This is a follow-up to question about a transmuting 3D-printer

Assume you need to store all stable elements in a spaceship. On board, a chemical assembler is used to compose everything, if you have a blueprint and the right amount of needed elements.

Is there a common way to store the, maybe as salt or in a certain composition to make handling easier?

Density is critical here, you want to store as much of the elements as possible in a limited volume.

How would you keep them separate? Would you? Can there be a universal element mix, composed of all elements? I guess not, because some of the are rather reactive.

Is there a way to generate unstable elements on-demand, if you have a fusion reactor?

EDIT: Assume the main products are

  • Food, Water, Personal Care, Medicine
  • Technical components (simple) and Ammo. So mostly metal and future alloys.
  • Electronics and magnetic components.

What would you need to hold in storage for such products?

Assume future tech, I'll accept plausible handwaves, but please keep them as minor as possible.

  • $\begingroup$ You can typically use a particle accelerator to make small quantities of unstable elements. Some hospitals have them for Tc-99 production. You can't have a fusion 'reactor' because it requires energy, it doesn't emit any. The particle accelerator can work through fusion though. $\endgroup$
    – Lacklub
    Apr 22, 2016 at 12:12
  • $\begingroup$ You probably won't need all. Even for food you would only need say a dozen elements in quantities and another dozen in traces. Same goes for technology - one could come up with a system of like 20 elements to create all products one needs. I would consider adding some recycling system if space is an issue. $\endgroup$
    – bdecaf
    Apr 22, 2016 at 13:50
  • $\begingroup$ Thanks for the input. That was what I had in mind, although I was not sure it was possible to go with just 20 something. $\endgroup$
    – user6415
    Apr 22, 2016 at 14:26
  • 1
    $\begingroup$ Why would you store the elements, rather than useful compounds? You mentioned salt: why store (table) salt as highly reactive sodium metal and reactive, poisonous chlorine gas, when you can keep plain old sodium chloride in a low-tech bottle practically forever? $\endgroup$
    – jamesqf
    Apr 22, 2016 at 17:25
  • 1
    $\begingroup$ I was not talking about table salt here. It was about the derivative form of an element en.wikipedia.org/wiki/Salt_%28chemistry%29 $\endgroup$
    – user6415
    Apr 22, 2016 at 21:56

4 Answers 4


This is a pretty broad question, but those are my favorite. Let's give it a shot!

Your first set of products, Foods, Medicines, Toiletries, etc.

In the case of Food and Medicine, most of the constituent molecules are going to be organic. This is actually a boon in our case because with Carbon, Oxygen, Nitrogen, and Hydrogen, we can produce multitudinous products, including almost every food and plastic. So where do we get these four things?

  • Hydrogen is the most common element in the universe. Depending on the tech level in your world, Hydrogen is also likely the fuel you will be using to generate power via nuclear fusion. Thus, Hydrogen will likely need to be stored in isolation and replenished frequently (perhaps via scooping around stars/gas giants?).
  • Oxygen is also relatively common in the universe, since secondary stellar fusion tends to produce our favorite breathable gas. Oxygen is very reactive, so storing it by itself might be a problem (also molecular oxygen is not very dense, and stores inefficiently). I would suggest storing oxygen in the form of water stores. Your people will need water, and this will also provide supplementary Hydrogen supplies if needed.
  • Carbon is not so common in the universe, but it isn't exactly rare, either. Carbon comes in more forms than I can count, and provides many storage options. I see three good possibilities for Carbon storage. Firstly, CO2 has carbon and oxygen both, so you'd get a twofer, but it takes a lot of energy to rend this molecule into its constituent components. Another option is hydrocarbons, which have a lot of carbon and hydrogen, and are pretty dense. Personally I'd go with the last option which would be Ethanol. It has Carbon, Hydrogen, and Oxygen all in one molecule, and you can drink it to get drunk! The only downside is it's relatively lightweight.
  • Nitrogen is tricky. While abundant in the atmosphere, Nitrogen is pretty rare compared to the first three elements. Diatomic nitrogen is a gas, and hard to store, but liquid nitrogen is useful and more dense. Personally I'd go with a mix of Nitrates and Nitrites, which typically exist when bonded to cations like Potassium or Calcium, or other molecular ions, and thus could provide access to both Nitrogen and Oxygen, as well as the various inorganic things you find bonded to them. Some of the nitrated molecules might require separate storage in case of reaction, but the number of potential combinations is too vast to list here.

Simple Technical Components and Ammunition

Assuming your components are fairly simple, metals like Steel or Aluminum could suffice to construct them. Ammunition sometimes uses other metals, like lead, brass, or copper, but none of these are super difficult to acquire nor difficult to store. In fact, ALL metals are fairly simple to store in their pure form if they are isolated from other elements to prevent corrosion or reaction. The real issue is going to come from the propellants for your ammunition, but luckily most of these chemicals are going to be made from the four elements listed in the above section, so there shouldn't be a huge issue.

Complex Electronics

This is tricky. Modern electronics rely mostly on silicon and copper/gold for circuit construction, but I have no way of knowing from what sorts of exotic materials your future computers might be constructed. If they use superconductors or anything like that you'll have to figure out from what they are made and if any of those materials need special consideration. For more contemporary electronics, silicon can be stored in the form of silicates which are very abundant in rocks and sand, as well as synthetic gels, and copper/gold is simply another pure metal to store.

Exotic Materials

The stuff I listed above is all pretty common on Earth and fairly easy to keep in storage. If you want anything Transuranic, or any of the less common metals like Iridium or Palladium, you'll probably want to figure out how to synthesize them via nuclear fusion in a particle accelerator, since the pure metals are very rare. Energy requirements for such a synthesis are immense, but hey it's Science Fiction.

Other Considerations

There are other things you might need that are less common but still necessary. An example might be Alkalis or Noble Gasses, or maybe some specific metals like Platinum or Mercury, etc. These things you might not need in great quantities but might need for some specific task. As a result, storage efficiency might be less of a priority and you can simply store them as pure elements, or in their most common molecular form.

If I were the chief engineer aboard this ship I would designate a permanent crew position dedicated entirely to making sure material storage is up to code. If, for example, a store of even a small amount of Potassium somehow interacted with the water stores, there would be a tremendously violent reaction and the ship would be damaged, crew killed, etc. Any nuclear stores also need special babysitting to ensure they don't accidentally go critical. Certain of these elements might also require specific temperatures and pressures to ensure safety or efficiency, though most of what I listed exists at STP just fine. My advice would be to invent all the things you might need aboard the ship, up to a comfortable level of specificity, and research what those things are made of and discover and special dangers associated with them.

Beyond that, I'm afraid, is above my payscale! Good luck!

  • $\begingroup$ Such answers are the reason why I like this site so much. Thanks! $\endgroup$
    – user6415
    Apr 22, 2016 at 22:10
  • $\begingroup$ Don't know why you would need significant quantities of the noble gases, not useful in large quantities for many purposes, maybe some helium for cryogenics. Sure, there are applications for them, but none of the fit into the main categories identified in the question that I can think of. $\endgroup$ Apr 23, 2016 at 0:49
  • $\begingroup$ You forgot sulfur and phosphorus (which come up all over the place in amino acids and stuff like that). And calcium (probably mostly needed for food). Then again, there'd be all sort of things needed in micro-quantities - for food especially... $\endgroup$ Apr 23, 2016 at 16:01


Look at real-life (pun intended) examples of replicators that locate the proper kinds of atoms and produce a complex structure.

In fact, working versions might first be based on natural living things, just producing particularly interesting fruit or wood.

In a more mature form of the technology, you still expect form to follow function. roots will probe the raw material and locate the correct atoms, using a variety of specialized mechanisms to deal with each type. They are transported back where needed as part of a molecule that's handy for the purpose of transport. As plants really do today for all the exotic trace elements they use and all metals they use, which are not a common part of typical organic molecules.

A production facility may have stockpikes of small grains containing exotic materials in forms easy to use, and will mix these in to the soil when fabrication needs more of that material. Each grain type may contain several types of atoms, so you don't need dozens of types; just a few types, containing feedstock in proportion to match common fabrication needs.

Such technology will probably use composites more than pure metal for structural needs and anywhere possible: a device won't have an aluminium case, but will seem to be more like wood or bone or shell, materials that are fabricated in such a manner naturally. An engineered bone-like material can be much stronger and need more or different atoms, but look at actual bone for inspiration, as it uses large quantities of calcium and phosphorus laid down in a form not composed of organic molecules.

The best way to enrich the soil will be from trash: recycle junk that was produced by the same technology. A preliminary pass will break it down, taking care of inert materials and making forms that are more available for fabrications. In other words, compost. The soil-fungi analogue is designed to go along with the fab tech, working in reverse.

So, the best store is the old junk to recycle, presumably made of the same stuff (in long-term average) using the same technology.

Bulk suppliments used to supply missing kinds of atoms will be "mineral" grains of a few differerent types.

If there is a surplus of some kind of material found when breaking down old stuff, it will be concentrated into nodules, which you will pick out of the soil and toss into the color-coded bucket. That is, you want the bulk-storage to be round-trip capable as well.


Store stable for how long? In theory no element is perfectly and infinitely stable. Quantum effects preclude it. (Hydrogen nucleus maybeee excepting, depends on the half-life of the proton when they figure it out).

So I'd be looking at transmuting not storing. Preferably very common universally, and very dense indeed, and use that as raw material to to make other stuff on demand or to replenish needed stocks to the right level.

Hydrogen is one obvious universal candidate for a raw material - and I think future hand waving allows us to project a means of storing it in its very dense metallic form (also helpful for its useful heat/conduction effects as well as density, and energy density too). Alternatively, if you can handle compact matter, a few teaspoons of that (think neutron star material either from a star or human-made) will give you supplies for ages.

Containment and control would be tricky but probably solved for either of these by the time you can get these in useful quantities. For example, maybe stability is possible at a temperature or pressure we can realistically achieve, or specific forms or methods mean these are less of an issue. After all we dont know much right now except that they exist, but terms like "compact matter" cover many many kinds of physical entity, perhaps some will turn out to be more stable or amenable than others, when we get more able to research them in depth. That's about how room temperature superconductor research is progressing, and just when you thought that was an absolute limit, it turns out it wasnt. Even if we dont know an exact solution right now, hand waving the containment issue away or just about manageable or solved by that time, seems fair.

Your next need is a way to transmute these to useful basic building blocks. I think if we grant a technology that can store and manipulate these, it can also probably make from them a wide range of useful basic elements, molecules and simple compounds without much effort.

This actually isn't "too" far ahead technologically. We've had tentative reports we might have briefly created metallic hydrogen in the lab, laser fusion research has created exceedingly high densities fleetingly, the LHC has reported quark-gluon plasma, so perhaps compact matter should be feasible to create or obtain in the order of several decades to a couple of centuries, and by then turning these into most other elements, or elements into basic molecules won't be far behind.

At that point you need a means of manufacturing prototype objects from schematics (that's your complex devices, protein molecules, tasty food etc) and from these. Think 3d printing in a couple of centuries time. Should be reasonable even for extremely complex molecules, food, device parts, even on a large scale (scaling up is what industry does all the time with discoveries, so I imagine a way will be found!)

Which brings us to the last requirement: Your biggest need then is likely to be energy. Lots of it. This stuff will not be cheap in energy terms. That's the last ingredient. Fortunately dense hydrogen (and indeed many other universally available things) are able to sort that out for you -again in a few decades to a couple of centuries.

Last problem is... People! Will they get bored!

Update: choice of raw material

A comment below asked why these exotic materials and not more familiar dense items such as lead or gold. The trouble is these are rare, hard to find, require a lot of extra processes to extract and to break down compared to the others - and after all that they still aren't nearly dense enough (probably by a couple or more orders of magnitude depending on the scenario!) to be useful for solving the problem as described.

  1. Elements with even lowish atomic numbers are quite rare in universal terms (hydrogen (74%) helium (24%), then the ratios drop off very quickly, and moreso for the many elements that don't occur in the common stellar fusion cycles: Source. Notice the next common elements are O, C, Ne , Fe, N, Si, Mg, S, all fusion products and none are "usefully" dense, you might as well store the actual supplies you need);
  2. Dense elements also aren't normally readily available. You generally need to find workable ores, then large scale mining and extraction processes to get relatively small amounts. If everything's transmuted the supply need to be plentiful and easily obtained;
  3. AFAIK they simply can't be compressed/stored to anything like a sufficient density to be practical for these purposes, compared to basic options like hydrogen and compact matter;
  4. They are comparatively complex raw materials compared to hydrogen and compact matter, you have to break them down before you can use them.
  • $\begingroup$ But if you want to store things as a single element that can be transmuted, why not something like lead or gold, which can be compactly stored at room temperature & pressure (or in a vacuum) without the need for complex containers. $\endgroup$
    – jamesqf
    Apr 23, 2016 at 18:10
  • $\begingroup$ @jamesqf - Update above to explain why this wouldn't help - good question though! $\endgroup$
    – Stilez
    Apr 24, 2016 at 7:31

I would consider a different approach: Instead of having a magic printer you could just have a highly automated laboratory and high precision 3D-Printer.

I feel like you underestimate how much magic/high-tech one would need to synthesize most things. As an example, consider making ammonia (main ingredient of fertilizer) out of the nitrogen in the air: This needs high pressure and temperature differences, all of which requires extensive plumbing, heavy and specialized containers/valves/etc. even though it is a relatively simple (but endothermic!) process. Exothermic reactions on the other hand need only basic lab/kitchen equipment, like containers and heating. I feel like all the equipment you need for complex reactions from elements is way heavier than having a large stock of useful reagents on hand.

Assuming instead that you have a some multi-purpose high precision manipulator, temperature control, a way of doing weight and volume measurements and a high-pressure pump you would be able to do the things outlined below, needing only raw materials, a relatively compact machine (see above) and moderate amounts of energy. The added storage room for compounds is compensated by way less need for complex machinery and energy storage. To me this seems a lot less handwavy than arguing that doing energetically expensive things on a small scale is suddenly feasible; yet you still retain the capabilities you explicitly mentioned in your post. The raw materials could be stored in some standardized containers.

3D-print using thermoplastics: You need some pellets and a nozzle. Let's say that the future engineers have actually gotten all the bugs out and things are of usable quality, similar to injection moulded stuff today. This would be the go-to for non-critical components.

Synthesize bakelite: This is a duroplast similar to hard wood. Needs 2 components (and some catalyst). Moulds could be made by 3D printing (sintering?) some fancy ceramics.

3D-print metals: This can actually done even today. Storage of pure metals is no problem.

Viscose: Useful fiber: Clothing etc.

some (futuristic?) high explosive: Ammunition

Electronics: Arguing that with an advanced, high-precision printer you can build stuff on the same die, manufacture resistors and such on the fly with whatever value you need this turns out to be really easy if you can already above things. You basically need pure silicon, plastics (isolation, mechanical substrate etc.), copper/silver, and perhaps some reagents like acid. Most of this you already have. Regarding 'exotic materials your future computers' I would just say that those are only needed in trace amounts for doping and perhaps some special components (like sensors). Computing equipment is surely not going to get bigger so you won't need lots of them. Additionally, you could also say that you have a box of microcontrollers lying around (instead overtaxing your printers capabilities / adding more machinery), those do not take up any space.

Add other things if the story needs them, I could think of aramide, fancy carbon (nanotubes etc.)

Regarding Food I do not see a compact solution either, hydrocarbons are already a rather dense form of energy storage. Considering that you need the energy as food, and any conversion would surely be inefficient, you should basically just hoard dense foods like butter, flour, sugar etc. or some equivalent.

Just having an automated storage system is going to save a lot of dead space, so the multitude of containers is not a problem as you can stack them almost optimally, acessible by a small robot.

In summary, if you have a means for manufacture, you only need a few select materials in bulk (food and plastics) and in addition to that some catalysts and special materials in rather small amounts. All these materials are already as compact as we can reasonably make them (i.e. almost no gases) and easily stored.

  • $\begingroup$ I am really thankful for you effort. But I do not want to go in depth with the creation process. For all purposes the design of the assembler is 'magical'. Put the parts in, get the finished thing out. These questions (its a series) will just enable me to describe some of the implications with a bit of detail and perhaps a bit of mumbo-jumbo. $\endgroup$
    – user6415
    Apr 23, 2016 at 21:50
  • $\begingroup$ [It was certainly fun to answer, great question!] But you don't need to go into details: I provided this mostly to give you a sufficient mental model of how it would work. You can just describe it by saying [protagonists] have a state of the art fabrication machine and some raw materials tucked away somewhere. Exactly because the methods outlined above are at least imaginable with today's technology you do not need to describe them that much. $\endgroup$
    – caconyrn
    Apr 23, 2016 at 22:08
  • $\begingroup$ (First post queue here:) Hi caconym and welcome to Worldbuilding.SE. As pointed out by opened you kind of missed the point of the question. To limit the scope of questions, here we usually just ask about a specific part of a process and assume the rest works (some way). As I read it here, the question is to store as much raw material as compact as possible, prioritizing some elements over others. You answered the question "How can I use stored elements to produce stuff?" (roughly), which is one step ahead. Thanks for your effort, I really appreciate it. Keep it going and have fun. $\endgroup$
    – JFBM
    Apr 23, 2016 at 22:11
  • $\begingroup$ Well, the main thing I wanted to point out is that you indeed should not store them too compact if this would bring many problems with it. I had the impression that openend did constrain the design space too much and therefore asked a too narrow question. How should one proceed in that case? $\endgroup$
    – caconyrn
    Apr 23, 2016 at 22:15

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