Recycling could make a tremendous difference in the number of alien civilizations present at any one time in the galaxy. Suppose, just for a number, that there are 1,000 alien civilizations that have passed some hurdle that makes them capable of star flight, let’s say, their first fusion ignition experiment that lights off. Let’s suppose that they were started about one per year, so one is in its first year after the experiment and they are still celebrating. There is also one that is 1000 years old, and for the sake of this discussion, let’s say this is the year that they run out of some critical resource, say, neodymium, and their last fusion power station shuts down for the last time. Also for the sake of the discussion, none of them recycle things at all. Some alien civilization thing about developing technology or overcoming factionalism or life-style choices or whatever caused this, and for the discussion it doesn’t matter what it was.
Now, let’s suppose a different example, of the same galaxy, same number of alien civilizations pass the fusion hurdle each year, but instead of no recycling of neodymium, they recycle it with a 90% recovery rate. This means, for every use of neodymium taking 1 kilogram of it, they get 0.9 kilograms when they are done using the thing it was used for. Now fast-forward ten-thousand years, and we have 10,000 alien civilizations in the galaxy. Ten times as many exist as in the first example, and that means ten times as many can decide to go to Earth on a voyage of discovery, or get mean and try to colonize our planet, or send some neat encoded and hidden message they think will make us all tear our hair out trying to find and decipher it. By the way, they all can easily figure out that primitive civilizations try to do SETI at around our age, and that we are here, so, if they have a positively wicked sense of humor, they send us a hidden signal, encrypted to mean, “Gotcha!”
If star travel is possible at all, the amount of it is related, not necessarily proportionally, but somehow positively correlated with the number of alien civilizations present in the galaxy, and if recycling at even 90% is enough to multiply that number by ten, it is an extremely important thing to figure out if we want to know something about alien visitations to Earth, in the abstract.
One place that might be hard to do recycling would be at the fusion reactors they most likely use to generate power to run their civilization. We on Earth don’t know how to build one of these power plants yet, but we are working on it. Perhaps it will take another hundred years for us to figure it out, but we can still make some estimates based on what we do know. Power plants are pretty easy things to understand, as is nuclear physics. That leaves confinement and heating as the big unknowns, and this in an engineering problem. Let’s just suppose they solve the confinement and heating problem, and then use DT reactions, but with the density tilted toward deuterium. Tritium is a problem to make, so perhaps they can’t make enough in a practical reactor to produce amount needed for equally balanced DT fuel, so they use as much as they can get. It increases the power density to have T there.
Either way, there are a number of pieces of the power station that can be discussed. The DT reaction is just another way to make heat, although the neutrons spewing out of it can be used to generate T out of Li as a side benefit. Once you have the heat in some fluid, molten salt, liquid metal, water, heavy water, organics, or whatever advanced alien civilizations figure out is the best, you pump it over to something to turn the heat in the liquid to electricity, which probably will be the distributable form of energy. It could be something else, like hydrogen or an organic gas for example, but either way, heat comes out of the reactor half of the power station, into the conversion half, and electricity or something else comes out of that and gets distributed.
What would prevent recycling the gizmos that do the conversion? For the case we use on Earth, hot water under pressure might come over to a set of cylinders which turn from the conversion of hot pressurized water into steam. What gets used up so it can’t be recycled? The piping, cylinders, pumps, tanks, control systems, and all the rest are made of materials, and with a good design of them, they are simply returned to the recycling facility after their life of a hundred years or whatever it was designed to be. If the pipe was made of something which oxidizes a bit, even though preventive measures are taken, the oxidized material can be recycled as well, just at a higher cost. If the oxidation was on the inside of the piping, it would be caught in a filter if it separated from the source area. If the oxidation was on the outside of the piping, it would be collected during maintenance.
Lubrication would likely be used, and as it gets dirty, it is replaced. Recycling cleans it up. Electronic components would have to be designed to be taken apart or melted down together and the elements separated. Recycling consists of physical separation of different things to the extent possible, then separation by chemical methods. The point is to get something like raw materials out, although there would be adulterants in any material that is recycled. The amount of the adulterants depends on the effort, meaning energy and resource costs, that go into the recycling. By and large, it does not seem that the conversion side of the fusion power station would lead to a problem for the alien civilization. To visualize a problem, it would be necessary to have some mixing of materials, in large amount, that are very energy expensive in separations. Not much mixing happens in the conversion side of the power station; oxidation or other chemical reactions, electronics parts, and perhaps metal dust accumulating in lubrication. Surely there are more things going on which would lead to costs for recycling, but to get to 90% for each and every material used in its construction does not seem hard to do.
One part that has not been considered is the buildings themselves. Is it possible to design recyclable buildings? If recycling is a prime factor in design, weathering would be designed to be small, at some costs, and then we are left with the same factors as go into any other ordinary recycling venture. Liquids and surfaces get dirty, so the air is filtered and the building partially sealed. Gases escape, so working gases are encased in well-designed containments. Solids oxidize, get abraded, and these are both designed to be minimal.
Without some knowledge, available only in the future here on Earth, of the details of such a conversion system, a cost of recycling the materials in a power plant cannot be compared to the total power production of the plant. It does seem that it is unlikely to be a large fraction, provided recycling is a principal factor in the design of each and every component.
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