Re: Standardized container cargo system for Cargo MCT
« Reply #26 on: 06/07/2016 02:42 PM »
Why not hexagonal standard container to allow for a better use of the available volume? Also for pressurised cargo, a cylindrical pressure container inside a hexagonal frame does not waste too much space or mass. Cylinder inside a standard shipping container sounds much more wasteful, both on the inside as well as for fitting in the BFS outer frame.

Offline envy887

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Re: Standardized container cargo system for Cargo MCT
« Reply #27 on: 06/07/2016 03:47 PM »
Why not hexagonal standard container to allow for a better use of the available volume? Also for pressurised cargo, a cylindrical pressure container inside a hexagonal frame does not waste too much space or mass. Cylinder inside a standard shipping container sounds much more wasteful, both on the inside as well as for fitting in the BFS outer frame.

If SpaceX is adopting a system similar to the 100t lander roughly outlined in the video embedded upthread, then there might not be a need for individual pressurized modules. The lower half of the ~10m diameter spaceship would be left on the surface, and it could just be one large pressure vessel which is FAR more mass-efficient.

The concept changes a lot ideas around cargo handling since the tanks and engines return to Earth while the whole cargo hold is left on Mars, presumably to be entirely re-purposed and used. A passenger hab could just remain a hab, while a cargo module could have the aeroshell split off so containers could be lifted and carried away.

Offline ThereIWas3

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Re: Standardized container cargo system for Cargo MCT
« Reply #28 on: 06/07/2016 09:47 PM »
That was my thought - don't unload it at all, if what you are delivering is a "factory".  The only thing that has to unload from the first landings will be robot mechanical things that are presumably self-powered - they just drive off from a garage space at the lowest level.   ISRU machinery, tanks, and such can just stay where they are.
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Offline Impaler

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Re: Standardized container cargo system for Cargo MCT
« Reply #29 on: 06/08/2016 12:34 AM »
Standard 20ft containers are ideal because they would be movable AFTER getting to Mars, a single massive pressurized container is essentially immovable once landed and landing zones will need to be re-used so you need to clear out everything as the vehicle unloads not simply leave it strewn about.  If you tried to connect the large pressurized module to the existing base via some kind of tunnel-tube then that would force the MCT to land dangerously close to the settlement. 

Thus the only viable container is one that is easily road transportable over the several miles that connect landing zone to the settlement.  While a smaller container say the size of a pallet might work for very small settlements the shipping container has already been found to be ideal on Earth in exactly this situation where a large vehicle needs to be unloaded quickly and the cargo distributed by roads.

These shipping containers will be dimensionaly identical to Earth ones, but built of far more light weight materials such as lithium-aluminum or carbon-fiber.  They will need to be strong enough to take several g's when underneath a stack of ~3 other containers, they may also need to take significant tensile loads depending on what then entry orientation of the MCT is.

They will not be pressurize and will carry only building materials equipment or smaller containers which are air-tight, most food-stuffs are pouched and dried and can be exposed to vacuum or kept in a larger container at very low pressure, just enough to prevent out-gassing, wrapped frozen foods, dry goods like cereal grains, vegetables etc all would be fine in vacuum.  Everything else man-made we can think of is likewise going to be fine, electronics and machinery even if they are intended for use in pressurized space so long as they are off and not generating heat will be fine.

I think people are misunderstanding the ISS resupply process, they send most cargo in pressurized containers because of the pressurized berthing process and the by-hand unloading, not because the cargo itself can't withstand a vacuum.  Once your into large logistical volume you would be unloading pallets from a 20ft container using pallet-jacks, with either the whole container put into an air-lock for shirt-sleeve unloading, or the containers can be dropped next to the base and a pallet-jack robot can move them into a small air-lock and a person inside unloading the airlock each cycle.


Offline envy887

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Re: Standardized container cargo system for Cargo MCT
« Reply #30 on: 06/08/2016 01:28 AM »
Standard 20ft containers are ideal because they would be movable AFTER getting to Mars,

Agreed, for cargo. People won't be coming or living in a container though.

Quote
a single massive pressurized container is essentially immovable once landed
Why? Once people and consumables are removed, it won't mass over 50 tons, which is less than 20 tons of weight on Mars. That's readily moveable with similar equipment to what container handling would require.
« Last Edit: 06/08/2016 01:46 AM by envy887 »

Offline biosehnsucht

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Re: Standardized container cargo system for Cargo MCT
« Reply #31 on: 06/08/2016 01:40 AM »
It's entirely possible that each humans + cargo launch (and possibly also cargo only launch) will only fit (assuming ~20ft intermodal size) 4-6  containers in a single horizontal plane, with none stacked above them.

It's not hard to hit 100 tons with only 4-6 containers with some clever packing, especially if you can take the long sides off to more easily pack/unpack and fill "empty" space.

Offline GWH

Re: Standardized container cargo system for Cargo MCT
« Reply #32 on: 06/08/2016 06:50 AM »

Agreed, for cargo. People won't be coming or living in a container though.
Google "shipping container homes" it's not just doable but downright trendy.

Offline envy887

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Re: Standardized container cargo system for Cargo MCT
« Reply #33 on: 06/08/2016 12:47 PM »

Agreed, for cargo. People won't be coming or living in a container though.
Google "shipping container homes" it's not just doable but downright trendy.

It won't be trendy in places where the air inside is trying to blow the container in every direction with over 1,000,000 lbf of net force.

Offline JamesH65

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Re: Standardized container cargo system for Cargo MCT
« Reply #34 on: 06/08/2016 12:53 PM »
Standard 20ft containers are ideal because they would be movable AFTER getting to Mars, a single massive pressurized container is essentially immovable once landed and landing zones will need to be re-used so you need to clear out everything as the vehicle unloads not simply leave it strewn about.  If you tried to connect the large pressurized module to the existing base via some kind of tunnel-tube then that would force the MCT to land dangerously close to the settlement. 

Thus the only viable container is one that is easily road transportable over the several miles that connect landing zone to the settlement.  While a smaller container say the size of a pallet might work for very small settlements the shipping container has already been found to be ideal on Earth in exactly this situation where a large vehicle needs to be unloaded quickly and the cargo distributed by roads.

These shipping containers will be dimensionaly identical to Earth ones, but built of far more light weight materials such as lithium-aluminum or carbon-fiber.  They will need to be strong enough to take several g's when underneath a stack of ~3 other containers, they may also need to take significant tensile loads depending on what then entry orientation of the MCT is.

They will not be pressurize and will carry only building materials equipment or smaller containers which are air-tight, most food-stuffs are pouched and dried and can be exposed to vacuum or kept in a larger container at very low pressure, just enough to prevent out-gassing, wrapped frozen foods, dry goods like cereal grains, vegetables etc all would be fine in vacuum.  Everything else man-made we can think of is likewise going to be fine, electronics and machinery even if they are intended for use in pressurized space so long as they are off and not generating heat will be fine.

I think people are misunderstanding the ISS resupply process, they send most cargo in pressurized containers because of the pressurized berthing process and the by-hand unloading, not because the cargo itself can't withstand a vacuum.  Once your into large logistical volume you would be unloading pallets from a 20ft container using pallet-jacks, with either the whole container put into an air-lock for shirt-sleeve unloading, or the containers can be dropped next to the base and a pallet-jack robot can move them into a small air-lock and a person inside unloading the airlock each cycle.

So you want different container shapes for pressurised vs unpressurised? Because at some point you ARE going to need pressurised containers, and box shaped ones are not going to work (too heavy).

I would be interesting to know how much cargo can be transported unpressurised.

Offline GWH

Re: Standardized container cargo system for Cargo MCT
« Reply #35 on: 06/08/2016 04:13 PM »
It won't be trendy in places where the air inside is trying to blow the container in every direction with over 1,000,000 lbf of net force.

Of course they would need to be built to withstand internal pressure.  My point is specific to what can be done to increase the utilization of a mass manufactured goods transportation enclosure.  One that by it's own inherent construction simplifies the logistics of moving goods so that manufactured product can be moved in and out of shipping bottlenecks with as little fuss and cost as possible.

I disagree that these shipping containers should be built to be unpressurized as a majority.  It goes against the principle of using the transported goods enclosure and support structure to the greatest possible utilization as habitable volume.   Reducing the internal structure within an MCT to the bare minimum, shifting the task of load distribution to individual containers would go a long way to minimizing return mass and delivering the greatest usable volume to Mars surface.
If Mars Colonization is to happen the logistics of getting freight loaded on and off an MCT needs to be as cost efficient and expedient as possible, right down to road transport on Earth as the primary delivery mechanism of cargo containers.  Leveraging these cargo containers to the point that they can serve double duty as habitable volume is the best solution IMO, unless the MCT can be built in such a way that it can land cargo modules an entire order of magnitude larger.   

Offline GWH

Re: Standardized container cargo system for Cargo MCT
« Reply #36 on: 06/08/2016 04:18 PM »

So you want different container shapes for pressurised vs unpressurised? Because at some point you ARE going to need pressurised containers, and box shaped ones are not going to work (too heavy).

A more mass efficient means (cylindrical) of building a pressurized container within a rectangular shipping frame isn't a deal breaker, see attached.  More elegant construction methods are very doable.

Offline oldAtlas_Eguy

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Re: Standardized container cargo system for Cargo MCT
« Reply #37 on: 06/08/2016 04:28 PM »
My current WAG is 50% split initially. Without a great deal of self sufficient systems (farm, 3D printers, feedstock melters/formers, atmosphere recycle and production from Mars atmosphere) the base will need a lot of pressurized supplies. As the base matures more supplies/cargo will be un-pressurized (mining equipment, material processing, solar arrays, etc).

Having these supplies used inside the base shipped as un-pressurized will mean it all has to transition through an airlock. This is extremely time consuming and waste a lot of base atmosphere in purge Mars atmosphere and pressure cycling. Also dust control will be very difficult to manage as well with so many cycles.

If you design your pressurized container/habitat so that most of it can be manufactured from ISRU, this will also shift the % of type of cargo as well from bulk materials to complex machines/electronics. This would allow the base to increase its volume and provide even greater m^3 space per person than what was available initially.

The containers need to be simple constructable on Mars even though they may weigh more. Its not weight but costs that is important in the $/effective task/utility:
-cost of the equipment,
-shipping costs [trip on MCT to Mars $/kg, NOTE: SpaceX goal is to get this below $500/kg, initially it will be ~$8,000/kg],
-handling time loading and unloading [this is probably the most precious resource both on Mars and Earth], and
-other considerations such as multi use so that there is little dead weight shipped everything has a use on Mars especially pressurized containers)

Offline envy887

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Re: Standardized container cargo system for Cargo MCT
« Reply #38 on: 06/08/2016 04:46 PM »
...
Leveraging these cargo containers to the point that they can serve double duty as habitable volume is the best solution IMO, unless the MCT can be built in such a way that it can land cargo modules an entire order of magnitude larger.   

I'm personally convinced MCT will do both of these, by landing a single 10m-ish container and leaving it on the surface. Unpressurized cargo versions would have aeroshells that readily be split in half and turned into 10m Quonset huts, while pressurized versions could just be inhabited without further construction.

There's no real reason to return an empty cargo hold or pressure vessel to Earth. Just bring back the fuel tanks and engines.

Offline GWH

Re: Standardized container cargo system for Cargo MCT
« Reply #39 on: 06/08/2016 07:12 PM »
There's no real reason to return an empty cargo hold or pressure vessel to Earth. Just bring back the fuel tanks and engines.

Only if said cargo hold was an intrinsic part to the required surface area and aerodynamic profile of the vehicle and it's re-entry to Earth.
That's where I'm split on the MCT and what I'm especially interested in for the September reveal.  The architecture loosely pictured by Max Fagin posted above would enable some truly massive modules to be deposited given the size of MCT that was leaked (enabling small apartment building sized modules).  But the HOW is a massive question, as that picture doesn't lend itself to efficient in-space propulsion that an entirely self contained architecture would.

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